Exhibit 99.1
Technical Report on the Brucejack Gold Mine,
Northwest British Columbia
PRESENTED TO
Pretium Resources Inc.
EFFECTIVE DATE: APRIL 4, 2019
704-ENG.VMIN03070-01
QUALIFIED PERSONS:
IVOR W.O. JONES, M.SC., P.GEO., FAUSIMM, CP(GEO)
JIANHUI (JOHN) HUANG, PH.D., P.ENG.
MARK HORAN, P.ENG.
CATHERINE SCHMID, M.SC., P.ENG.
ED CAREY, P.ENG.
HASSAN GHAFFARI, P.ENG.
MARITZ RYKAART, PH.D., P.ENG.
ROLF SCHMITT, M.SC., P.GEO.
HAMISH WEATHERLY, M.SC., P.GEO
TREVOR CROZIER, M.ENG., P.ENG
ALISON SHAW, PH.D., P.GEO.
Tetra Tech Canada Inc.
Suite 1000 – 10th Floor, 885 Dunsmuir Street
Vancouver, BC V6C 1N5 CANADA
Tel 604.685.0275 Fax 604.684.6241
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
TABLE OF CONTENTS | ||||
1.0 | SUMMARY | 1-1 | ||
1.1 | Introduction | 1-1 | ||
1.2 | Property Description and Location | 1-2 | ||
1.3 | Geology and Mineralization | 1-2 | ||
1.4 | Mineral Resource Estimates | 1-3 | ||
1.4.1 | Drilling, Sampling, Assaying and Data Verification | 1-3 | ||
1.4.2 | Mineral Resource Estimation | 1-4 | ||
1.5 | Mineral Reserve Estimates | 1-6 | ||
1.5.1 | Validation of 2019 Mineral Reserve to 2018 Actual Mined and Milled Production | 1-7 | ||
1.6 | Mining Methods | 1-8 | ||
1.7 | Mineral Processing and Metallurgical Testing | 1-9 | ||
1.7.1 | Metallurgical Testing | 1-9 | ||
1.7.2 | Mineral Processing | 1-12 | ||
1.8 | Project Infrastructure | 1-15 | ||
1.9 | Environmental Studies, Permitting and Social and Community Impact | 1-19 | ||
1.10 | Capital and Operating Cost Estimates | 1-20 | ||
1.10.1 | Capital Cost Estimate | 1-20 | ||
1.10.2 | Operating Cost Estimate | 1-20 | ||
1.11 | Economic Analysis | 1-22 | ||
1.12 | Conclusions and Recommendations | 1-22 | ||
2.0 | INTRODUCTION | 2-1 | ||
2.1 | Terms of Reference | 2-1 | ||
2.2 | Site Visits | 2-2 | ||
2.3 | Qualified Persons | 2-2 | ||
2.4 | Information and Data Sources | 2-3 | ||
3.0 | RELIANCE ON OTHER EXPERTS | 3-1 | ||
3.1 | Introduction | 3-1 | ||
3.2 | Status of Mining Leases and Mineral Claims | 3-1 | ||
3.3 | Economic Analysis | 3-1 | ||
4.0 | PROPERTY DESCRIPTION | 4-1 | ||
4.1 | Location | 4-1 | ||
4.2 | Tenure | 4-2 | ||
4.3 | Status of Mining Titles | 4-2 | ||
5.0 | ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY | 5-1 | ||
5.1 | Climate and Physiography | 5-1 | ||
5.2 | Vegetation | 5-1 | ||
5.3 | Accessibility | 5-1 |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
6.0 | HISTORY | 6-1 | ||
6.1 | Early Exploration | 6-1 | ||
6.2 | Exploration by Silver Standard Resources Inc. (2001-2010) | 6-2 | ||
7.0 | GEOLOGICAL SETTING AND MINERALIZATION | 7-1 | ||
7.1 | Regional Geological Setting | 7-1 | ||
7.2 | Local Geology | 7-3 | ||
7.3 | Brucejack Project Area Geology | 7-6 | ||
7.3.1 | Lithology | 7-10 | ||
7.3.2 | Geochronology | 7-12 | ||
7.3.3 | Structure | 7-12 | ||
7.3.4 | Alteration | 7-14 | ||
7.3.5 | Mineralization | 7-14 | ||
8.0 | DEPOSIT TYPES | 8-1 | ||
9.0 | EXPLORATION | 9-1 | ||
9.1 | Exploration – 2011 to 2014 | 9-1 | ||
9.2 | Exploration – 2015 to 2018 | 9-2 | ||
10.0 | DRILLING | 10-1 | ||
10.1 | Pretivm Drilling (2017-2018) | 10-4 | ||
10.1.1 | Drilling Activities | 10-4 | ||
10.1.2 | Drilling Contractors and Equipment | 10-4 | ||
10.1.3 | Drill Coordinates and Downhole Surveys | 10-4 | ||
10.1.4 | Diamond Drill Core Logging Procedures | 10-5 | ||
10.1.5 | RC Sampling Procedures | 10-5 | ||
10.1.6 | Summary of Results | 10-5 | ||
10.2 | Professional Opinion of Qualified Person | 10-8 | ||
11.0 | SAMPLE PREPARATION, ANALYSES, AND SECURITY | 11-1 | ||
11.1 | Sample Preparation, Analysis, and Security | 11-1 | ||
11.1.1 | Drillhole Sampling | 11-1 | ||
11.1.2 | Production Sampling | 11-2 | ||
11.1.3 | Sample Preparation and Analysis by Analytical Laboratory | 11-2 | ||
11.1.4 | Specific Gravity and Bulk Density | 11-2 | ||
11.2 | Quality Assurance and Quality Control | 11-4 | ||
11.3 | Qualified Person | 11-5 | ||
11.4 | Qualified Person’s Opinion on Sample Preparation, Security, and Analytical Procedures | 11-5 | ||
12.0 | DATA VERIFICATION | 12-1 | ||
12.1 | Data Verification by Qualified Person | 12-1 | ||
12.2 | Qualified Person’s Opinion on Data Validity | 12-1 | ||
13.0 | MINERAL PROCESSING AND METALLURGICAL TESTING | 13-1 | ||
13.1 | Previous Bench-scale Test Work | 13-1 | ||
13.1.1 Sample Description and Characteristics | 13-1 |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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13.1.2 | Gold and Silver Recovery Tests – Gravity Concentration | 13-3 | ||
13.1.3 | Gold and Silver Recovery Tests – Flotation Concentration | 13-5 | ||
13.1.4 | Gold and Silver Recovery Tests – Cyanidation | 13-5 | ||
13.1.5 | Variability Tests | 13-6 | ||
13.1.6 | Locked Cycle Tests | 13-7 | ||
13.1.7 | Other Processing Related Tests | 13-9 | ||
13.2 | 2013 Pilot Plant Testing | 13-9 | ||
13.3 | Production Data 2017 to 2018 | 13-11 | ||
13.4 | Mill Operation Optimization/Expansion Test Work | 13-11 | ||
13.4.1 | Sample Description | 13-12 | ||
13.4.2 | Mineralogy Analysis on Flotation Concentrates | 13-14 | ||
13.4.3 | Comminution Test Work | 13-15 | ||
13.4.4 | Gold and Silver Recovery Test Work | 13-17 | ||
13.4.5 | Solid and Liquid Separation Test Work | 13-26 | ||
13.5 | Mill Operations Optimization/Expansion Process Simulations | 13-27 | ||
13.5.1 | Grinding Circuit | 13-28 | ||
13.5.2 | Gravity Simulations | 13-31 | ||
13.5.3 | Flotation Simulations | 13-31 | ||
13.6 | Metallurgical Performance Projection | 13-31 | ||
14.0 | MINERAL RESOURCE ESTIMATES | 14-1 | ||
14.1 | Disclosure | 14-1 | ||
14.2 | Known Issues that Materially Affect Mineral Resources | 14-1 | ||
14.3 | Modelling Approach | 14-3 | ||
14.4 | Data Provided for Estimation | 14-4 | ||
14.4.1 | Assay Dataset for Grade Estimation | 14-4 | ||
14.4.2 | Assay Data Import Procedure | 14-5 | ||
14.4.3 | Triangulations | 14-5 | ||
14.5 | Geological Interpretation and Modelling | 14-7 | ||
14.6 | Data Selection and Preparation | 14-9 | ||
14.6.1 | Update Area | 14-9 | ||
14.6.2 | Compositing | 14-10 | ||
14.6.3 | Grade Populations | 14-11 | ||
14.6.4 | Summary Statistics | 14-13 | ||
14.7 | Estimation | 14-15 | ||
14.7.1 | Methodology | 14-15 | ||
14.7.2 | Parameter Optimization | 14-16 | ||
14.7.3 | Variography | 14-16 | ||
14.7.4 | Search Parameters | 14-21 | ||
14.7.5 | Upper Tail Modelling of High-grade Population in MIK Estimation | 14-22 | ||
14.7.6 | Specific Gravity and Bulk Density | 14-23 | ||
14.7.7 | Other variables | 14-23 | ||
14.8 | Model Validation | 14-24 | ||
14.8.1 | Statistical Checks – Final Gold and Silver Grade Estimates | 14-24 | ||
14.8.2 | Grade Trend Plots | 14-25 |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
14.8.3 | Visual Validation | 14-29 | ||
14.8.4 | Reconciliation of the Resource Model with 2018 Production | 14-31 | ||
14.9 | Mineral Resource Classification | 14-32 | ||
14.10 | Mineral Resource Reporting | 14-34 | ||
14.10.1 | January 2019 Mineral Resource for the Brucejack Deposit | 14-34 | ||
14.10.2 | Resource Sensitivity | 14-35 | ||
14.11 | Comparison with the July 2016 Mineral Resource Estimate | 14-36 | ||
15.0 | MINERAL RESERVE ESTIMATES | 15-1 | ||
15.1 | General | 15-1 | ||
15.2 | Cut-off Grade | 15-1 | ||
15.3 | NSR Model | 15-2 | ||
15.4 | Mining Shapes | 15-3 | ||
15.5 | Dilution and Recovery Estimates | 15-4 | ||
15.6 | Orebody Description | 15-6 | ||
15.6.1 | Valley of the Kings Zone | 15-6 | ||
15.6.2 | West Zone | 15-6 | ||
15.7 | Mineral Reserves | 15-6 | ||
15.8 | Mineral Reserve Validation | 15-10 | ||
15.9 | Mineral Reserve Comparison | 15-10 | ||
16.0 | MINING METHODS | 16-1 | ||
16.1 | General | 16-1 | ||
16.2 | Mine Design | 16-1 | ||
16.2.1 | Access and Ramp Infrastructure | 16-1 | ||
16.2.2 | Level Development | 16-3 | ||
16.2.3 | Stope Design | 16-7 | ||
16.3 | Mining Method and Sequence | 16-9 | ||
16.3.1 | Block Definition | 16-9 | ||
16.3.2 | Stope Cycle | 16-9 | ||
16.3.3 | Stope Sequence | 16-11 | ||
16.3.4 | Backfilling | 16-13 | ||
16.3.5 | Paste Backfill Test Work | 16-13 | ||
16.4 | Development and Production Schedule | 16-15 | ||
16.4.1 | Production Rate | 16-15 | ||
16.4.2 | Sustaining Development | 16-16 | ||
16.4.3 | LOM Production Schedule | 16-17 | ||
16.5 | Geotechnical | 16-18 | ||
16.5.1 | Rock Mass Properties | 16-19 | ||
16.5.2 | Mine-scale Fault Zones | 16-20 | ||
16.5.3 | Underground Rock Mechanics | 16-21 | ||
16.6 | Mobile Equipment Requirements | 16-26 | ||
16.6.1 | Production Phase | 16-26 | ||
16.6.2 | Support Equipment | 16-28 | ||
16.7 | Ventilation | 16-29 |
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704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
16.7.1 | Design Criteria | 16-30 | ||
16.7.2 | Total Airflow Requirements | 16-30 | ||
16.7.3 | Auxiliary Ventilation | 16-31 | ||
16.7.4 | Permanent Primary Fans | 16-32 | ||
16.7.5 | Mine Air Heating | 16-32 | ||
16.7.6 | Conveyor Decline | 16-33 | ||
16.7.7 | Emergency Preparedness | 16-34 | ||
16.8 | Underground Infrastructure | 16-35 | ||
16.8.1 | Mine Dewatering | 16-35 | ||
16.8.2 | Solids and Slimes Handling | 16-37 | ||
16.8.3 | Materials Handling | 16-37 | ||
16.8.4 | Power Requirements and Electrical Distribution | 16-39 | ||
16.8.5 | Compressed Air | 16-43 | ||
16.8.6 | Service Water Supply | 16-43 | ||
16.8.7 | Fueling and Lubrication | 16-44 | ||
16.8.8 | Workshop and Stores | 16-44 | ||
16.8.9 | Explosives Magazine | 16-45 | ||
16.8.10 | Refuge Stations | 16-46 | ||
16.8.11 | Communications | 16-47 | ||
16.8.12 | Portal Structure | 16-48 | ||
16.8.13 | Heating System and Propane Storage | 16-49 | ||
16.8.14 | Propane Supply | 16-49 | ||
16.9 | Paste Fill Distribution | 16-50 | ||
16.9.1 | Distribution System Design | 16-51 | ||
16.9.2 | Distribution Approach | 16-51 | ||
16.9.3 | Distribution System Layout | 16-52 | ||
16.9.4 | Manpower Requirements | 16-53 | ||
16.9.5 | Schedule | 16-53 | ||
16.9.6 | Organization and Manpower | 16-53 | ||
17.0 | RECOVERY METHODS | 17-1 | ||
17.1 | Mineral Processing | 17-1 | ||
17.1.1 | Introduction | 17-1 | ||
17.1.2 | Mill Operation Data | 17-1 | ||
17.1.3 | Flowsheet Development | 17-2 | ||
17.1.4 | Plant Design | 17-4 | ||
17.1.5 | Process Plant Description | 17-5 | ||
17.2 | Annual Production Estimate | 17-13 | ||
18.0 | PROJECT INFRASTRUCTURE | 18-1 | ||
18.1 | Overview | 18-1 | ||
18.2 | Mine Site Surface Infrastructure | 18-5 | ||
18.2.1 | Mill Facility Description | 18-5 | ||
18.2.2 | Mine Waste Management | 18-8 | ||
18.2.3 | Mine Site Ancillary Facilities | 18-10 |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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18.2.4 | Km 72 NPAG Quarry | 18-13 | ||
18.3 | Off-site Infrastructure | 18-13 | ||
18.3.1 | Transmission Line | 18-13 | ||
18.3.2 | Access Road | 18-14 | ||
18.3.3 | Knipple Transfer Station Facilities | 18-15 | ||
18.3.4 | Bowser Aerodrome | 18-16 | ||
18.3.5 | Wildfire Security and Camp | 18-17 | ||
18.4 | Site Geotechnical Assessment | 18-18 | ||
18.5 | Avalanche Hazard Assessment | 18-19 | ||
19.0 | MARKET STUDIES AND CONTRACTS | 19-1 | ||
19.1 | Markets | 19-1 | ||
19.2 | Smelter Terms | 19-1 | ||
19.3 | Concentrate Transportation | 19-2 | ||
19.4 | Mining Development Contracts | 19-2 | ||
20.0 | ENVIRONMENTAL STUDIES, PERMITTING AND SOCIAL OR COMMUNITY IMPACT | 20-1 | ||
20.1 | Environment, Social and Sustainability | 20-1 | ||
20.1.1 | Corporate Policies, Guiding Principles and Criteria | 20-1 | ||
20.1.2 | Social Setting | 20-4 | ||
20.1.3 | Consultation | 20-7 | ||
20.2 | Environmental Assessment Certifications and Permitting | 20-8 | ||
20.2.1 | Environmental Assessment Certifications | 20-8 | ||
20.2.2 | Permits and Other Authorizations | 20-9 | ||
20.3 | Environment | 20-13 | ||
20.3.1 | Environmental Setting | 20-13 | ||
20.3.2 | Geochemistry | 20-16 | ||
20.3.3 | Hydrogeology | 20-20 | ||
20.3.4 | Water Management | 20-22 | ||
20.3.5 | Water Quality | 20-27 | ||
20.3.6 | Waste Management | 20-28 | ||
20.3.7 | Air Emission Control | 20-28 | ||
20.3.8 | Closure Plan and Costs | 20-29 | ||
21.0 | CAPITAL AND OPERATING COST ESTIMATES | 21-1 | ||
21.1 | Capital Cost Estimate | 21-1 | ||
21.1.1 | Summary | 21-1 | ||
21.1.2 | Initial Capital Cost Estimate | 21-2 | ||
21.1.3 | Sustaining Capital Cost Estimates | 21-5 | ||
21.2 | Operating Cost Estimate | 21-6 | ||
21.2.1 | Summary | 21-6 | ||
21.2.2 | Mining Operating Cost Estimate | 21-7 | ||
21.2.3 | Process Operating Cost Estimate | 21-8 | ||
21.2.4 | G&A and Site Services Operating Cost Estimate | 21-9 | ||
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
22.0 | ECONOMIC ANALYSIS | 22-1 | ||
22.1 | Introduction | 22-1 | ||
22.2 | Pre-tax Model | 22-2 | ||
22.2.1 | Metal Price Scenarios | 22-4 | ||
22.3 | Smelter Terms | 22-4 | ||
22.4 | Markets and Contracts | 22-5 | ||
22.5 | Taxation and Royalty Considerations | 22-5 | ||
22.5.1 | Canadian Income Tax System | 22-5 | ||
22.5.2 | Provincial (BC) Mining Tax System | 22-6 | ||
22.6 | Royalties | 22-7 | ||
22.7 | Sensitivity Analysis | 22-7 | ||
23.0 | ADJACENT PROPERTIES | 23-1 | ||
23.1 | Snowfield Property | 23-1 | ||
23.2 | Bowser Property | 23-1 | ||
23.3 | Kerr-Sulphurets-Mitchell Property | 23-4 | ||
23.4 | Treaty Creek Property | 23-5 | ||
23.5 | Catear | 23-5 | ||
24.0 | OTHER RELEVANT DATA AND INFORMATION | 24-1 | ||
24.1 | Health, Safety, Environmental and Security | 24-1 | ||
25.0 | INTERPRETATIONS AND CONCLUSIONS | 25-1 | ||
25.1 | Geology | 25-1 | ||
25.2 | Mineral Resource | 25-1 | ||
25.3 | Mining | 25-2 | ||
25.3.1 | Underground Mine Geotechnical | 25-2 | ||
25.3.2 | Mining Methods | 25-3 | ||
25.3.3 | Waste Rock | 25-3 | ||
25.4 | Mineral Processing and Metallurgical Testing | 25-3 | ||
25.4.1 | Metallurgical Testing | 25-3 | ||
25.4.2 | Mineral Processing | 25-4 | ||
25.5 | Environmental | 25-5 | ||
25.5.1 | Geochemistry | 25-5 | ||
25.5.2 | Hydrogelogy | 25-5 | ||
25.5.3 | Water Management | 25-6 | ||
25.5.4 | Water Quality | 25-7 | ||
25.6 | Capital Cost and Operating Cost Estimates | 25-8 | ||
25.7 | Economic Analysis | 25-8 | ||
25.8 | Mineral Reserves | 25-9 | ||
26.0 | RECOMMENDATIONS | 26-1 | ||
26.1 | Introduction | 26-1 | ||
26.2 | Geology | 26-1 | ||
26.3 | Mineral Resource | 26-2 | ||
26.4 | Mining | 26-3 |
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704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
26.4.1 | Underground Mine Geotechnical | 26-3 | ||
26.4.2 | Mining Methods | 26-3 | ||
26.4.3 | Waste Rock | 26-3 | ||
26.5 | Mineral Processing and Metallurgical Testing | 26-4 | ||
26.6 | Environmental | 26-4 | ||
26.6.1 | Geochemistry | 26-4 | ||
26.6.2 | Hydrogelogy | 26-5 | ||
26.6.3 | Water Management | 26-6 | ||
26.6.4 | Water Quality | 26-6 | ||
27.0 | REFERENCES | 27-1 | ||
27.1 | Geology | 27-1 | ||
27.2 | Metallurgy and Recovery Methods | 27-6 | ||
27.3 | Mining | 27-7 | ||
27.4 | Mining Geotechnical | 27-8 | ||
27.5 | Waste Rock Disposal | 27-8 | ||
27.6 | Environmental | 27-9 | ||
27.7 | Water Management | 27-10 | ||
27.8 | Water Quality | 27-10 | ||
27.9 | Geochemistry | 27-10 | ||
27.10 | Hydrogeology | 27-11 | ||
27.11 | Adjacent Properties | 27-11 |
LIST OF TABLES | ||
Table 1-1: | January 2019 Valley of the Kings and West Zone Mineral Resource(1,2,3,4,5,6) | 1-5 |
Table 1-2: | January 2019 Valley of the Kings Zone Mineral Resource(1) | 1-6 |
Table 1-3: | West Zone Mineral Resource, April 2012(1) | 1-6 |
Table 1-4: | Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Zone and Reserve Category, Effective January 1, 2019 | 1-7 |
Table 1-5: | Comparison of 2018 Actuals vs. 2019 Reserve Validation Shapes | 1-7 |
Table 1-6: | Locked Cycle Tests Results | 1-10 |
Table 1-7: | Bulk Sample Processing Metallurgical Performances | 1-10 |
Table 1-8: | Locked Cycle Test Results | 1-11 |
Table 1-9: | Bruckejack Mill Production Data 2017-2018 | 1-12 |
Table 1-10: | Initial and Sustaining Capital Cost Estimates | 1-20 |
Table 1-11: | LOM Average Operating Cost Summary | 1-21 |
Table 1-12: | Brucejack Gold Mine Economic Performance Forecast | 1-22 |
Table 2-1: | Summary of QPs | 2-3 |
Table 4-1: | Mineral Claims for the Brucejack Property | 4-2 |
Table 6-1: | Exploration History of the Sulphurets Property between 1960 and 2008 | 6-1 |
Table 7-1: | Vein Generations in the Valley of the Kings Zone | 7-16 |
Table 8-1: | Principal Field-oriented Characteristics of Intermediate- and Low-sulphidation Epithermal Systems | 8-2 |
Table 9-1: | Exploration of the Brucejack Property between 2011 and 2014 | 9-1 |
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704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Table 10-1: | Drilling Summary for the Brucejack Property | 10-1 |
Table 11-1: | Sample Preparation and Analytical Methods Conducted on Pretivm Drill Samples Between 2014 and 2018 | 11-3 |
Table 13-1: | Conventional Grindability and Crushability Test Results | 13-2 |
Table 13-2: | SMC Test Results (2012) | 13-3 |
Table 13-3: | Gravity Recoverable Gold Test Results (2012) | 13-4 |
Table 13-4: | Precious Metal Material Balance | 13-4 |
Table 13-5: | Cyanidation Flowsheet Development Test Results | 13-6 |
Table 13-6: | Locked Cycle Tests Results | 13-8 |
Table 13-7: | Bulk Sample Processing Metallurgical Performances | 13-11 |
Table 13-8: | Bruckejack Mill Production Data 2017-2018(1) | 13-11 |
Table 13-9: | Major Metallurgical Testing and Simulations Programs 2014-2018 | 13-12 |
Table 13-10: | Head Assay Results (Gekko 2017) | 13-13 |
Table 13-11: | Head Assay Results (ALS 2018) | 13-13 |
Table 13-12: | Head Assays of Processing Samples | 13-13 |
Table 13-13: | Gold Deportment and Associations of Two Flotation Con BV 2017 | 13-15 |
Table 13-14: | Bond Test Results (ALS 2018) | 13-16 |
Table 13-15: | JK Drop Weight Test Results (ALS 2018) | 13-16 |
Table 13-16: | SMC Test Results and Parameters Derived from SMC Tests (ALS 2018) | 13-17 |
Table 13-17: | Locked Cycle Testing Conditions | 13-23 |
Table 13-18: | Locked Cycle Test Results | 13-23 |
Table 13-19: | Third Cleaner Flotation Results on the Second Locked Cycle Test | 13-24 |
Table 13-20: | Head Assays of Processing Samples | 13-24 |
Table 13-21: | Conventional and Column Flotation Results | 13-25 |
Table 13-22: | JKSimMet 3,800 t/d Results at 92% Availability | 13-29 |
Table 14-1: | Valley of the Kings Zone Mineralized Domains | 14-7 |
Table 14-2: | Summary Statistics of Gold and Silver Composited Data by Grouped Domain in 2019 Model Updated Area | 14-14 |
Table 14-3: | Thresholds Discretizing High-grade Distribution by Grouped Domain | 14-17 |
Table 14-4: | Indicator Variogram Parameters for High-grade Gold in Grouped Domain Bigdom 600 | 14-18 |
Table 14-5: | Variogram Model for the Probability of High-grade Gold Indicator Variable at 3.5 g/t Au | 14-19 |
Table 14-6: | Variogram Model for the Probability of High-grade Silver Indicator at 20 g/t Ag | 14-20 |
Table 14-7: | Variogram Model for Low-grade Gold and Silver Mineralization | 14-21 |
Table 14-8: | Search Parameters for High-grade and Probability of High-grade Variables for Gold and Silver by Grouped Domain Inside the Update Area | 14-21 |
Table 14-9: | Search Parameters for Low-grade Gold and Silver Inside the Update Area | 14-22 |
Table 14-10: | Mathematical Model Parameters for the Top MIK Threshold for Each Grouped Domain | 14-23 |
Table 14-11: | Specific Gravity Values and Bulk Density Conversion Factors for Resource Modelling in the Update Area | 14-23 |
Table 14-12: | Global Comparison of Mean Estimated and Input Composite Grade Data for Gold and Silver by Domain | 14-25 |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Table 14-13: | January 2019 Model to 2018 Mill Gold Production Reconciliation | 14-31 |
Table 14-14: | January 2019 Valley of the Kings and West Zone Mineral Resource(1,2,3,4,5,6) | 14-34 |
Table 14-15: | January 2019 Valley of the Kings Zone Mineral Resource(1) | 14-34 |
Table 14-16: | West Zone Mineral Resource, April 2012(1) | 14-35 |
Table 14-17: | Comparison Between January 2019 and July 2016 Resource Estimates for the Valley of the Kings Zone Inside the Update Area | 14-36 |
Table 15-1: | Cut-off Grade Costs | 15-2 |
Table 15-2: | NSR Parameters | 15-3 |
Table 15-3: | Main Valley of the Kings Mining Thickness by Mining Block | 15-6 |
Table 15-4: | Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Zone | 15-7 |
Table 15-5: | Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Block | 15-7 |
Table 15-6: | Comparison of 2018 Actuals vs. 2019 Reserve Validation Shapes | 15-10 |
Table 15-7: | Comparison of 2019 Mineral Reserves with Mined Actuals to Previous Reserve | 15-11 |
Table 16-1: | Development Design Parameters | 16-6 |
Table 16-2: | Stope Design Parameters | 16-7 |
Table 16-3: | LOM Paste Fill Requirements | 16-13 |
Table 16-4: | Summary of Stage 2 UCS Results | 16-14 |
Table 16-5: | LOM Backfilling – Waste Rock and Mill Tailings | 16-15 |
Table 16-6: | LOM Development Requirements | 16-16 |
Table 16-7: | LOM Tonnes and Grades | 16-18 |
Table 16-8: | Rock Mass Properties | 16-20 |
Table 16-9: | Ground Support Recommendations | 16-23 |
Table 16-10: | Mine Infrastructure Excavations – Ground Support Recommendations | 16-25 |
Table 16-11: | Major Underground Development and Production Equipment List | 16-26 |
Table 16-12: | Support Equipment List | 16-28 |
Table 16-13: | Primary Fan Specifications | 16-32 |
Table 16-14: | 2018 Propane Consumption | 16-49 |
Table 16-15: | Manpower by Operational Group | 16-54 |
Table 17-1: | Brucejack Mill Production Data 2017-2018 | 17-2 |
Table 17-2: | Major Design Criteria | 17-4 |
Table 17-3: | Projected Gold and Silver Production | 17-14 |
Table 19-1: | Gold and Silver Prices | 19-1 |
Table 20-1: | List of Amendments to EAC #M-15-01 | 20-9 |
Table 20-2: | List of BC Major Authorizations, Licenses, and Permits Obtained to Develop and Operate the Brucejack Project | 20-11 |
Table 20-3: | List of Federal Approvals and Licenses Obtained to Develop and Operate the Brucejack Project | 20-12 |
Table 20-4: | Average Monthly Climate Data for the Brucejack Gold Mine Site | 20-15 |
Table 21-1: | Summary of Initial Capital Costs | 21-1 |
Table 21-2: | Summary of LOM Sustaining Capital Costs | 21-2 |
Table 21-3: | Foreign Exchange Rates | 21-2 |
Table 21-4: | Mining Sustaining Capital Costs over the LOM | 21-5 |
Table 21-5: | Mining Sustaining Capital Costs by Year (US$000) | 21-5 |
Table 21-6: | Process Sustaining Capital Costs Over the LOM (US$ million) | 21-6 |
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Table 21-7: | Site Services and Infrastructure Sustaining Capital Costs Over the LOM (US$ million) | 21-6 |
Table 21-8: | LOM Average Operating Cost Summary | 21-6 |
Table 22-1: | Cash Flow Results Summary (including Discounted Post-tax NPV) | 22-1 |
Table 22-2: | Metal Production Quantities | 22-3 |
Table 22-3: | Economic Results Summary for Different Metal Price Scenarios | 22-4 |
Table 22-4: | Payment, Smelting and Refining Terms | 22-4 |
Table 22-5: | LOM Taxes Summary | 22-5 |
Table 23-1: | February 2011 Snowfield Mineral Resource | 23-1 |
Table 23-2: | March 2019 KSM Property Mineral Reserve | 23-4 |
Table 23-3: | March 2019 KSM Property Measured and Indicated Mineral Resources | 23-5 |
Table 25-1: | LOM Average Operating Cost Summary | 25-8 |
Table 25-2: | Brucejack Gold Mine Economic Performance Forecast | 25-9 |
LIST OF FIGURES | ||
Figure 1-1: | Simplified Process Flowsheet | 1-14 |
Figure 1-2: | Brucejack Gold Mine On-site Infrastructure Layout | 1-17 |
Figure 1-3: | Brucejack Gold Mine Off-site Infrastructure Layout | 1-18 |
Figure 1-4: | Overall Operating Cost Distribution by Area | 1-21 |
Figure 4-1: | Brucejack Property Location Map | 4-1 |
Figure 4-2: | Brucejack Property Mineral Claims | 4-3 |
Figure 4-3: | Pretivm Mineral Claims | 4-4 |
Figure 5-1: | Project Access | 5-3 |
Figure 6-1: | Visible Electrum in Valley of the Kings Zone Discovery Drillhole SU-012 | 6-3 |
Figure 7-1: | Regional Geological Setting of the Brucejack Deposit | 7-2 |
Figure 7-2: | Select Mineral Showings and Deposits in the Stewart-Iskut Culmination, Highlighting the Metal-rich Nature of this Structure | 7-4 |
Figure 7-3: | District-scale Geological Setting of the Brucejack Deposit on the East Side of the McTagg Anticlinorium | 7-5 |
Figure 7-4: | Geological Map of the Brucejack Project Area Showing Location of Mineralized Zones and their Association with the Band of Quartz-Sericite-Pyrite Alteration (shown in yellow) | 7-7 |
Figure 7-5: | Brucejack Property Geology Legend for Figure 7-4 | 7-8 |
Figure 7-6: | Three-dimensional Block Geological Interpretation Through the Brucejack Deposit, Showing Key Geological, Structural, and Mineralization Relationships Developed in the Valley of the Kings Zone and West Zone | 7-11 |
Figure 7-7: | Oblique View Down and Towards the West-Northwest of the Brucejack Deposit Showing Drillhole Intersections Greater than 5 g/t Gold Relative to Underground Workings in both the Valley of the Kings Zone and the West Zone | 7-15 |
Figure 7-8: | Mineralized Veins in the Valley of the Kings Zone of the Brucejack Deposit | 7-18 |
Figure 8-1: | Schematic Section of Calc-alkaline Volcanic Arc Showing High and Intermediate Sulphidation Epithermal Deposits and Porphyry Deposits | 8-3 |
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Figure 8-2: | Conceptual Model of Different Arc-related Porphyry and Epithermal Copper-Gold-Silver Mineralization Deposits | 8-4 |
Figure 9-1: | Plan View of the Brucejack Deposit Showing Significant Electrum Intersections from the 2015 Surface Exploration Drilling of the Flow Dome Zone | 9-4 |
Figure 9-2: | Plan View of ITEM Conductivity Data on the Western Edge of Pretivm’s Claim Block, Illustrating the Potential Scale of the Hydrothermal System Footprint (Warmer Colours) of which the Brucejack Deposit is a Part (also shown are Peripheral Known Mineralized Zones on the Brucejack and Snowfield Properties and Drill trances from the 2015 Surface Exploration Drill Program) | 9-5 |
Figure 9-3: | Cross Section of the Brucejack Deposit (Looking North) Showing Gold Assay Intersections from the 2015 Surface Exploration Drilling and 2018 Underground Deep Exploration Drilling of the Flow Dome Zone, as well as the Zone of Anomalous Copper and Molybdenite Assays | 9-6 |
Figure 9-4: | Plan View Part of the Brucejack Project Showing Location of the 2018 Frontier Geosciences Inc. Surface Reflection Seismic and IP Survey Lines | 9-7 |
Figure 10-1: | Plan View of Brucejack Property Drilling in and Around the Brucejack Deposit | 10-3 |
Figure 10-2: | Example Plan View on the 1,410 m Level in the Brucejack Gold Mine Showing 2017-2018 Drilling (Coloured by Gold Grade) and Valley of the Kings Zone Mineralized Domain Interpretations (Viewing Window ±20 m) | 10-6 |
Figure 10-3: | Example SW-NE Cross Section Through Along Mining Crosscut 20 (Central Parts of the Mine) Showing Drilling (Coloured by Gold Grade) and Mineralized Domain Interpretations in the Valley of the Kings Zone of the Brucejack Deposit (Viewing Window ±20 m) | 10-7 |
Figure 10-4: | Oblique View of the Valley of the Kings Zone Showing only 2017 and 2018 Drilling (Coloured by Gold Grade) and Mineralized Domain Interpretations | 10-8 |
Figure 13-1: | Cumulative Stage GRG versus Grind Size for Gold and Silver | 13-4 |
Figure 13-2: | Bulk Sample Process Flowsheet | 13-10 |
Figure 13-3: | Gold Grains Distributions with Size Range | 13-15 |
Figure 13-4: | Gravity Results Summary – Composite Samples – ALS 2018 | 13-18 |
Figure 13-5: | E-GRG Test Results | 13-19 |
Figure 13-6: | Rougher Flotation Tests on Composite H and L | 13-20 |
Figure 13-7: | Rougher Flotation Tests on Composite M | 13-20 |
Figure 13-8: | Cleaner Flotation Tests on Composite L, A, H, GH, WZ, and M | 13-21 |
Figure 13-9: | Locked Cycle Test Flowsheet No. 1 | 13-22 |
Figure 13-10: | Locked Cycle Test Flowsheet No. 2 | 13-22 |
Figure 13-11: | Gravity and Flotation Optimization Tests | 13-25 |
Figure 13-12: | Concentrate Thickener Capacity | 13-26 |
Figure 13-13: | Tailing Thickener Underflow Concentration with Time | 13-27 |
Figure 14-1: | Plan View of the Brucejack Deposit Showing the Location of the Valley of the Kings (VOK) Model Area Updated as Part of the January 2019 Resource Estimate | 14-2 |
Figure 14-2: | Topography and lithological wireframes Used in the Generation of the January 2019 Mineral Resource Estimate (Shown in Maptek’s Vulcan Mining Software) | 14-6 |
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Figure 14-3: | Plan View of Mineralized Domain triangulations used in the Generation of the January 2019 Mineral Resource | 14-8 |
Figure 14-4: | North-South Cross Section Along 426635 mE of Mineralized Domain Triangulations used in the Generation of the January 2019 Mineral Resource | 14-8 |
Figure 14-5: | Plan View Showing the Main Grouped Valley of the Kings Mineralized Domains used in the Generation of the January 2019 Mineral Resource | 14-9 |
Figure 14-6: | Plan View Showing Model Update Area Solid (blue) and Drillholes (red) from the 2017 – 2018 Infill Drill Campaign | 14-10 |
Figure 14-7: | Log Probability Plots of A) Gold and B) Silver Composited Data Inside the Valley of the Kings Mineralization Domains | 14-12 |
Figure 14-8: | Log-normal Histogram Plot of A) Gold and B) Silver Composited Data Inside the 2019 Updated Area Mineralization Domains | 14-13 |
Figure 14-9: | Example of Modelling the Upper Tail of the A) High-grade Gold and B) High-grade Silver Populations using a Hyperbolic Model; Data Shown for Grouped Domain Bigdom 600 | 14-22 |
Figure 14-10: | Example Gold Grade Trend Plots by Easting for Grouped Domain Bigdom 600 | 14-26 |
Figure 14-11: | Example Gold Grade Trend Plots by Northing for Grouped Domain Bigdom 600 | 14-26 |
Figure 14-12: | Example Gold Grade Trend Plots by Elevation for Grouped Domain Bigdom 600 | 14-27 |
Figure 14-13: | Example Silver Grade Trend Plots by Easting for Grouped Domain Bigdom 600 | 14-27 |
Figure 14-14: | Example Silver Grade Trend Plots by Northing for Grouped Domain Bigdom 600 | 14-28 |
Figure 14-15: | Example Silver Grade Trend Plots by Elevation for Grouped Domain Bigdom 600 | 14-28 |
Figure 14-16: | Plan View of the 1,290 m Level Showing Block Grade Estimates and Input Drillhole Composite Data Colour Coded by Gold Grade | 14-30 |
Figure 14-17: | North-South Cross Section Along 426630E Showing Block Grade Estimates and Input Drillhole Composite Data Coloured by Gold Grade | 14-30 |
Figure 14-18: | Cumulative Ounces Plot for the January 2019 Model Relative to 2018 Mill Production | 14-32 |
Figure 14-19: | January 2019 Valley of the Kings Zone Measured + Indicated Mineral Resource Sensitivity | 14-35 |
Figure 15-1: | Sources of Stope Dilution | 15-5 |
Figure 15-2: | 2019 Reserve Shapes and Mining Blocks in the Main Valley of the Kings Zone | 15-8 |
Figure 15-3: | Reserve Shapes and Mining Blocks in the West Zone | 15-9 |
Figure 15-4: | Combined 2019 Reserves and LOM Development by Mining Blocks, Looking West | 15-9 |
Figure 16-1: | Mine Access and Development Infrastructure | 16-2 |
Figure 16-2: | Brucejack Ramp System – Perspective View | 16-3 |
Figure 16-3: | Valley of the Kings Zone Sublevel Arrangement – Long Section | 16-4 |
Figure 16-4: | Typical Level Development – Valley of the Kings Zone | 16-5 |
Figure 16-5: | Standard Designs – General Layout for all | 16-7 |
Figure 16-6: | MSO Stope Shapes – VOK Zone | 16-8 |
Figure 16-7: | MSO Stope Shapes – West Zone | 16-9 |
Figure 16-8: | Typical LHOS Design | 16-11 |
Figure 16-9: | Example of Primary/Secondary LHOS at Brucejack Gold Mine | 16-12 |
Figure 16-10: | LOM Production Schedule by Mining Horizon | 16-17 |
Figure 16-11: | LOM Production Schedule by Activity | 16-17 |
Figure 16-12: | Brucejack Gold Mine Ventilation System (Looking West) | 16-30 |
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Figure 16-13: | Typical Production Level | 16-31 |
Figure 16-14: | Conveyor Fire Isolation | 16-33 |
Figure 16-15: | Dewatering Plan | 16-36 |
Figure 16-16: | Tipple and Ore Bin Sectional Projection | 16-37 |
Figure 16-17: | Crusher Feed and Crusher | 16-38 |
Figure 16-18: | Underground Power Requirement Profile | 16-39 |
Figure 16-19: | West Zone Portal Underground Single-line Diagram | 16-41 |
Figure 16-20: | Borehole Underground Single-line Diagram | 16-42 |
Figure 16-21: | Mine Service Water Distribution Schematic | 16-43 |
Figure 16-22: | Underground Equipment Service Facility | 16-44 |
Figure 16-23: | Bulk Emulsion/Powder Magazine Storage Plan | 16-45 |
Figure 16-24: | Permanent Refuge Station | 16-46 |
Figure 16-25 | Underground Communications System Schematic | 16-47 |
Figure 16-26: | Paste Fill Distribution System Schematic Showing Paste Pumping Zones | 16-52 |
Figure 16-27: | Paste Fill Distribution System Schematic | 16-53 |
Figure 17-1: | Simplified Process Flowsheet | 17-3 |
Figure 18-1: | Brucejack Gold Mine General Arrangement | 18-2 |
Figure 18-2: | Brucejack Gold Mine On-site Infrastructure Layout | 18-3 |
Figure 18-3: | Brucejack Gold Mine Off-site Infrastructure Layout | 18-4 |
Figure 18-4: | Knipple Transfer Station | 18-15 |
Figure 18-5: | Bowser Aerodrome | 18-16 |
Figure 18-6: | Wildfire Camp | 18-18 |
Figure 20-1: | Estimated Inflow to Underground Workings for Base Case Predictive Simulation and Selected Sensitivity Scenarios | 20-22 |
Figure 20-2: | Brucejack Lake Water Balance Model Schematic – Operations (Average Conditions) | 20-26 |
Figure 21-1: | Overall Operating Cost Distribution by Area | 21-7 |
Figure 21-2: | Mining Operating Cost Distribution by Area | 21-8 |
Figure 21-3: | Process Operating Cost Distribution by Area | 21-9 |
Figure 22-1: | Pre-tax Cash Flow | 22-13 |
Figure 22-2: | Post-tax NPV Sensitivity to Metal Prices | 22-17 |
Figure 22-3: | Post-tax NPV Sensitivity to Operating Costs | 22-18 |
Figure 23-1: | Detailed Geological Map of KSM-Brucejack Area and McTagg Anticlinorium and Section Locations | 23-2 |
Figure 23-2: | Legend for Detailed Geological Map of KSM-Brucejack Area and McTagg Anticlinorium and Section Locations | 23-3 |
Figure 25-1: | Simulated vs. Observed Inflow Rates | 25-6 |
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ACRONYMS & ABBREVIATIONS |
Acronyms/Abbreviations | Definition | |
.csv | comma separated values | |
portable document format | ||
AA | atomic absorption | |
AAS | atomic absorption spectroscopy | |
ABA | acid base accounting | |
AES | atomic emission spectroscopy | |
Ag | silver | |
AI | Bond abrasion index | |
ALS Global | ALS | |
AMC | AMC Mining Consultants (Canada) Ltd. | |
AMT | Audio Magnetotelluric | |
APS | aluminum phosphate sulphate minerals | |
Apy | arsenopyrite | |
Ar-Ar | argon-argon | |
ARD | acid rock drainage | |
As | arsenic | |
Au | gold | |
AuEq | gold equivalent | |
BC | British Columbia | |
BCEAA | BC Environmental Assessment Act | |
BCMWRP | British Columbia Mine Waste Rock Pile Research Committee | |
BGC | BGC Engineering Inc. | |
Bi | bismuth | |
Black Hawk | Black Hawk Mining Inc. | |
Brucejack Deposit | the Brucejack Gold-Silver Deposit | |
BV | Bureau Veritas Commodities Canada Ltd. | |
BWi | Bond ball mill work index | |
BZ | Bridge Zone | |
Cal | calcite | |
CCTV | closed-circuit television | |
CDE | Canadian Development Expense | |
CEA | cumulative expenditures account |
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Acronyms/Abbreviations | Definition | |
CEAA | Canadian Environmental Assessment Act | |
CEE | Canadian Exploration Expense | |
Chl | chlorite | |
CIM | Canadian Institute of Mining, Metallurgy and Petroleum | |
CMS | Cavity Monitoring System | |
CNCF | cumulative net cash flow | |
Corona | Corona Corporation | |
Cpy | chalcopyrite | |
CSS | Contact Support Service Inc. | |
CTCA | cumulate tax credit account | |
Cu | copper | |
CV | coefficient of variation | |
CWi | Bond crushing work index | |
CWP | Contact Water Pond | |
DCS | distributed control system | |
DO | dissolved oxygen | |
Dol | dolomite | |
DPS | diesel power station | |
DWi | drop weight index | |
EAC | Environmental Assessment Certificate | |
EAO | Environmental Assessment Office | |
EDS | energy dispersive spectrometer | |
EGL | effective grinding length | |
E-GRG | extended gravity recoverable gold | |
EIS | Environmental Impact Statement | |
El | electrum | |
EMP | Environmental Management Plan | |
EOR | engineer of record | |
ERM | Environmental Resources Management | |
ESEMP | Economic and Social Effects Mitigation Plan | |
ESS | electrical substation service | |
Esso | Esso Minerals Canada Ltd. | |
FA | fly-ash |
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Acronyms/Abbreviations | Definition | |
FCA | free carrier | |
FLS-DM | FLSmidth Dawson Metallurgical | |
FOB | free on board | |
FOS | factor of safety | |
FS | Feasibility Study | |
G&A | general and administrative | |
Gekko | Gekko Systems Pty Ltd. | |
GeoSpark | GeoSpark Consulting Inc. | |
GeoSpark Core | GeoSpark Core Microsoft® Access front-end interface | |
GH | Galena Hill | |
GIS | geographical information system | |
Gn | galena | |
GP | General Purpose | |
GPS | global positioning system | |
Granduc | Granduc Mines Ltd. | |
GRG | gravity recoverable gold | |
GSI | Geological Strength Index | |
Hazen | Hazen Research Inc. | |
HDPE | high-density polyethylene | |
Hg | mercury | |
HGT | high-grade threshold | |
HPGR | high-pressure grinding roll | |
HSE | health, safety and environmental | |
HSRCM | Healthy, Safety and Reclamation Code for Mines in British Columbia | |
HVAC | heating, ventilation and air conditioning | |
HW | hanging wall | |
Hy-Tech | Hy-Tech Drilling Limited | |
ICP | inductively coupled plasma | |
IMC | information management center | |
Inspectorate | Inspectorate Exploration and Mining Services Ltd. | |
IP | induced polarization | |
ISO | International Organization for Standardization | |
JV | joint venture |
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Acronyms/Abbreviations | Definition | |
K-Ar | potassium-argon | |
Knelson | FLSmidth Knelson | |
Krebs | Krebs-FLSmidth | |
KSM | Kerr-Sulphurets-Mitchell | |
Lancana | Lancana Mining Corp. | |
LHD | load-haul-dump | |
LHOS | long-hole open stoping | |
LIDAR | light detection and ranging | |
LNG | liquefied natural gas | |
LOM | life-of-mine | |
Lorax | Lorax Environmental Services Ltd. | |
LRMP | Land and Resource Management Plan | |
LSA | Local Study Area | |
MC | MineCem | |
MCC | motor control center | |
MDMER | Metal and Diamond Mining Effluent Regulation | |
MEMPR | Ministry of Energy, Mines & Petroleum Resources | |
Metso | Metso Corporation | |
Met-Solve | Met-Solve Laboratories Inc. | |
MFLNRORD | Ministry of Forests, Lands and Natural Resource Operations and RuralDevelopment | |
MIK | Multiple Indicator Kriging | |
ML | metal leaching | |
Mo | molybdenum | |
MSALabs | MS Analytical | |
MSO | Mineable Shape Optimizer | |
MT | Magnetotelluric | |
MTO | Mineral Titles Online | |
NaCN | sodium cyanide | |
NAD | North American Datum | |
NCF | net cash flow | |
Newhawk | Newhawk Gold Mines Ltd. | |
NI 43-101 | National Instrument 43-101 | |
NPAG | non-PAG |
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Acronyms/Abbreviations | Definition | |
NPR | Neutralization Potential Ratio | |
NPV | net present value | |
NSR | net smelter return | |
OK | Ordinary Kriging | |
OMS | Operations, Maintenance and Surveillance | |
PAG | potentially acid generating | |
PAX | potassium amyl xanthate | |
Pb | lead | |
PD | positive displacement | |
PEA | preliminary economic assessment | |
Placer Dome | Placer Dome Inc. | |
PLC | programmable logic controller | |
PMA | Particle Mineral Analysis | |
PMCL | Process Mineralogical Consulting Ltd. | |
Pocock | Pocock Industrial Inc. | |
Pretivm | Pretium Resources Inc. | |
Procon | Procon Mines and Tunneling | |
PRV | pressure reducing valves | |
Py | pyrite | |
QA | quality assurance | |
QC | quality control | |
QEMSCAN | Quantitative Evaluation of Materials by Scanning Electron Microscopy | |
QP | Qualified Person | |
QPO | Quantifiable Performance Objectives | |
Qz | quartz | |
RAR | return-air raise | |
RC | reverse circulation | |
RC | reverse circulation | |
REF-ET | Reference Evapotransiration | |
Re-Os | rhenium-osmium | |
RMS | RMS Corp. | |
ROM | run-of-mine | |
RQD | rock quality designation |
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Acronyms/Abbreviations | Definition | |
Rt | rutile | |
RWi | Bond rod mill work index | |
S | sulphur | |
SABC | SAG mill/ball mill/pebble crushing | |
SAG | semi-autogenous grinding | |
Sb | antimony | |
SBT | Stewart Bulk Terminal | |
SCADA | supervisory control and data acquisition | |
SCSE | SAG Circuit Specific Energy | |
Seabridge Gold | Seabridge Gold Inc. | |
SEM | scanning electron microscope | |
Ser | sericite | |
SFA | screen fire analysis | |
SGS | SGS Canada Inc. | |
SI | International System of Units | |
Silver Standard | Silver Standard Resources Inc. | |
SIPX | sodium isopropyl xanthate | |
SLS | solid liquid separation | |
SMC | SAG mill comminution | |
Sn | tin | |
SNF | SNF Canada | |
SOP | Standard Operating Procedure | |
Sp | sphalerite | |
SPI | SAG power Index | |
SQL | Structured Query Language | |
SRK | SRK Consulting (Canada) Inc. | |
SRMP | Sustainable Resource Management Plan | |
SS | Sunset Slag Blend | |
Strategic Minerals | Strategic Minerals LLC | |
Tetra Tech | Tetra Tech Canada Inc. | |
TIMA | Tescan Integrates Mineral Analyzer | |
TK/TU | Traditional Knowledge/Traditional Use | |
TMS | Trace Mineral Search |
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Acronyms/Abbreviations | Definition | |
TSS | total suspended solids | |
UCS | universal compressive strength | |
UDS | underground distribution system | |
UHF | ultra-high frequency | |
UPS | uninterruptable power supply | |
UTM | Universal Transverse Mercator | |
UV | ultraviolet | |
VEC | valued ecosystem component | |
VFD | variable frequency drive | |
VG | visible gold | |
VHF | very-high frequency | |
VMS | volcanogenic massive sulphide | |
VoIP | voice over internet protocol | |
VOK | Valley of the Kings | |
VSF | volcanosedimentary | |
VSI | vertical shaft impactor | |
W | tungsten | |
WAC | Wildlife Advisory Committee | |
WAP | wireless access point | |
Wardrop | Wardrop Engineering Inc. | |
WBS | work breakdown structure | |
WQG | Water Quality Guidelines | |
WRTSF | waste rock/tailings storage facility | |
WTP | water treatment plant | |
WZ | West Zone | |
XRD | x-ray diffraction | |
Zn | zinc |
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1.0 | SUMMARY |
1.1 | Introduction |
The Brucejack Gold Mine, located in northwest British Columbia (BC), is a high-grade underground mining operation that commenced commercial production in July 2017. The Brucejack Gold Mine uses conventional gravity concentration and sulphide flotation to produce gold (Au)-silver (Ag) doré and gold-silver flotation concentrate.
Pretium Resources Inc. (Pretivm), a low-cost intermediate gold producer, owns 100% of the Brucejack Property.
In 2014, prior to mine construction and the start of operations, Pretivm commissioned a team of consultants to complete a Feasibility Study (FS) update for the Brucejack Project in accordance with National Instrument 43-101 (NI 43-101) Standards of Disclosure for Mineral Projects, the NI 43-101 Companion Policy, and Form 43-101F1 (Ireland et al. 2014).
In December 2018, Pretivm commissioned Tetra Tech Canada Inc. (Tetra Tech) to complete an update to the 2014 FS. This NI 43-101 Technical Report updates the operating parameters considered in the 2014 FS to assess the potential of increasing the mine and process plant throughput from 2,700 to 3,800 t/d. This assessment has incorporated six quarters of mining operation information from the Brucejack Gold Mine.
The following consultants were commissioned to complete work and reviews for the purpose of the Technical Report:
n | Tetra Tech – mineral processing and metallurgical testing; mineral reserve estimates; mining methods; recovery methods; project surface and underground infrastructure; market studies and contracts; capital and operating cost estimates, and economic analysis. |
n | Ivor Jones Pty Ltd – property description and location; accessibility, climate, and physiology; history; geological setting and mineralization; deposit types; exploration; drilling; sample preparation and analysis; data verification; adjacent properties; and mineral resource estimates. |
n | BGC Engineering Inc. (BGC) – underground and surface geotechnical design; hydrogeology, water management. |
n | Environmental Resources Management (ERM) – aspects of environmental studies, permits, and social or community impacts; waste management; and closure plans. |
n | Lorax Environmental Services Ltd. (Lorax) – geochemistry and water quality. |
n | SRK Consulting (Canada) Inc. (SRK) – waste rock and tailings storage facility. |
The effective date of the Mineral Resource and Mineral Reserve estimates is January 1st, 2019 and the effective date of this Technical Report is April 4th, 2019.
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1.2 | Property Description and Location |
The Brucejack Property is centered ″NapproximatelyLatitudeby at130°11′31″W56°28′20 L approximately 950 km northwest of Vancouver, 65 km north-northwest of Stewart, and 21 km south-southeast of the Eskay Creek Mine in the Province of BC. The Brucejack Property consists of four mining leases and six mineral claims that cover the target Mineral Resource, totaling 3,305.85 ha in area. All mining leases are in good standing until September 17, 2019; all mineral claims are in good standing until January 31, 2030.
The Brucejack Property and the surrounding region have a history rich in exploration for precious and base metals dating back to the late 1800s. More recently in 2010, Silver Standard Resources Inc. (Silver Standard), pursuant to a purchase and sale agreement between Silver Standard (as the seller) and Pretivm (as the buyer), sold to Pretivm all of the issued shares of 0890693 BC Ltd., the owner of the Brucejack Project and the adjacent Snowfield Project. Subsequently, the name of 0890693 BC Ltd. was changed to Pretium Exploration Inc.
1.3 | Geology and Mineralization |
The Brucejack Deposit, currently defined as incorporating the Valley of the Kings Zone and the West Zone, is located on the western side of the Stikine Terrane in the Intermontane morphogeologic belt of the Canadian Cordillera. The Brucejack Deposit occurs in an exceptionally metals-rich tectonic assemblage hosted in volcanic island arc-related rocks of the Lower Jurassic Hazelton Group in BCs Golden Triangle.
At the district level, the Brucejack Deposit forms part of a well mineralized north-south gossanous trend (the Sulphurets Mineral District) associated with a regional unconformity and proximal mineralized Early Jurassic porphyry intrusions on the eastern limb of the McTagg Anticlinorium. Rocks of the Sulphurets Mineral District record a long history of volcanism, telescoping magmatic-hydrothermal alteration, mineralization, and deformation.
The Brucejack Deposit is interpreted to be a deformed, porphyry-related transitional to intermediate sulphidation epithermal high-grade gold-silver deposit that was formed between 184 to 183 Ma in an active island arc setting similar to the modern-day Philippines. Intermediate sulphidation epithermal deposits are considered to be a sulphide-rich sub-type of carbonate-base metal gold deposits, of which there are numerous examples in the southwest Pacific Rim region.
High-grade gold-silver mineralization was formed in association with a telescoped, multi-pulsed magmatic-hydrothermal system beneath an active local volcanic center. The high-grade precious metal mineralization appears to have been predominantly transported as colloidal suspensions, the destabilization of which during fluid mixing resulted in the ubiquitous yet highly locally variable distribution of gold and silver mineralization in the Brucejack Deposit. Precious metal precipitation from the colloidal suspension appears to have been concentrated along structural corridors within broader stockwork zones, including along faults, fractures, pre-existing foliation planes, and lithological contacts. Within the structural corridors the high-grade precious metal mineralization occurs as coarse dendritic aggregates of electrum and silver sulfosalts hosted in steeply dipping, east-trending quartz-carbonate to carbonate veins and vein breccia. The occurrence of structural corridors of higher-grade east-west mineralization within the broader stockwork zones represents an opportunity for longitudinal mining. The high-grade epithermal veins co-spatially overprint low-grade intrusion-related phyllic alteration. Epithermal vein development is interpreted to have occurred during the waning stages of Early Jurassic sinistral transpression in a compressive arc environment, followed by a limited Cretaceous deformation overprint.
There is a distinct precious metal zonation between the Valley of the Kings Zone, which contains higher gold grades, and the West Zone, which is significantly more silver rich. The Valley of the Kings Zone is currently defined over 1,200 m in east-west extent, 700 m in north-south extent, and 650 m in depth, and remains open to the east, west, and at depth. The West Zone is currently defined over 590 m along its northwest strike, 560 m across strike, and down to 650 m in depth, and remains open to the northwest, southeast, and at depth to the northeast.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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Recent Brownfields exploration drilling conducted from within the Brucejack Gold Mine targeting the Flow Dome Zone at depth demonstrated the continuation of Valley of the Kings Zone style mineralization to the east of the currently defined zone.
At least two porphyry mineralization targets are present on the Brucejack Property: the Bridge Zone and the Flow Dome Zone. Recent work suggests that the Flow Dome Zone may be the surface expression of the porphyry system that drove the development of the epithermal mineralization in the Brucejack Deposit. The Bridge Zone porphyry system is older (approximately 191 to 189 Ma) and is similar to the low-grade bulk tonnage copper (Cu)-molybdenum (Mo) ±gold Snowfield-Mitchell system further north. Additional exploration is currently testing the porphyry potential beneath the Flow Dome Zone.
Similar epithermal vein-hosted precious metal mineralization to the Brucejack Deposit is present throughout a 5 km by 1.5 km wide arcuate band of phyllic alteration on the Brucejack Property. More than 40 mineralization showings, at least eight of which are currently considered as mineralized zones (i.e., Bridge Zone, Waterloo Zone, Flow Dome Zone, Gossan Hill Zone, Shore Zone, SG Zone, Golden Marmot Zone, and Hanging Glacier Zone), are recognized in this band. The alteration and mineralization band has yet to be explored in sufficient detail for mineral resource estimation and represents upside potential on the Brucejack Property.
1.4 | Mineral Resource Estimates |
1.4.1 | Drilling, Sampling, Assaying and Data Verification |
Drilling has been the primary tool used in the exploration of the Brucejack Property, with 511,580 m of core drilling in 3,300 drillholes and 9,246 m of reverse circulation (RC) drilling in 349 drillholes having been completed between 1960 and 2018. The majority of the 2017-2018 drilling (64,268 m in 62 drillholes) was HQ diameter diamond core resource definition, stope infill, and stope definition drilling. Underground exploration drilling totaled 8,426 m in 20 drillholes, including 18 drillholes targeting potential north-south structures and the Brucejack Fault and two deep drillholes testing the eastern extent of the Valley of the Kings Zone and the porphyry potential beneath the Flow Dome Zone.
No significant north-south structures, including along the Brucejack Fault, were intersected in the west-oriented underground exploration drilling. Mineralized veins intersected as part of this program were generally east-west trending.
The underground exploration drilling targeting the Flow Dome Zone was successful in demonstrating the presence of Valley of the Kings Zone style mineralization from the Brucejack Gold Mine workings to the Flow Dome Zone, as well as in intersecting porphyry-style alteration and mineralization at depth beneath the Flow Dome Zone.
Limited RC drilling was introduced on a test basis in 2018 to determine the viability of the method for stope infill, definition, and production drilling. Both dry (5,049 m in 97 infill drillholes) and wet (4,197 m in 252 production drillholes) sampling options were used. The dry sample RC drilling program did not achieve the hoped-for cost and time efficiencies over diamond core drilling and was discontinued for resource definition and infill drilling. Wet sample RC drilling, did, however, provide sufficient cost and time efficiencies over diamond core drilling for grade control and production. Pretivm aims to sequentially bring additional RC-modified blasthole drill rigs online for grade control and production drilling through 2019.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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All infill diamond core drillholes were whole core sampled over 1 m sample lengths, whereas exploration drillholes were half-core sampled over 1.5 m lengths. Dry RC samples were collected as two 2 kg samples directly from the cyclone splitter over 1.52 m lengths. Infill core and RC samples were sent to the ALS Global (ALS) facility in Terrace, BC for sample preparation, and then to the ALS Vancouver laboratory in North Vancouver, BC for analysis. Umpire check laboratories included the MS Analytical (MSALabs) and Met-Solve Laboratories Inc. (Met-Solve) in Vancouver, BC. Production RC samples were not subject to the same level of rigor as infill core and RC drilling, and were prepared and analyzed at the Pretivm-run on-site laboratories. Whilst production RC samples are mainly used for grade control, a small number of these on the 1,260 m level were deemed to be of sufficient quality to be used in the estimation of the January 2019 Mineral Resource (Section 14.0).
Pretivm’squalityassurance (QA)/quality control (QC) protocols for the Brucejack Deposit included tests for data accuracy, precision, and sample cross-contamination through the frequent submission of field control samples together with drillhole samples. Field control samples were inserted into the sample stream at a frequency of one standard, one duplicate, and one blank sample per twenty regular samples. Additional field control blank samples were inserted immediately following samples with logged visible gold to quantify and avoid any potential cross-contamination between samples as a result of smearing from high grade samples. Pretivm has retained GeoSpark Consulting Inc. (GeoSpark), a Nanaimo, BC based geological database software and services company, to independently conduct routine QA/QC checks on its database and compile QA/QC reporting through its GeoSpark Assure Quality Service program. The results of numerous external and internal QA/QC checks conducted on Pretivm’s drilling and sampling databasetheBrucejackacrossPropertybetweenall of P 2011 and 2018 indicated acceptable levels of accuracy and precision, given the nature of the precious metal mineralization, with sample cross-contamination during sample preparation and assaying being within acceptable tolerance limits.
The Qualified Person (QP), Mr. I.W.O. Jones, P.Geo., FAusIMM CP(Geo) has conducted sufficient data and underground verification checks to satisfy himself that the drilling, core logging, sample handling, assaying, and data QA/QC procedures were conducted using industry best practices and that the data generated were of suitable quality for use in resource modelling and estimation of the Brucejack Deposit. Furthermore, Mr. Jones considers the geological interpretation to be appropriate and representative of the mineralization in the Brucejack Deposit.
1.4.2 | Mineral Resource Estimation |
An updated Mineral Resource, with an effective date of January 1, 2019, has been prepared for the Brucejack Deposit, incorporating information from additional tightly-spaced infill drilling, mapping of underground geological exposures, and mine production. The updated resource estimate is presented for the combined Valley of the Kings Zone and the West Zone in Table 1-1 and separately for the Valley of the Kings Zone in Table 1-2 and the West Zone in Table 1-3.
The new resource estimate comprises that part of the Valley of the Kings Zone update where new information was available: the December 2013 resource estimates for the Valley of the Kings Zone (Jones 2014) outside the update area and the April 2012 resource estimate for the West Zone (Jones 2012). The January 2019 Mineral Resource inside the update area is reported inclusive of Mineral Reserves and exclusive of material mined to December 31, 2018.
At the time of this report, the QP Mr. I.W.O. Jones, P.Geo., FAusIMM CP(Geo) was not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant factors that could materially affect the Mineral Resource presented in this Technical Report or its potential development.
The January 2019 Mineral Resource was estimated using the same methodology as for previous resource estimates for the Brucejack Deposit. The non-linear split population-based approach used is a similar one to that used in earlier estimates and is currently considered the most appropriate method for estimating the mixed and positively-skewed precious metal mineralization for the Brucejack Deposit.
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The model was validated against input drillhole data and mine production for the year 2018 and found to provide a reasonable to good representation of the input data and production information: the tonnes and grade reported by production in 2018 were within 10% of those reported from the 2019 resource model from within the mined outlines.
The resource model was classified as Measured, Indicated, and Inferred in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) (2014) Definition Standards. Measured Resources are expected to be within 10% and Indicated Resources are expected to be within 15% of mine production on an annual production basis. Shorter-term reconciliation is not considered appropriate given the highly variable and nuggety nature of the precious metal mineralization at Brucejack.
The January 2019 Mineral Resource effectively overwrites the July 2016 Mineral Resource inside the update area. Comparisons between these models (inclusive of mine production) show that the new estimate is lower by approximately 1.9 Mt, 0.9 Moz Au, and 0.5 Moz Ag in the Measured + Indicated Resource at similar estimated gold and silver grades, using the same cut-off grade. Inferred Resources also decreased by approximately 0.7 Mt, 0.9 Moz Au, and 1.6 Moz Ag, with a grade drop in both estimated gold and silver, using the same cut-off grade. The differences between the two models are largely data-driven. Additional tightly-spaced infill drilling, increased exposure of the mineralized system during mining, and over 1.5 Mt of actual production since mine commissioning have resulted in improved domain and local estimation parameter definition. Additional infill drilling in areas outside of the update area could result in similar changes in future resource updates.
Table 1-1:January 2019 Valley of the Kings and West Zone Mineral Resource(1,2,3,4,5,6)
Tonnes | Au | Ag | Contained Au | Contained Ag | ||||||
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | |||||
Measured | 4.2 | 10.71 | 204.8 | 1.5 | 27.8 | |||||
Indicated | 14.4 | 15.19 | 45.6 | 7.1 | 21.0 | |||||
Measured + Indicated | 18.7 | 14.18 | 81.6 | 8.5 | 48.7 | |||||
Inferred | 7.8 | 12.0 | 51.3 | 3.0 | 13.0 |
Notes: | (1) Mineral Resources which are not Mineral Reserves do not have demonstrated economic viability. The estimate of Mineral Resources may be materially affected by environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant issues. The Mineral Resources in this Technical Report were estimated using the (CIM 2014), CIM Standards on Mineral Resources and Reserves, Definitions and Guidelines prepared by the CIM Standing Committee on Reserve Definitions and adopted by CIM Council. |
(2)The quantity and grade of reported Inferred Resources in this estimation are uncertain in nature and there has been insufficient exploration to define these Inferred Resources as an Indicated or Measured Mineral Resource and it is uncertain if further exploration will result in upgrading them to an Indicated or Measured Mineral Resource category. |
(3)Contained metal and tonnes figures in totals may differ due to rounding. |
(4)Resources depleted for production to December 31, 2018. |
(5)For comparative purposes only, the January 2019 Mineral Resource is reported above a gold equivalent cut-off grade of 5 g/t gold equivalent (AuEq) (where AuEq=Au+Ag/53 as per previous models). |
(6)Mineral Resource is reported inclusive of Mineral Reserve. |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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Table 1-2:January 2019 Valley of the Kings Zone Mineral Resource(1) |
Tonnes | Au | Ag | Contained Au | Contained Ag | ||||||
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | |||||
Measured | 1.8 | 17.15 | 16.4 | 1.0 | 1.0 | |||||
Indicated | 11.9 | 17.15 | 15.4 | 6.6 | 5.9 | |||||
Measured + Indicated | 13.7 | 17.15 | 15.5 | 7.6 | 6.8 | |||||
Inferred | 3.8 | 17.7 | 19.4 | 2.2 | 2.4 |
Notes: | (1)Notes from Table 1-1 apply |
Table 1-3:West Zone Mineral Resource, April 2012(1) |
Tonnes | Au | Ag | Contained Au | Contained Ag | ||||||
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | |||||
Measured | 2.4 | 5.85 | 347 | 0.5 | 26.8 | |||||
Indicated | 2.5 | 5.86 | 190 | 0.5 | 15.1 | |||||
Measured + Indicated | 4.9 | 5.85 | 267 | 0.9 | 41.9 | |||||
Inferred | 4.0 | 6.4 | 82 | 0.8 | 10.6 |
Notes: | (1)Notes from Table 1-1 apply (see Jones (2012a) for more details) |
Source: | Jones (2012a) |
1.5 | Mineral Reserve Estimates |
A net smelter return (NSR) cut-off value of Cdn$237/t ore was used to define the Mineral Reserves. This cut-off value increased from the previous value of Cdn$180/t ore and reflects the change to a 3,800 t/d mining operation. The average site cost calculated for the LOM is Cdn$215/t ore, which provides an average Cdn$22/t margin.
The NSR for each block in the Mineral Reserve model was calculated as the payable revenue for gold and silver, less the costs of refining, concentrate treatment, transportation, assays, consultants, penalties, and insurance. The metal price assumptions associated with the NSR value are US$1,200/oz Au and US$15.6/oz Ag.
The dilution factors used in the Mineral Reserve were calculated from standard overbreak assumptions, based on Pretivm’s experience and -holebenchmarkingopen-stop(LHOS)operationsofother.Theverall longLOM recovery is estimated to be 94%, with a dilution of 12%.
The Mineral Reserves were developed from the Mineral Resource model “res1901_finmod_20190115_v3”, which was created by Pretivm and provided to Tetra Tech in January 2019. The orebody consists of numerous lenses in the Valley of the Kings Zone and two distinct lenses in the West Zone (Table 1-4).
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Table 1-4: Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Zone and Reserve Category, Effective January 1, 2019
Grade | Contained Metal | |||||||||||
Ore | ||||||||||||
Tonnes | Au | Ag | Au | Ag | ||||||||
Zone | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | |||||||
Valley of the | Proven | 2.0 | 11.2 | 11.8 | 0.7 | 0.7 | ||||||
Kings Zone | Probable | 11.1 | 14.3 | 10.5 | 5.1 | 3.8 | ||||||
Total | 13.1 | 13.8 | 10.7 | 5.8 | 4.5 | |||||||
West Zone | Proven | 1.4 | 7.2 | 383.0 | 0.3 | 17.4 | ||||||
Probable | 1.5 | 6.5 | 181.0 | 0.3 | 8.6 | |||||||
Total | 2.9 | 6.9 | 278.5 | 0.6 | 26.0 | |||||||
Total Mine | Proven | 3.4 | 9.5 | 166.5 | 1.0 | 18.1 | ||||||
Probable | 12.6 | 13.4 | 30.8 | 5.4 | 12.4 | |||||||
Total | 16.0 | 12.6 | 59.3 | 6.4 | 30.5 |
Note: | (1)Rounding of some figures may lead to minor discrepancies in totals. |
(2)Based on US$185/t cut-off grade, US$1,200/oz Au price, US$15.6/oz Ag price, and a Cdn$1.00:US$0.78 foreign exchange rate. |
1.5.1 | Validation of 2019 Mineral Reserve to 2018 Actual Mined and Milled Production |
In order to validate the methodology applied to the delineation of the 2019 Mineral Reserves, the process used in the delineation of the 2019 Mineral Reserves was replicated on the depleted portions of the 2019 Mineral Resource model (in particular areas mined in 2018). These generated shapes, referred to as Reserve Validation Shapes, overlap with mined-out development stopes from prior mining activities.
The 2019 Mineral Resource model contained within the 2019 Reserve Validation Shapes, which broadly coincide with the 2018 actual stope and development ore positions, were compared to the 2018 milled and mined results. Applicable validation shapes were determined using Cavity Monitoring System (CMS) scans of the mined material for 2018. Table 1-5 summarizes the comparison.
Table 1-5: Comparison of 2018 Actuals vs. 2019 Reserve Validation Shapes
Contained Gold | ||||||
Tonnes | Gold Grade | Ounces | ||||
Year | (’000 t) | (g/t) | (’000oz) | |||
2018 Actuals | 1,006 | 11.9 | 385 | |||
2019 Reserve Validation Shapes | 801 | 15.4 | 397 | |||
Difference | 20% | 29% | 3% |
The tonnage from the 2019 Reserve Validation Shapes was 20% less than actual mined, while ounces produced are comparable. The primary cause for this is the mining of material outside of the 2019 validation shapes that were originally part of the 2016 Mineral Reserves. This additional material is not encompassed within the validation shapes and therefore would not be a part of the 2019 Mineral Reserves if these areas were to be mined again. The inclusion of uneconomic material (waste) within the mined stopes resulted in mining more tonnage at a lower grade in 2018 than would have been mined based on the 2019 Mineral Reserve validation shapes.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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1.6 | Mining Methods |
The updated underground mine design supports the extraction of 3,800 t/d of ore through a combination of transverse and longitudinal LHOS. Closely matching the previously stated plan disclosed in the 2014 FS (Ireland et al. 2014), paste backfill and trackless mobile equipment will be employed in the majority of mining activities.
Access to the mine is via the Valley of the Kings decline, situated near the concentrator. The Valley of the Kings decline is also utilized as a conveyor way, with two conveyors installed at a combined length of 800 m. The existing West Zone portal provides the main access for large underground equipment and waste haulage.
Development initiated during the two pre-production years of the LOM continues, with the mine operating at a rate of 2,700 t/d since commercial production began in July 2017. The ramp-up period to a maximum output of 3,800 t/d occurs over three years, with production over this time averaging 1.3 Mt annually.
Geotechnical designs and recommendations are based on the results of site investigations and geotechnical assessments which include: rock mass characterization, structural geology interpretations, excavation and pillar stability analyses, and ground support design. No new rock mechanics site investigations or analysis work was completed for this Technical Report update.
The groundwater flow system was conceptualized to provide inflow estimates to mine workings. Total inflows were estimated to be approximately 100 L/s including service water. This estimate referenced results of site investigations and hydrogeologic testing that was used to determine the capacity of dewatering equipment, which allows for maximum inflows of 139 L/s to account for uncertainty in the water inflow model.
The mining contractor supplies the majority of the heavy equipment with the exception of supplemental long-hole drills for production and sampling, and some auxiliary vehicles. Key equipment required includes a fleet of load-haul-dump (LHD) vehicles and trucks for material loading and transport to surface. In addition, bolters, shotcrete sprayers, a long-hole drill, and a cable bolter are all required.
Mining is largely conducted through a mine contractor, with Pretivm providing planning and technical services. The underground mining department consists of technical staff, mining crews, mechanics, electricians and logistical or other support personnel. Total manpower required once the mine reaches full production will be 580, with approximately 380 on site at any time.
Ventilation has been designed to comply with BC regulations. Permanent fans at surface are located at each of the main portals and exhaust to surface is via a dedicated raise. An electric air heating system operates to ensure all air entering the mine is above freezing point.
Paste fill is distributed using a two-stage pumping system. A positive displacement pump in the paste fill plant located in the mill provides paste to all of the West Zone and the lower portion of the Valley of the Kings Zone (below 1,350 m). The paste fill plant feeds a booster pump located near the main Valley of the Kings decline. This booster pump supplies paste to the Upper Valley of the Kings Zone and (all above 1,350 m).
Ore is trucked from working areas to the centrally located underground crusher and subsequently transferred to surface via the two conveyors. Waste rock is utilized for backfill wherever possible or trucked to surface for disposal in Brucejack Lake.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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The location and method of the mine dewatering system has been changed since the 2014 FS (Ireland et al. 2014). Mine dewatering locations are included in the long-term mine plans, with adjustments to locations based on underground observations. No settling of sediments or slimes is conducted underground with sediments and slimes pumped directly to the mill clarifier by a system of submersible and horizontal centrifugal pumps located throughout the Valley of the Kings Zone and West Zone working levels.
For underground worker safety, both permanent and portable refuge stations have been installed at Brucejack Gold Mine. A permanent, 40-person station has been established at the 1,335 m elevation, with six, 16-person portable rescue chambers located elsewhere throughout the mine. Emergency warning systems include phones, cap lamp warning systems, and stench gas.
1.7 | Mineral Processing and Metallurgical Testing |
1.7.1 | Metallurgical Testing |
Extensive metallurgical testing programs have been conducted on the Brucejack Property since 1988, with major metallurgical test work performed between 2009 and 2014 to support the design and construction of the 2,700 t/d process plant at the Brucejack Gold Mine. Tetra Tech completed a test work review and process design descriptions for the 2014 FS (Ireland et al. 2014). Since commercial operations began in Q4 2017, additional test work and process simulations have been completed to support the current operation and assess the potential of increasing the process plant throughput to a target capacity of 3,800 t/d.
1.7.1.1 | Previous Test Work and Pilot Plant Operation |
The previous test work was conducted to investigate mineralization amenability to gravity concentration, gold-silver bulk flotation, and cyanidation processes. Sample characteristics, including chemical composition, mineralogy, and hardness, were investigated. Other processing tests, including melting and solid liquid separation (SLS) tests, were also carried out. The tested samples were obtained from the Valley of the Kings Zone, the West Zone, and adjacent gold deposits such as the Galena Hill Zone, the Gossan Hill (R-8) Zone, and others.
Most of the individual samples responded well to gravity separation, which consisted of a centrifugal separation and panning concentration. The test results also showed that the tested samples responded well to bulk flotation and cleaner flotation. With further verification tests on variability samples and locked-cycle tests on composite samples from the Valley of the Kings Zone and the West Zone, a conventional process combined gravity concertation and flotation on gravity tailings was recommended for the Brucejack Gold Mine. Table 1-6 summarizes the locked-cycle test results.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA
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Table 1-6:Locked Cycle Tests Results
Gravity Concentration | Flotation | |||||||||||||||||||||||||||
Head Grade | Concentrate | Concentrate | ||||||||||||||||||||||||||
Calculated | Recovery | Grade | Grade | Recovery | ||||||||||||||||||||||||
Test | Au | Ag | S | Au | Ag | Au | Ag | Au | Ag | S | As | Au | Ag | |||||||||||||||
Composite | No. | (g/t) | (g/t) | (%) | (%) | (%) | (kg/t) | (kg/t) | (g/t) | (g/t) | (%) | (ppm) | (%) | (%) | ||||||||||||||
VOK-1 to -4 | FLC1 | 24.2 | 33.6 | 2.92 | 54.2 | 30.5 | 11.7 | 9.1 | 181.3 | 354 | 48.1 | 8,249 | 43.9 | 61.7 | ||||||||||||||
VOK-1 to -4 | FLC2 | 24.2 | 31.8 | 2.96 | 48.6 | 27.1 | 9.9 | 7.9 | 175.6 | 341 | 46.9 | 6,930 | 49.3 | 67.0 | ||||||||||||||
WZ-1 and -2 | FLC3 | 6.0 | 225 | 3.03 | 32.0 | 1.3 | 1.7 | 2.7 | 52.6 | 3,096 | 43.5 | 2,622 | 59.2 | 88.5 | ||||||||||||||
WZ-1 and -2 | FLC4 | 6.3 | 240 | 3.10 | 36.5 | 1.1 | 2.5 | 2.8 | 44.6 | 2,490 | 34.7 | 2,228 | 60.2 | 90.7 | ||||||||||||||
VOK ML | FLC2 | 10.3 | 12.5 | 3.41 | 48.0 | 21.6 | 4.3 | 2.4 | 83.8 | 152 | 52.2 | 5,801 | 48.5 | 71.7 | ||||||||||||||
VOK MU | FLC1 | 12.1 | 13.4 | 2.70 | 64.9 | 35.1 | 6.0 | 3.6 | 78.1 | 160 | 49.5 | 6,059 | 33.9 | 62.4 |
Note: | S – sulphur; As – arsenic; VOK – Valley of the Kings; WZ – West Zone |
Between September 2013 and February 2014, Strategic Minerals LLC (Strategic Minerals) processed two batches of bulk mineral samples generated from the Valley of the Kings Zone at the Contact Mill facility located in Philipsburg, Montana. Samples totalling 11,500 t were processed in two batches. A combined process of gravity separation and rougher/scavenger flotation with rougher concentrate cleaner flotation was employed to treat the bulk material. The gravity circuit included a Knelson concentrator and a Gemini table, while a jigging and tabling circuit to recover coarse free gold was also added when high-grade material was fed to the mill. No regrind circuit was applied to the rougher/scavenger concentrates. The test results, as shown in Table 1-7, indicated that the combined gravity and flotation method can effectively recover gold and silver from the material, which had a wide range in feed grade.
Table 1-7: Bulk Sample Processing Metallurgical Performances
Feed | Metal Recovery (%) | Product Grade (g/t) | ||||||||||||||||||||||||
Table | ||||||||||||||||||||||||||
Calculated | Concentrate + | Gravity+ | ||||||||||||||||||||||||
Grade | Table | Table | Flotation | Table | Flotation | |||||||||||||||||||||
Tonnage | (g/t) | Concentrate | Middlings | Concentrate | Concentrate | Concentrate | ||||||||||||||||||||
Year | (t) | Au(2) | Ag(2) | Au(1) | Ag(1) | Au(1) | Ag(1) | Au | Ag | Au(1) | Ag(1) | Au(3) | Ag(3) | |||||||||||||
2013 | 10,302 | 17.5 | 17.1 | 41.8 | 18.2 | 47.6 | 21.0 | 97.5 | 86.9 | 259,487 | 110,146 | 79 | 129 | |||||||||||||
2014 | 1,203 | 82.6 | 59.7 | 47.9 | 36.6 | 56.2 | 44.0 | 98.0 | 96.3 | 247,999 | 136,877 | 398 | 402 |
Notes: | (1) Based on assay data from Contact Mill laboratory. |
(2) Including cleanout. | |
(3) Flotation concentrate only. |
1.7.1.2 | Recent Test Work for Mill Operation Optimization |
Beginning in 2017, a series of test work was conducted to support the Brucejack Gold Mine process plant optimization and throughput increase. The test work covered mineralogy analysis, grindability, gravity separation, intensive leaching, and flotation concentration. In addition, SLS tests and tailings paste backfill related tests were also performed. The results were used to optimize the current process plant operation and to assess the performance of the relevant circuits in the proposed 3,800 t/d throughput scenario.
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The metallurgical tests confirmed that significant amounts of gold and silver are gravity recoverable, which varies with the mineralization and gold head grades. Batch flotation tests were completed to examine the impacts of varied flotation conditions with various samples. Two locked-cycle flotation tests were performed based on the batch flotation test results (Table 1-8). The overall gold and silver recoveries achieved using Flowsheet No. 1 were 94.4% and 95.1%. The overall gold and silver recoveries achieves using Flowsheet No. 2 were 95.4% and 94.5%, respectively. It appears that the lower-grade concentrates of 28 g/t Au and 450 g/t Ag produced using Flowsheet No.2 can be upgraded by modifying the flowsheet configurations.
Table 1-8: Locked Cycle Test Results
Wt | Grade (g/t or %) | Recovery (%) | ||||||||||||
Products | (%) | Au | Ag | S | Au | Ag | S | |||||||
Flowsheet No. 1 | ||||||||||||||
Gravity Concentrate | 0.2 | 897 | 1,400 | 54.8 | 31.4 | 4.3 | 2.4 | |||||||
Flotation Concentrate | 9.1 | 34.2 | 559 | 40.5 | 63.0 | 90.8 | 92.3 | |||||||
Tailings | 90.7 | 0.30 | 3 | 0.24 | 5.6 | 4.8 | 5.4 | |||||||
Head | 100 | 4.97 | 56 | 4.01 | 100 | 100 | 100 | |||||||
Flowsheet No. 2 | ||||||||||||||
Gravity Concentrate | 0.1 | 1,596 | 2,053 | 53.5 | 36.7 | 4.5 | 1.7 | |||||||
Flotation Concentrate | 11.3 | 28.0 | 450 | 33.0 | 58.7 | 90.0 | 94.5 | |||||||
Tailings | 88.6 | 0.28 | 4 | 0.17 | 4.6 | 5.5 | 3.8 | |||||||
Head | 100 | 5.39 | 56 | 3.94 | 100 | 100 | 100 |
Note: | Flowsheet No. 1: three stages of cleaner flotation |
Flowsheet No. 2: two stages of cleaner flotation with rougher concentrate, the first reporting to the second cleaner flotation |
1.7.1.3 | Recent Process Simulations for Mill Expansion |
Several simulations were conducted to evaluate primary grinding, gravity, flotation, and concentrate and tailings thickening processes for the 3,800 t/d increased plant capacity. The primary grinding circuit modelling was based on comminution test data and operation data and performed using JKSimMet software. All simulation results indicated that the current primary grinding circuit will be capable of reaching the target throughput capacity of 3,800 t/d. With further optimization of the grinding operation parameters, the grinding efficiency is anticipated to be improved. The existing cyclones and slurry handling systems could readily accommodate the increased throughput through minor modifications.
According to the simulation results, the primary gravity circuit may reach its recommended capacity at the increased throughput, which may slightly affect the recovery of the gravity recoverable gold and silver. For the current flotation circuit, the rougher and scavenger existing cells should be able to provide sufficient flotation retention time to handle the 3,800 t/d throughput. However, the capacity of the second and third cleaner flotation cells will require some upgrades to accommodate the increased throughput, in particular the second cleaner flotation cell. According to the existing circuit layout and flotation cell sizing, it is recommended to convert the existing third cleaner flotation cell to the second cleaner flotation (two, 15 m3 tank cells operating in series) and to install a new 30 m3 cell for the third cleaner flotation.
The process flowsheet used for the current mine operation is a combination of conventional gravity concentration and bulk sulphide flotation to recover gold and silver into gold doré and gold-silver bearing flotation concentrates. Ore was first introduced to the mill in May 2017 with a focus on ramping up to the designed production throughput using ore from the low-grade ore stockpiles. On July 1, 2017, Pretivm declared commercial production at the Brucejack Gold Mine. Table 1-9 summarizes the production data from July 2017 to the end of 2018 based on Pretivm’sannualreports and news releases.
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Table 1-9: | Bruckejack Mill Production Data 2017-2018 |
2017 | 2018 | |||||||||||||||
Unit | Q3 | Q4 | Q1 | Q2 | Q3 | Q4 | 2018 Total | |||||||||
Milled Ore | t | 261,262 | 271,501 | 261,443 | 236,990 | 240,122 | 267,048 | 1,005,603 | ||||||||
Average Daily Tonnage | t/d | 2,840 | 2,951 | 2,905 | 2,604 | 2,610 | 2,903 | 2,755 | ||||||||
Head Grade | ||||||||||||||||
Gold | g/t | 10.5 | 8.2 | 9.1 | 14.9 | 12.4 | 11.5 | 11.9 | ||||||||
Silver | g/t | n/a | 13.8 | 13.0 | 17.1 | 14.1 | 15.8 | 15.0 | ||||||||
Metal Recovery (Gravity + Flotation) | ||||||||||||||||
Total Gold | % | 96.5 | 95.8 | 96.8 | 97.7 | 97.4 | 97.0 | 97.3 | ||||||||
Total Silver | % | n/a | 81.0 | 85.7 | 88.3 | 88.1 | 85.9 | 87.0 | ||||||||
Flotation Concentrate Grade | ||||||||||||||||
Gold | g/t | n/a | 52.5 | 55.5 | 63.7 | 58.2 | 53.6 | 57.7 | ||||||||
Silver | g/t | n/a | 147.3 | 130.6 | 128.1 | 116.0 | 143.4 | 129.8 |
1.7.2 | Mineral Processing |
The Brucejack Property mineralization typically consists of quartz-carbonate-adularia, gold-silver bearing veins, stockwork and breccia zones, along with broad zones of disseminated mineralization. There is a significant portion of gold and silver present in the form of nugget or metallic gold and silver.
The concentrator was designed to process gold and silver ore at a nominal rate of 2,700 t/d to produce gold doré and gold flotation concentrate. The mill was successfully commissioned between March and May of 2017 and reached full operation in Q4 2017. In 2018, various review and assessment work was conducted to evaluate the potential of increasing mill throughput to 3,800 t/d and potential bottlenecks that may limit a further increase in the mill feed rate. Equipment suppliers and independent consultants conducted various reviews through various supporting test work and simulations. The review work indicated that with some minor modifications, such as increasing some of the slurry pump sizing and increasing the second and third cleaner flotation capacities, the process plant can handle the increased throughput of 3,800 t/d. The upgraded flowsheet, shown in Figure 1-1, remains identical to the existing operation flowsheet, including the following components:
n | one stage of crushing underground |
n | a 2,500 t semi-autogenous grinding (SAG) mill feed surge bin on surface |
n | a SAG mill/ball mill/pebble crushing (SABC) primary grinding circuit equipped with a gravity concentration circuit |
n | rougher flotation and scavenger flotation of hydrocyclone overflow |
n | three stages of cleaner flotation on combined rougher and scavenger concentrates |
n | flotation concentrate dewatering |
n | flotation tailings dewatering circuits. |
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The mill feed ore is crushed and ground to the particle size of 80% passing approximately 90 to 100 µm. Two gravity centrifugal concentrators, together with two upgrading tables and one associated gravity centrifugal concentrator, recover the free nugget gold grains from the ball mill discharge. The resulting gravity concentrate is further refined in the gold room on site to produce gold-silver doré.
The gold and gold bearing minerals of the hydrocyclone overflow from the primary grinding circuit are floated using rougher and scavenger flotation. The resulting rougher flotation and scavenger flotation concentrates are upgraded through three stages of cleaner flotation. The first cleaner scavenger flotation tailings report to the rougher scavenger flotation to further recover the residual gold, silver, and their bearing minerals. The third cleaner concentrate, or the final flotation concentrate, is dewatered using a high-rate thickener and a tower filter press prior to being loaded in customized bulk containers for shipping.
The final rougher scavenger flotation tailings are dewatered in a deep cone thickener. Approximately 30 to 40% of the flotation tailings are used to make paste to backfill excavated stopes in the underground mine, and the balance is pumped to Brucejack Lake where the tailings are stored under water. The concentrate and tailings thickener overflows are recycled as process make-up water. The underground and collected water are treated in the water treatment plant in the mill. The treated water is used for mill cooling, gland seal service, reagent preparation, and make-up water.
The upgraded process plant will continue to operate as two, 12-hour shifts per day, 365 days per year. The overall availability for the underground primary crusher circuit is 60%. The grinding, flotation, and gravity concentration availability is 92%. The gold room operates during the day shift only.
Based on the life-of-mine (LOM) annual average, approximately 8,490 kg of gold and 4,740 kg of silver contained in doré and 6,710 kg of gold and 54,170 kg of silver contained in 62,300 t of gold-silver bearing flotation concentrate will be produced. On average, the flotation concentrate is expected to contain approximately 99 g/t Au and 869 g/t Ag. The arsenic content of the flotation concentrate is expected to be marginally higher than the penalty thresholds set up by most smelters.
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Figure 1-1:Simplified Process Flowsheet
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1.8 | Project Infrastructure |
During mine construction between 2015 and 2017, a number of on-site and off-site infrastructure components were built to support the operation. The locations of facilities and infrastructure items were selected to take advantage of local topography, accommodate environmental considerations, avoid avalanche hazards, and ensure efficient and convenient underground crew shift changes. Figure 1-2 shows the on-site infrastructure layout and Figure 1-3 illustrates the off-site infrastructure layout.
Facilities and infrastructure at or near the Brucejack Gold Mine site are currently in operation and include the following:
n | 73.5 km access road at Highway 37, travelling westward to Brucejack Lake with the 12 km section of road, from km 59 to km 71 traversing the main arm of the Knipple Glacier |
n | 138 kV power supply line from the Long Lake Hydro Substation to the substation at the Knipple Transfer Station, where the voltage reduces from 138 to 69 kV; the transmission line carries on to the Brucejack Gold Mine site. |
n | site roads and pads |
n | mill building containing process equipment, water treatment plant (WTP), paste backfill plant, and metallurgical laboratory |
n | water management infrastructure, including diversion ditches for both contact and non-contact water, interceptor ditches, and a contact water drainage collection pond and pump(s) to direct contact water to the water treatment plant |
n | water treatment infrastructure to treat underground infill water and surface contact water via a treatment plant that discharges the treated water to process and fresh/fire water tanks |
n | sewage treatment infrastructure |
n | potable water treatment facility |
n | incinerator |
n | solid waste management systems, including domestic waste disposal |
n | power distribution from the mine site substation to all the facilities |
n | process control and instrumentation |
n | communication systems |
n | ancillary facilities including: |
− | on-site fuel storage |
− | on-site explosive storage |
− | detonator magazine storage |
− | camp accommodation with recreation area, commissary, laundry facilities, mine dry, and medical clinic and first aid/emergency response |
− | truck shop |
− | helipad |
− | laydown areas |
− | covered storage building. |
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The Brucejack Access Road is an all-season, two-way access road that commences at Highway 37 at km 215 and travels generally westward to Brucejack Lake, a distance of 73.5 km. The access road is maintained throughout the year by road grooming equipment and snow plows. Regular patrols are conducted, particularly, in potential avalanche areas with avalanche control measures in place. The 12 km section of the access road (km 59 to km 71) traverses the main arm of the Knipple Glacier. During winter months the route is a groomed snow surface, but is an ice surface during the summer months.
The Knipple Transfer Station is located approximately 12 km southeast of Brucejack Gold Mine site. The Knipple Transfer Station facilities include a camp, maintenance and emergency vehicle building, cold storage, fuel dispensing system, helipad, incinerator, assay laboratory, truck scale, and laydown areas. All deliveries to and from the mill site report to this facility for intermediate storage or transfer to a different vehicle before delivery to the mine or off-site. Similarly, loads from the mill site are managed in reverse order.
There is a security gatehouse and camp at the Wildfire Camp site, located on the Brucejack Access Road near the intersection of Highway 37. The security gatehouse provides access control to the inbound and outgoing traffic along the Brucejack Access Road.
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Figure 1-2:Brucejack Gold Mine On-site Infrastructure Layout
Source: | Pretivm (2019) |
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Figure 1-3:Brucejack Gold Mine Off-site Infrastructure Layout
Source: | Pretivm (2019) |
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The tailings delivery system discharges thickened tailings slurry to the bottom of Brucejack Lake (approximately 80 m deep) when not used for paste backfill (approximately 40 to 50% of the time). For discharge to the lake, the tailings slurry is pumped to an agitated slurry mixing tank and then diluted at the nominal solids throughput rate of approximately 180 t/h. The diluted slurry is pumped overland and then underwater along the suspended discharge lines to the discharge point.
Both pipes are suspended on cables to allow for vertical and horizontal repositioning over the LOM to ensure the pipe is not covered by tailings and to meet permit conditions for vertical positioning above the lake bottom.
A 138 kV overhead power supply line from the substation at Long Lake Hydro Substation was constructed in 2016/2017 and connects to the Knipple Substation.
The main site power steps down from 138 to 69 kV via two 20/26 MVA oil-filled transformers, complete with neutral grounding resistors, located in the main substation yard at the Knipple Substation. Each transformer is capable of carrying the entire site load. The 69 kV transmission line is transported to Brucejack Gold Mine where it enters into the mill.
The voltage is further stepped down from 69 kV to 4.16 kV via 2 x 15/20/25 MVA oil-filled transformers and distributed to the site via 4.16 kV rated switchgear. The rating for site on a distribution end is 4.16 kV and further transformed to 0.6 kV for smaller loads.
The main mill and underground loads are fed via power cables in cable tray. The main substation is located inside the mill. Power feeds to the mill building, camps, truck shop, and underground are all underground buried services.
Within the mill, large loads are powered at 4.16 kV. Smaller loads are powered at 600 V via switchgear and motor control centers (MCCs). Variable frequency drives (VFDs) and soft starters are employed strategically to optimize process and energy performance.
An avalanche hazard assessment of the mine site, access road, and transmission line route was presented in the 2014 FS (Ireland et al. 2014). Generally, the avalanche hazard assessment of the mine site, access road, and transmission line route remains unchanged from the 2014 FS (Ireland et al. 2014). The avalanche season for infrastructure below the 1,000 m elevation level is generally from November to May, while for elevations above 1,200 m the season is from October to June, or if cool and wet conditions persist avalanches can occur in summer months. Snow avalanches generally occur in areas where there are steep open slopes or gullies, and deep (more than 50 cm) mountain snow packs. Risks associated with avalanches are normally due to exposure to the high impact forces that occur, as well as the effects of extended burial for any person caught in an avalanche. An avalanche path generally consists of a starting zone, a track, and a runout zone.
Pretivm has full time mountain safety technicians who monitor avalanche risk, develop hazard ratings for the Brucejack Access Road for specific sections, and release hazard bulletins with avalanche ratings for those road sections and glacier hazard ratings for travel on the glacier. The mountain safety technicians regularly survey the ice road and work with road maintenance to ensure safe travel on the ice.
1.9 | Environmental Studies, Permitting and Social and Community Impact |
Pretivm remains committed to operating the Brucejack Gold Mine in a sustainable manner and according to its corporate guiding principles. Every reasonable effort has and will continue to be made to minimize long-term environmental impacts and to ensure that the mine provides lasting benefits to local communities while generating substantial economic and social advantages for shareholders, employees, and the broader community. Pretivm respects the traditional knowledge of the Aboriginal peoples who have historically occupied or used the area. Pretivm’s ncludeobjectivescontinuingtoretainithe integrity of ecosystems within which mine infrastructure is located to the extent feasible during the remainder of mine operations. Upon mine closure, the intent will be to reclaim mine infrastructure disturbance areas to the approved end land uses in accordance with the approved reclamation plan, thereby returning the disturbed areas to levels of land productivity equal to or better than existed prior to mine development.
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1.10 | Capital and Operating Cost Estimates |
1.10.1 | Capital Cost Estimate |
The total estimated capital cost to upgrade the Brucejack Gold Mine mill capacity to 3,800 t/d is US$22.5 million, excluding cost related to mining operations which are included in the sustaining capital cost. The estimated surface facility expansion capital cost includes design, construction, installation, and commissioning to increase the throughput of the current mine operation from 2,700 to 3,800 t/d. The total estimated sustaining capital cost is US$200.7 million, including related costs for mining, processing and site infrastructure and services. Table 1-10 summarizes the surface facility expansion and LOM sustaining capital costs. All costs, including quotations received from vendors, were converted from Canadian to US dollars using a foreign exchange rate of Cdn$1.00:US$0.775. This is a Class 4 estimate, which according to AACE International, is expected to be in the range of -15%/+20%.
Table 1-10: Initial and Sustaining Capital Cost Estimates
Initial | LOM Sustaining | |||
Area | Capital Costs | Capital Cost | ||
Description | (US$ million) | (US$ million) | ||
Mining | included in sustaining capital cost | 51.6 | ||
Processing | 22.5 | 33.5 | ||
Site Infrastructure and Services | 115.7 | |||
Total | 22.5 | 200.7 |
1.10.2 | Operating Cost Estimate |
The estimated LOM average operating cost for the Brucejack Gold Mine is US$168.02/t milled. Table 1-11 shows the cost breakdown for each area and Figure 1-4 shows the cost distribution by area.
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Table 1-11: | LOM Average Operating Cost Summary |
Unit Operating Cost | ||
Area | (US$/t milled) | |
Mining | 74.42 | |
Processing | 21.87 | |
Overall Site Services, including Office(1) | 36.19 | |
G&A | 35.54 | |
Total Operating Cost | 168.02 |
Note: | (1) Including the costs for off-site and satellite offices. | |
G&A – general and administrative. |
Figure 1-4: Overall Operating Cost Distribution by Area
The operating cost estimate is based on the Brucejack Gold Mine operating experience, including consumable supplies, power supply, contractor services, camp services, personnel transportation, and labour salaries/wages in Q4 2018 and Q1 2019. The expected accuracy range of the operating cost estimate is +15%/-15%. All the costs have been estimated in US dollars, unless otherwise specified.
The operating costs exclude shipping charges and sale costs for the gold-silver doré and gold-silver concentrate and royalties, which are included in financial analysis.
All operating cost estimates exclude taxes unless otherwise specified.
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1.11 | Economic Analysis |
Tetra Tech prepared an economic evaluation of the Brucejack Gold Mine based on a discounted cash flow model for the remaining 14-year LOM and 15.74 Mt of ore included in the mine plan. For this mine plan, a post-tax net present value (NPV) of US$2,587 million at a discount rate of 5% and US$2,225 million at a discount rate of 8% was estimated.
The Brucejack Gold Mine economic model is based on the following assumptions:
■ | gold price of US$1,300/oz |
■ | silver price of US$16.90/oz |
■ | foreign exchange rate of Cdn$1.00:US$0.778 |
The production schedule was incorporated into the pre-tax financial model to develop annual recovered metal production. Capital expenditures include mill feed throughput expansion capital costs to increase mining and mill capacity from 2,700 to 3,800 t/d and ongoing sustaining capital costs for mining and milling additions and equipment replacement. The total LOM capital cost is US$223.2 million, including US$22.5 million in surface facility expansion capital.
The NPV was estimated at the beginning of the mining schedule and therefore has an effective date of January 1st, 2019.
Table 1-12 summarizes the forecast for economic performance for the Brucejack Gold Mine operation for the remaining LOM.
Table 1-12: Brucejack Gold Mine Economic Performance Forecast
Unit | Amount | |||
Tonnes Mined and Processed | kt | 15,754,279 | ||
Gold Head Grade | g/t | 12.6 | ||
Silver Head Grade | g/t | 58.4 | ||
Total Project Revenue | US$ million | 7,911 | ||
Operating Costs | US$ million | (2,647) | ||
Royalties | US$ million | (139) | ||
Sustaining Capital Costs | US$ million | (223) | ||
Other Expenses | US$ million | (29) | ||
Taxes Payable | US$ million | (1,445) | ||
Post-tax NPV (8% Discount Rate) | US$ million | 2,225 |
1.12 | Conclusions and Recommendations |
The Brucejack Gold Mine expansion plan is considered to be economically viable based on the results of the work presented in this Technical Report. The process plant is anticipated to be capable of processing 3,800 t/d of ore or higher with minor modifications on some existing circuits. Section 26.0 outlines detailed recommendations for the Brucejack Gold Mine.
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2.0 | INTRODUCTION |
The Brucejack Gold Mine, located in northwest BC, is a high-grade underground mining operation that commenced commercial production in July 2017. Brucejack uses conventional gravity concentration and sulphide flotation to produce gold-silver doré and gold-silver flotation concentrate.
Pretivm, a low-cost intermediate gold producer, owns 100% of the Brucejack Property.
In December 2019, Pretivm commissioned Tetra Tech to complete an update to the 2014 FS. This NI 43-101 Technical Report updates the operating parameters considered in the 2014 FS to assess the potential of increasing the process plant throughput from 2,700 to 3,800 t/d. This assessment is based on six quarters of mining operations at the Brucejack Gold Mine.
The following consultants were commissioned to complete work and reviews for the purpose of the Technical Report:
■ | Tetra Tech – mineral processing and metallurgical testing; mineral reserve estimates; mining methods; recovery methods; project surface and underground infrastructure; market studies and contracts; capital and operating cost estimates, and economic analysis. |
■ | Ivor Jones Pty Ltd – property description and location; accessibility, climate, and physiology; history; geological setting and mineralization; deposit types; exploration; drilling; sample preparation and analysis; data verification; adjacent properties; and mineral resource estimates. |
■ | BGC – underground and surface geotechnical design; hydrogeology, water management. |
■ | ERM – aspects of environmental studies, permits, and social or community impacts; waste management; and closure plans. |
■ | Lorax – geochemistry and water quality. |
■ | SRK – waste rock and tailings storage facility. |
The effective date of the Mineral Resource and Mineral Reserve estimates is January 1st, 2019 and the effective date of this Technical Report is April 4th, 2019.
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2.1 | Terms of Reference |
The following terms of reference are included throughout this report:
■ | The Brucejack Property refers to the mineral claims that were acquired as the property, as listed in Table 4-1. |
■ | The Brucejack Gold Mine refers to the property only on the mining leases, as listed in Table 4-1. |
■ | The Brucejack Project refers to all geological or engineering work completed on and around the Brucejack Gold Mine that leads to the short-term advancement of the existing mining operation. It includes near-mine exploration and all of the off-mining leases infrastructure. |
■ | The April 2012 Mineral Resource for the West Zone is detailed in Jones (2012a). There has been no change to the April 2012 West Zone Mineral Resource since that time. All references to the Mineral Resource for the Brucejack Deposit from November 2012 to present incorporate the April 2012 West Zone Mineral Resource. |
■ | The November 2012 Mineral Resource for the Valley of the Kings Zone is detailed in Jones (2012c). |
■ | The December 2013 Mineral Resource for the Valley of the Kings Zone is detailed in Jones (2014). |
■ | The December 2016 Mineral Resource for the Valley of the Kings Zone is detailed in Pretivm (2016) and Board et al. (2017). |
■ | The January 2019 Mineral Resource is detailed in the current Technical Report. |
2.2 | Site Visits |
In accordance with NI 43-101 guidelines, the following QPs completed a visit to the Brucejack Property:
■ | Trevor Crozier, M.Eng., P.Eng., of BGC visited the Brucejack Property from September 18thto 20th, 2017. |
■ | Hassan Ghaffari, P.Eng. of Tetra Tech visited the Brucejack Property on March 13th, 2019. |
■ | Mark Horan, P.Eng. of Tetra Tech visited the Brucejack Property from April 4th to 6th, 2019. |
■ | Jianhui (John) Huang, Ph.D., P.Eng. of Tetra Tech visited the Brucejack Property on March 6thand 7th, 2018 and on June 5th and 6th, 2018. |
■ | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) of Ivor Jones Pty Ltd visited the Brucejack Property from August 20th to 24th, 2018. |
■ | Catherine Schmid, M.Sc., P.Eng., of BGC visited the Brucejack Property on December 1st and 2nd, 2018. |
■ | Rolf Schmitt, M.Sc., P.Geo., of ERM visited the Brucejack Property from April 1st to 3rd, 2019. |
■ | Alison Shaw, Ph.D., P.Geo. of Lorax visited the Brucejack Property from July 17th to 24th, 2014. |
■ | Hamish Weatherly, M.Sc., P.Geo. of BGC visited the Brucejack Property on August 28th, 2018. |
■ | Maritz Rykaart, Ph.D., P.Eng. visited the Brucejack Property from September 19th to 20th, 2018. |
2.3 | Qualified Persons |
The QPs responsible for this technical report are listed in Table 2-1.
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Table 2-1: | Summary of QPs |
Report Section | Company | QP | |
1.0 | Summary | All | Sign-off by Subsection |
2.0 | Introduction | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. |
3.0 | Reliance on Other Experts | Tetra Tech | Sign-off by Subsection |
4.0 | Property Description and Location | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
5.0 | Accessibility, Climate, Local Resources, Infrastructure, and Physiography | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
6.0 | History | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
7.0 | Geological Setting and Mineralization | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
8.0 | Deposit Types | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
9.0 | Exploration | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
10.0 | Drilling | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
11.0 | Sample Preparation, Analyses and Security | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
12.0 | Data Verification | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
13.0 | Mineral Processing and Metallurgical Testing | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. |
14.0 | Mineral Resource Estimate | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
15.0 | Mineral Reserve Estimate | Tetra Tech | Mark Horan, P.Eng. |
16.0 | Mining Methods | Tetra Tech/ BGC | Mark Horan, P.Eng./ Catherine Schmid, M.Sc., P.Eng. Ed Carey, P.Eng, |
17.0 | Recovery Methods | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. |
18.0 | Project Infrastructure | Tetra Tech/ SRK | Hassan Ghaffari, P.Eng./ Maritz Rykaart, Ph.D., P.Eng. |
19.0 | Market Studies and Contracts | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. |
20.0 | Environmental Studies, Permitting, and Social or Community Impact | ERM/ BGC/ Lorax | Rolf Schmitt, M.Sc., P.Geo./ Hamish Weatherly, M.Sc., P.Geo./ Trevor Crozier, M.Eng., P.Eng./ Alison Shaw, Ph.D., P.Geo. |
21.0 | Capital and Operating Costs | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. Mark Horan, P.Eng. |
22.0 | Economic Analysis | Tetra Tech | Mark Horan, P.Eng. |
23.0 | Adjacent Properties | Ivor Jones Pty Ltd | Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) |
24.0 | Other Relevant Data | Tetra Tech | Jianhui (John) Huang, Ph.D., P.Eng. |
25.0 | Interpretations and Conclusions | All | Sign-off by Subsection |
26.0 | Recommendations | All | Sign-off by Subsection |
27.0 | References | All | Sign-off by Subsection |
2.4 | Information and Data Sources |
A complete list of references is provided in Section 27.0.
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3.0 | RELIANCE ON OTHER EXPERTS |
3.1 | Introduction |
The QPs who prepared this Technical Report relied on information provided by experts who are not QPs. The relevant QPs believe that it is reasonable to rely on these experts, based on the assumption that the experts have the necessary education, professional designations, and relevant experience on matters relevant to the Technical Report.
3.2 | Status of Mining Leases and Mineral Claims |
Ivor Jones, P.Geo., FAusIMM, CP(Geo) relied upon public information, as well as information from Max Holtby, P.Geo., Director of Permitting for Pretivm, regarding the status and circumstances of the Brucejack Property mining leases and mineral claims as reported in Section 4.0.
3.3 | Economic Analysis |
Mark Horan, P.Eng. relied on Velibor Petric, Site Mine Controller from Pretivm, for guidance on applicable taxes and royalties relevant to revenue or income from the Brucejack Gold Mine as detailed in Section 22.0.
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4.0 | PROPERTY DESCRIPTION |
Information in this section has been excerpted from Jones (2014) and updated.
4.1 | Location |
The Brucejack Property is centered approximately at 56°28’20“N Latitude by 130°11’31“W Longitude (Universal Transverse Mercator (UTM) 426,967E 6,258,719N North American Datum (NAD) 83 Zone 9), a position approximately 950 km northwest of Vancouver, 65 km north-northwest of Stewart, and 21 km south-southeast of the Eskay Creek Mine (Figure 4-1). The Brucejack Property coordinates used in this Technical Report are located relative to the NAD83 UTM coordinate system.
Figure 4-1: Brucejack Property Location Map
Source: | Pretivm |
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4.2 | Tenure |
In 2010, pursuant to a purchase and sale agreement between Silver Standard (as the seller) and Pretivm (as the buyer), Silver Standard sold to Pretivm all of the issued shares of 0890693 BC Ltd., the owner of the Brucejack Gold Mine and the Snowfield Project. Subsequently, the name of 0890693 BC Ltd. changed to Pretium Exploration Inc.
4.3 | Status of Mining Titles |
The Brucejack Property is located on provincial Crown land and consists of four mining leases and six mineral claims that cover the target Mineral Resource, totalling 3,305.85 ha in area. According to the BC Mineral Titles Office official information, all mining leases are in good standing until September 17, 2019; all mineral claims are in good standing until January 31, 2030 (Table 4-1).
Brucejack Property mineral claims and mining leases are contiguous with the Snowfield and Bowser properties, a large block of mineral claims held by Pretivm (Figure 4-2). The Snowfield and Bowser Properties form a block of mineral claims that total 338 mineral claims and measure approximately 122,078 ha (Figure 4-3). Pretivm mineral claims extend from the Brucejack Gold Mine site area east to Highway 37, including parts of the Bowser River, Scott Creek, and Wildfire Creek watersheds, and along parts of the transmission line right-of-way. The Brucejack Gold Mine is situated within the Sulphurets District, Skeena Mining District.
Table 4-1: | Mineral Claims for the Brucejack Property |
Pretivm | |||||||
Tenure | Tenure | Map | Interest | In Good | Area | ||
No. | Type | No. | Owner | (%) | Status | Standing To | (ha) |
509223 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 428.62 |
509397 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 375.15 |
509400 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 178.63 |
1027399 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 983.61 |
1027400 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 500.39 |
1034915 | Mineral Claim | 104B | Pretium Exploration Inc. | 100 | Good | 31-Jan-30 | 89.35 |
1038597 | Mining Lease | 104B | Pretium Exploration Inc. | 100 | Good | 17-Sep-19 | 53.60 |
1038598 | Mining Lease | 104B | Pretium Exploration Inc. | 100 | Good | 17-Sep-19 | 533.61 |
1038599 | Mining Lease | 104B | Pretium Exploration Inc. | 100 | Good | 17-Sep-19 | 35.70 |
1038600 | Mining Lease | 104B | Pretium Exploration Inc. | 100 | Good | 17-Sep-19 | 107.20 |
Total (ha) | 3,305.85 |
The QP relied upon public information, as well as information from Pretivm, regarding the Brucejack Property claims and has not undertaken an independent verification of title and ownership. However, the QP verified information relating to tenure, to the extent possible, using public information available through the Mineral Titles Branch of the BC Ministry of Energy, Mines & Petroleum Resources (MEMPR) Mineral Titles Online (MTO) land tenure database.
A legal land survey of the mining leases was undertaken in June 2015 and approved by the BC Surveyor General on September 3, 2015. A legal survey of the mineral claims has not been undertaken.
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The QP understands that there are no annual holding costs for any of the six mineral claims at this time, as the claims are paid up until January 31, 2030. Annual rental holding fees for the four mining leases total Cdn$15,002.
Figure 4-2: Brucejack Property Mineral Claims
Source: | Pretivm (2019) |
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Figure 4-3: Pretivm Mineral Claims
Source: | Pretivm (2019) |
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The majority of the Brucejack Property lies within the boundaries of the Cassiar-Iskut-Stikine Land and Resource Management Plan (LRMP) area, with only a minor south-eastern segment of Mineral Claim No. 1027399 and Mining Lease No. 1038600 occurring outside this area. All claims and leases located within the boundaries of the LRMP are considered areas of General Management Direction, with none of the leases or claims occurring inside any Protected or Special Management Areas.
As of the effective date of this report, the land claims in the area are in review and subject to ongoing discussions between various First Nations and the Government of BC.
The mining operation is fully permitted. AMines ActPermit and twoEnvironmental Management Act Permits along with a BCEnvironmental Assessment Act Certificate and the Decision Statement of July 27, 2015, under Section 54 of theCanadian Environmental Assessment Act, 2012 provide the basis for approvals of the mine and use of the site for mining purposes. Mine infrastructure and infrastructure along the road are permitted under a variety of permits for water use and camps with land use held under various Licenses of Occupation and the access road held under a provincial Special Use Permit. Tailings storage and waste rock are permitted under anEnvironmental Management Act discharge permit while surface and underground operations are regulated by theMines Act permit.
There are no known environmental liabilities or other significant factors that may affect access, title, or the ability or right to operate the mine or perform work on the Brucejack Property.
4.4 | Confirmation of Tenure |
The QP is not qualified to provide legal comment on the mineral title to the reported properties and has relied on the provided information. No warranty or guarantee, be it expressed or implied, is made by the QP with respect to the completeness or accuracy of the tenement description referred to in this document.
4.5 | Royalties, Fees and Taxes |
The royalties applicable to the original Brucejack area, not including mining lease 1038600, are as follows:
■ | “Royalty” means the amount payable by the Owner, calculated as 1.2% of the NSR, with the following exemptions: |
– | gold: the first 503,386 oz produced from the Brucejack Gold Mine |
– | silver: the first 17,907,080 oz produced from the Brucejack Gold Mine. |
The QP understands that the 1.2% NSR royalty is, at the time of this report, in favour of the Franco-Nevada Corporation.
Mining Lease 1038600 is subject to a 2% NSR royalty, minimum annual payments of Cdn$50,000 with a buy out provision of Cdn$4 million per 1%, i.e. a total of Cdn$8 million. Mining lease 1038600 does not cover any of the area within the current mine plan.
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5.0 | ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY |
Information in this section has been excerpted and updated from Jones (2014). It does not cover the majority of the mine infrastructure which is covered under Section 18.0.
5.1 | Climate and Physiography |
The climate at the Brucejack Property is typical of northwestern BC with cool, wet summers, and relatively moderate but wet winters. Annual temperatures range from +20 to -20°C. Precipitation is high with heavy snowfall accumulations ranging from 10 to 15 m at higher elevations and 2 to 3 m along the lower river valleys. Snowpacks cover the higher elevations from October to June. The optimum field season for surface works is from late June to mid-October.
Mine infrastructure is located at 1,360 to 1,415 masl along Brucejack Creek and immediately southwest of Brucejack Lake. Topographic relief is moderate to low in the immediate mine site; however, across the Brucejack Property, the terrain is generally steep with local reliefs of 1,000 m from valleys occupied by receding glaciers, to ridges at elevations of 1,900 masl. Elevations within the mine area range from 1,360 masl along Brucejack Lake to 1,500 masl at the Valley of the Kings meteorological station.
5.2 | Vegetation |
The Brucejack Gold Mine site is devoid of trees with only sparse mosses along drainages; the tree line is at an elevation of approximately 1,200 m. On the Brucejack Property, sparse fir, spruce, and alder grow along the valley bottoms with only scrub alpine spruce, juniper, alpine grass, moss, and heather covering the steep valley walls. Rocky glacial moraine and polished glacial-striated outcrops dominate the terrain above the tree line.
5.3 | Accessibility |
The Brucejack Property is located in the Boundary Range of the Coast Mountain Physiographic Belt.
Pretivm completed construction of its 73 km access road that links Brucejack Camp to Highway 37 at km 215, approximately 60 km north of Meziadin Junction. From Highway 37 the road crosses the Bell Irving River to Wildfire Camp and then traverses Wildfire Creek valley to the headwaters of Scott Creek, traverses along Scott Creek valley to Bowser River valley and then proceeds along Bowser River valley to Knipple Glacier, a distance of 58 km. A 12 km road is established along Knipple Glacier to the headwaters of the Brucejack Creek watershed at which point the road extends 3 km to the mine site.
Provincial permits and federal authorization of the mine prohibit public use of the access road. A gate is located at the Highway 37 junction, and security screening is undertaken at Wildfire Camp. Along the access road, a 5,400 ft aerodrome has been established at Bowser Aerodrome 5 km east of Knipple Camp (Lake) (Figure 5-1). Personnel, equipment, fuel and camp provisions are driven to a staging area at Knipple Camp, before being taken over the glacier to the Brucejack Camp.
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The Brucejack Property area is also easily accessible with the use of a chartered helicopter from the town of Stewart, or seasonally from the settlement of Bell II. The flight time from Stewart is approximately 30 minutes and slightly less from Bell II; however, Stewart has the advantage of having an established year-round helicopter base.
The larger communities of Smithers and Terrace, located 326 km and 300 km respectively by road, provide hubs for mine personnel to live and airports for out-of-the-region staff to commute to site. Charter busses provide transport from these communities and other communities along Highway 16 to the Brucejack Gold Mine.
Rail traffic can load and unload in Terrace, and port facilities at Stewart and Prince Rupert are available for off-shore transport.
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Figure 5-1: Project Access
Source: | Pretivm (2019) |
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5.4 | Infrastructure |
The access road from Highway 37 is complete and in use (Figure 5-1).
Local resources are limited to what is brought into the mine and camps. Infrastructure along the access road includes camps at Wildfire and Knipple and Bowser Aerodrome, 5 km east of Knipple Lake. At the mine, the camp comprises accommodation for 542 with recreational, office, and multiple support facilities. The nearest off-site infrastructure is located in the town of Stewart, approximately 65 km to the south, which has a minimum of supplies and personnel. The towns of Terrace and Smithers are also located in the same general region as the Brucejack Property, and both are directly accessible by daily air service from Vancouver.
The nearest railway is the Canadian National Railway Yellowhead route, which is located approximately 220 km to the southeast. This line runs east-west and terminates at the deepwater port of Prince Rupert on the west coast of BC.
Stewart, BC, the most northerly ice-free shipping port in North America, is accessible to store and ship concentrates. At the effective date of this report, the Red Chris Mine ships material via this terminal.
A BC Hydro high-voltage, 138 kV transmission line services Stewart, BC. The Long Lake transmission line extends north from Stewart and connects their generating facilities with a BC Hydro high-voltage transmission line. The 57 km Brucejack transmission line extends from the Long Lake generation station to the mine via the Knipple Substation. Electric power is stepped down at the Knipple Substation from 138 to 69 kV and is then delivered to Brucejack Mine site. Emergency power is available from diesel generators located at Brucejack.
Mine infrastructure and infrastructure along the road are permitted under a variety of permits for water use and camps with land use held under various Licenses of Occupation. Tailings storage and waste rock are permitted under discharge permits with adequate storage capacity in Brucejack Lake. The access road is permitted under a provincial Special Use Permit.
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6.0 | HISTORY |
Information in this section has been updated from Ireland et al. (2014).
6.1 | Early Exploration |
The earliest known prospecting in the Brucejack Lake area occurred in the 1880s (McPherson 1994). In 1935, copper-molybdenum mineralization was discovered on the Sulphurets Property by prospectors in the vicinity of the Main Copper Zone, approximately 6 km northwest of Brucejack Lake; however, these claims were not staked until 1960. From 1935 to 1959, the area was relatively inactive with respect to prospecting; however, it was intermittently evaluated by a number of different parties and resulted in the discovery of several small copper and gold-silver occurrences in the Sulphurets-Mitchell Creek area. In 1959, Granduc Mines Ltd. (Granduc) and Alaskan prospectors staked the main claim group, covering the known copper and gold-silver occurrences, which collectively became known as the Sulphurets Property. This was the start of what could be termed the era of modern exploration (Table 6-1).
Table 6-1: | Exploration History of the Sulphurets Property between 1960 and 2008 |
Date | Exploration | |
1960 to 1979 | Granduc continued exploration, conducting further geological mapping, lithogeochemical sampling, trenching, and diamond drilling on known base and precious metal targets north and northwest of Brucejack Lake. This resulted in the discovery of gold-silver mineralization in the Hanging Glacier area and molybdenum on the south side of the Mitchell Zone. | |
1980 | Esso Minerals Canada Ltd. (Esso) optioned the Sulphurets Property from Granduc and subsequently completed an extensive program consisting of mapping, trenching, and geochemical sampling that resulted in the discovery of several showings including the Snowfield Zone, Shore Zone, West Zone, Galena Hill Zone, and Electrum Zone targets. Gold was discovered on the peninsula at Brucejack Lake near the Shore Zone. | |
1982 and 1983 | Exploration was confined to gold- and silver-bearing vein systems in the Brucejack Lake area at the southern end of the Sulphurets Property from 1982 to 1983. Drilling was concentrated in 12 silver and gold-bearing structures, including the Near Shore Zone and West Zone, located 800 m apart near Brucejack Lake. Drilling commenced on the Shore Zone. | |
1983 and 1984 | Esso continued work on the Sulphurets Property and (in 1984) outlined a deposit on the West Zone at Brucejack. | |
1985 | Esso dropped the option on the Sulphurets Property. | |
1985 | The Sulphurets Property was optioned by Newhawk Gold Mines Ltd. (Newhawk) and Lancana Mining Corp. (Lancana) from Granduc under a three-way joint venture (JV) (the Newcana JV). The Newcana JV completed work on the Snowfield Zone, Mitchell Zone, Golden Marmot Zone, Sulphurets Gold Zone, and Main Copper Zone targets, along with lesser known targets. | |
1986 to 1991 | Between 1986 and 1991, the Newcana JV spent approximately Cdn$21 million developing the West Zone and other smaller precious metal veins, on what would later become the Bruceside Property. Newhawk completed 35,241.6 m in 511 surface diamond drillholes, 5,276 m of exploratory underground drifting, and 35,981 m of drilling in 442 underground drillholes on the West Zone between 1987 and 1990. This work resulted in the discovery of more than 40 additional showings and the outlining of a historical and no longer current mineral reserve for the West zone of 750,000 t grading 15.4 g/t Au and 678 g/t Ag (Schroeter 1994). Newhawk acquired a 60% interest in the Bruceside Property after buying out Lancana’s interest in 1987. |
table continues…
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Date | Exploration | |
1991 and 1992 | Newhawk officially subdivided the Sulphurets claim group into the Sulphside, Snowfield, and Bruceside Properties in 1991, and sold the Sulphside Property (including the Sulphurets Zone and Mitchell Zone) to Placer Dome Inc. (Placer Dome) in 1992. Newhawk continued exploration of the Bruceside Property between 1991-1994, including property-wide trenching; mapping; airborne surveys; and surface drilling, evaluating various surface targets including the Shore Zone; Gossan Hill Zone; Galena Hill Zone; Maddux Zone; and SG Zone targets. Six holes were drilled at the Shore Zone, totalling 1,200 m, to test its continuity and to determine its relationship to the West Zone and R-8 Zone. Results varied from 37 g/t Au over 1.5 m, to 13 g/t Au over 4.9 m (Payie 2017). Newhawk purchased Granduc’s interest in the Snowfield Property in early 1992. | |
1993 | A LOM Development Certificate was issued to Newhawk for the West Zone by the provincial government (under the BC Environmental Assessment Office (EAO); certificate 92-06). | |
1994 | Exploration on the Bruceside Property consisted of detailed mapping and sampling in the vicinity of the Gossan Hill Zone, and 7,352 m of diamond drilling (in 20 drillholes) primarily on the West Zone, R-8 Zone, Shore Zone, and Gossan Hill Zone targets. Mapping, trenching, and drilling were completed on the ten best and highest priority targets (including the West Zone). | |
1996 | Granduc merged with Black Hawk to form Black Hawk Mining Inc. (Black Hawk). The Mine Development Certificate, renewed until 1998, was replaced by a Project Approval Certificate (M98- 03). | |
1997 and 1998 | No exploration or development work was carried out on the Snowfield and Bruceside properties (Budinski et al. 2001). | |
1999 | Silver Standard acquired Newhawk and with it, Newhawk’s 100% interest in the Snowfield Property and 60% interest in the Bruceside Property, and created separate projects for the Snowfield and Brucejack deposits (Payie 2017). | |
1999 to 2001 | No exploration or development work was carried out on the Snowfield and Brucejack properties. | |
2001 | Silver Standard entered into an agreement with Black Hawk whereby Silver Standard acquired Black Hawk’s 40% direct interest in the Bruceside Property, giving Silver Standard a 100% interest in the Bruceside Property, which it subsequently renamed the Brucejack Property. Black Hawk retained a 1.2% NSR royalty on the Bruceside Property. | |
2001 to 2008 | No exploration or development work was carried out on the Snowfield and Brucejack properties during the period from 1999 to 2008. The Project Approval Certificate was amended in January 2004 and expired in September 2006. |
6.2 | Exploration by Silver Standard Resources Inc. (2001-2010) |
Silver Standard initiated exploration on the Brucejack Property in 2009 as a result of its successful bulk tonnage drilling on the Snowfield Property (Narciso et al. 2010). Silver Standard designed the 2009 Brucejack drill program test for additional bulk tonnage resources on the Brucejack Property. The program included drilling, rock-chip and channel sampling, and re-assaying of historical drill core pulps. Silver Standard retained GeoSpark to assess the integrity of the historical (pre-2009) drilling on the Brucejack Property (Vallat 2009). Results of this work confirmed that assay data from the majority of the historical drillholes on the Brucejack Property (849 out of 901 holes targeting the West Zone, Galena Hill Zone, SG Zone, Shore Zone, and vicinity) were suitable for use in geological modeling and resource estimation. Field work included the collection of 2,739 rock-chip and channel samples from the Galena Hill Zone, Bridge Zone, SG Zone, and Mammoth Zone, as well as at the Hanging Glacier Zone, where historical surface sampling had identified rocks enriched in gold and silver. A total of 17,964 m in 37 diamond drillholes were completed during the 2009 field season. Twelve drillholes were targeted at what would become the Valley of the Kings Zone. Drillhole SU-012 (Figure 6-1) is credited as being the discovery drillhole for the Valley of the Kings Zone intersecting 16,948.5 g/t Au over 1.5 m. Other notable drillhole intersections that suggested the presence of a gold deposit in the Valley of the Kings Zone included: 5,344 g/t Au over 0.5 m (SU-029), 184.5 g/t Au over 1.5 m (SU-006), 51.1 g/t Au over 1.5 m (SU-035), 47.5 g/t Au over 1.5 m (SU-033), and 46.1 g/t Au over 1.5 m (SU-017).
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Figure 6-1: Visible Electrum in Valley of the Kings Zone Discovery Drillhole SU-012
Source: | Pretivm |
Notes: | Dendritic latticework electrum in quartz-carbonate vein in HQ diameter core (drillhole SU-012). |
The 2010 drill program, which totalled 33,480 m in 73 drillholes, was designed to continue definition of bulk tonnage mineralization on the Brucejack Property and to determine the nature and continuity of the high-grade mineralization intersected in the Valley of the Kings Zone. Approximately one third of the 2010 drilling targeted the Valley of the Kings Zone and included gold intersections of up to 5,850 g/t Au over 1.5 m (SU-040). The bulk tonnage drilling achieved its intended goal when a sizeable Mineral Resource was estimated for the Brucejack Property (Ghaffari et al. 2011). The Mineral Resource estimate included the West Zone, West Zone Footwall Zone, Shore Zone, Gossan Hill Zone, Galena Hill Zone, SG Zone, Valley of the Kings Zone, Bridge Zone, and the Bridge Zone Halo, and was reported at a cut-off of 0.30 g/t AuEq inside an optimized open pit shell (Ghaffari et al. 2010b; 2011). This estimate is no longer current. The relatively dense drilling from the bulk tonnage drilling program, with drill spacings of 100 m by 100 m to 50 m by 50 m, formed the basis upon which the bulk tonnage resource model was built. Numerous high-grade intervals were intersected as part of this drilling, which allowed for the initial delineation of high-grade mineralization trends and preliminary domain definition in the Valley of the Kings Zone. These included:
■ | 5,850 g/t Au over 1.63 m (SU-040) | ■ | 430 g/t Au over 0.50 m (SU-040) |
■ | 5,480 g/t Au over 0.43 m (SU-084) | ■ | 231 g/t Au over 1.50 m (SU-046) |
■ | 2,490 g/t Au over 1.59 m (SU-054) | ■ | 182.5 g/t Au over 0.50 m (SU-077) |
■ | 1,025 g/t Au over 1.50 m (SU-053) | ■ | 171 g/t Au over 0.68 m (SU-106) |
■ | 536 g/t Au over 0.57 m (SU-040) | ■ | 170.5 g/t Au over 0.50 m (SU-058) |
■ | 164.5 g/t Au over 0.50 m (SU-058) | ■ | 83.4 g/t Au over 1.50 m (SU-086) |
■ | 131 g/t Au over 1.00 m (SU-093) | ■ | 53.7 g/t Au over 1.50m (SU-056) |
■ | 92.5 g/t Au over 1.50 m (SU-106) | ■ | 50.0 g/t Au over 1.50 m (SU-055). |
Subsequent drilling programs conducted by Pretivm have focussed on further delineating the corridors of high-grade mineralization in the Valley of the Kings Zone.
Additional details relating to Silver Standard’s 2009-2010 Brucejack Property exploration and drilling programs are summarised in Ghaffari et al. (2010a; 2011) and Board and McNaughton (2013).
In 2010, Silver Standard sold the Snowfield and Brucejack properties to Pretium Resources Inc., a start-up company formed by the former president specifically to acquire the properties.
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6.3 | Previous Feasibility Studies on the Property (1990) |
Corona Corporation (Corona) completed a FS on a proposed underground mine with decline access for the Sulphurets Project (West Zone and R-8 Zone only) in 1990 (Corona 1990). Total operating costs of $145/t were estimated based on a 350 t/d mill facility for processing and resulted in a capital cost estimate of $42.7 million with a 6.7% pre-tax return at a price of US$400/oz Au and $5/oz Ag. The study concluded that higher metal prices were needed before a production decision could be taken.
The reader is cautioned that the Corona Sulphurets Project Feasibility Study (Corona 1990) is no longer relevant, is not NI 43-101 compliant, and should not be relied upon.
6.4 | Prior Mineral Production |
In the 1980s, more than 5 km of underground ramps, level development, and raises were completed on the West Zone down to the 1100 Level. In 1993, a Project Approval (LOM Development) Certificate was issued for the Brucejack Property by the Minister of Sustainable Resource Management and Minister of Energy and Mines for the Province of BC. The mine was not developed further, and the certificate expired in 2006. Prior to Pretivm’s Bulk Sampling Program conducted in 2013, no ore had been processed from the Brucejack Property, including from the West Zone.
6.5 | Preliminary Economic Assessment (2010) |
Silver Standard commissioned Wardrop Engineering Inc. (Wardrop; now Tetra Tech) to complete a preliminary economic assessment (PEA) on the combined bulk-tonnage resources of the Brucejack and Snowfield properties in 2010 (Ghaffari et al. 2010a).
Based on the results of the PEA, it was recommended that Silver Standard continue with the next phase, a prefeasibility study, in order to identify opportunities and further assess bulk-tonnage viability of the two projects. The PEA was revised and re-issued to Pretivum as two separate documents: one for the combined Snowfield-Brucejack Property in October 2010 (Ghaffari et al. 2010b), and the other for the Brucejack Property as a standalone project in June 2011 (Ghaffari et al. 2011). However, these reports are no longer current.
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7.0 | GEOLOGICAL SETTING AND MINERALIZATION |
The Brucejack Gold-Silver Deposit (the Brucejack Deposit) is currently defined as incorporating the West Zone and the Valley of the Kings Zone. A brief overview of the geological setting and mineralization of the Brucejack Deposit is presented in this section to provide context for Pretivm’s approaches to geological modelling, resource estimation, and mining. The information presented in this section has been excerpted from Roach and Macdonald (1992), Board and McNaughton (2013), Jones (2014), Board et al. (2017), Tombe et al. (2018), McLeish et al. (2019), and Board et al. (submitted). Readers interested in additional detail on the geology of the Brucejack Deposit should refer to these documents.
7.1 | Regional Geological Setting |
The Brucejack Deposit is situated on the western side of the Stikine Terrane (Stikinia; Figure 7-1) of the Canadian Cordillera. Stikinia is the largest and westernmost of several exotic terranes in the Intermontane morphogeologic belt of the Canadian Cordillera (Monger and Price 2002). Stikinia is interpreted as a Philippine-style intra-oceanic island arc terrane, formed between mid-Palaeozoic to Middle Jurassic time, when it was accreted to the North American continental margin (at about 173 Ma; Nelson and Colpron 2007; Evenchick et al. 2007; Gagnon et al. 2012). Western Stikinia was subsequently affected by thin-skinned deformation during Cretaceous accretion of the outboard Insular Belt terranes (at about 110 Ma; Evenchick 1991; Kirkham and Margolis 1995).
The deposit is located in the northern part of the northwest-trending Stewart-Iskut Culmination, a major structural feature in western Stikinia that lies between the Stikine and Skeena Arches to the west of the Bowser Basin (Figure 7-1). The Stewart-Iskut Culmination has variably been interpreted as a structural culmination that formed in response to Cretaceous deformation and, more recently, as having been an Early Jurassic structural highland upon which rocks of the Hazelton Group were deposited prior to Stikinia being accreted to the western North American continent (Nelson and Kyba 2014). The culmination contains an exceptionally metal-rich tectonic assemblage hosted in volcano-sedimentary and related comagmatic plutonic rocks of the Triassic Stuhini and latest Triassic to Middle Jurassic Hazelton Groups (Figure 7-2; Nelson et al. 2013). This area includes structurally-controlled high-potassic calc-alkaline porphyry copper-gold deposits (e.g., Kerr, Sulphurets, Mitchell, Iron Cap, Snowfield), transitional epithermal intrusion-related precious metal deposits (e.g., Brucejack, Silbak-Premier, Big Missouri, Red Mountain, and Homestake Ridge), and volcanogenic massive sulphide deposits (e.g., Granduc, Dolly Varden-Torbrit, Anyox, and Eskay Creek). These deposits are considered to have been formed while Stikinia was in a state of compression or sinistral transpression (Nelson and Colpron 2007).
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Figure 7-1: Regional Geological Setting of the Brucejack Deposit
Note: | The Brucejack Deposit is located on the western side of the Stikine Terrane (Stikinia). |
The deposit is hosted in Lower Jurassic volcanic arc rocks on the northern side of the Stewart-Iskut Culmination, to the west of the Bowser Basin. Detail inside rectangular outline provided in Figure 7-2. |
Sources: | Ghaffari et al. (2012) and Jones (2014) |
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7.2 | Local Geology |
The Brucejack Deposit, part of the Sulphurets Mineral District, is located on the eastern limb of the north-plunging McTagg Anticlinorium, the northern closure of the Stewart-Iskut Culmination (Figure 7-2). Volcanic arc-related rocks of the Triassic Stuhini Group form the core of the anticlinorium, and are successively replaced outwards by volcanic arc-related rocks of the Jurassic Hazelton Group and clastic basin-fill sedimentary rocks of the Middle Jurassic to Lower Cretaceous Bowser Lake Group (Figure 7-3). A major unconformity separates the Stuhini and Hazelton Group rocks. As a consequence of its location relative to the axis of the culmination, Brucejack Deposit rocks are tilted and generally display a progressive younging towards the east.
The Brucejack and neighbouring Kerr-Sulphurets-Mitchell (KSM) deposits display a strong spatial association to the unconformity between the Stuhini and Hazelton Group rocks and north-south structures to the east of this contact (Figure 7-3), suggesting that these features were important for deposit genesis (Nelson and Kyba 2014). The unconformity between the Stuhini and Hazelton Groups is associated with numerous Triassic-Jurassic mineral showings and porphyry copper-gold deposits throughout northwestern BC and is considered a key feature for mineral exploration in the area (Kyba 2014; Nelson and Kyba 2014). The KSM copper-gold-molybdenum porphyry deposits are associated with Mitchell Suite intrusive rocks of the Texas Creek Intrusive Suite (Kirkham and Margolis 1995). Campbell and Dilles (2017) noted that the deposits are broadly contemporaneous and have similar mineralogy, alteration, and textures. They noted that large areas of hydrothermal alteration affected rocks in and around the Mitchell Suite intrusions, with overprinting alteration relationships indicating that the magmatic-hydrothermal systems underwent telescoping as they evolved between about 196 and 190 Ma. Early syn-mineral potassic alteration was locally overprinted by propylitic, albitic, and chlorite-sericite alteration, before being pervasively overprinted by quartz-sericite-pyrite (phyllic) alteration. Final stage system telescoping included local advanced argillic alteration and massive pyrite vein emplacement (Mitchell) overprinting earlier assemblages before being overprinted by high-level gold-rich veins (Campbell and Dilles 2017).
West-directed thrusts and west-vergent overturned folds affect rocks on the western limb of the anticlinorium, whereas rocks on the eastern limb display east- to southeast-directed thrusts and east-vergent overturned folds (Kirkham and Margolis 1995). These structures have been kinematically linked to the mid-Cretaceous Skeena Fold and Thrust Belt. In addition to the thrust faults, the McTagg Anticlinorium is cut by late-stage brittle faults that are likely of Tertiary age and which represent reactivated older structures (e.g., the north-trending Brucejack Fault; Nelson and Kyba 2014; Board et al. submitted).
A penetrative foliation of variable orientation is preferentially developed in altered Hazelton Group rocks in the Sulphurets mineral district, with fabric intensity proportional to mica and/or clay mineral content (Kirkham and Margolis 1995). Timing of penetrative fabric development is difficult to ascertain due to the absence of unambiguous cross-cutting relationships and appropriate non-reset geochronologic data. Although it is most commonly considered to have developed in response to the mid-Cretaceous Skeena Fold and Thrust Belt deformation (Kirkham and Margolis 1995; Nelson and Kyba 2014), the possibility that it is a reactivated composite fabric recording older deformation events cannot be ruled out (Margolis 1993; Roach and Macdonald 1992; Tombe et al. 2018; Board et al. submitted).
Rocks in the Sulphurets Mineral District are affected by regional sub-greenschist facies metamorphism, which is associated with development of the mid-Cretaceous Skeena Fold and Thrust Belt (Alldrick 1993). Maximum temperatures and pressures reached approximately 290ºC and 4.5 kbar, respectively, corresponding to thermally reset potassium-argon (K-Ar) and argon-argon (Ar-Ar) ages for foliation-parallel sericite in older porphyry-related phyllic alteration zones at approximately 110 Ma (Alldrick 1993; Kirkham and Margolis 1995).
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Figure 7-2: Select Mineral Showings and Deposits in the Stewart-Iskut Culmination, Highlighting the Metal-rich Nature of this Structure
Note: | Pretivm’s Brucejack and Snowfield Deposits are located towards the north of the culmination. Detail inside rectangular outline presented in Figure 7-3. |
Source: | Ghaffari et al. (2012) |
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Figure 7-3: District-scale Geological Setting of the Brucejack Deposit on the East Side of the McTagg Anticlinorium
Note: | Detail inside rectangular outline presented in Figure 7-4. |
Source: | Jones (2014) |
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7.3 | Brucejack Project Area Geology |
The Brucejack Project area is largely underlain by volcano-sedimentary rocks of the Lower Jurassic Hazelton Group (Figure 7-4). These rocks unconformably overlie volcanic arc sedimentary rocks of the Upper Triassic Stuhini Group along the western-most part of the Brucejack Project area. The rocks are variably altered and deformed, with zones of intense quartz-sericite-pyrite (phyllic) alteration being associated with increased deformation due to preferential strain partitioning in sericite-rich zones.
A north-south trending, broadly arcuate, concave-westward 0.5 to 1.5 km wide band of variably phyllic-altered rocks and associated quartz stockwork extends over 5 km across the Brucejack Property area (Figure 7-4). The band straddles the Brucejack Fault across the Brucejack project area, shifting from the west side of the fault in the north of the Brucejack Project area to the fault’s east side further south. The phyllic alteration typically contains between two and 20% pyrite, affects rocks from the bottom to the top of the lithological sequence (see Section 7.3.1), and, depending on the alteration intensity, can preclude protolith recognition. More than 40 mineralization showings, associated with the alteration band, have been identified on the Brucejack Project area, highlighting the exceptional exploration potential of the area (McPherson 1994; Board et al. submitted).
Ten mineralized zones are currently recognized on the Brucejack Project area, extending from the Hanging Glacier Zone in the north to the Bridge Zone in the south (Figure 7-5). Although five of these zones have been explored in some detail (West Zone, Valley of the Kings Zone, Bridge Zone, Gossan Hill Zone, and Shore Zone), mining is focused on just the two zones for which there are current Mineral Resources and Reserves: the Valley of the Kings Zone and the West Zone. A newly-discovered zone, the Flow Dome Zone, is the focus on near-mine exploration (Section 9.2). This Technical Report focuses on the Valley of the Kings Zone and West Zone, with additional details on the Bridge Zone, Gossan Hill Zone and Shore Zone provided in Jones (2012c).
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Figure 7-4: Geological Map of the Brucejack Project Area Showing Location of Mineralized Zones and their Association with the Band of Quartz-Sericite-Pyrite Alteration (shown in yellow)
Note: | Enlarged legend provided in Figure 7-5 |
Source: | Jones (2014) |
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Figure 7-5: Brucejack Property Geology Legend for Figure 7-4
figure continues…
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Figure 7-5 (con’t) Brucejack Property Geology Legend for Figure 7-4
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Figure 7-5 (con’t) Brucejack Property Geology Legend for Figure 7-4
7.3.1 | Lithology |
The key lithologic sequence hosting the Brucejack Deposit is characterized by a basal marine volcanosedimentary (VSF) package unconformably overlain by an immature polylithic volcanic conglomerate (Cong) that grades upward through a sandy epiclastic unit (Trans) into a predominantly pyroclastic trachyandesite (latite) fragmental unit (Andx) (Figure 7-6; Board et al. submitted). This simplified lithologic sequence represents a relatively complex volcanic stratigraphy characterized by rapid lateral facies changes, which defines a general younging direction upward and to the east, and which is interpreted as having been deposited in a series of small fault-bounded half-grabens on the eastern side of the Brucejack Fault (Figure 7-6).
The Brucejack Deposit lithologic sequence is bounded to the south and northwest by massive and relatively fine-grained plagioclase feldspar±potassium feldspar±hornblende-phyric rocks (P1 porphyry) of the Bridge Zone and Office porphyries (Figure 7-6). The Office P1 and Bridge Zone P1 porphyry bodies display sharp contacts with the volcaniclastic rocks and have been variably interpreted as comagmatic subvolcanic/hypabyssal monzonitic intrusions or latite flows (Kirkham and Margolis 1995; Jones 2014). Coarser-grained feldspar-hornblende-phyric porphyry rocks (P2 porphyry) are locally present within the sequence, especially to the north and east of West Zone. East of the Brucejack Deposit, in the Flow Dome Zone, the lithologic sequence is overlain by a felsic unit that includes potassium feldspar±plagioclase feldspar±hornblende-phyric flows, breccia, bedded nonwelded and welded felsic tuffs, and a comagmatic intrusion which is flow-banded and plagioclase-hornblende phyric (Figure 7-4; Macdonald 1993). This unit is interpreted as a flow-dome complex, representing high-level intrusive and extrusive parts of a local magmatic center.
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Figure 7-6: Three-dimensional Block Geological Interpretation Through the Brucejack Deposit, Showing Key Geological, Structural, and Mineralization Relationships Developed in the Valley of the Kings Zone and West Zone
Source: | After Board et al. (submitted). Dated February 2019. |
Hydrothermal breccia bodies are present throughout the lower Hazelton Group rocks on the Brucejack Project area and follow faults and fractures. The breccia bodies are generally 2 to 15 cm wide and consist of angular to subrounded wall-rock fragments set in a fine-grained matrix of rock flour and pyrite. Wall-rock fragments are heterolithic and commonly derived from the immediate host rock. Hydrothermal breccia bodies cut all host-rock units and are discordant to the penetrative foliation. Mineralized veins cut and are cut by breccia bodies and hydrothermal breccia grades into mineralized manganese-carbonate veins (see Section 7.3.5), suggesting that the breccia bodies are syn-mineralization in timing.
Relatively uncommon post-mineralization altered amygdaloidal intermediate to mafic dikes cut all lithological units, mineralized veins, and vein stockwork of the Brucejack Deposit (Figure 7-6; Tombe et al. 2018; Board et al. submitted). The dikes are subvertical, up to 1.5 m wide, and commonly east- to southeast-trending. Dikes in the Valley of the Kings Zone strike east to east-southeast, have a strike length of at least 900 m, and extend for more than 1,000 m down dip. Dikes in the West Zone trend northwest-southeast, have strike lengths of at least 500 m, and extend for more than 450 m down dip. The dikes follow faults and fractures in staggered zig-zag patterns, having been emplaced along variably oriented structures during local extension. Dike emplacement partially utilized the same structures as the mineralized veins. The dikes are undeformed to weakly deformed and generally discordant to the dominant foliation. The dikes have the same geochemical signature as the latite P1 porphyry bodies, flows, and the Flow Dome Zone felsic flows, indicating derivation from a similar magmatic source (Tombe 2015).
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Late-stage, undeformed, and unaltered mafic dikes (up to several meters wide) are present to the west of and along the Brucejack Fault, but are rare on the Brucejack Project area. The north-trending dikes are subvertical and cut all host rock units, alteration, mineralization, foliation, post-mineralization intermediate to mafic dikes, and thrust faults. They are geochemically distinct from the post-mineralization intermediate to mafic dikes (Tombe 2015).
7.3.2 | Geochronology |
Detailed geochronological work conducted on the Brucejack Project area, which has included uranium-lead (U-Pb) on zircon, rhenium-osmium (Re-Os) on molybdenite, and Ar-Ar on sericite/muscovite (Kirkham and Margolis 1995; Tombe et al. 2018; Board et al. submitted), indicates that the Brucejack Deposit lithological sequence is between about 195 and 184 Ma in age: the VSF unit is dated at 195 to 188 Ma, the Cong and Trans units were formed between about 188 and 185 Ma, the Andx unit formed at about 185 to 184 Ma. The Office P1 porphyry is dated at about 194 Ma, and the Bridge Zone P1 porphyry is dated at about 189 Ma. Both intrude rocks of the VSF.
Molybdenite mineralization associated with the Bridge Zone P1 porphyry was formed between about 190 and 189 Ma. The Office and Bridge Zone porphyry rocks are similar in age and geochemistry to the KSM intrusive rocks (196 to 190 Ma) and are likely related to the Mitchell Intrusive Suite (Board et al. submitted).
Mineralized veins in the Brucejack Deposit (Section 7.3.5) cut the 188 to 184 Ma lithological sequence that hosts the Brucejack Deposit, and are cut by the intermediate to mafic dikes, which are dated at about 183 Ma. The mineralized veins cut rocks as young as about 184 Ma thereby indicating an age of about 184 to 183 Ma for the precious metal mineralization in the Brucejack Deposit. The Brucejack mineralization is clearly significantly younger than the KSM magmatic-hydrothermal system, and this has triggered near-mine exploration in search of the causative system (see Section 9.2).
Ar-Ar ages of sericite at about 110 Ma indicate isotopic resetting during low grade regional metamorphism associated with the mid-Cretaceous deformation event. The undeformed and barren late mafic dikes are considered to be Tertiary in age (Tombe et al. 2018).
7.3.3 | Structure |
Reactivation of older basement structures is considered to have played an important role in controlling magmatic and hydrothermal system development in the Sulphurets mineral district (Nelson and Kyba 2014). The Brucejack Fault, the largest of numerous north-south lineaments that occur on the Brucejack Project area, is interpreted as the latest expression of a reactivated growth fault that was active during Early Jurassic volcanism and mineralization. Evidence for this includes:
■ | There is a significant change in thickness of the lowermost units of the lower Hazelton Group over short distances across the fault (Jones 2014; Tombe et al. 2018). |
■ | The development of small secondary half-graben structures along the eastern side of the fault that are filled with locally derived, immature clastic detritus. |
■ | The presence of abundant short-scale facies variations in the half-graben basins, indicating rapid infilling. |
■ | Alteration and mineralization are broadly cospatial with the fault along its entire 11 km strike length, from Bridge Zone in the south through to Iron Cap in the north (Nelson and Kyba 2014). |
■ | Multistage vein stockwork and vein breccia occur along half-graben normal faults, indicating reactivation of lower order structures. |
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Latest movement on the Brucejack Fault on the Brucejack Property is dextral and east block down, with displacement on the order of tens of meters.
A post-alteration, composite penetrative foliation is variably developed in rocks in the Burcejack Project area, with foliation intensity being closely associated with phyllic alteration intensity. The foliation is characterized by two predominantly east- to east-southeast-striking, slightly oblique steeply dipping foliations (S1 and S2), which are cut by a later north-striking, steeply dipping S3 foliation (Davis 2017). Progressive deformation has commonly resulted in S1 being rotated into parallelism with S2 in higher strain zones, forming a composite S1-S2 cleavage (Davis 2017). S3 cuts the S1-S2 foliation at high angles, with crosscutting relationships suggesting its formation during sinistral transpression (Davis 2017).
Mineralized veins (see Section 7.3.5) in the Brucejack Deposit predominantly strike southeast to east-southeast (more than 90% of all mineralized veins), with east-west and north-south striking veins being uncommon to rare (Figure 7-6). The mineralized veins occur as multistage thin sheeted veins, vein breccia, and vein stockwork, which anastomose and grade vertically and laterally into one another along fractures, faults, foliation planes, lithological contacts, and shears defining internally complex vein system structural corridors of between approximately 5 and 30 m wide. The veins range from being relatively undeformed to locally moderately deformed, and display both foliation-parallel and low- to moderate-angle foliation-discordant relationships, irrespective of rock competency and strain intensity (Tombe et al. 2018; Roach and Macdonald 1992; Board et al. submitted). Both extensional and shear vein features are developed in areas of differential strain partitioning throughout the deposit, with later mineralized veins being less deformed than earlier mineralized veins (Harrichhausen et al. 2016; Davis 2017; Tombe et al. 2018). A late- to post-deformation structural origin is envisaged for the mineralized veins, with fluid influx and hydrothermal alteration coeval with, and outlasting, ductile deformation and associated periodic brittle failure evolving in response to progressive sinistral transpression (Roach and Macdonald 1992; Davis 2017; Board et al. submitted).
The post-mineralization intermediate to mafic dikes are generally undeformed, unfoliated, and cut all lithological units, mineralized vein generations, and the S1, S2, and S3 fabrics, placing a minimum age of about 183 Ma on foliation development (Tombe et al. 2018; Board et al. submitted). Localized fabric development is present in weakly altered dikes, suggesting that the dikes formed during the waning stages of the alteration and deformation events. The dikes display apparent gentle warping about north-trending axes at the deposit scale, small sharp m-scale offsets along late-stage reverse faults, and retain their planar shape vertically over at least 900 m in the Valley of the Kings Zone (Figure 7-6). These features suggest that the intermediate to mafic dikes were subjected to limited post-emplacement deformation.
Post-mineralization reverse and thrust faulting is developed throughout the Brucejack Deposit. The brittle structures cut all host-rock lithological units, alteration assemblages, mineralized veins, and intermediate to mafic dikes, but are cut by the late mafic dikes, indicating that the causative deformation occurred after about 183 Ma. High- and low-angle reverse faults are generally southwest dipping, with a top-to-the-northeast sense of movement in the Brucejack Deposit. Barren, low angle, chlorite-bearing shear veins, tension gash veins, and undeformed, en echelon, sub-horizontal quartz veins are associated with the faults, as are local top-to-the-southwest back thrusts. Fault displacement is relatively minor (m-scale), indicating limited shortening during the thrust-related deformation. The post-mineralization faulting is considered to be mid-Cretaceous in age (about 110 Ma) based on kinematic similarities to structures in the Skeena Fold and Thrust Belt (Evenchick 1991) and Ar/Ar geochronology (Tombe et al. 2018).
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7.3.4 | Alteration |
Phyllic (sericite) alteration is the dominant alteration style on the Brucejack Project area and is typically a fine-grained admixture of white mica (muscovite), pyrite, quartz, and calcite that replaces the matrix of the volcanosedimentary rocks, varying in intensity from trace to complete replacement. Relicts of earlier-formed alteration (e.g., potassic, albitic, propylitic) are locally preserved in the intensely phyllically altered rocks, indicating that the phyllic alteration overprinted earlier alteration assemblages and that the hydrothermal system (or systems) that drove this alteration was (were) likely telescoping.
Weak silicification has affected most of the host lithological units in the Brucejack Deposit, with moderate to intense texture destruction occurring locally. Pod-like zones (meters- to tens-of-meters in size) of intense silicification are commonly developed in the polylithic conglomerate (especially at its upper and lower contacts) and locally in rocks of the underlying VSF unit (Figure 7-6). Zones of intense silicification consist of microcrystalline quartz, pyrite, and sericite, and are associated with horizons of massive pyrite and almost monomineralic green muscovite. Irregular stockworks of unmineralized cloudy to translucent quartz veinlets of varying intensity are limited to the more intensely silicified zones, and are thought to be related to their formation. Hairline, clear, crack-seal quartz veinlets are locally present in the hardest and most intensely silicified zones, possibly reflecting local fluid overpressures developed beneath these impermeable features.
Cross-cutting relationships between mineralized veins and altered wall rock indicate that the phyllic and silica alteration predated all stages of electrum mineralization (Tombe et al. 2018). Spatial and textural associations between pyrite, sericite, and the silicified zones suggest coeval formation. Mineralized veins and the 183 Ma intermediate to mafic dikes are generally spatially associated with the phyllic assemblage, suggesting that these structures preferentially utilized pre-altered zones.
7.3.5 | Mineralization |
Visible gold and silver mineralization in the Brucejack Deposit occurs as electrum and is predominately hosted in quartz-carbonate to carbonate vein and vein breccia structural corridors within broader stockwork zones (Section 7.3.3; McPherson 1994; Kirkham and Margolis 1995; Tombe et al. 2018; Board et al. submitted). Additionally, low-grade (less than 5 g/t) gold mineralization occurs sub-microscopically in vein- and wall rock-hosted arsenian pyrite (invisible gold) throughout the Valley of the Kings Zone and possibly within the West Zone as well. Electrum-bearing quartz-carbonate veins and stockwork overprint and are co-spatial with earlier porphyry-related phyllic alteration in the Brucejack Deposit.
The Valley of the Kings Zone is currently defined over 1,200 m in east-west extent, 700 m in north-south extent, and 650 m in depth. Deep drilling has indicated that the alteration, mineralization, and veining in this zone extend to a depth of at least 1,100 m. Mineralization in the Valley of the Kings Zone is open to the east, west, and at depth. Deep exploration drilling conducted under the Flow Dome Zone in 2018 (Section 9.2) was successful in confirming the presence of Valley of the Kings Zone-style mineralization from the eastern edge of the Valley of the Kings Zone to beneath the Flow Dome Zone, which lies approximately 1,000 m further east. The West Zone is currently defined over 590 m along its northwest strike, 560 m across strike, and down to 650 m in depth, is open to the northwest, southeast, and at depth to the northeast. The Valley of the Kings Zone contains higher gold and lower silver grades than the West Zone.
Precious metal mineralization is ubiquitous throughout the vein systems (Figure 7-7); however, its continuity is not correlated to any specific geologic continuity; although mineralized structural corridors can be continuous on the meters- to tens-of-meters scale, the within-vein gold and silver distribution is highly erratic. Nevertheless, the distribution and grade of precious metal mineralization within the mineralized structural corridors within the broader stockwork system is of significant economic interest (Figure 7-7).
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Figure 7-7: Oblique View Down and Towards the West-Northwest of the Brucejack Deposit Showing Drillhole Intersections Greater than 5 g/t Gold Relative to Underground Workings in both the Valley of the Kings Zone and the West Zone
Source: | Pretivm (2019) |
7.3.5.1 | Valley of the Kings Zone |
Six stages of veining have been recognized in the Valley of the Kings Zone (Table 7-1). Discontinuous, deformed, and variably oriented pyrite-quartz-calcite stringer veinlets represent the earliest stage of veining (Stage I). These veinlets are widespread in zones of phyllic alteration, and may represent D-type veinlets associated with early porphyry-style alteration (Tombe et al. 2018). Stage II veins are translucent to white, discontinuous, microcrystalline quartz veinlets found exclusively within pervasively silicified rocks. Stage I and II veins are pre-mineral with respect to precious metal mineralization as they are always cut by electrum-bearing epithermal veins. Electrum mineralization occurs in quartz-carbonate (Stage III), base metal sulphide-quartz-carbonate (Stage IV), and manganoan calcite (Stage V) sheeted veinlets, veins, vein breccia, and vein stockwork (Figure 7-8). Stages III-V veins are considered to have formed coevally as they display complex multiple overprinting relationships. Barren, thrust-related quartz-chlorite veins and tension gashes (Stage VI) cut all earlier vein generations and are likely mid-Cretaceous in age (Tombe et al. 2018). Stage III veins increase in abundance at depth, to the west, and to the east in the Valley of the Kings Zone.
Stages III to V veins are locally undeformed to weakly deformed, but display pinch-and-swell textures in high strain zones. Classic epithermal vein textures, including crustiform banding, sparse cockade textures, and vugs are locally present in Stage III and IV veins (Tombe et al. 2018). Electrum in all mineralized vein stages occurs in a variety of textures, including: common fine- to coarse-grained dendrites, lesser amounts of coarse subhedral clots and aggregates, and uncommon fine- to medium-grained, subhedral to euhedral sheet- to plate-like crystals. The gold/silver ratio of electrum varies significantly, with each of the three main mineralized vein stages displaying unique gold/silver signatures, ranging from 30 to 70% Au. Stage V veins typically contain electrum with the highest proportion of gold, whereas Stage IV veins contain predominantly silver-rich electrum that is locally chemically zoned (gold-rich cores surrounded by silver-rich rims; McLeish et al. 2018). There does not appear to be any significant compositional zonation of electrum as a function of spatial location.
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Table 7-1: | Vein Generations in the Valley of the Kings Zone |
Mineralogy | |||||
Vein | Typical | ||||
Stage | Description | Timing | Size | Metals | Gangue |
I | Discontinuous stringer veinlets | Pre-mineral | Thickness: mm Continuity: cm | Invisible Au in Py tr. Cpy | Py-Qz-Cal- Ser±Chl |
II | Discontinuous translucent veinlets | Pre-mineral | Thickness: mm Continuity: mm | - | Qz-Py |
III | IIIa: sheeted veinlets | Syn-mineral | Thickness: cm Continuity: dam | El, tr. Sp±Gn±Cpy | Py-Qz-Cal- Dol±Ser±Rt |
IIIb: breccia/flooded zones | Syn-mineral | Thickness: cm to dm Continuity: m | El, tr. Sp±Gn±Cpy | Py-Qz-Cal- Dol±Ser±Rt | |
IIIc: stockwork veins/blow- outs | Syn-mineral | Thickness: dm to m Continuity: dam to hm | El, tr. Sp±Gn±Cpy, tr. Ag sulphosalts | Py-Qz-Cal- Dol±Ser±Apy±Rt | |
IV | Ag-rich base metal sulphide veins | Syn-mineral | Thickness: cm to dm Continuity: m to dam | Sp-Gn-Cpy-El-Ag- sulphide+ sulphosalts: acanthite, pearcite, pyrargyrite, freibergite, proustite, polybasite, argentotennantite. | Py-Qz-Cal- Dol±Ser±Apy±Rt |
V | Mn-carbonate veins | Syn-mineral | Thickness: cm to dm Continuity: m to dam | El, tr. Cpy | Cal±Qz±Py±Rt |
VI | Tectonic shear/tension gash veins | Post-mineral | Thickness: cm Continuity: cm to m | - | Qz-Cal-Chl |
Notes: | tr. – trace; Apy – arsenopyrite; Cal – calcite; Chl – chlorite; Cpy – chalcopyrite; Dol – dolomite; El – electrum, Gn – galena; Py – pyrite; Qz – quartz; Rt – Rutile, Ser – sericite, Sp – sphalerite. |
Stage I, III, IV, V, and VI correspond to Vn0, Vn1, Vn2, Vn3, and Vn4 according to the mine vein nomenclature. | |
Source: Modified after Tombe et al. (2018) and Board et al. (submitted). |
7.3.5.2 | West Zone |
Mineralization and veining in the West Zone were investigated in the late 1980s and early 1990s by Newhawk and research geologists (Roach and Macdonald 1992; Macdonald 1993; Davies et al. 1994; Kirkham and Margolis 1995). These studies documented mineralization and vein parageneses broadly similar to that described above for the Valley of the Kings Zone, with two notable exceptions: ore stage veins have a lower modal abundance of electrum and higher modal abundance of base metal sulphide and silver sulphosalt minerals and, therefore, a lower gold/silver ratio than those in the Valley of the Kings Zone, and the mineralogy of pre-mineralization-stage veining in the West Zone is different to that of the Valley of the Kings Zone: Stage I veinlets in the West Zone are represented by potassium feldspar-quartz veinlets.
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7.3.5.3 | Genetic Considerations |
Previously gold transportation was considered to have occurred as bi-sulphide complexes in solution (e.g., Board 2015a; McLeish et al. 2018; 2019), with the porphyry-associated pre-sulphidization and pre-sericitization of the host rock facilitating extended residency time of gold-bearing fluids due to minimal rock buffering of sulphur by host-rock iron (all taken up in the form of pre-mineral pyrite) and maintenance of near neutral fluid pH (muscovite-buffering; Heinrich et al. 2004). Recent work conducted by McLeish et al. (2018; 2019) has demonstrated that gold (and silver) was being transported as electrum nanoparticles in suspension (colloids) in association with carbonate (i.e., likely in the gas phase) rather than silica (quartz). This allows for increased capacity of mineralizing fluids to carry gold by physical transport over and above that dissolved in solution.
Controls on gold precipitation from colloidal suspensions include mixing with meteoric (including heated seawater) waters, decreasing temperature, boiling (to a lesser extent), and local destabilization near pyrite zones. McLeish et al. (2019) documented a multiphase history of porphyry to epithermal mineralization (alluded to in Board (2015a)) in pyrite grains in the Valley of the Kings Zone and the Flow Dome Zone. Early porphyry-related pyrite is resorbed and overgrown by gold-bearing arsenian-banded epithermal pyrite. Similar pyrite growth zonation patterns have been observed in the porphyry to epithermal transition at the Lihir porphyry-epithermal deposit in Papua New Guinea (Sykora et al. 2018). Overprinting of earlier porphyry alteration and mineralization by later co-spatial epithermal events (arsenian pyrite and subsequent electrum mineralization) complicates domain definition for geological modelling (see Section 14.3).
Mixing with meteoric waters (likely heated seawater) triggered explosive phreatomagmatic events that resulted in destabilization of the electrum colloids and their precipitation. This likely occurred again and again, in different faults, fractures, foliation planes, and along lithological contacts that were experiencing variable dilation and closure due to local variations in compressional and extensional stress, and resulted in the globally ubiquitous, yet locally variable and difficult to predict distribution of electrum throughout the Brucejack Deposit (Figure 7-8). As a result of the nature of gold transportation (above) and complex multistage geological history, mineralization continuity appears to better on the larger (structural corridor) scale than on the local (individual discontinuous structures) scale. It is difficult to interpret individual mineralized structures with the information available, whereas it is relatively easy to model the mineralized structural corridors with a high degree of confidence.
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Figure 7-8: Mineralized Veins in the Valley of the Kings Zone of the Brucejack Deposit
Source: | Pretivm (2019) |
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8.0 | DEPOSIT TYPES |
The Brucejack Deposit is interpreted to be a deformed porphyry-related transitional to intermediate sulphidation epithermal high-grade gold-silver vein, vein stockwork, and vein breccia deposit that formed between 184 to 183 Ma (Board and McNaughton 2013; Tombe et al. 2018; Board et al. submitted). High-grade gold-silver mineralization was formed in association with a telescoped, multi-pulsed magmatic-hydrothermal system beneath an active local volcanic center (Board et al. submitted).
The Brucejack Deposit has many characteristics in common with intermediate sulphidation epithermal systems (Sillitoe and Hedenquist 2003). These are highlighted (in yellow) in Table 8-1. Intermediate sulphidation epithermal systems occur in calc-alkaline andesite-dacite arcs and can be spatially associated with porphyry systems and individual volcanic centers (Sillitoe and Hedenquist 2003). Mineralization in these systems is overwhelmingly hosted in veins, sheeted veins, vein stockwork, and vein breccia, with gold-silver occurring as electrum (Sillitoe and Hedenquist 2003). Whilst the majority of these types of epithermal systems form in arcs with neutral to extensional tectonic environments, Victoria (the gold-rich type example) and the giant Baguio Au district (both in the Philippines) were formed in a compressive island arc (Sillitoe and Hedenquist 2003). The Brucejack Deposit appears to have formed in compressive island arc setting (Tombe et al. 2018; Board et al. submitted). Intermediate sulphidation epithermal deposits contain significant quantities of precious metals (Sillitoe and Hedenquist 2003). Examples of intermediate sulphidation deposits with significant contained gold include: Rosie (Montana; approximately 414 t Au), Baguio (Philippines; approximately 400 t Au), Comstock Lode (Nevada; approximately 260 t Au), Kelian (Indonesia; approximately 240 t Au), Tayoltita (Mexico; approximately 150 t Au), Sacarimb (Romania; approximately 84 t Au), and Victoria (Philippines; approximately 80 t Au). The Brucejack Deposit has similarities in terms of vein style, mineralization paragenesis, and alteration to the Fruta del Norte high-grade gold deposit in Ecuador (e.g., Leary et al. 2016; greater than 155 t Au) and the Porgera gold deposit in Papua New Guinea (e.g., Richards and Kerrich 1993; Ronacher et al. 2004; greater than 660 t Au).
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Table 8-1: | Principal Field-oriented Characteristics of Intermediate- and Low-sulphidation Epithermal Systems |
High Sulphidation | Low Sulphidation | ||||
Oxidized | Reduced | Intermediate | Subalkaline | Alkaline | |
Magma | Magma | Sulphidation | Magma | Magma | |
Type Example | El Indio, Chile (vein); Yanacocha, Peru (disseminated) | Potosí, Bolivia | Baguio, Philippines (Au- rich); Fresnillo, Mexico (Ag-rich) | Midas, Nevada | Emperor, Fiji |
Genetically Related Volcanic Rocks | Mainly andesite to rhyodacite | Rhyodacite | Principallyandesite to rhyodacite but locally rhyolite | Basalt to rhyolite | Alkali basalt to trachyte |
Key Proximal Alteration Minerals | Quartz- alunite/APS; quartz- pyrophyllite/dickite at depth | Quartz- alunite/APS; quartz-dickite at depth | Sericite;adularia generally uncommon | Illite/smectite- adularia | Roscoelite-illite- adularia |
Silica Gangue | Massive fine-grained silification and vuggy residual quartz | Vein-filling crustiform and comb quartz | Vein-filling crustiform and colloform chalcedony and quartz; carbonate- replacement texture | Vein-filling crustiform and colloform chalcedony and quartz; quartz deficiency common in early stages | |
Carbonate Gangue | Absent | Common, typically including manganiferous varieties | Present by typically minor and late | Abundant but not manganiferous | |
Other Gangue | Barite common, typically late | Barite and manganiferous silicates present locally | Barite uncommon; fluorite present locally | Barite, celestite, and/or fluorite common locally | |
Sulphide Abundance | 10 to 90 vol % | 5 to >20 vol % | Typically, <1 to 2 vol % (but up to 20 vol % where hosted by basalt) | 2 to 10 vol % | |
Key Sulphide Species | Enargite, luzonite, famatinite, covellite | Acanthite, stibnite | Sphalerite, galena, tetrahedrite- tennantite, chalcopyrite | Minor to very minor arsenopyrite ± pyrrhotite; minor sphalerite, galena, tetrahedrite-tennantite, chalcopyrite | |
Main Metals | Au-Ag, Cu, As-Sb | Ag, Sb, Sn | Ag-Au, Zn, Pb, Cu | Au ± Ag | |
Minor Metals | Zn, Pb, Bi, W, Mo, Sn, Hg | Bi, W | Mo, As, Sb | Zn, Pb, Cu, Mo, As, Sb, Hg | |
Te and Se Species | Tellurides common; selenides present locally | None known but few data | Tellurides common locally; selenides uncommon | Selenides common; tellurides present locally | Tellurides abundant; selenides uncommon |
Note: | Key features noted in the Brucejack Deposit are highlighted in yellow. The presence of adularia in the West Zone is still in accordance with an intermediate sulphidation classification. |
APS – aluminum-phosphate-sulphate minerals; Sb – antimony; Hg – mercury; Zn – zinc; Pb – lead; Bi – bismuth; W – tungsten; Sn – tin |
Source: | Modified after Table 3 in Sillitoe and Hedenquist (2003). |
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Corbett (2013) generally considers intermediate sulphidation epithermal deposits as a sulphide-rich sub-type of low sulphidation epithermal deposits known as carbonate-base metal gold deposits (Corbett and Leach 1998; Figure 8-1). These types of deposits are formed from magmatic fluids that evolve to low sulphidation as they migrate from the intrusive to shallower crustal levels and mix with substantial meteoric waters (Corbett 2013). Corbett (2013) prefers the use of (sulphide-rich low sulphidation) carbonate-base metal gold for these types of deposits to intermediate sulphidation as the former more correctly accounts for the wide temperature range and paragenetic sequence related to the transition from intrusion-related quartz-sulphide gold-copper deposits through carbonate-base metal gold to epithermal gold-silver deposits. Veins in this transition show a continuum from sulphide-rich (“D-type” veinlets:proximal to porphyry; Vein Stage I at Brucejack; see Section 7.3.5.1) through carbonate (manganese-rich; Vein Stage V at Brucejack), carbonate-quartz (Vein Stage V at Brucejack), to quartz-carbonate (distal to porphyry and shallower levels; Vein Stages III and IV at Brucejack; Corbett and Leach 1998). Considering Corbett’s (2013) classification, the ubiquitous Vein Stage I veins in the phyllic alteration throughout the Brucejack Deposit being overprinted by carbonate and quartz-carbonate veins provides evidence for temperature fluctuations in the volcanic sequence: a telescoping porphyry system. The presence of increased carbonate veins at depth (Section 7.3.5.1 of this report) is encouraging as gold mineralization in the Brucejack Deposit appears to be associated with the carbon dioxide gas phase (McLeish et al. 2019).
Examples of carbonate-base metal deposits from the southwest Pacific Rim include: Porgera Waruwari, Hidden Valley, Woodlark, and the Wafi Link Zone in Papua New Guinea; Cowal, Kidston, Mt Leyshon, and Mt. Rawdon in Australia, Gold Ridge in the Soloman Islands; Acupan, Antamok, Victoria, and Bulawan in the Philippines; and Kelian and Mt. Muro in Indonesia (Corbett 2013). Corbett (2013) considers Fruta del Norte (Ecuador), Golden Sunlight, Montana Tunnels, and Cripple Creek (USA), Rio Medio and San Cristobal (Chile) to be examples of carbonate-base metal gold deposits. Examples of quartz-sulphide gold-copper deposits include Kerimenge and Lihir in Papua New Guinea (Corbett 2013). Interestingly, mixing with substantial meteoric water (seawater due to caldera collapse) and overprinting of earlier porphyry mineralization by later epithermal mineralization is recorded at Lihir (Sykora et al. 2018). Similar features (to those at Lihir) have recently been documented in the Brucejack Deposit (McLeish et al. 2018; 2019; Board et al. submitted).
Figure 8-1: Schematic Section of Calc-alkaline Volcanic Arc Showing High and Intermediate Sulphidation Epithermal Deposits and Porphyry Deposits
Note: | Location of Brucejack Deposit is highlighted in red. |
Source: | Modified after Figure 3 in Sillitoe and Hedenquist (2003). |
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Figure 8-2: Conceptual Model of Different Arc-related Porphyry and Epithermal Copper-Gold-Silver Mineralization Deposits
Note: | Interpreted position of the Brucejack Deposit is highlighted in transparent red ellipse |
Source: | Modified after Figure 1 in Corbett (2013). |
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9.0 | EXPLORATION |
9.1 | Exploration – 2011 to 2014 |
Following acquisition of the Brucejack Property in late 2010, Pretivm management changed the exploration focus from an open-pit bulk-tonnage approach to targeting high-grade resources amenable to more selective underground mining. Surface and underground drilling was the main tool used in the exploration of the Brucejack Deposit and Property between 2011 and 2014. Geophysical surveys were conducted in 2014 to assess the exploration potential on the Brucejack Property and broader claim block scales. Table 9-1 provides a summary of the exploration carried out on the Brucejack Property between 2011 and 2013 by Pretivm. Additional detailed information on Pretivm’s 2011-2014 exploration of the Brucejack Property is provided in Jones (2014) and Ireland et al. (2014).
Table 9-1: | Exploration of the Brucejack Property between 2011 and 2014 |
Date | Exploration | |
2011 | A bulk-tonnage resource update was released in February 2011 (Ghaffari et al. 2011), with an initial high-grade resource for the Valley of the Kings Zone. An additional high-grade resource estimate, with sensitivity testing, was released in November 2011 (Armstrong et al. 2011). | |
Brownfields exploration included detailed surface geological mapping, limited surface sampling, and limited geophysics (an initial Spartan magnetotelluric survey conducted by Quantec Geoscience Ltd.; Turkoglu et al. 2011; Ireland et al. 2013). | ||
A total of 178 diamond drillholes were completed, totaling 72,805 m. The program targeted previously defined high- grade intersections primarily in the Valley of the Kings Zone (60% of the total), but also in the Gossan Hill Zone, Shore Zone, West Zone, and Bridge Zone targets. | ||
Dewatering of the historical West Zone underground development was carried out to assess the condition of the workings and determine if the workings could be used as a launching point for a development drive to the Valley of the Kings Zone. | ||
2012 | Detailed brownfields surface geological mapping and associated supplementary surface geochemical sampling was continued. | |
A total of 301 drillholes were completed, totaling 105,500 m of drilling during the 2012 drilling program. Zones within 150 m of surface were drilled at 12.5 m centers, with the deeper parts (down to about 350 m below surface) being drilled at approximately 25 m centers. Drilling at greater depths was generally only able to reliably achieve 50 m centers. | ||
The results of the 2012 drilling were incorporated into a revised Mineral Resource (Jones 2012c). This resource estimate formed the basis for a feasibility study on the Brucejack Property, which was completed in June 2013 (Ireland et al. 2013). | ||
2013 | A total of 24 surface diamond drillholes (5,200 m) were completed (drillholes SU-590 to SU-613) on the main and eastern parts of the Valley of the Kings Zone. An additional 575 m of shallow geotechnical drilling was conducted in 13 drillholes (drillholes SU-614 to SU-626). . | |
Pretivm extracted a 10,000 t bulk sample to further evaluate the geological interpretation and Mineral Resource estimate for the Valley of the Kings Zone (Jones 2014). Geological mapping (face, back, and ribs), channel, and chip sampling were conducted on a round-by-round basis for all the underground workings developed as part of the bulk sample. Bulk sample material from each round (approximately 100 t) was sampled through a sampling tower and sent as defined rounds to the Contact Mill in Philipsburg, Montana, for processing. A total of 5,923 oz Au were produced from 10,302 t of bulk sample material processed through the mill at an average grade of 17.88 g/t Au (Ireland et al. 2014). The results provided confidence in the November 2012 Mineral Resource and were used for parameter calibration and confidence classification in the December 2013 Mineral Resource (Jones 2012c; Jones 2014). |
table continues…
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Date | Exploration | |
2013 | A total of 16,500 m of underground drilling was conducted to augment the bulk sample results by drilling off a larger area around the bulk sample workings on the 1,345 m level. Drilling was conducted on approximately 7.5 m centers over an area of 120 m east-west by 60 to 90 m north-south by 120 m vertically. Additional underground exploration drilling was conducted to test targets outside of the bulk sample area. Underground drilling totaled 38,840 m in 409 drillholes. | |
Surface geological mapping and supplementary surface geochemical sampling was continued, albeit with a more greenfields exploration goal than in previous years. The majority of this exploration was conducted on Pretivm’s claims outside of the Brucejack Property area. | ||
2014 | Approximately 11,200 m of surface drilling in 12 drillholes (SU-627 to SU-632, SU-640, SU-644, and SU-650 to SU-653) testing the mineralization potential at depth beneath the Valley of the Kings Zone was conducted in 2014. Geotechnical drilling totaled 725 m in 15 drillholes (SU-633 to SU-639, SU-641 to SU-643, SU-645 to SU-649). | |
An airborne magnetic and radiometric survey was conducted over the Brucejack Property and the wider Pretivm claim area by Precision GeoSurveys Inc. (Pezzot 2015). Approximately 750-line km (of a total 1,185-line km) were flown at a 200 m line spacing over the Brucejack Property (Block 1 of the survey). Line spacings of between 400 and 500 m were flown on the broader Pretivm claim area (Blocks 2 and 3). A Scintrex Cs vapour CS-3 magnetometer and an IRIS were used to collect the data. Ancillary equipment included base station magnetometers, a laser altimeter, a Pilot Guidance Unit, GPS navigation, and an AGIS data acquisition system. Additional Spartan MT data were acquired from both the Snowfield and Brucejack Properties in August and September 2014 by Quantec Geoscience Ltd (Tuncer 2014a; b). This work, which expanded on the 2011 Spartan MT data (Turkoglu et al. 2011), was aimed at targeting porphyry and epithermal mineralization and improving geological knowledge on the two property areas. Spartan MT data were collected over a frequency range of 10 KHz to 0.001 Hz, with AMT data collected over a frequency range of 10 KHz to 3 Hz, from a total of 78 MT stations. Following 1D and 3D inversion modelling of the data, a total of ten conductive feature anomalies were identified, the most significant of these on the Brucejack Property being beneath the large flow foliated latite dome to the east of the Valley of the Kings Zone (now known as the Flow Dome Zone). These features were interpreted as reflecting increased alteration with abundant sericite content. Results of the geophysical surveys were used for enhanced structural interpretations as well as porphyry and epithermal deposit vectoring, targeting, and exploration program planning. A total of 605 surface rock outcrop grab, chip, and channel samples were collected on the Brucejack Property. |
Notes: | GPS – global positioning system; MT – Magnetotelluric; AMT – Audio Magnetotelluric; |
IRIS – Integrated Radiometric Information System |
9.2 | Exploration – 2015 to 2018 |
Pretivm’s main focus between 2015 and 2017 was on the permitting, financing, construction, and commissioning of the Brucejack Gold Mine. Brucejack Property exploration between 2015 and 2018, consequently, largely targeted resource and reserve expansion of the Valley of the Kings Zone through underground drilling (see Section 10.0). Limited brownfields (near deposit/mine) exploration conducted on the Brucejack Property included drilling, geophysics, surface mapping, and very limited surface sampling for petrography, mineral chemistry, and geochronological analyses. Greenfields exploration of the broader Pretivm claims also occurred from 2015 through 2018, as part of the Bowser Regional Property (see Flasha 2017a; b; c; Wafforn 2018a; b).
All exploration conducted on the Brucejack Property (termed brownfields or near-mine exploration) initially followed a model that suggested the epithermal vein system was genetically linked to the long-lived KSM porphyry deposits (approximately 196 to 190 Ma; Febbo et al. 2015). The gold-bearing veins were considered to have been formed in the waning stages of the telescoping porphyry system, which was interpreted as having lasted from approximately 191 to 183 Ma (Board and McNaughton 2013). Additional geochronological data, coupled with detailed geological and geophysical reviews, resulted in the discovery that rocks as young as approximately 184 Ma were affected by phyllic alteration and cut by auriferous epithermal veins (Board et al. submitted). As none of the porphyry intrusions recognized to date in the region were as young as this, an alternative exploration model was proposed in which a younger porphyry center, as yet undiscovered, was the driver of the hydrothermal system that was responsible for the formation of the Brucejack Deposit. Detailed reviews of surface samples, drilling data, geological mapping, structural data, geophysical data, geochemical data, alteration intensity, post-mineral dyke orientations, hydrothermal breccia distribution, and geochronological data appeared to vector to the Flow Dome Zone in the east.
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Limited surface exploration drilling (8,380 m in 10 drillholes and two wedges) was conducted on the Brucejack Property in 2015, with 6,199 m in 8 drillholes (including two wedges) targeting the Flow Dome Zone. Other zones targeted included the Hanging Glacier Zone (987.33 m in three drillholes) and one drillhole in the South Zone (southwards from Bridge Zone; see Flasha 2016). Surface mapping and limited surface sampling of the Flow Dome Zone augmented the drilling. Results of this drilling highlighted the continuation of Valley of the Kings Zone style phyllic alteration and electrum mineralization beneath the main part of the Flow Dome Zone (Figure 9-1), as well as isolated occurrences of relic potassic and propylitic alteration, bornite, and chalcopyrite. The drilling did not intersect the interpreted causative porphyry.
Additional airborne geophysical surveys (1TEM electromagnetic, magnetic, and radiometric) were conducted as part of Pretivm’s claim block-wide airborne survey by Precision GeoSurveys Inc. between July and October 2015, as a follow-up to the 2014 airborne survey (see Section 9.1; Boyd and Poon 2015; Poon 2015; Flasha 2016b; c). Although no new magnetic or radiometric lines were flown over the Brucejack Property in 2015, 1TEM electromagnetic data were obtained as part of Block 2 of this survey (Boyd and Poon 2015). The Block 2 survey was flown at a 200 m spacing between lines, with most of the lines flown in an east-west direction. Two of six north-south tie lines (spaced at 4,500 m) were flown over the Brucejack Property. Precision GeoSurveys Inc. used a towed 1TEM structure, 1TEM transmitter (TX), 1TEM receiver (RX), laser altimeter, data loggers, a Pico data acquisition system, a Pico pilot navigation unit, and a Honda V-twin gas engine and alternator system (340A, 80V), all installed on its Eurocopter AS350BA helicopter. The 1TEM structure was towed 40 m below the helicopter at a nominal height of 50 m above the ground, ranging up to 74.3 m above the ground in areas of challenging relief. Results of the 1TEM electromagnetic survey over the Brucejack Property indicated the presence of an extensive hydrothermal footprint in this area, characterized by elevated conductivity (Figure 9-2). Known mineralized zones on the Brucejack Property are located within the elevated conductivity footprint. All of the 2015 surface diamond drillholes drilled into this footprint intersected extensively altered (generally phyllic alteration) and anomalously mineralized rocks. The electromagnetic data are being used in conjunction with other geological and geophysical data for brownfields exploration targeting.
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Figure 9-1: Plan View of the Brucejack Deposit Showing Significant Electrum Intersections from the 2015 Surface Exploration Drilling of the Flow Dome Zone
Note: | (1)Outline of Measured, Indicated, and Inferred Mineral Resource as at July 21, 2016. |
(2) Outline of Proven and Probable Mineral Reserve, based on the 2014 FS (Ireland et al. 2014). |
Source: | Pretivm (2019) |
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Figure 9-2: Plan View of 1TEM Conductivity Data on the Western Edge of Pretivm’s Claim Block, Illustrating the Potential Scale of the Hydrothermal System Footprint (Warmer Colours) of which the Brucejack Deposit is a Part (also shown are Peripheral Known Mineralized Zones on the Brucejack and Snowfield Properties and Drill trances from the 2015 Surface Exploration Drill Program)
Source: | Pretivm (2016) |
Underground exploration drilling aimed at connecting the Valley of the Kings Zone to the Flow Dome Zone and testing the porphyry potential at depth beneath the Flow Dome Zone was conducted from the 1,200 m level in the Brucejack Gold Mine in 2018. A total of 3,138 m was drilled in two underground exploration drillholes (VU-820 and VU-911). Results of this drilling showed that Valley of the Kings style mineralization and alteration was continuous from the Brucejack Gold Mine to the Flow Dome Zone (Figure 9-3). Anomalous copper and molybdenite mineralization coincided with a zone of relic potassic alteration between 1,400 and 1,485 m downhole depth in drillhole VU-911, and occurs more diffusely over a broader area in drillhole VU-820 (between downhole depths 1,260 and 1,585 m). A coarse-grained porphyry intrusive was intersected and has been dated (U-Pb zircon) at approximately 186 Ma (Board et al. submitted), in keeping with the interpretation of a younger porphyry system driving the Brucejack Deposit. McLeish et al. (2019) showed how zoned pyrites changed with depth along these two drillholes: closer to the Valley of the Kings Zone, zoned pyrites show resorbed porphyry cores overgrown with epithermal arsenian pyrite that is then cut by electrum; epithermal zonation diminishes with depth in the drillholes being replaced with porphyry pyrite (with inclusions of chalcopyrite) in the vicinity of the anomalous copper and molybdenum mineralization. Additional drilling is required to provide a three-point problem for source porphyry vectoring. The key to intersecting the source porphyry is to highlight the extent of the porphyry to epithermal transition zone and its potential for additional Valley of the Kings Zone style electrum mineralization, in addition to assessing the gold potential of the source porphyry.
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Figure 9-3: Cross Section of the Brucejack Deposit (Looking North) Showing Gold Assay Intersections from the 2015 Surface Exploration Drilling and 2018 Underground Deep Exploration Drilling of the Flow Dome Zone, as well as the Zone of Anomalous Copper and Molybdenite Assays
Source: | Pretivm (2018) |
Additional ground-based geophysical surveys were conducted as part of the 2018 Flow Dome Zone exploration program by Frontier Geosciences Inc. A total of 8,560 m of surface induced polarization (IP) and 6,640 m of reflection seismic ground surveys were conducted on four lines across the Brucejack Property in 2018 (Figure 9-4). Both IP and seismic surveys were conducted on each of the three northeast-southwest trending lines, with only IP being conducted on the north-northwest trending linking line. A Frontier Geosciences Inc. 24-bit full waveform time domain IP system with a GDD 3.6 kW transmitter was used for apparent resistivity and chargeability measurements as part of the IP survey. Electrodes were emplaced every 100 m. The reflection seismic survey employed a Geometric Geode 24 channel signal enhancement seismograph with Oyo Geo Space 10 Hz geophones connected at 5 m intervals in 96 phone arrays (480 m spreads) by network cables along the three survey lines (Figure 9-4). Downhole magnetic total field, self-potential, single point resistance, resistivity, chargeability, and gamma geophysical measurements were collected from VU-911, the deeper drillhole drilled into the Flow Dome Zone, using a combination of a Mount Sopris MGX II borehole logging system, a three-component fluxgate magnetometer, and a Geonics Ltd. PROTEM transmitter and receiver system. Downhole current injection electrodes were placed in both drillholes to provide additional depth resolution to the 2018 IP surface survey. Preliminary results are currently being used in conjunction with other geological and geophysical data for brownfields exploration targeting below the Flow Dome Zone. Final results and a final report have not yet been received from Frontier Geosciences Inc. at the time of writing.
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Figure 9-4: Plan View Part of the Brucejack Project Showing Location of the 2018 Frontier Geosciences Inc. Surface Reflection Seismic and IP Survey Lines
Source: | Pretivm (2019) |
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10.0 | DRILLING |
Drilling has been the primary tool used in the exploration of the Brucejack Property (Table 10-1; Figure 10-1). Details of drilling conducted by Pretivm up to and including 2016 is provided in Jones (2012c, 2014) and Board et al. (2017). This section provides a summary of resource definition and exploration drilling conducted by Pretivm between 2017 and 2018.
Table 10-1: | Drilling Summary for the Brucejack Property |
Hole | |||||
Type & | |||||
Year/ | Collar | Sample | No. of | Total | |
Program | Location | Size | Holes | Meters | Goal and Targets |
Historical 1960-1994 | Surface | Core (BQ, NQ, HQ) | 405 | 52,142 | West Zone, Shore Zone, Galena Hill Zone,and Gossan Hill Zone. |
Underground* | 442 | 33,750 | West Zone definition, drilled proximal to the West Zone exploration ramp, drill density of approximately 5 m centres between 5 and 10 m spaced sections. | ||
Silver Standard 2009-2010 | Surface | Core (HQ) | 110 | 51,382 | Exploration and discovery of areas with bulk tonnage mineralization locally associated with discreet high-grade intersections; Valley of the Kings Zone targeting confirmed the high-grade exploration potential of the zone. |
Pretivm 2011-2013 | Surface | Core (NQ, HQ, PQ) | 529 | 184,788 | Definition of high-grade resources in Valley of the Kings Zone, West Zone, and surrounding areas (HQ, some NQ at depth). Zones within 150 m of surface were drilled at 12.5 m centers. Drilling at 350 m below surface generally achieved 25 m centers, and drilling at greater depths generally achieved 50 m centers. Water well and geotechnical PQ drilling included 674 m in 13 drillholes. |
Underground | Core (HQ) | 409 | 38,840 | Definition of the bulk sample area and related proximal targets. | |
Pretivm 2014-2016 | Surface | Core (HQ) | 41 | 11,919 | Tested deep high-grade Inferred blocks in the December 2013 Mineral Resource, tested depth potential of the Valley of the Kings Zone mineralization system, and included geotechnical (condemnation and water well) drilling. |
Underground | Core (HQ) | 368 | 64,022 | Infill drilling to achieve a nominal 7.5 to 10 m spacing with a goal of increasing confidence in grade estimates for the stopes to be mined in the first three years of operation. A service drillhole linking the mine and surface was drilled in 2016. |
table continues…
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Hole | |||||
Type & | |||||
Year/ | Collar | Sample | No. of | Total | |
Program | Location | Size | Holes | Meters | Goal and Targets |
Pretivm 2017-2018 | Surface(1)& Underground | Core (NQ, HQ, PQ) | 996 | 74,737 | Predominantly stope infill (7.5 to 10 m center), stope definition (4 to 7.5 m center), and resource expansion (15 to 20 m center) HQ drilling; west-directed drilling testing north-south structures around Brucejack Fault (18 drillholes, 5,288 m, HQ); two deep exploration holes for porphyry targeting (3,138 m, HQ¨NQ), 14 surface water wells (2,043 m, PQ). |
RC (4") | 97 (Infill) 74 (Defn) 178 (Prod) | 5,049 1,736 2,461 | Testing of reverse circulation method and definition and infill of stopes; nominal 7.5 to 10 m spacing (infill); 4 to 7.5 m spacing (definition), and 2 m spacing (production). | ||
Notes: | (1) Limited surface drilling. |
Defn – Definition; Prod – Production |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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Figure 10-1: Plan View of Brucejack Property Drilling in and Around the Brucejack Deposit
Source: | Pretivm (2019) |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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10.1 | Pretivm Drilling (2017-2018) |
10.1.1 | Drilling Activities |
Underground drilling conducted on the Brucejack Property in 2017-2018 included exploration (widely-spaced), resource expansion (15 to 25 m centers), stope infill (7.5 to 10 m centers), stope definition (4 to 7.5 m centers), and stope production (approximately 2 m centers) fan drilling in the Valley of the Kings Zone (Figure 10-1). The majority of 2017-2018 drilling was HQ diamond core resource expansion, stope infill, and stope definition drilling (64,268 m in 62 diamond drillholes; Table 10-1). Underground exploration drilling totaled 8,426 m in 20 drillholes. Eighteen underground exploration drillholes were drilled on west-oriented azimuths targeting potential north-south trending structures, including the Brucejack Fault. Two deep exploration drillholes were drilled towards the east, testing the eastern extension potential of the Valley of the Kings Zone mineralization and porphyry mineralization at depth beneath the Flow Dome Zone (see Section 9.0). A total of 14 short vertical PQ diameter drillholes were drilled from surface to serve as water wells. Limited reverse circulation (RC) drilling was introduced on a test basis in 2018 to determine the viability of the method for stope infill, definition, and production drilling on the Brucejack Property, using both dry (97 infill drillholes) and wet (252 production drillholes) sampling options.
10.1.2 | Drilling Contractors and Equipment |
Hy-Tech Drilling Limited (Hy-Tech), based out of Smithers, BC, has been the primary drilling contractor on the Brucejack Project since 2013. Hy-Tech’s TECH B5000 underground diamond core drill rigs have been used for all surface and underground exploration, resource expansion, and stope infill drilling on the Brucejack Property. Additional infill and stope definition diamond core drilling was conducted using Pretivm’s Hydracore 2000 mobile underground drill rig (manufactured by Hydracore Drills Ltd.) operated by Procon Mines and Tunneling (Procon). In 2019, Hy-Tech is testing a newly developed modified TECH B5000 underground diamond core rig on a smaller feed frame to improve mobility between drill sites as part of the underground resource definition drilling program.
The pilot RC drilling test program was conducted between March and May 2018 by Boart Longyear using an RC-modified LM90 drill rig with a cyclone and rotary sample splitter for sample collection. Following the completion of the pilot program, additional stope definition and production RC drilling was conducted using a Cubex Aries ITH drill with a modified Sandvik RC head and a Drill Sampling Technologies Pty Ltd TS-02 Drill Sampling System.
10.1.3 | Drill Coordinates and Downhole Surveys |
Drillhole survey procedures in 2017 and 2018 were similar to previous years (e.g., Jones 2014).
Diamond drillhole collar locations were surveyed and marked up by Pretivm’s mine survey team prior to drilling, and re-surveyed post-drilling. All collar surveys were obtained using a total station theodolite in conjunction with a regular array of permanent ground control stations. Collar azimuth and dip information was recorded for each diamond core drillhole using a Reflex TN-14 Gyro instrument operated by the drill contractor. Downhole dip and azimuth data were measured for diamond core drillholes by the drill contractor using a Reflex EZ single shot instrument at nominal 25 to 50 m intervals.
RC drillhole collar surveys were conducted in a similar way to the diamond drillhole collars. Infill (pilot program) and stope definition drillhole collars were surveyed pre- and post-drilling. Production RC drillhole collars were only surveyed pre-drilling. Downhole surveys were not obtained for the short (29 to 71 m long holes, averaging approximately 52 m) RC drillholes conducted as part of the limited pilot program, nor for the definition and production RC drilling (10 to 30 m long holes, averaging approximately 23 m). Significant downhole deviation in such short drillholes is considered unlikely. Pretivm plans to conduct downhole deviation surveys on a subset of future stope definition and production RC drillholes to see if there is any significant deviation in the short RC drillholes as a function of host rock and drillhole orientation.
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Drillhole survey data were collected, entered into the GeoSpark logging interface, and processed by Pretivm mine geologists. The data were verified and imported in the GeoSpark back-end geological database by Pretivm’s database manager. Additional 3D checks were conducted in the Maptek Vulcan mining software: collar locations were checked in relation to surveyed topography and underground mine development solids; downhole survey traces were checked for wayward deviations.
10.1.4 | Diamond Drill Core Logging Procedures |
Core logging procedures previously established for the Brucejack Property (Jones 2014) were followed during the 2017-2018 drilling. Details on core handling and sampling are presented in Section 11.0.
Core logging is conducted in well-lit core shacks on appropriately labelled core boxes. Exploration and resource expansion drill core was geotechnically (recovery, rock quality designation (RQD), faults, fractures, joints, etc.) and geologically (lithology, structure, veining, alteration, and mineralization) logged prior to being marked up for sampling and photographed. Stope infill and definition drill core was geologically logged, marked up for sampling, and photographed. Geotechnical logging of the stope definition and infill drill core was not considered necessary as this information was already available from exploration and resource expansion drilling in the vicinity, thereby facilitating a more rapid sampling turnaround for timely production decision making.
Core logging information was recorded in the GeoSpark core logging software, which includes data validation, picklists, and minimum required fields to ensure data capture is consistent and valid. Additional data validation is conducted by Pretivm’s database manager prior to importing core logging data into the Structured Query Language (SQL) GeoSpark database. These include collar, survey, and interval (missing/overlapping geological and sampling intervals) checks and actual to planned cross-referencing.
10.1.5 | RC Sampling Procedures |
Stope infill RC drilling conducted by Boart Longyear used 5 ft (1.52 m) rods. Dry samples were collected each rod length through a cyclone and rotary splitter system. Stope definition and production drilling conducted by Procon used 6 ft (1.83 m) rods. Wet samples were collected at intervals of one or two rod lengths through a coupled cyclone and rotary splitter sampling system specially designed to handle wet cuttings (Section 10.1.2). All RC drillholes were sampled in their entirety. The possibility of sample cross-contamination was mitigated by ensuring the driller completed a blow down to clear the cuttings from the rods after every rod length and sample. Cyclones and sample splitters were constantly checked by Pretivm geologists to ensure that there was no sample material being retained in these components between samples; this being particularly important for the wet sample cyclone and splitter Cyclone-sample splitter systems were fully cleaned out between drillholes. Stope infill, definition, and production RC drillhole chips were not logged. Additional details on RC sampling are presented in Section 11.0.
10.1.6 | Summary of Results |
The relatively tightly-spaced stope infill and definition drilling (including RC drilling) conducted during 2017 and 2018 was primarily used to validate and optimize stope shapes ahead of mining. The drilling confirmed the geological interpretation of continuous, dominantly east-southeast-west-northwest trending structural vein and vein stockwork corridors containing ubiquitous yet highly variable and erratically distributed gold and silver mineralization in the Valley of the Kings Zone (Figure 10-2, Figure 10-3, and Figure 10-4).
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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Figure 10-2: Example Plan View on the 1,410 m Level in the Brucejack Gold Mine Showing 2017-2018 Drilling (Coloured by Gold Grade) and Valley of the Kings Zone Mineralized Domain Interpretations (Viewing Window ±20 m)
Source: | Pretivm (2019) |
The pilot dry sample RC drilling program did not achieve the hoped-for cost and time efficiencies over diamond core drilling: diamond drilling was continued for the remainder of the 2018 stope definition and infill drilling. Wet sample RC drilling did, however, provide sufficient cost and time efficiencies over diamond core drilling for grade control and production. Furthermore, the use of RC for stope definition and production drilling is considered to provide better stope boundary resolution and improved sample representativity over the current grade control sampling protocol (see Section 11.1.2). Pretivm aims to sequentially bring additional RC-modified blasthole drill rigs online for grade control and production drilling through 2019.
The west-oriented exploration drilling did not intersect any significant mineralized north-south structures, nor did it intersect significant mineralization along the Brucejack Fault and its peripheral structures. Numerous mineralized veins were, however, intersected running at low angles to the core axis, indicating the presence of east-southeast-west-northwest, east-west, and east-northeast-west-southwest trending veining. These drillholes were not included in the January 2019 Mineral Resource update (Section 14.0) owing to their wide spacing and less-than-optimal orientation in relation to the mineralization.
The two-deep exploration drillholes drilled under the Flow Dome Zone were successful in demonstrating the presence of Valley of the Kings Zone style mineralization between the two zones, and in intersecting porphyry-style alteration and mineralization at depth beneath the Flow Dome Zone (see Section 9.2).
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Figure 10-3: Example SW-NE Cross Section Through Along Mining Crosscut 20 (Central Parts of the Mine) Showing Drilling (Coloured by Gold Grade) and Mineralized Domain Interpretations in the Valley of the Kings Zone of the Brucejack Deposit (Viewing Window ±20 m)
Source: | Pretivm (2019) |
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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Figure 10-4: Oblique View of the Valley of the Kings Zone Showing only 2017 and 2018 Drilling (Coloured by Gold Grade) and Mineralized Domain Interpretations
Source: | Pretivm (2019) |
10.2 | Professional Opinion of Qualified Person |
The QP believes that drilling, core logging, and sample handling procedures have been conducted using industry best practices. The appropriate level and quality of information has been obtained to provide sufficient confidence in drillhole spatial location for three-dimensional geological, geotechnical, and grade modelling of the Brucejack Deposit. There are no apparent drilling or recovery factors that would materially impact the accuracy and reliability of the drilling results.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
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11.0 | SAMPLE PREPARATION, ANALYSES, AND SECURITY |
Sample preparation, analysis, and security for the years 2014 to 2018 inclusive are summarized in this section. For detailed sample preparation and analysis information prior to 2014, the reader is referred to Jones (2014) and Ireland et al., (2014).
11.1 | Sample Preparation, Analysis, and Security |
11.1.1 | Drillhole Sampling |
The majority of the samples collected between 2014 and 2018 were from HQ diameter diamond drillcore. Drillcore was placed in core boxes at the drill rig (both on surface and underground), with drill footage markers recorded on wooden spacers and drillhole numbers and box numbers recorded on each box. Batches of core boxes were sealed and transported to Pretivm’s core logging and processing facilities on site under the control of geological staff. Core was then geologically and geotechnically logged and photographed prior to being sampled.
Sample intervals were delineated by the core logging geologist, taking geology into account. Samples were generally broken at lithological and stockwork zone contacts. Samples were collected at intervals of 1.5 m in length for surface and underground exploration drillholes and 1 m in length for underground resource definition and infill drillholes. Up to the end of 2017, significant intervals of visible gold were sampled down to a minimum length of 0.5 m. All exploration drillholes testing poorly drilled or undrilled areas were marked for half core sampling with a centerline drawn down the core axis by the core logging geologist. All resource definition and/or infill drillholes were whole core sampled. Each of the diamond drillholes from the 2017 and 2018 programs was sampling in its entirety. Whole core sampling was conducted in an effort to eliminate any sampling bias potentially associated with preferential half core selection as a function of visible electrum occurrences, as well as to ensure that any electrum in a given length of core would have a chance of being sampled.
Sampled drillcore was placed in plastic bags with appropriate sample tags. Sealed sample bags were then grouped and sealed in appropriately labelled rice sacks and sent by ground transportation to the ALS sample preparation facility in Terrace, BC. Hard copies of sample manifests were enclosed with each shipment and also e-mailed directly to the sample preparation facility ahead of shipping. Ground sample preparation was either by an independent operator (Bandstra Transportation Systems or Tsetsaut Ventures Ltd.) or by a Pretivm operated vehicle depending on quantity of samples being shipped.
RC samples were collected as part of the underground RC drillhole trial conducted in early 2018. Two, 2 kg dry RC sample splits were collected from a cyclone splitter directly into pre-labelled plastic sample bags every 1.52 m. Bags of single sample splits were grouped into four samples per rice bag. Rice bags were then collected in apple crates, sealed with a lid, and then shipped to the ALS sample preparation facility in Terrace, BC in the same way as for the drillcore (see above).
Sampling and shipment creation procedures were conducted by Pretivm personnel prior to dispatch off site to the ALS sample preparation facility in Terrace, BC. ALS checked all samples against the electronic and hard copy sample manifest and assumed custody of the sealed samples upon receipt.
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11.1.2 | Production Sampling |
Production samples, collected as part of Pretivm’s mine grade control process, were not subject to the same level of rigor as the diamond and RC drilling discussed above. A brief discussion is included here for the sake of completeness. Whilst every effort is made to generate as representative a sample as is possible under the exigencies of mining along with practical QA/QC appropriate for production samples, these samples are not considered to be as high quality as the exploration and resource definition/infill drilling samples. Production samples include approximately 600 to 800 kg bulk samples collected from longhole drill cuttings by ring (in stope) representing approximately 2,000 t per sample, approximately 60 kg bulk samples collected from Jumbo cuttings by development round representing approximately 230 t per sample, and RC samples collected over 1.83 m sample lengths from modified longhole drill rigs. Longhole bulk samples are reduced in size through a customized sample splitting station to 10 kg samples. Jumbo cuttings bulk samples are reduced through a riffle splitter to 10 kg samples. Concentrate and tails samples are then generated at the Pretivm-run on-site Bulk Gravity Sample Preparation Laboratory. All production samples are analyzed at the on-site analytical laboratory operated by Pretivm. Internal QA/QC checks are conducted by the on-site analytical laboratory to assess accuracy, precision, and potential sample cross-contamination and ensure assay data quality. Bulk production samples are used for grade control and not used, other than in a general validation sense, for resource. Limited production RC samples from the 1,260 m level were considered to be of sufficient quality, considering nearby diamond drilling, to be used in the estimation of the January 2019 Mineral Resource (Section 14.0).
11.1.3 | Sample Preparation and Analysis by Analytical Laboratory |
ALS Vancouver has been the primary analytical laboratory for the analysis of samples from the Brucejack Property since 2009. Umpire check analytical laboratories used include MSALabs and Met-Solve. The ALS laboratory is used to provide umpire checks on the quality of production sample assays conducted at the on-site laboratory. The ALS analytical laboratory in Vancouver is an International Organization for Standardization (ISO) 9001-2015 certified and ISO 17025:2005 United Kingdom Accreditation Service (UKAS) ref. 4028 accredited laboratory. MSALabs has both ISO 17025 and ISO 9001 accreditation. Primary sample preparation methods and analytical packages used for Pretivm drill samples from 2014-2018 are summarized in Table 11-1. The ALS, MSALabs, and Met-Solve analytical laboratories are independent of Pretivm. After sample shipments reach the sample preparation facility, they are in ALSs custody for sample preparation, inter-laboratory shipping, and analyses. It is ALSs standard operating procedure to check all samples received from Pretivm against the electronic and hard copy sample manifests, as well as for any potentially missing sample material, compromised plastic sample bags, broken zip closures, or torn/broken rice bags upon receipt. Pretivm has not been alerted to any potential sample tampering by ALS. Laboratory sample reduction and analytical procedures have been conducted by independent accredited companies using industry standard methods. Pretivm ensured quality control was monitored through the frequent insertion of blanks, certified reference materials, and duplicates.
11.1.4 | Specific Gravity and Bulk Density |
Density determinations to support the resource model were carried out prior to 2014 as described in Jones (2014). Comparison between the pulp specific gravity and core density measurements indicated that the core density is on average the same as the pulp specific gravity within the siliceous zone and approximately 3% lower, on average, for all other rock types. Consequently, all specific gravity estimates in the Mineral Resource model (which are based on the pulp specific gravity measurements), with the exception of the siliceous zone, were factored down by 3% to provide the bulk density. Bulk density estimates have been reasonable predictors of tonnage for production. Additional specific gravity and bulk density measurements will be needed as the resource model is expanded in areas away from the current workings to reflect the change in lithology at depth, across, and along strike from the known mineralized zones.
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Table 11-1: | Sample Preparation and Analytical Methods Conducted on Pretivm Drill Samples Between 2014 and 2018 |
Year | Sample Preparation | Gold Analytical Methods | Multi-element methods (incl. Ag and overlimits) |
2014-2018 (Q1) | Diamond Drill Core Samples 1.Crush entire sample to 70% <2 mm 2.Riffle split 3.Pulverize 500 g to 85% <75 µm | 30 g charge weight fire assay by AA finish to upper limit at 10 ppm (Au-AA23) Au overlimit trigger at 10 ppm to complete 30 g fire assay with gravimetric finish (Au-GRA21) Au overlimit trigger at 10,000 ppm to complete high precision analysis by fire assay with gravimetric finish (Au-CON01) Visible Gold (VG) Samples: Au by screen fire assay for VG-bearing samples (Au-SCR21, using 30 g charge weights) | 33 element package (including Ag) using a four-acidnear-total digestion and an ICP-AES analysis (ME-ICP61). Ag overlimit trigger at 100 ppm Ag for three-acid digestion with HCL leach and ICP-AES or AAS finish (AG-OG62) Ag overlimit trigger at 1,500 ppm Ag by 30 g fire assay with gravimetric finish (Ag-GRA21) Overlimit triggers also for Zn, Pb, Cu by their respective OG62 methods (Zn-OG62, Pb-OG62, Cu-OG62) |
2018 (Q2) | 1.Crush entire sample to 70% <2 mm Diamond Drill Core Samples 2.Riffle split to 1x1 kg pulp for SFA 3.Pulverize to 85% passing 75 µm Resource RC Drill Samples 2.Riffle split into two, 2 kg splits 3.Pulverize 2 kg to 85% <75 µm 4.Riffle split pulp in half for analysis | Whole Core and Resource RC Drill Samples Au total parts per million by screen fire assay for all samples (Au-SCR24, 50 g charge weights) RC Samples Only Au parts per million by Leachwell head/tails (Au-AA15) | Diamond Drill Core Samples: unchanged from 2014 Multielement data not collected for RC drill samples |
2018 (Q3) onwards | Diamond Drill Core Samples 1.Crush entire sample to 70% <2 mm 2.Riffle split 3.Pulverize 2 kg to 85% <75 µm Production RC Samples 1.Crush entire sample to 70% <2 mm 2.Riffle split 500 g 3.Pulverize to 85% <75 µm | Diamond Drill Core Samples Au parts per million by 50 g fire assay with AA finish to 18 ppm (Au-AA26; upper limit 100 ppm) Requested trigger for Au overlimit at 18 ppm for completion of 50 g fire assay by gravimetric finish (Au-GRA22) Au overlimit trigger at 10,000 ppm to complete high precision analysis by fire assay with gravimetric finish (Au-CON01) Production RC Samples Au by fire assay with AA finish (20 to 30 g charge) with upper limit of 10 ppm Au overlimit trigger for >10 ppm by fire assay with gravimetric finish | Diamond Drill Core Samples: unchanged from 2014 Multielement data not collected for production samples |
Note: | ALS method codes shown in parentheses. |
SFA – screen fire analysis; AA – atomic absorption; VG – visible gold; ICP – inductively coupled plasma; AES – atomic emission spectroscopy; AAS – atomic absorption spectroscopy
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11.2 | Quality Assurance and Quality Control |
Pretivm’s QA/QC protocols for the Brucejack Property included tests for data accuracy, precision, and sample cross-contamination. Field control samples were submitted together with drillhole samples to control and assess these key indicators of database quality.
Accuracy, a measure of the closeness to the true value, was tested using matrix-matched round-robin certified standard samples (certified by Smee and Associates Consulting Ltd.). Analytical precision (repeatability of results) was checked using field duplicate samples. Potential cross-contamination between samples as a result of smearing of high-grade samples was checked through the use of field blank samples.
Field control samples were inserted into the sample stream at a frequency of one standard, one duplicate, and one blank sample per twenty regular samples. Additional field control blank samples were inserted immediately following samples with logged visible gold to quantify and avoid any potential cross-contamination between samples as a result of smearing from high-grade samples. Quarter core samples served as field duplicate control samples for exploration drillholes. Coarse reject duplicate samples have been used as field control duplicate samples to assess precision for whole core resource definition and infill drillholes from 2014 through to the present (2019). Coarse rejects were used as field control duplicates for resource RC drilling. Umpire check pulp duplicate assays were conducted on approximately 5% of the ALS pulp duplicates at the Met-Solve (2014-2015) and MSALabs laboratories (2016-2018) using comparable analytical methods.
From 2011-2016, GeoSpark, a Nanaimo, BC based geological database software and services company that is independent of Pretivm, managed the Brucejack assay imports and completed assay QA/QC for the database. From 2017 to present, assay data has been imported into the same database and managed by Pretivm; however, GeoSpark has been retained to independently conduct routine QA/QC checks on Pretivm’s database and compile QA/QC reporting through its GeoSpark Assure Quality Service program. Real-time QA/QC review of Pretivm’s drillhole sample data includes batch reruns where field control standard results warrant further investigation. Pretivm’s drilling and sampling database has been collected, imported, stored, and managed using GeoSpark’s GeoSpark Core Database System software since 2011.
Numerous independent QA/QC reports have been written verifying the quality of Pretivm’s assay data and its applicability for use in resource estimation. QA/QC results from the 2011 through 2013 program are summarized in Jones (2014), Graindorge and Carlson (2014), and Vallat (2011; 2012; 2013; 2014). QA/QC results from the 2014 through 2016 programs are summarized in Board et al. (2017), Mooney (2015), and Vallat (2015; 2016a; b). QA/QC results from the 2017 and 2018 drilling programs are summarized in Vallat (2018; 2019).
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Results of the QA/QC analyses indicate acceptable levels of accuracy and precision across all of Pretivm’s drill programs on the Brucejack Property considering the nuggetty nature of the precious metal mineralization. The main conclusions are:
■ | Errant values on field standard control charts are minimal and usually reflective of mislabeled standards or blanks. |
■ | Duplicate assay analysis of field control samples indicates an improved degree of precision between quarter core and coarse reject duplicate samples, for both gold and silver. Using the half absolute relative difference (HARD) statistic, it can be seen that 90% of all quarter core field duplicates collected between 2009 and 2015 reported at a precision of better than 30% for gold and 25% for silver, whereas 90% of all coarse reject samples collected from whole core sampling between 2013 and 2018 reported at a precision of better than 14% for gold and 11% for silver (17% for gold and 12% for silver for the 2017-2018 coarse reject subset). Coarse reject duplicate samples are at the same sample support (mass) as the original field sample, and are therefore better than quarter core duplicate samples for representatively assessing precision at the field duplicate level, especially given the nuggetty nature of Brucejack Deposit mineralization. |
■ | The HARD statistic demonstrated that 90% of all pulp duplicate analyses conducted by ALS during 2017 and 2018 reported at a precision of better than 11% for gold and 9% for silver comparable to previous years. This level of precision in pulp duplicate samples is expected, given the nature of precious metal mineralization in the Brucejack Deposit. |
■ | Overall, sample cross-contamination during sample preparation and assaying is considered to be within acceptable tolerance intervals. |
■ | Umpire pulp check assays for gold show a good comparison between analytical laboratories with an acceptable level of precision being achieved. |
■ | Gold and silver assay data used as input for resource modelling of the Brucejack Deposit should be considered as having a variance of ±15%, nine times out of ten. |
11.3 | Qualified Person |
Mr. Ivor W.O. Jones, P.Geo., FAusIMM CP(Geo) of Ivor Jones Pty Ltd. is the QP responsible for Pretivm’s January 2019 Mineral Resource and, by extension, suitability of data for use in resource estimation. Mr. Jones is independent of Pretivm.
11.4 | Qualified Person’s Opinion on Sample Preparation, Security, and Analytical Procedures |
It is the QPs opinion that the sample preparation, sample security, and analytical procedures are satisfactory and appropriate for generating data of suitable quality for use in resource modelling and estimation of the Brucejack Deposit.
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12.0 | DATA VERIFICATION |
Details on data verification conducted prior to 2014 is presented in previous technical reports on the Brucejack Property (Ghaffari et al. 2010a; 2010b; 2011; Jones 2012a; b; c; 2014; Ireland et al. 2013; 2014).
12.1 | Data Verification by Qualified Person |
Continued verification of geological information and data used for mineral exploration and resource estimation on the Brucejack Property has been conducted by Mr. I.W.O. Jones, P.Geo., FAusIMM CP(Geo), Pretivm’s independent QP for resource estimation.
Mr. Jones has been involved with the evaluation of the Brucejack Deposit since 2011, and has conducted numerous site visits (refer to Section 2.0) to the Brucejack Property through the various exploration drilling, resource definition drilling, bulk sample extraction, mine development, and production stages between 2011 and 2018. During his mine visits, Mr. Jones reviewed sufficient surface, drill core, and underground exposures to confirm the presence and nature of the mineralization and appropriateness of the interpreted geological framework.
Mr. Jones has verified Pretivm’s drilling, sample preparation, handling, security, and chain of custody procedures on site, as well as surface and underground drillhole locations, core handling, and core logging. He has also reviewed Pretivm’s database integrity and data quality for use in resource estimation (see Section 11.0). Mr. Jones has reviewed and been involved in all stages of the geological modelling and domain definition for the Brucejack Deposit between 2011 and present and has assessed the applicability and robustness of these interpretations in the underground mine workings at the Brucejack Gold Mine.
Mr. Jones visited the Contact Mill in Philipsburg, Montana, during the 2013 Bulk Sample Program and has visited the Brucejack Gold Mine mill on multiple occasions, both to understand the nature of coarse- versus fine-gold mineralization as part of resource estimation process improvement, and to improve approaches to reconciliation. Mr. Jones has observed abundant visible electrum intersections in drill core as well as in underground workings, verifying the presence, nature, and deportment of gold mineralization in the Brucejack Deposit. Mr. Jones developed and has continually assessed the appropriateness of the technique used for estimation of the Mineral Resource for the Brucejack Deposit through his ongoing working relationship with Pretivm.
Mr. Jones did not deem it necessary to collect and analyze additional independent drill core samples between 2014 and 2018 for the following reasons:
■ | a total of 5,923 oz of gold was produced from the 10,302 t bulk sample in 2013 (Ireland et al. 2014) |
■ | Mr. Jones has inspected abundant visible gold showings in underground workings |
■ | the Brucejack Gold Mine is in production: 528,496 oz of gold was produced by the end of 2018. |
12.2 | Qualified Person’s Opinion on Data Validity |
Sufficient checks have been completed to satisfy Mr. Jones that the Brucejack Gold Mine drilling and sampling data and geological interpretations are suitable for resource modelling and estimation.
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13.0 | MINERAL PROCESSING AND METALLURGICAL TESTING |
Metallurgical testing programs have been conducted on the Brucejack Property since 1988, with major work performed between 2009 and 2014, to investigate the amenability of mineralization of the Valley of the Kings Zone and West Zone to conventional separation processes for gold and silver recovery. A 2,700 t/d process plant was designed based on these test results. The test work review and process design descriptions were filed in 2014 FS (Ireland et al. 2014).
Between March and May of 2017, the Brucejack Gold Mine was successfully commissioned with the first gold pour on June 20, 2017. The plant reached full operation in Q3 2017. The average production rate reached 2,950 t/d during Q4 2017, which is higher than the design capacity. Plant throughput has been tested for 3,800 t/d.
To optimize and increase the process plant throughput to reach the target capacity of 3,800 t/d, Pretivm conducted a comprehensive review, including new flotation and gravity tests and grinding circuit simulations and operation test trials. This section provides a summary of previous test work, including bench scale tests and bulk sample tests; plant production data since the beginning of full operation; and new test work to support plant expansion.
13.1 | Previous Bench-scale Test Work |
The main testing programs on the Brucejack Property were conducted between 1988 to 2014 and are noted in Ireland et al. (2014).
Test work conducted between 1988 and 1990 investigated the mineralization’s amenability to gravity concentration, flotation concentrate cyanidation, as well as gravity concentration plus whole ore cyanidation. Samples collected from the West Zone and the R-8 Zone were used for this test work and the results indicated that gravity separation would recover a significant portion of the contained gold. Cyanide leaching on the gravity tailings produced good overall gold recoveries, but poor silver recoveries. The samples appeared to respond well to flotation concentration; however, results showed that the R-8 mineralization might require finer primary grinding.
Test work conducted between 2009 and 2014 established the design basis for the 2014 FS (Ireland et al. 2014), which investigated head sample characteristics; varied processing methods, including gravity concentration, gold/silver bulk flotation, and cyanidation; and melting and SLS tests. The tested samples were obtained from the Valley of the Kings Zone, the West Zone, and from adjacent gold deposits such as the Galena Hill (GH) Zone and the Gossan Hill (R-8) Zone. Ireland et al. (2014) design work focused on the Valley of the Kings Zone and the West Zone.
13.1.1 | Sample Description and Characteristics |
The test programs utilized core samples and their composites, along with assay reject material. The head assays showed a large variation of gold content from less than 1 g/t to over 70 g/t. The occurrence of nugget gold was identified using parallelized gold assay tests, by comparing the conventional fire assay and screen metallic assay methods.
13.1.1.1 | Mineralogy Analysis |
Process Mineralogical Consulting Ltd. (PMCL), in 2012, and Inspectorate Exploration and Mining Services Ltd. (Inspectorate), in 2014, conducted mineralogical analysis work on head samples. The PMCL work indicated that electrum was the primary gold bearing mineral in the tested samples. Fine gold grains, from 2 to 32 µm in size, were reported and occurred as fracture fillings in pyrite and as disseminated grains and inclusions to gangue minerals and pyrite. Carbonate mineral content was approximately 2 to 3%. Major silver-bearing minerals included electrum, polybasite, acanthite, and selenopolybasite. Most silver-bearing minerals presented as liberated grains with a lesser amount associated with pyrite and gangue minerals. The work completed by Inspectorate showed that the observed gold grains were all finer than 5 µm in circular diameter and mostly liberated. The unliberated gold was associated with pyrite. At a primary grind size of 80% passing 87 μm, 90% of the pyrite was liberated.
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13.1.1.2 | Comminution Studies |
Gekko Systems Pty Ltd. (Gekko) conducted vertical shaft impactor (VSI) crushing test, which resulted in a positive conclusion that the samples are amenable to VSI crushing. The specific gravity measured from the samples were in the range of 2.71 to 2.87. Inspectorate and Hazen Research Inc. (Hazen) performed grindability tests during various test programs and, in general, the mineralization appears to be moderately hard. Table 13-1 shows the Bond ball mill work index (BWi) results, which were observed between 13.8 and 17.2 kWh/t, and Table 13-2 show the SAG mill comminution (SMC) test results.
Table 13-1: | Conventional Grindability and Crushability Test Results |
Cut Particle | ||||||
Sample | BWi | Size | RWi | CWi | UCS | Ai |
ID | (kWh/t) | (µm) | (kWh/t) | (kWh/t) | (psi) | (g) |
Inspectorate (2013) | ||||||
MU (Upper Zone Master Composite) | 15.6 | 106 | - | - | - | - |
ML (Lower Zone Master Composite) | 15.0 | 106 | - | - | - | - |
Hazen (2012) | ||||||
VOK HW 1 | 14.2 | 149 | 14.4 | 12.3 | 20,910 | 0.2254 |
VOK Ore 1 | 14.4 | 149 | 15.6 | 11.4 | 15,680 | 0.2125 |
VOK Ore 2 | 14.4 | 149 | 14.6 | 11.1 | 8,510 | 0.1384 |
VOK Ore 3 | 15.4 | 149 | 17.9 | 10.4 | 9,000 | 0.0903 |
VOK Ore 4 | 14.2 | 149 | 15.2 | 9.3 | 11,800 | 0.3820 |
VOK Ore 5 | 13.8 | 149 | 14.3 | 7.9 | 5,770 | 0.2474 |
VOK Ore 6 | 14.4 | 149 | 13.5 | 8.9 | 11,500 | 0.2385 |
WZ HW 1 | 12.2 | 149 | 13.2 | 6.9 | 2,520 | 0.0388 |
WZ Ore 1 | 16.7 | 149 | 16.7 | 11.8 | 22,390 | 0.3069 |
WZ Ore 2 | 15.3 | 149 | 15.1 | 10.7 | 15,530 | 0.3535 |
WZ Ore 3 | 15.8 | 149 | 15.5 | 10.3 | 20,310 | 0.6599 |
WZ Ore 4 | 15.5 | 149 | 17.0 | 9.5 | 26,460 | 0.2479 |
Inspectorate (2012) | ||||||
VOK-1 Master Composite | 15.8 | 74 | - | - | - | - |
VOK-2 Master Composite | 15.3 | 74 | - | - | - | - |
VOK-3 Master Composite | 15.8 | 74 | - | - | - | - |
VOK-4 Master Composite | 15.7 | 74 | - | - | - | - |
WZ-1 Master Composite | 17.2 | 74 | - | - | - | - |
WZ-2 Master Composite | 15.7 | 74 | - | - | - | - |
Inspectorate (2009 to 2010) | ||||||
BZ Composite | 16.4 | 105 | - | - | - | - |
GH Composite | 15.6 | 105 | - | - | - | - |
R-8 Composite | 16.2 | 105 | - | - | - | - |
Note: | RWi – Bond rod mill work index; CWi – Bond crushing work index; UCS – universal compressive strength; Ai – Bond abrasion index; BZ – Bridge Zone; Cut Particle Size – screen aperture |
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Table 13-2: | SMC Test Results (2012) |
Sample | DWi | Mia | Mih | Mic | Specific | ||||
ID | (kWh/m3) | A | b | Axb | (kWh/t) | (kWh/t) | (kWh/t) | ta | Gravity |
VOK HW 1 | 5.76 | 52.8 | 0.92 | 48.6 | 16.7 | 12.0 | 6.2 | 0.45 | 2.79 |
VOK Ore 1 | 6.37 | 56.6 | 0.77 | 43.6 | 18.1 | 13.2 | 6.8 | 0.41 | 2.79 |
VOK Ore 3 | 7.12 | 62.9 | 0.62 | 39.0 | 20.2 | 15.0 | 7.8 | 0.40 | 2.75 |
VOK Ore 5 | 4.61 | 52.3 | 1.16 | 60.7 | 13.9 | 9.5 | 4.9 | 0.56 | 2.81 |
WZ HW 1 | 4.89 | 55.2 | 1.08 | 59.6 | 14.1 | 9.8 | 5.1 | 0.53 | 2.90 |
WZ Ore 2 | 7.08 | 66.7 | 0.59 | 39.4 | 19.9 | 14.8 | 7.7 | 0.37 | 2.76 |
WZ Ore 4 | 6.32 | 69.9 | 0.62 | 43.3 | 18.3 | 13.3 | 6.9 | 0.41 | 2.75 |
Average | 6.02 | 59.5 | 0.82 | 47.7 | 17.3 | 12.5 | 6.5 | 0.44 | 2.79 |
Average – VOK | 5.97 | 56.2 | 0.87 | 48.0 | 17.2 | 12.4 | 6.4 | 0.45 | 2.79 |
Average – WZ | 6.10 | 63.9 | 0.76 | 47.4 | 17.4 | 12.6 | 6.6 | 0.44 | 2.80 |
Note: | DWi – drop weight index; Mia = coarse ore work index provided directly by SMC Test®; Mih – high-pressure grinding roll (HPGR) ore work index provided directly by SMC Test®; Mic – crushing work index provided directly by SMC Test®; ta – low-energy abrasion component of breakage; HW – hanging wall |
13.1.2 | Gold and Silver Recovery Tests – Gravity Concentration |
Two-stage gravity separation programs (2009/2010, 2012/2013), including centrifugal and panning concentration, were carried out on head composite samples, head variability samples, and flotation concentrate samples. The results indicated that most of samples responded well to the tested gravity separation methods. Reground concentrate samples presented better performance compared with their head samples. The reported gold gravity recovery ranged between 2.7 to 56.0%, and silver recovery varied between 1.0 to 44.0% for composite head samples. The average metal recovery of variability head samples was 45.8% for gold and 21.4% for silver; the average metal recovery of the flotation concentrates produced from 11 variable samples was 24.5% for gold and 11.6% for silver.
In 2012, FLSmidth Knelson (Knelson) and Met-Solve conducted gravity recoverable gold (GRG) tests and related simulations. Table 13-3 shows the test results and Figure 13-1 shows the GRG versus grind size.
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Figure 13-1: Cumulative Stage GRG versus Grind Size for Gold and Silver
Table 13-3: | Gravity Recoverable Gold Test Results (2012) |
Sample Head | GRG | Cyanide Leaching | Gravity Upgrading | |||||||
Primary Grind/ | Grade (g/t) | Recovery (%) | Recovery (%) | Tabling Recovery (%) | ||||||
Lab | Tests | Regrind Size | Au | Ag | Au | Ag | Au | Ag | Au | Ag |
Knelson | E-GRG | P8074 µm | 17.0 | 58.6 | 80.3 | 9.1 | 99.5 | 86.9 | n/a | n/a |
Met-Solve | GRG | TBD | 18.7 | 63.0 | 80.7 | 33.7 | 99.2 | 92.2 | 61.1 | 42.5 |
Note: | E-GRG – extended gravity recoverable gold |
In 2014, FLSmidth Dawson Metallurgical (FLS-DM) conducted tabling tests on gravity concentrates samples (Table 13-4). Further, Gekko tested the amenability of the samples to in line pressure jigging technology. The results indicated that when the mass pull was reduced to 5%, the gold recovery ranged from 43 to 67%.
Table 13-4: | Precious Metal Material Balance |
Weight | Assay (g/t) | Distribution (%) | |||
Product | (g) | Au | Ag | Au | Ag |
Table Concentrate | 60.4 | 199,935 | 107,297 | 23.0 | 21.1 |
Table Middlings 1 | 250.7 | 40,571 | 24,715 | 19.3 | 20.2 |
Table Middlings 2 | 2,655.2 | 9,058 | 5,290 | 45.7 | 45.8 |
Table Tailings | 6,308.6 | 1,000 | 629 | 12.0 | 12.9 |
Calculated Head | 9,274.9 | 5,672 | 3,309 | 100.0 | 100.0 |
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13.1.3 | Gold and Silver Recovery Tests – Flotation Concentration |
Inspectorate conducted a preliminary test program between 2009 and 2011 and further optimization tests from 2011 to 2013, which included bulk flotation tests and cleaner flotation tests on samples from the Valley of the Kings Zone, the West Zone, and adjacent gold deposits. Met-Solve tested slime material response to flotation in 2014.
13.1.3.1 | Bulk Flotation |
The bulk flotation tests were conducted to investigate the effects of varied primary grind size, reagent types, and pH levels. The primary grind size of 80% passing a range of 38 to 143 µm was tested on different mineralization samples. The overall gold recovery from gravity concentration and bulk flotation was found to increase with a finer primary grind size; however, for most samples, this increase become insignificant when the primary grind size was finer than 74 µm. The reagent schedule and pH level were found to have an insignificant effect on gold flotation recovery.
13.1.3.2 | Cleaner Flotation |
The cleaner flotation tests were carried out on rougher and scavenger concentrates. The results indicated that the upgrading efficiencies were good for both gold and silver. The gold upgrading efficiency, which was better than silver, still varied significantly in the tests. Attempts to solve this problem were tested by introducing a regrinding circuit prior to the cleaner flotation stage, adjusting flotation pH level, applying different collectors, and/or adding sulphide depressants but were met with little success.
13.1.3.3 | Other Flotation |
Met-Solve conducted a preliminary flotation test to recover gold from the fine fraction generated in a de-sliming classifier. Significant gold was able to be recovered, but a low flotation pulp density, as well as a high dosage of sodium silicate (dispersant reagent) were required to control the viscosity of the slurry.
13.1.4 | Gold and Silver Recovery Tests – Cyanidation |
Between 2009 and 2013, Inspectorate conducted cyanidation tests on head samples of composite and individual mineralization, flotation concentrates, and gravity concentrates. A significantly varied gold recovery range was reported in direct leaching tests. Improved gold recoveries were generated when using a combined method of gravity + leaching flotation concentrates or gravity + leaching gravity tailings.
Inspectorate conducted flowsheet development tests to incorporate these observations. The following three flowsheets were examined:
■ | Flowsheet A: Primary grind, gravity concentration, rougher/scavenger flotation, and cyanidation on the reground flotation concentrates. |
■ | Flowsheet B: Primary grind, rougher/scavenger flotation, and a gravity separation on the reground concentrates prior to cyanidation on the gravity tailings. |
■ | Flowsheet C: Primary grind, primary gravity concentration, rougher/scavenger flotation, a secondary gravity separation on the reground concentrates prior to cyanidation on the gravity tailings, and intensive leaching on the panning tailings. |
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Table 13-5 summarized the overall gold recoveries of the three flowsheets.
Table 13-5: | Cyanidation Flowsheet Development Test Results |
Gravity | Leaching | Overall | ||||
Recovery (%) | Recovery (%) | Recovery (%) | ||||
Samples | Au | Ag | Au | Ag | Au | Ag |
Flowsheet A | ||||||
Composite BZ (Test GF35) | 17.0 | 4.4 | 72.2 | 66.6 | 89.2 | 71.0 |
Composite R-8 (Test GF37) | 2.7 | 1.8 | 86.4 | 85.3 | 89.1 | 87.1 |
Composite GH (Test GF36) | 11.0 | 1.8 | 72.6 | 82.9 | 83.6 | 84.7 |
Composite GH (Test GF41) | 25.7 | 1.4 | 59.6 | 83.4 | 85.3 | 84.8 |
Flowsheet B | ||||||
Composite R-8 (Test GF38) | 33.5 | 2.3 | 50.5 | 63.7 | 84.0 | 66.0 |
Composite GH (Test GF39) | 43.5 | 4.4 | 43.8 | 63.9 | 87.3 | 68.3 |
Composite BZ (Test GF40) | 24.9 | 5.7 | 38.3 | 61.1 | 63.3 | 66.8 |
Composite SU-32B (Test GF42) | 21.0 | 1.3 | 51.7 | 63.7 | 72.7 | 65.0 |
Composite SU-33 (Test GF43) | 43.2 | 4.6 | 47.1 | 64.5 | 90.4 | 69.1 |
Composite SU-36A (Test GF44) | 41.0 | 3.8 | 32.6 | 56.6 | 73.7 | 60.4 |
Composite SU-36B (Test GF45) | 9.7 | 2.3 | 42.1 | 55.7 | 51.8 | 58.0 |
Flowsheet C | ||||||
Composite GH2 (Test GF26) | 68.3 | 8.31 | 21.9 | 62.7 | 90.4 | 71.2 |
Composite SU98 (Test GF27) | 85.6 | 27.7 | 13.5 | 51.0 | 99.1 | 78.9 |
Composite SU98 (Test GF25) | 62.0 | 9.23 | 26.4 | 62.9 | 88.7 | 72.5 |
13.1.5 | Variability Tests |
In 2012, variability tests based on primary gravity concentration and bulk flotation were conducted with varied core samples. In general, the overall metal recoveries were consistent with the results from the composite samples. Gold recovery varied from 82.8 to 99.8%, averaging 97.2%, while the head gold grade fluctuated from 0.5 to 200 g/t, averaging 21.5 g/t. At a silver head grade range of 3.9 to 1,897 g/t, the silver recovery varied from 51.2 to 99.1%, averaging 88.5%.
In 2011, variability tests based on Flowsheet C were performed, which indicated there was no significant variation in metallurgical performance between the West Zone and the Galena Hill Zone mineralization. The overall average gold recovery was 94.5%, which was approximately 19% higher than the average silver recovery. The regrind size was finer than 80% passing 10 μm. The variability tests based on Flowsheet B showed a significant variation of the overall gold recoveries, while the overall silver recovery fluctuation was moderate.
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13.1.6 | Locked Cycle Tests |
In 2012/2013, six locked cycle tests were conducted on four composite samples from the Valley of the Kings Zone and the West Zone based on the test conditions developed from comprehensive batch test work, including primary grind size, gravity separation, rougher/scavenger flotation, and rougher concentrate cleaner flotation. Four locked cycle tests were completed in 2012 on two master composites, which consisted of one blend from the Valley of the Kings Zone (VOK 1, 2, 3, and 4) and one from the West Zone (WZ 1 and 2). The procedure included:
■ | primary grinding targeting a moderate size of 80% passing 80 to 85 µm |
■ | gravity concentration |
■ | rougher and scavenger flotation with the scavenger concentrate recycled |
■ | rougher concentrate cleaner flotation. |
For tests FLC1 and FLC3, the rougher concentrates were reground prior to cleaner flotation. In an effort to activate gold- and silver-bearing minerals, copper sulphate was added during the rougher and cleaner flotation stages.
In 2013, two separate locked cycle tests were conducted on two composites generated from the upper and lower zones of the Valley of the Kings Zone. The test procedure used was similar to that used for the locked cycle tests in 2012. Table 13-6 shows the results of the six locked cycle tests, which are summarized as follows:
■ | The average metal recoveries from the Valley of the Kings Zone composites were approximately 97.8% for gold and 94.3% for silver. Approximately 53.9% of the gold and 28.6% of the silver reported to the gravity separation concentrate. The flotation concentrate contained approximately 130 g/t Au, 252 g/t Ag, and 0.68% As. |
■ | Average recoveries from the master composite of the West Zone were approximately 94.0% for gold and 90.8% for silver. Approximately one-third of the gold reported to the gravity separation concentrate. The flotation concentrate contained 48.6 g/t Au, 2,800 g/t Ag, and 0.24% As. |
■ | The addition of copper sulphate, together with regrinding the rougher flotation concentrates, did not appear to improve the recoveries of the target metals. |
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Table 13-6: | Locked Cycle Tests Results |
Gravity Concentration | Flotation | |||||||||||||
Head Grade Calculated | Recovery | Concentrate Grade | Concentrate Grade | Recovery | ||||||||||
Test | Au | Ag | S | Au | Ag | Au | Ag | Au | Ag | S | As | Au | Ag | |
Composite | No. | (g/t) | (g/t) | (%) | (%) | (%) | (kg/t) | (kg/t) | (g/t) | (g/t) | (%) | (ppm) | (%) | (%) |
VOK-1 to -4 | FLC1 | 24.2 | 33.6 | 2.92 | 54.2 | 30.5 | 11.7 | 9.1 | 181.3 | 354 | 48.1 | 8,249 | 43.9 | 61.7 |
VOK-1 to -4 | FLC2 | 24.2 | 31.8 | 2.96 | 48.6 | 27.1 | 9.9 | 7.9 | 175.6 | 341 | 46.9 | 6,930 | 49.3 | 67.0 |
WZ-1 and -2 | FLC3 | 6.0 | 225 | 3.03 | 32.0 | 1.3 | 1.7 | 2.7 | 52.6 | 3,096 | 43.5 | 2,622 | 59.2 | 88.5 |
WZ-1 and -2 | FLC4 | 6.3 | 240 | 3.10 | 36.5 | 1.1 | 2.5 | 2.8 | 44.6 | 2,490 | 34.7 | 2,228 | 60.2 | 90.7 |
VOK ML | FLC2 | 10.3 | 12.5 | 3.41 | 48.0 | 21.6 | 4.3 | 2.4 | 83.8 | 152 | 52.2 | 5,801 | 48.5 | 71.7 |
VOK MU | FLC1 | 12.1 | 13.4 | 2.70 | 64.9 | 35.1 | 6.0 | 3.6 | 78.1 | 160 | 49.5 | 6,059 | 33.9 | 62.4 |
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13.1.7 | Other Processing Related Tests |
13.1.7.1 | Melting Test Work |
In 2014, FLS-DM conducted a preliminary melting test on the tabling concentrate generated from the pilot testing program (Section 13.2). The table concentrate contained approximately 20% of gold and 11% of silver. Smelted doré metal grades were 64% gold, 34% silver, and 2% lead.
13.1.7.2 | Solids Liquid Separation Tests Work |
In 2012, Pocock Industrial Inc. (Pocock) conducted SLS tests on the flotation concentrate and flotation tailings samples. The test program included sample particle size analysis, flocculants screening and evaluation, and static and dynamic thickening tests.
13.2 | 2013 Pilot Plant Testing |
Between September 2013 and February 2014, Pretivm contracted Strategic Minerals to process two batches of bulk mineral samples generated from the Valley of the Kings Zone using the Contact Mill facility located in Philipsburg, Montana. Approximately 10,300 t was processed for the first campaign and approximately 1,200 t was processed for the second run. A combined process of gravity separation and rougher/scavenger flotation with rougher concentrate cleaner flotation was employed to treat the bulk materials. The gravity circuit included a Kneslon concentrator and a Gemini table while a jigging and tabling circuit to recover coarse free gold was also added towards the end of the pilot plant test. No regrind circuit was applied to the rougher/scavenger concentrates. Figure 13-2 shows the pilot plant flowsheet.
The daily feed grades to the mill ranged widely from less than 1 g/t to more than 130 g/t Au for the samples processed by the 2013 processing campaign and from approximately 40 to 300 g/t Au for the Cleo sample processed in 2014. Table 13-7 shows the test results summary reported the 2014 FS (Ireland et al. 2014). The results demonstrated that the flowsheet used for the program can effectively recover gold and silver and adapt well for a wide range of feed grades experienced during the pilot testing.
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Figure 13-2: Bulk Sample Process Flowsheet
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Table 13-7: | Bulk Sample Processing Metallurgical Performances |
Feed | Metal Recovery (%) | Product Grade (g/t) | |||||||||||
Calculated | Table | Table Con + | Gravity+ | Table | Flotation | ||||||||
Tonnage | Grade (g/t) | Con | Table Middlings | Flotation Con | Con | Con | |||||||
Year | (t) | Au(2) | Ag(2) | Au(1) | Ag(1) | Au(1) | Ag(1) | Au | Ag | Au(1) | Ag(1) | Au(3) | Ag(3) |
2013 | 10,302 | 17.5 | 17.1 | 41.8 | 18.2 | 47.6 | 21.0 | 97.5 | 86.9 | 259,487 | 110,146 | 79 | 129 |
2014 | 1,203 | 82.6 | 59.7 | 47.9 | 36.6 | 56.2 | 44.0 | 98.0 | 96.3 | 247,999 | 136,877 | 398 | 402 |
Notes: | (1)Based on assay data from Contact Mill laboratory. |
(2)Including cleanout. |
(3)Flotation concentrate only. |
13.3 | Production Data 2017 to 2018 |
The process flowsheet developed for the Brucejack Property mineralization is a combination of conventional bulk sulphide flotation and gravity concentration to recover gold and silver into gold doré and gold-silver bearing flotation concentrates. In May 2017, ore was first introduced to the mill with a focus on ramping up to designed production throughput using ore from the low-grade ore stockpiles. The first gold was poured on June 20, 2017. During commissioning, 8,510 oz Au were produced in June. On July 1, 2017, Pretivm declared commercial production at the Brucejack Gold Mine. Table 13-8 lists the production data from July 2017 to the end of 2018 based on the Pretivm’s reports and news releases.
Table 13-8: | Bruckejack Mill Production Data 2017-2018(1) |
Mill Feed | Mill Feed | Total | ||||
Tonnage (t) | Grade (g/t) | Recovery (%) | ||||
Time | Total | Daily | Au | Ag | Au | Ag |
Q3 2017 | 261,262 | 2,840 | 10.5 | n/a | 96.5 | n/a |
Q4 2017 | 271,501 | 2,951 | 8.2 | 13.8 | 95.8 | 80.8 |
Total Average 2017 | 532,763 | 2,895 | 9.4 | 13.8 | 96.2 | 80.8 |
Q1 2018 | 261,443 | 2,905 | 9.1 | 13.0 | 96.8 | 85.7 |
Q2 2018 | 236,990 | 2,604 | 14.9 | 17.1 | 97.7 | 88.3 |
Q3 2018 | 240,122 | 2,610 | 12.4 | 14.1 | 97.4 | 88.1 |
Q4 2018 | 267,048 | 2,903 | 11.5 | 15.8 | 97.0 | 85.6 |
Total Average 2018 | 1,005,603 | 2,755 | 11.9 | 15.0 | 97.3 | 87.0 |
Notes: | (1)Excluding gold and silver from pre-commercial production. |
13.4 | Mill Operation Optimization/Expansion Test Work |
To support the process plant optimization and throughput increase at the Brucejack Gold Mine, Pretivm began a series of test work on the samples collected from operation since 2017. The test work involved mineralogy analysis, grindability, gravity separation, intensive leaching, and flotation concentration aspects. The results were used to optimize the current plant operation and to project the performance of the relevant circuits for the 3,800 t/d scenario. In addition, SLS tests and tailings tests relating to mine backfill were also performed for similar purposes. Table 13-9 lists the current test work programs, including simulations, since the 2014 FS (Ireland et al. 2014).
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Table 13-9: | Major Metallurgical Testing and Simulations Programs 2014-2018 |
Lab Year | Mineralogy | Grindability | Gravity | Leaching | Flotation | Thickening | Tailings |
SNF 2016/2017 | ✓ | ||||||
Gekko 2017 | ✓ | ||||||
ALS 2018 | ✓ | ✓ | ✓ | ||||
BV 2017 | ✓ | ||||||
PMCL 2018 | ✓ | ||||||
FLSmidth 2018 | ✓ | ✓ | |||||
Pocock 2019 | ✓ | ||||||
RMS 2018 | ✓ |
Note: | SNF Canada (SNF); BV – Bureau Veritas Commodities Canada Ltd.; RMS – RMS Corp.; FLSmidth Inc. (FLSmidth) |
13.4.1 | Sample Description |
Samples collected from the Brucejack Gold Mine operation and drill core composites at the site were used in different testing programs by different laboratories, as described in the following subsamples.
13.4.1.1 | Mineralogy Analysis Samples – BV 2017 and PMC2018 |
In 2017 and 2019, BV and PMCL, respectively, conducted separate gold deportment studies on final flotation concentrates to support the plant operation. BVs work was based on two flotation concentrate samples labelled as 17-07-03 NS Concentrate and 17-07-04 NS Concentrate. PMCL used one flotation concentrate sample labelled as “LoCon”.
13.4.1.2 | Comminution Test Work Samples – ALS 2018 |
ALS, located in Kamloops, BC, performed comminution, gravity, and flotation tests. For the comminution tests, nine samples were received and tested, which included eight drill core samples and one plant SAG mill feed sample. Chemical analyses were conducted on all nine samples and mineralogical analyses were completed on six of samples through x-ray diffraction (XRD).
13.4.1.3 | Metallurgical Processing Test Work Samples – Gekko 2017 and ALS 2018 |
An intensive cyanide leaching test program conducted at SGS Canada Inc. (SGS) laboratory facility in Burnaby, BC by using the Gekko’s intensive leach procedure. Two sealed pails of Kneslon concentrate pulp samples labelled as Table Feed Sample 21-22/July/2017 (TF2) and Table Feed Sample 23-24/July/2017 (TF1) were used for the testing at the SGS Burnaby laboratory. The pulp samples were decanted to remove the supernatant water and then prepared for subsequent head characterization and intensive leaching tests. Table 13-10 shows the sample head assay results.
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Table 13-10: | Head Assay Results (Gekko 2017) |
Au (g/t) | Ag (g/t) | |||
Assay Method | TF1 | TF2 | TF1 | TF2 |
Screen Metallic – Fire Assay | 8,105 | 5,992 | 3,836 | 3,521 |
Fire Assay | 8,875 | 6,510 | 4,925 | 3,740 |
ALS performed metallurgical test work, including comminution, gravity, and flotation testing. For the metallurgical tests, four composites (H, M, L, and A) with varying feed grades were prepared from 42 subsamples. The metallurgical composite samples were used in flotation tests to develop test conditions. Two selected variability composite samples (West Zone (WZ) and Galena Hill (GH) Zone) were tested at the developed test conditions. Table 13-11 lists the sample head assaying results. The gold and silver assays were completed using a metallic gold assay (by screening) method except for Sample A, WZ, GH and GRG Comp 2. Gold and silver concentrations varied from 3.1 to 16.2 g/t Au and 49 to 398 g/t Ag.
Table 13-11: | Head Assay Results (ALS 2018) |
Au | Ag | S | As | S(-2) | C | TOC | |
Sample ID | (g/t) | (g/t) | (%) | (%) | (%) | (%) | (%) |
Composite L | 3.13 | 49 | 4.00 | 0.063 | 3.95 | 0.73 | 0.03 |
Composite M | 5.73 | 60 | 3.60 | 0.087 | 3.56 | 0.82 | 0.04 |
Composite H | 16.20 | 76 | 3.12 | 0.043 | 3.08 | 0.56 | 0.08 |
Composite A | 4.10 | 53 | 4.02 | 0.062 | 3.98 | - | - |
Composite WZ | 14.70 | 398 | 2.68 | 0.016 | - | - | - |
Composite GH | 5.42 | 73 | 2.61 | 0.044 | - | - | - |
GRG Comp 2 | 9.50 | 36 | 3.64 | 0.048 | - | - | - |
Notes: | S(-2)– sulphide sulphur; C – carbon; TOC – total organic carbon |
For the operation optimization tests, two flotation samples were used—one was a rougher concentrate sample and the other was a third cleaner concentrate—from the Brucejack Gold Mine process streams. The purpose of the test was to investigate the potential gravity concentration of rougher concentrate following regrinding and for further upgrading of the third cleaner concentrate using conventional flotation and flotation column methods. Table 13-12 shows the head assay results of the two processing samples.
Table 13-12: | Head Assays of Processing Samples |
Grade (g/t or %) | ||||
Sample | Au | S | S(s) | As |
Rougher Concentrate | 85 | 37.5 | 37.5 | 0.21 |
Third Cleaner Concentrate | 111 | 44.2 | 44.2 | - |
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13.4.1.4 | Solid/Liquid Separation Test Work Samples – SNF 2016/2017, FLSmidth 2018, and Pocock 2019 |
In 2016 and 2017, SNF provided a preliminary flocculant and coagulant screening tests using static settling methods. Tailings samples were used in both tests; the 2016 samples contained 27.9% solids at an initial pH of 6.8 to 7.0; however, the 2017 samples were not specified in the report.
FLSmidth conducted the SLS test work in Midvale, Utah on both the flotation concentrate and tailings samples collected from the Brucejack Gold Mine. The objectives were to optimize settling characteristics and to evaluate the performances of the two tailings and concentrate thickeners to accommodate the 3,800 t/d throughput.
Pocock tested two tailings samples collected from the Brucejack mill during the operation upset conditions in 2019. Elevated fine clay materials were found suspended in the thickener overflow which were not flocculating properly with the plant flocculant reagent. The two samples came from tailings material produced on January 5 and January 8, 2019. The purpose of this testing was to assist plant operations to clarify the tailings thickener overflow.
13.4.2 | Mineralogy Analysis on Flotation Concentrates |
Pretivm retained BV and PMCL to understand the gold deportment in the final flotation concentrates from 2017 and in 2018, respectively, to support plant operation optimization.
In 2017, BV conducted its investigation on two concentrate samples by using Quantitative Evaluation of Materials by Scanning Electron Microscopy (QEMSCAN) Particle Mineral Analysis (PMA) and QEMSCAN Trace Mineral Search (TMS) protocols. The gold concentration was determined by using an energy dispersive spectrometer (EDS) and Brucker software. BVs study outlines the following major observations and conclusions:
■ | The gold grades of the two concentrates are 154 g/t Au and 57 g/t Au. The majority of the gold occurred as native gold and gold electrum. Table 13-13 lists gold grade and deportment percentage with minerals by mass of the two samples. |
■ | The average gold grain size was 11 to 13 µm for both samples; however, the majority of gold grains were in a range of 1 to 5 µm, as shown in Figure 13-3. |
■ | Approximately 75% of the gold by weight in the two concentrates was liberated as determined by two dimensions. The unliberated gold presented as exposed surfaces and mostly attached to sulphide minerals. The liberated and attached gold accounted for over 99.5% the gold in the concentrates. The unliberated gold was found locked with pyrite and non-sulphide gangue minerals and accounted for less than 0.5% of the total gold. |
■ | The investigation into the mineral composition of the two samples indicated that sulphide minerals were approximately 89% by weight, which were dominated by pyrite. The non-sulphide minerals were approximately 11%, which were mainly included quartz and clay minerals. |
■ | High liberation of sulphide minerals was reported as 90% for both samples; approximately 56% non-sulphide gangue minerals were also presented as liberated. |
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Table 13-13: | Gold Deportment and Associations of Two Flotation Con – BV 2017 |
Grade | Au Mass Deportment % by Minerals | ||||
Au | Native Au | Electrum | Acanthine | Uytenbogaardtite | |
Sample | (g/t) | (Au) | (Au, Ag) | (Ag2S) | (Ag3AuS2) |
17-07-03 NS Concentrate | 153.6 | 9.2 | 86.3 | 3.6 | 0.9 |
17-07-04 NS Concentrate | 57.2 | 86.0 | 4.5 | 0.7 | 8.8 |
Figure 13-3: Gold Grains Distributions with Size Range
In 2018, PMCL conducted a separate gold deportment study and mineralogy determination on one sample labelled as “LoCon”. Tescan Integrated Mineral Analyser (TIMA) was used to determine the sample mineral composition, the mineral abundance, liberation, and grain size information. Gold deportment was investigated using a Tescan Vega 3 3 scanning electron microscope (SEM) equipped with an EDS on polished sections of the gravity products obtained from a Mozley table and CNT Hydroseparator.
The gold grade of the tested sample was assayed as 34.4 g/t Au. Similar to BVs observations, gold was found largely present in the form of electrum grains which were mainly finer than 8 µm. The overall gold grain size was between 16 to 32 µm. Approximately 71% of the gold grains were free and 21% of the gold was attached to silicates but with exposed surfaces. Only a trace amount of the gold was locked in grains within pyrite in a size typically less than 2 µm. The minerals are mainly composed of 76% pyrite, 12% quartz, 6% sercite/muscovite, 2% feldspar with some clay minerals.
13.4.3 | Comminution Test Work |
The key comminution test work generated such parameters as crushing work index, grinding work index (JK Drop Weight, SMC, and Bond ball mill work index), rock hardness, and abrasion. SGS conducted an additional comminution test using the SAG Power Index (SPI) test procedure.
Table 13-14 shows the Bond test results. The Bond ball work index ranged from 13.5 to 19.8 kWh/t of the twelve comminution samples, including three tests on three composite samples producing relatively average values between 15.1 and 16.0 kWh/t. The Bond crushing index was observed to be 6.5 to 17.6 kWh/t. All the samples showed relatively mild abrasive values except for SIL H8 sample.
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Table 13-14: | Bond Test Results (ALS 2018) |
BWi | CWi | Ai | Specific | |
Sample ID | (kWh/t) | (kWh/t) | (g) | Gravity |
SAG Feed | 14.4 | 15.4 | 0.078 | 2.73 |
AND | 16.6 | 17.6 | 0.025 | 2.78 |
SIL H8 | 16.8 | 11.6 | 0.445 | 2.66 |
CGL | 16.5 | 6.5 | 0.043 | 2.84 |
VSF | 14.9 | 10.0 | 0.135 | 2.77 |
ARG | 19.8 | 7.5 | 0.174 | 2.70 |
V6 | 17.2 | 13.4 | - | 2.85 |
P1 | 15.4 | 14.8 | - | 2.83 |
P2 | 13.5 | - | - | - |
Composite H | 16.0 | - | - | - |
Composite M | 15.1 | - | - | - |
Composite L | 15.5 | - | - | - |
Table 13-15 lists the results of JK Drop Weight testing for the SAG Feed, AND, CGL, SIL H8, and VSF samples. The remaining four samples were subjected to SMC testing and results are shown in Table 13-16. The test results show that the SAG parameters (A x b) vary significantly from 29.1 to 78.7. SAG Circuit Specific Energy (SCSE) values ranged from 7.49 to 11.97 kWh/t for all the tested samples.
Table 13-15: | JK Drop Weight Test Results (ALS 2018) |
Sample | SCSE | Specific | ||||
ID | A | b | A*b | ta | (kWh/t) | Gravity |
SAG Feed | 60.2 | 0.76 | 45.8 | 0.48 | 9.43 | 2.78 |
AND | 65.9 | 0.50 | 33.0 | 0.49 | 11.14 | 2.82 |
CGL | 51.1 | 1.32 | 67.5 | 1.05 | 7.96 | 2.76 |
SIL H8 | 67.9 | 0.90 | 61.1 | 0.54 | 8.21 | 2.70 |
VSF | 58.0 | 0.82 | 47.6 | 0.84 | 9.21 | 2.75 |
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Table 13-16: | SMC Test Results and Parameters Derived from SMC Tests (ALS 2018) |
Sample | DWi | Mia | Mih | Mic | Specific | SCSE | ||||
ID | (kWh/m3) | (kWh/t) | (kWh/t) | (kWh/t) | Gravity | A | b | A*b | ta | (kWh/t) |
ARG | 3.5 | 11.3 | 7.3 | 3.8 | 2.75 | 64.5 | 1.22 | 78.7 | 0.74 | 7.49 |
P1 | 6.4 | 17.9 | 13.1 | 6.8 | 2.82 | 63.6 | 0.69 | 43.9 | 0.40 | 9.7 |
P2 | 5.3 | 15.1 | 10.6 | 5.5 | 2.88 | 57.6 | 0.95 | 54.7 | 0.49 | 8.88 |
V6 | 9.9 | 25.1 | 20.1 | 10.4 | 2.85 | 67.6 | 0.43 | 29.1 | 0.26 | 11.97 |
13.4.3.1 | Comminution Circuit Simulations |
Contact Support Service Inc. (CSS) performed a primary grinding circuit modelling using JKSimMet. An additional comparison was performed by Weir Minerals using their proprietary modeling simulations. The input data was generated using comminution testing performed by ALS and SGS and site operating information. The underground mine samples consisted of eight rock types representing various lithologies of the mill feed. On November 23, 2017, a grinding circuit survey was conducted to collect operation data on the samples from belt cuts and process slurry streams. The simulations indicated that the grinding circuit has a sufficient capacity for the increased mill feed rate of 3,800 t/d.
13.4.4 | Gold and Silver Recovery Test Work |
In 2017, under the Gekko’s guide SGS conducted an intensive cyanide leaching test program at SGSs laboratory facility in Burnaby, BC. The test program was to determine the amenability of the Kneslon concentrate samples from the Brucejack Gold Mine to intensive cyanide leaching. ALS conducted a comprehensive metallurgical test program to investigate the gravity and flotation response of the new samples to various test conditions, mainly primary grind size, reagent scheme, and circuit arrangement of the flotation circuit. Both the open and locked cycle tests were conducted using a flowsheet similar to the Brucejack Gold Mine operation.
The major conclusions and recommendations of the metallurgical test work by Gekko and ALS are summarized in the following subsections.
13.4.4.1 | Gravity Testing Results – ALS 2018 |
Figure 13-4 shows the gravity testing results. Similar to previous gravity testing findings and the current operation, a significant amount of the gold is gravity recoverable gold. The gravity gold recoveries vary with the mineralization and gold head grades of the feed samples.
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Figure 13-4: Gravity Results Summary – Composite Samples – ALS 2018
13.4.4.2 | E-GRG Testing Results – ALS 2018 |
ALS performed an extended gravity recoverable gold test using GRG determination procedure on the Composite 2 sample. The results confirmed that most of the gold within the sample was gravity recoverable. The gold recovered at each of the three grind sizes is plotted in Figure 13-5. The overall gold recovery was 70.5% after the three recovery passes, which is lower than the previous tests by Knelson in 2012 that showed 80.3% GRG (Section 13.1.2), but still showed a high amenability to gravity recovery.
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Figure 13-5: E-GRG Test Results
13.4.4.3 | Intensive Leaching – Gekko 2017 |
Five intensive cyanide leaching tests were performed on the two Knelson concentrates samples with varied cyanide concentrations and pulp densities. The leaching pH level was maintained between 10.5 to 11.0 with the dissolved oxygen (DO) concentration of over 20 ppm for all tests. SGS used the Gekko’s test procedure. The following observations were made from the leaching tests:
■ | Sample TF1 produced an over 99% extraction rate of gold and silver based on assays of the residual solids; Sample TF2 reached a similar extraction rate of over 99% extraction of gold and silver. |
■ | In addition, a further increase in cyanide concentration to 3% sodium cyanide (NaCN) or using hydrogen peroxide as an alternative oxidant did not improve the overall leaching recoveries. |
13.4.4.4 | Batch Flotation Test Results – ALS 2018 |
Both rougher and cleaner flotation tests were conducted to explore the impact of various testing conditions on gold and silver metallurgical performances. The flotation tests were conducted on the gravity tailings obtained from various composite samples.
The major observations/conclusions of the rougher flotation tests are noted in the following bullet points and shown in Figure 13-6 and Figure 13-7.
■ | At the tested primary grind sizes of 80% passing between 88 and 216 µm, the primary grid sizes had a modest effect on the flotation performance of the tested composite samples. |
■ | There was no obvious effect between using mild steel rod grinding media and using stainless steel rod media in a rubber liner mill. |
■ | Little success was obtained at the rougher and scavenger stages by modifying test conditions for concentrate grade improvement, including potassium amyl xanthate (PAX) vs. A208/sodium isopropyl xanthate (SIPX) or D233/MX-900; higher pH cleaner flotation; pH adjustment reagents (lime vs. soda ash); collector dosage; and incorporation of copper sulphate. |
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Figure 13-6: Rougher Flotation Tests on Composite H and L
Figure 13-7: Rougher Flotation Tests on Composite M
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The major observations/conclusions of the cleaner flotation tests are noted in the following bullet points and shown in Figure 13-8.
■ | Varied cleaner flotation responses were observed among the tested samples. At a primary grind size of 80% passing between 88 and 102 µm, Composites L and A produced low-grade cleaner concentrates of 32 g/t Au and 34 g/t Au at a gold recovery of 84% and 86%, respectively. Composites H, GH, and WZ produced higher-grade cleaner concentrates of 67 g/t Au, 85 g/t Au, and 104 g/t Au with higher gold recoveries of 95%, 94%, and 88%, respectively. |
■ | Finer primary grind size appeared to slightly improve the gold grade of the cleaner flotation concentrate. At a primary grind size of 80% passing 165 µm, the cleaner gold recovery was 87% grading at 62 g/t Au. At a finer primary grind size of 80% passing 91 µm, the gold grade increased to 69 g/t and the gold recovery decreased to 84%. |
■ | Regrinding the rougher concentrates to an 80% passing range of 36 to 72 µm, as well as increasing pH level to 10 and 10.5 noticeably improved the cleaner concentrate gold grade. The highest gold grade was 149 g/t at a recovery of 82% when regrinding the rougher concentrates to an 80% passing of 36 µm. |
■ | Rougher scavenger tailings were found mainly composed of quartz and muscovite, as well as small amounts of sulphide minerals and other non-sulphide gangue minerals. |
■ | The current flotation reagent scheme should remain. The reagent optimization tests confirmed that some alternatives can improve the concentrate grades; however, this may also result in a high sulphur content in the tailings. |
■ | Reducing rougher and rougher scavenger retention time did not significantly reduce gold recovery, although a reduced cleaning retention time may slightly impact final concentrate grade. |
■ | A coarse floatation feed grind size resulted in only a modest decrease in gold recovery. |
Figure 13-8: Cleaner Flotation Tests on Composite L, A, H, GH, WZ, and M
13.4.4.5 | Locked Cycle Flotation Testing Results – ALS 2018 |
Two locked cycle flotation tests were conducted using a combination of gravity and flotation concentrations for gold and silver recovery. The gravity circuit for both tests was completed as a separate stage, following which the gravity tailings were tested in the locked cycle flotation tests. Figure 13-9 and Figure 13-10 show locked cycle test flowsheet No. 1 and No. 2, respectively, which differ from each other at the flotation stage. Flowsheet No. 1 uses a three-stage cleaner flotation circuit which is fed by rougher concentrates. Flowsheet No. 2 is based on a two-stage cleaner flotation fed by rougher concentrates 2 to 4, while rougher concentrate 1 reports to the second cleaner flotation stage.
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Figure 13-9: Locked Cycle Test Flowsheet No. 1
Figure 13-10: Locked Cycle Test Flowsheet No. 2
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Table 13-17 summarizes the test conditions for the two locked cycle flotation tests. Both locked cycle tests were completed at a primary grind size of 80% passing 100 µm and at a natural pH with PAX as sulphide collector.
Table 13-17: | Locked Cycle Testing Conditions |
Testing Conditions | Unit | Flowsheet No. 1 | Flowsheet No. 2 |
Primary Grinding Size P80 | µm | 100 | 100 |
Rougher/Scavenger Flotation | |||
pH | - | Natural | Natural |
Collector PAX | g/t | 20/10 | 5/15/10 |
Retention Time | min | 8/4 | 2/6/4 |
Cleaner/Scavenger Flotation | |||
pH | - | Natural | Natural |
Collector PAX | g/t | 0/0/0/5 | 0/0/5 |
Retention Time | min | 4/3/2/2 | 4/6/2 |
Table 13-18 summarizes and compares the test results for the two flowsheets. In the first locked cycle test recovered approximately 31% gold and 4% silver to a gravity concentrate, grading at 897 g/t Au and 1,400 g/t Ag. The second locked cycle test recovered more gold and a similar amount of silver to a gravity concentrate of 37% gold and 4.5% silver grading at 1,596 g/t Au and 2,053 g/t Ag. The flotation concentrates produced in the first locked cycle test contained 34 g/t Au and 559 g/t Ag, which translated to recoveries of 63% gold and 91% silver. The second locked cycle flotation test produced a lower grade concentrate of 28 g/t Au and 450 g/t Ag which represented recoveries of 59% gold and 90% silver. The lower grade could be attributed to the flowsheet configurations.
Table 13-18: | Locked Cycle Test Results |
Wt | Grade (g/t or %) | Recovery (%) | |||||
Products | (%) | Au | Ag | S | Au | Ag | S |
Flowsheet No. 1 | |||||||
Gravity Concentrate | 0.2 | 897 | 1,400 | 54.8 | 31.4 | 4.3 | 2.4 |
Flotation Concentrate | 9.1 | 34.2 | 559 | 40.5 | 63.0 | 90.8 | 92.3 |
Tailings | 90.7 | 0.30 | 3 | 0.24 | 5.6 | 4.8 | 5.4 |
Head | 100 | 4.97 | 56 | 4.01 | 100 | 100 | 100 |
Flowsheet No. 2 | |||||||
Gravity Concentrate | 0.1 | 1,596 | 2,053 | 53.5 | 36.7 | 4.5 | 1.7 |
Flotation Concentrate | 11.3 | 28.0 | 450 | 33.0 | 58.7 | 90.0 | 94.5 |
Tailings | 88.6 | 0.28 | 4 | 0.17 | 4.6 | 5.5 | 3.8 |
Head | 100 | 5.39 | 56 | 3.94 | 100 | 100 | 100 |
A further cleaner flotation stage was added to the second locked cycle testing to treat the second cleaner flotation concentrates. As shown in Table 13-19, a high-grade concentrate was produced grading at 32.3 g/t Au and 536 g/t Ag.
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Table 13-19: | Third Cleaner Flotation Results on the Second Locked Cycle Test |
Flowsheet No.2 | |||||||
Grade (g/t or %) | Recovery (%) | ||||||
Wt | |||||||
Products | (%) | Au | Ag | S | Au | Ag | S |
Feed (Second Cleaner Concentrate) | 11.3 | 28.00 | 450 | 33.00 | 58.7 | 90.0 | 94.5 |
Third Cleaner Concentrate | 9.6 | 32.20 | 536 | 38.90 | 57.7 | 89.0 | 92.4 |
Third Cleaner Tailings | 1.7 | 3.03 | 32 | 4.87 | 1.0 | 0.9 | 2.1 |
ICP analysis, whole rock analyses, and sizing were conducted on concentrates and tailings samples generated from the two locked cycle tests. The following observations are made:
■ | Most of the sulphur was in sulphide form. |
■ | Organic carbon was concentrating into concentrates rather than tailings. |
■ | Arsenic assayed as 0.6% and 0.5 % for the first and second final concentrates, respectively. |
■ | Particle size of the concentrates was approximately 80% passing 100 µm, while cleaner scavenger tailings presented a much smaller size between 15 and 20 µm. |
13.4.4.6 | Optimization Tests – ALS 2018 |
Two samples—a rougher concentrate sample and a third cleaner concentrate—were collected from the Brucejack Gold Mine process streams and tested to investigate the potential gold recovery by gravity concentration from the rougher concentrate following regrinding and further upgrading the third cleaner concentrate using conventional flotation and flotation column methods. Table 13-20 shows the head assay results of the two samples.
Table 13-20: | Head Assays of Processing Samples |
Grade (g/t or %) | ||||
Sample | Au | S | S(-2) | As |
Rougher Concentrate | 85 | 37.5 | 37.5 | 0.21 |
Third Cleaner Concentrate | 111 | 44.2 | 44.2 | - |
The rougher concentrate samples were subject to a combined treatment of a gravity separation and a three-stage cleaner flotation along with a cleaner scavenger. Regrinding was incorporated prior to the gravity separation in four of five tests. Regrind time and pH level were varied to investigate the impacts. The following conclusions were made regarding the test work (also see Figure 13-11).
■ | Without regrinding (T31), gold recovered to gravity concentrate was low. The flotation circuit generated a gold recovery of 98% at a grade of 122 g/t Au. |
■ | At a regrind size 80% passing approximately 37 µm (Tests 32/33/34), the gravity gold recovery was between 19 and 25%, and the gold grade of the flotation concentrates was found to be 166 g/t Au at a gold recovery of 91%. Increasing the pH level seemed to have no impact on the gold grade. |
■ | At a regrind size 80% passing approximately 21 µm (T35), gold gravity recovery increased to 35%, while the flotation concentrates contained 611 g/t Au at a high pH level of 10 to 10.5. |
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Figure 13-11: Gravity and Flotation Optimization Tests
The third cleaner concentrate samples grading at 111 g/t Au were subject to a column flotation test and compared with a one-stage conventional flotation process. As shown in Table 13-21, the test results seem to show:
■ | The conventional flotation test (T28) upgraded the gold grade to 121 g/t Au at a gold recovery of 99%. |
■ | The column flotation test (T29), as a comparison, improved the gold grade to 147 g/t at a gold recovery of 95%. |
Table 13-21: | Conventional and Column Flotation Results |
Grade (g/t or %) | Recovery (%) | ||||||
Wt | |||||||
Products | (%) | Au | S | S(-2) | Au | S | S(-2) |
Conventional Flotation | |||||||
Feed | 100 | 110 | 44.6 | 44.5 | 100 | 100 | 100 |
Concentrate | 90.2 | 121 | 49.0 | 48.9 | 98.6 | 99.1 | 99.1 |
Tailings | 9.8 | 15.2 | 4.17 | 4.14 | 1.4 | 0.9 | 0.9 |
Column Flotation Tests | |||||||
Feed | 100 | 116 | 46.6 | 46.5 | 100 | 100 | 100 |
Concentrate | 75 | 147 | 51.0 | 50.9 | 95.3 | 82.1 | 82.1 |
Tailings | 25 | 22.0 | 33.4 | 33.3 | 4.7 | 17.9 | 17.9 |
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13.4.5 | Solid and Liquid Separation Test Work |
In 2016, SNF provided preliminary flocculant and coagulant screening tests using static settling methods. The test results showed that using 910 VHM alone can reach target supernatant clarity, settling rate, and compaction. In 2017, SNF performed another screen test to control the tailings thickener overflow clarity. The results indicated that using flocculant 910 VHM alone can not prevent carryover of fines; coagulant DB45 VHM should be also added after adding flocculant.
In 2018, FLSmidth performed a comprehensive SLS test program in its laboratory located in Midvale, Utah on both the flotation concentrate and tailings samples collected from the Brucejack Gold Mine operation. The objectives of this test program were to optimize settling characteristics and to evaluate the performance of the two thickeners to accommodate the 3,800 t/d throughput. The test results and conclusions are summarized as follows.
■ | The flocculant that produced the best overflow clarity and settling velocities was a non-ionic polyacrylamide flocculant with a medium molecular weight. The recommended flocculant is AN 920 SH, which can be applied for both the tailings and the concentrate thickening. The suggested flocculant dosage is between 50 to 80 g/t for the tailing thickener and approximately 15 g/t for the concentrate thickener. In addition, better overflow clarity results using AN 920 SH were noticed during thickening testing, compared to the treatment of thickening followed by coagulant clarification. The use of fresh water rather than process water for flocculant dilution and makeup is also critical in optimizing performance of thickeners. |
■ | The optimum solids concentration for flocculation was suggested to be 4 to 10% by weight for the tailings thickener feed materials and approximately 16% by weight for the concentrate thickener feed. |
■ | The solids density of the tailings thickening underflow was estimated between 51 to 63.5% by weight using the existing thickener. The corresponding solids density of the concentrate thickener underflow was estimated as 76% by weight. |
■ | With proper thickener feed conditioning including 15% by weight feed dilution and use of the AN-920 SH flocculant at the recommended dosages, the existing concentrate thickener would have sufficient capacity for the 3,800 t/d throughput. Careful consideration must also be given to froth suppression. Figure 13-12 shows the solids capacity as a function of underflow solids concentration for the concentrate thickener. |
Figure 13-12: Concentrate Thickener Capacity
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■ | With proper feed conditioning, including 10% solids by weight diluted feed and use of the approximately 80 g/t AN-920SH, the existing tailing thickener can handle the increased capacity of 3,800 t/d and achieve an underflow density of 64% solids. Going significantly beyond this throughput would require a new tailings thickener. FLSmidth recommended the 64% underflow solids concentration for the tailings thickener based on two considerations: the yield stress will be greater than 300 Pa at 65% by weight solids (a critical point for downstream slurry handling equipment) and the operation may encounter difficulty. Figure 13-13 shows the tailings thickener underflow solids density variations with retention time. |
Figure 13-13: Tailing Thickener Underflow Concentration with Time
In 2019, two tailings samples were collected from the mill during the upset operation conditions that elevated fine-clay materials suspended in the thickener overflow which were not flocculated properly with the flocculant reagent (SNF 910 HH). The two samples were sent to and tested at the Pocock laboratory in Salt Lake City, Utah. The purpose of this testing was to assist plant operation to clarify the tailings thickener overflow by evaluating settling rheology and filtration characteristics of the tailings.
Various flocculant and coagulant reagents were screened to achieve clear overflow (less than 150 ppm total suspended solids [TSS]), acceptable settling rates, and underflow densities in static and dynamic thickening tests. Pulp rheology tests were completed on all thickened materials to estimate the maximum underflow density. Pocock concluded that using both the low cationic (SNF 4125 SH) and the anionic plant flocculant (SNF 910) appeared to meet the requirements of overflow clarity. The resulted thickener underflow solids density was estimated between 53 to 57% for a conventional thickener. The solid density can be increased to over 57% solids density if a deep cone thickener is in place. The test results indicated that the feed solids density range needs to be maintained in a range of 10 to 12.5% by weight.
13.5 | Mill Operations Optimization/Expansion Process Simulations |
Simulations were conducted by various vendors and consultants to evaluate the major circuit performances for the Brucejack mill expansion. The grinding circuit, gravity recovery circuit, and flotation circuit modelling are described in the following subsections.
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13.5.1 | Grinding Circuit |
CSS performed simulations on the primary grinding circuit using JKSimMet software, which were compared with another simulation method proprietary to Weir Minerals. The input data for both simulations include comminution test results from ALS and SGS and site operating data.
13.5.1.1 | JKSimMet |
CSS used JKSimMet software to simulate comminution circuit performances in two phases. Phase 1 estimated the maximum mill throughput at standard operations, which was outlined in the plant survey data completed under routine operating conditions. Phase 2 estimated the increased mill throughputs supported by the Phase 1 data and a significantly coarsening grind product particle size.
Phase 1
Phase 1 results were reported in the January 18, 2017 Phase 1 report titledResults Simulation Study and Throughput Optimization of the Existing Brucejack Circuit Based on the November 23, 2017 Plant Survey(CSS 2017a). The report indicated that at the current 2,700 t/d mill feed rate, the grinding circuit was operated at well under the available grinding capacity, with the SAG mill operating at 51% of the installed motor capacity and the ball mill at 77% of the installed motor capacity. The pebble crusher was not being used. If the current grind size is maintained for future mill expansion, the existing grinding operation will be limited first by the ball mill capacity before reaching the maximum SAG mill capacity.
The simulations showed that the 3,800 t/d target could be readily achieved for all rock (ore) types while maintaining a targeted product size 80% passing of 90 µm for the ore hardness range tested. Table 13-22 shows the simulation results for the mill feed rate of 3,800 t/d. The current feed ore, as listed in Table 13-22, represents the November 23, 2018 baseline sample.
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Table 13-22: | JKSimMet 3,800 t/d Results at 92% Availability |
SAG Mill Circuit | Ball Mill Circuit | |||||||||||||||||
SAG | ||||||||||||||||||
New | Combined | SAG | Screen | |||||||||||||||
Feed | Feed | SAG Mill | Screen O/S | U/S | Ball Mill(2) | Cyclone | Cyclone U/F | Cyclone O/F | ||||||||||
Ball | ||||||||||||||||||
Critical | Power | Power | Charge | Circulation | Feed | |||||||||||||
Ore | Rate | F80 | Rate | F80 | Speed | Draw | Rate | P80 | P80 | Draw | v/v | Load | Solids | Pa | Solids | Solids | P80 | |
Type(1) | (t/h) | (mm) | (t/h) | (%) | (%) | (kW) | (t/h) | (mm) | (µm) | (kW) | (%) | (%) | (%) | No. | (kPa) | (%) | (%) | (µm) |
ARG | 172 | 112.8 | 176 | 111.8 | 55.3 | 937 | 4.13 | 18.0 | 731 | 1,980 | 34.0 | 316 | 52.6 | 6 | 123.0 | 79.4 | 25.4 | 90 |
CGL | 172 | 112.8 | 177 | 111.6 | 58.1 | 993 | 5.12 | 17.8 | 884 | 1,980 | 34.0 | 287 | 52.9 | 6 | 104.7 | 77.2 | 27.7 | 90 |
SIL H8 | 172 | 112.8 | 177 | 111.6 | 57.6 | 978 | 5.07 | 17.9 | 781 | 1,980 | 34.0 | 232 | 53.9 | 5 | 106.3 | 76.5 | 32.0 | 90 |
P2 | 172 | 112.8 | 178 | 111.4 | 58.3 | 1,008 | 5.63 | 17.9 | 879 | 1,980 | 34.0 | 206 | 56.2 | 5 | 80.0 | 73.6 | 37.7 | 90 |
VSF | 172 | 112.8 | 179 | 111.1 | 61.9 | 1,066 | 6.97 | 17.6 | 971 | 1,980 | 34.0 | 224 | 54.6 | 5 | 97.5 | 75.6 | 33.6 | 90 |
Current Feed Ore | 172 | 112.8 | 179 | 111.2 | 60.7 | 1,044 | 6.77 | 17.7 | 951 | 1,895 | 32.0 | 220 | 54.9 | 5 | 93.1 | 75.2 | 34.5 | 90 |
P1 | 172 | 112.8 | 179 | 111.1 | 60.6 | 1,048 | 6.91 | 17.7 | 946 | 1,980 | 34.0 | 218 | 55.3 | 5 | 90.0 | 74.9 | 35.2 | 90 |
AND | 172 | 112.8 | 182 | 110.4 | 64.9 | 1,132 | 9.80 | 17.4 | 1,145 | 1,980 | 34.0 | 229 | 55.1 | 5 | 97.4 | 76.1 | 33.8 | 90 |
V6 | 172 | 112.8 | 183 | 110.2 | 64.8 | 1,134 | 10.72 | 17.4 | 1,203 | 1,980 | 34.0 | 232 | 55.3 | 5 | 97.9 | 76.3 | 33.7 | 90 |
Notes: | (1)Ore types sorted by A x b values from softest to hardest resistance to impact breakage, hardness data can be found in Section 13.5.2 |
(2)Ball mill critical speed was set as of 79.0% to all simulations. |
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The simulation results indicated that by adjusting the SAG mill power draw, the target 3,800 t/d capacity can be reached for all the simulated ore types using the same grind size as the present operation. CSS noted that the maximum throughput could be as high as 4,239 t/d at the same grind size by increasing the SAG mill critical speed and steel ball charge rate, depending on ore characteristics. CSS recommended including an additional operating cyclone, adjust feed pressure of the cyclone, and feed solids density per the targeted operating conditions as outlined in the report (CSS 2017a).
Phase 2
The Phase 2 simulation work provided supplemental information to the Phase 1 work. The modelling was based on an increased product grind size to determine the potential of the existing grinding circuit. The results are included in the report titledOptimization to Maximize Throughput of the Existing Brucejack Circuit Based on the November 23, 2017 Plant Survey (CSS 2017b).
A coarse grind size used in the Phase 2 simulation was based on the ALS flotation testing results conducted in 2017/2018, which indicated that the impacts of increased grind size on flotation performance were minor to moderate for most ore types. It was reported that at a significantly coarser float feeds of up to 80% passing 160 µm, the recovery drop was relatively modest of up to 5%. At this coarse grind size, the simulations by CSS showed that the throughput of the grinding circuit can reach up to approximately 10,000 t/d depending on ore hardness.
The Phase 2 simulation findings concluded that to achieve the high throughput, using wider grate openings, maximizing the pebble crusher capacity, as well as adjusting the mill speed and charge load would be required, along with undertaking modifications to pumping, water supply, piping, and cyclones. However, it should be noted that the upstream crushing and downstream process/tailings handling circuits would be well under capacity. Therefore, the Phase 2 scenario was not incorporated into the mill upgrading.
13.5.1.2 | Weir Minerals |
Weir Minerals undertook modelling of the grinding circuit using their internal proprietary simulation software. The software incorporated the ALS laboratory comminution data, as well as SPI data generated by SGS. Several simulations were conducted by Weir Minerals, which showed that there is excess capacity in the current grinding circuit, which can reach the 3,800 t/d target
13.5.1.3 | Krebs -FLSmidth |
Four of the six hydro-cyclones are currently in operation with the remaining two on standby mode. Krebs-FLSmidth (Krebs) performed simulations to project the performance of these hydro-cyclones at a mill throughput of 3,800 t/d and higher. Using a 300% circulating load as a baseline, Krebs’ findings indicated that the existing arrangement of the cyclones could readily accommodate the 3,800 t/d scenario through a small increase in the product grind size and by selecting a larger vortex finder. Alternately, an additional cyclone can be put into operation to handle the increased feed rates.
When the mill throughput increases to 6,000 t/d, all six cyclones would be in operation at a much coarser cut-off size of 80% passing approximately 135 µm. Additional standby cyclone capacity is recommended if advancing throughput substantially above the 3,800 t/d scenario.
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13.5.2 | Gravity Simulations |
A gravity model was prepared by FLSmidth in May 2018 based on the 2018 E-GRG test results and the previous E-GRG test results to simulate the gravity recovery under the expansion of the Brucejack mill. Three scenarios were simulated: current operation rate of 2,700 t/d; planned operation rate of 3,800 t/d; and 6,000 t/d at varied primary grind sizes of 80% passing of 90 µm, 110 µm, and 135 µm, respectively. Major conclusions from the modelling are summarized as follows:
■ | Currently, each of the two Kneslon KC-QS40 units installed at the Brucejack Gold Mine have a recommended feed rate of 225 t/d, which can allow the two units to treat 100% of the ball mill discharge. The simulated gravity gold recovery was 59% and 65% at a 70.5% and 80.5% GRG content, respectively. |
■ | When the plant capacity increases, gold gravity recovery would decrease mainly considering: the efficiency of the Knelson KC-QS40 will decrease as the feed rate increases, the coarser primary particle size, and the lower residence time of GRG in the grinding circuit. |
– | In the 3,800 t/d scenario, the gold gravity recovery using the two KC-QS40 units may decrease by 5 to 7%; however, this could be compensated by installing an additional unit to 3 to 4%. |
– | In the 6,000 t/d scenario, the gold gravity recovery may significantly drop by 17 to 18% if using the existing two units only. Adding two more units can limit the gold recovery loss to about 9%. |
13.5.3 | Flotation Simulations |
The existing flotation circuit consists of a series of rougher and rougher scavenger flotation stage, and a three-stage cleaner flotation circuit including the first cleaner scavenger stage. The first cleaner scavenger tailings feeds to the rougher scavenger flotation stage.
Metso Corporation (Metso) and Weir Minerals performed simulations to evaluate the performance of the existing flotation circuit at a higher plant feed throughput.
Metso concluded that the retention time of the existing cells is sufficient to handle the 3,800 t/d throughput; however, due to the high froth carry rate and lip loading predicted from the increased 3,800 t/d throughput, it would be appropriate for additional cells to be installed for either (or both) second and third cleaners. The addition of new cells would increase operational flexibility and facilitate optimization of the cleaner circuit.
Weir Minerals recommended some modifications for slurry handling to improve overall operation performance for the increased throughput.
13.6 | Metallurgical Performance Projection |
Since the Brucejack Gold Mine was commissioned, Pretivm has focussed on improving gold and silver recoveries to the gravity concentration of doré and has been successful in its strategy.
In comparison to the 2014 FS (Ireland et al. 2014) projection for the Valley of the Kings mineralization, although similar overall gold and silver recovery was observed from the operation, the gold recovery to the gravity concentrate has significantly improved by approximately 20% or higher.
Because there is no operational data available for the West Zone, the metallurgical performance is assumed to be the same as previous projections.
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14.0 | MINERAL RESOURCE ESTIMATES |
Pretivm updated the December 2016 Mineral Resource (Pretivm 2016; Board et al. 2017) to incorporate significant new geological information on the Brucejack Deposit generated through additional underground drilling, underground mine development, and mine production at the Brucejack Gold Mine. Details of the resource estimation which forms the basis of the January 2019 Mineral Resource and the January 2019 Mineral Reserve, presented in Section 15.0, are described below.
The January 2019 Mineral Resource for the Brucejack Deposit incorporates estimates from the Valley of the Kings Zone and West Zone. No new information has been collected from the West Zone since 2012. As such, the West Zone part of the January 2019 Mineral Resource remains unchanged from the West Zone Mineral Resource generated by Snowden in April 2012 (Jones 2012a; Jones 2014). The Valley of the Kings Zone part of the January 2019 Mineral Resource has been updated in those areas around the underground workings informed by new mining and drilling data (Figure 14-1). The December 2013 Mineral Resource generated by Snowden (Jones 2014) is retained for the Valley of the Kings Zone in those parts of the deposit for which no new data has been obtained since 2013. No new information has been obtained for the Bridge Zone, Gossan Hill Zone, and Shore Zone targets. These zones are not considered part of the high-grade mineral resource on the Brucejack Project and are therefore not included in the January 2019 Mineral Resource. The Mineral Resource for the Bridge Zone, Gossan Hill Zone, and Shore Zone targets as reported in September 2012 (Jones 2012b) is no longer current.
The January 2019 Mineral Resource for the Brucejack Deposit, as documented in this report, used data and geologic interpretations provided by Pretivm. New data used to inform the updated January 2019 resource estimate included 90,342 m of underground drilling completed since the December 2016 Mineral Resource (see Section 10.0), extensive underground development mapping, and production reconciliation information.
14.1 | Disclosure |
Mineral Resources were prepared by Ms. Kristin Chislett, P.Geo. (Resource Geologist, Pretivm) under the direct supervision of the QP, Mr. Ivor Jones, P.Geo., FAusIMM CP(Geo). Mr. Jones is an employee of Ivor Jones Pty Ltd. Mr. Jones is a QP as defined by NI 43-101 through his experience, membership of a recognized professional organization and qualifications. Both Mr. Jones and Ivor Jones Pty Ltd are independent of Pretivm. Ms. Chislett is an employee of Pretivm.
14.2 | Known Issues that Materially Affect Mineral Resources |
At the time of this report, the QP was not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant factors issues that could materially affect the Mineral Resource presented herein.
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Figure 14-1: Plan View of the Brucejack Deposit Showing the Location of the Valley of the Kings (VOK) Model Area Updated as Part of the January 2019 Resource Estimate
Source: | Pretivm (2019) |
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14.3 | Modelling Approach |
The Brucejack Deposit records a complex magmatic, hydrothermal, and tectonic geological history associated with an active island arc environment that was subsequently deformed as a result of destructive plate margin tectonism (Section 7.0). Whilst geological complexity is partly the reason behind the gold tenor at Brucejack, it presents numerous challenges to effective geological and resource modelling of the deposit:
■ | Overprinting of an earlier, low-grade porphyry-associated mineralization system, by a later, co-spatial high-grade stockwork-hosted epithermal system precludes separation of the two different systems into separate domains. |
■ | The variable, composite, and broad nature of the epithermal vein stockwork necessitates modelling corridors of veins, vein breccia, and vein stockwork, rather than individual veins. |
■ | The presence of statistically significant high- to extreme gold grades that are an integral part of the gold grade distribution in the Valley of the Kings Zone precludes the use of traditional linear grade estimation techniques. |
Multiple Indicator Kriging (MIK) has an advantage over linear estimation techniques in that it can deal with mixed and inseparable strongly-skewed grade populations characterized by high coefficients of variation (CV) (e.g., Carvalho and Deutsch 2017). The QP considers the MIK technique appropriate for use in resource estimation of the Brucejack Deposit, as the deposit exhibits these characteristics at the deposit, domain, and local (within-domain) scales. In addition to the use of MIK, the distribution of high- and extreme gold grades during estimation was further controlled through the application of the split population approach to grade estimation used previously (Jones 2014). In this technique, low-grade, high-grade, and probability of high-grade variables for each of gold and silver are estimated at the point scale, recombined to generate final estimates and then re-blocked to an appropriate block size. This method considers the mixed, positively skewed, high CV, highly variable, and nuggety nature of the gold mineralization at Brucejack, as well as the potential hit-and-miss nature of drilling in such a deposit (Board et al. 2017). Order relations and volume-variance considerations are an integral part of this process.
■ | The January 2019 resource estimate for the Brucejack Deposit was prepared in the following steps: |
■ | digital data validation |
■ | data preparation |
■ | geological interpretation and domain modelling |
■ | establishment of block models |
■ | coding and compositing of assay intervals |
■ | derivation of kriging plan |
■ | variogram analysis and selection of kriging parameters |
■ | grade interpolation of gold and silver using a mix of ordinary kriging (OK) and MIK |
■ | validation of gold and silver grade estimates and models |
■ | reconciliation of the January 2019 resource estimate to mill production |
■ | confidence classification of estimates in accordance with CIM Definition Standards (CIM 2014) |
■ | deduction for prior mining |
■ | Mineral Resource tabulation and documentation. |
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14.4 | Data Provided for Estimation |
The January 2019 resource estimate is based upon an updated and expanded drillhole and assay data set, and updated triangulations including topography, lithological wireframes and mineralized domains. The source and composition of the assay data set is summarized in Section14.4.1, and a summary of how the triangulations are created and approved for use in the resource model is provided in Section 14.4.2.
14.4.1 | Assay Dataset for Grade Estimation |
Drillhole and assay data available as of January 7, 2019 were used in the generation of the January 2019 resource estimate. The GeoSpark SQL drillhole database, which included the results from the 2018 drilling program, was provided by Pretivm. Collars, surveys, lithology, assay/geochemical data, and specific gravity data were exported from the database in comma separated values (.csv) format, and imported into the Leapfrog® Geo, Snowden Supervisor, and Maptek Vulcan mining software for use in modelling and resource estimation.
Several different industry-standard gold assay techniques have been used as part of the exploration of the Brucejack Deposit (Section 11.0), including conventional fire assay with an AA or gravimetric finish (30 or 50 g charge weights), screen fire assay, and concentrate grade analyses. Where one sample had gold assay data determined using different analytical methods, an assay priority was applied. This was based on method and overlimit values in the following precedence sequence: concentrate grade analyses (for Au>10,000 ppm) > 50 g charge fire assay with gravimetric finish (overlimit Au to 10,000 ppm) > 30 g charge fire assay with gravimetric finish (overlimit Au to 10,000 ppm) > screen fire assay (1 kg pulp, 50 g charge; for overlimit Au) > screen fire assay (1 kg pulp, 30 g charge; for overlimit Au) > 50 g charge fire assay with AA finish (100 ppm Au upper detection limit) > 30 g charge fire assay with AA finish (10 ppm Au upper detection limit) > historical Au.
Silver results were determined using different analytical methods (Section 11.0) and are also method-ranked based on overlimit triggers. At concentrations below 100 ppm, silver is determined by a multi-element ICP method which uses a four acid near-total digestion (100 ppm Au upper detection limit). Above 100 ppm, an ore grade silver analysis is triggered (upper detection limit 1,500 ppm Ag), followed by a trigger to a 30 g charge fire assay and gravimetric finish (upper detection limit 10,000 ppm Ag), with a concentrate grade 30 g charge fire assay with a gravimetric finish conducted on those samples with silver above 10,000 ppm. There are 6,578 samples in the database which do not have silver data, representing 1.7% of gold data without associated silver results.
The Brucejack Property drilling database as at January 7, 2019 contained 394,775 gold assay data in 3,579 drillholes, the majority of which (87.6%) were determined using conventional fire assay with an AA finish. Statistical analyses comparing conventional fire assay technique by charge sizes for paired data show no significant differences between assay data types. Similar analyses conducted on paired data comparing the different overlimit analyses showed no significant bias or difference between the four overlimit techniques. Limited historic drilling was conducted in the Valley of the Kings Zone, with the majority concentrated on the West Zone (Section 10.0; Jones 2012a). A re-assaying campaign was conducted on select drillholes from the West Zone by Silver Standard (Jones 2012a), verifying the applicability of using this data for modelling and resource estimation. The Brucejack Property drilling database contains very few unsampled intervals (few historic drillholes only) and those with no sample recovery. Default values were not assigned to missing intervals in such cases. Sections 11.0 and 12.0 summarize data quality (QA/QC protocols and findings) and verification procedures for the Brucejack Property data.
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14.4.2 | Assay Data Import Procedure |
The certified raw assay data files are received by email directly from the analytical laboratory reporting services. Data are provided in a specified digital import format (in Microsoft® Excel) as well as in a secure portable document format (.pdf) certificate format. Each Microsoft® Excel data file is checked for inconsistencies prior to being imported into the SQL database via the GeoSpark Core Microsoft® Access front-end interface (GeoSpark Core). Laboratory data files are not modified in any way prior to import. The SQL database is stored on a secure server and data are backed up nightly. After import, an assay ranking script is run via an SQL query or stored procedure to provide the final ranked data set. Exports from the database (to .csv format) are conducted using a set of saved queries in the GeoSpark Core database interface.
14.4.3 | Triangulations |
14.4.3.1 | Topography |
Topographic constraint was provided by a digital terrain model (DTM) created from an aerial light detection and Ranging (LIDAR) survey in the summer of 2014. The survey was flown from a nominal height of 1,800 m above ground at 100 kn flying speed. The data were collected using a Riegel Q1560 laser scanner owned by Eagle Mapping, with the point data positioned with an average density of seven to nine points per square metre. Data processing was completed by Allnorth Consultants Ltd. before provision to Pretivm. The survey was measured to have a root mean square error of 0.050 m, and an absolute accuracy of ±0.098 m. Conversion of LIDAR to the DTM was completed by Pretivm’s geographical information system (GIS) personnel and reviewed and approved by Pretivm before being imported as a triangulation into the Maptek Vulcan mining software (v.10.1.6) for use in resource modelling (Figure 14-2).
14.4.3.2 | Lithology |
Lithological triangulations were created in the Seequent Limited’s Leapfrog® Geo (v.3.2) modelling software with a live link to Reflex Geoscience’s ioGAS software (v.6.1). The triangulations were generated based on interpretations from core logs (lithology and structure), geochemical data, core photos, and surface and underground mapping by a single experienced geological modeler to ensure consistency. The triangulations were imported in the Maptek Vulcan mining software and reviewed, refined, and validated by Pretivm (Figure 14-2). The lithological triangulations were used to code lithology into the block model for specific gravity and bulk density modelling.
14.4.3.3 | Mineralized Domains |
Mineralized domains were prepared by Pretivm using the Leapfrog® Geo mining software, informed by a combination of core logging data (primarily veining and structure), assay results, core photography, and underground mapping (see Section 14.5). Domain triangulations were iteratively updated as new information became available. The triangulations were imported into the Maptek Vulcan mining software, reviewed, and validated by Pretivm prior to being used for resource modelling.
14.4.3.4 | Underground Development and Production Solids |
As-built triangulations for underground mine development (Figure 14-1) and CMS stope void scans were generated by Pretivm’s mine engineering team at the Brucejack Gold Mine. The triangulations were imported into the Maptek Vulcan mining software, reviewed, validated, and used for coding mined out areas for Mineral Resource depletion and reporting. Blasthole design triangulations were generated for each stope in the Aegis mine planning software by Pretivm’s mine engineering team at the mine. Blasthole triangulations were used for reconciliation of the Mineral Resource to the mill (see Section 14.9).
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Figure 14-2: Topography and lithological wireframes Used in the Generation of the January 2019 Mineral Resource Estimate (Shown in Maptek’s Vulcan Mining Software)
Notes: | A) Plan view of topography draped with aerial photography |
B) Plan view showing lithological model triangulations and approximate location of cross section | |
C) South-north cross-section along 426525 mE (A-A’). | |
Source: | Pretivm (2019) |
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14.5 | Geological Interpretation and Modelling |
Mineralization in the Valley of the Kings Zone of the Brucejack Deposit is interpreted as occurring in a series of mineralized corridors (see Section 7.0). Triangulation solids generated as part of the November 2012 and December 2013 (Jones 2012c; Jones 2014) resource estimates form the basis for the mineral domain interpretations used for the January 2019 Mineral Resource update. Mineralization domain triangulation solids were iteratively reviewed and refined as additional geological information (drilling and mapping) was generated. Plan and cross-sectional views of the mineralization domain triangulations used in the generation of the January 2019 resource estimate are presented in Figure 14-3, Figure 14-4, and Figure 14-5. The QP considers there to be a relatively high degree of confidence in the mineralized domain interpretations as he has verified them in multiple underground exposures at the Brucejack Gold Mine (Section 12.0) as well as in new drilling information.
The main geological interpretations for the Valley of the Kings Zone were modified in the area updated as part of the estimation for the December 2016 Mineral Resource to provide a composite mineralization envelope that encompassed the majority of the mineralization above a 0.5 g/t Au (Board et al. 2017). A single mineralization envelope was constructed in the update area for that model on a section-by-section and plan view-by-plan view basis, cutting out zones associated with very low to no gold grade. The interpretation was verified against a simulated probability of grade model. Whilst the December 2016 domain interpretation was not significantly different to the December 2013 mineralized domain interpretation, integration of additional drilling, underground mapping, and production data indicated that an appropriately grouped set of spatially separated corridors, with the separation of a high-grade north-south domain, were better for grade interpolation in the main part of the Valley of the Kings Zone than a single composite mineralized domain triangulation. A total of 23 mineral domains were interpreted for the Valley of the Kings Zone. These 23 domains were grouped into 12 larger domains (Bigdom) for grade estimation, based on similarities in statistics and geology, for modelling purposes (Table 14-1). Six of the Bigdom domains were present in the model update area: 600, 700, 800, 801, 900, and 901 (Figure 14-5). A domain code of -99 was assigned to all blocks outside of the mineralized domains.
Table 14-1: Valley of the Kings Zone Mineralized Domains
Grouped Domain | Individual | Individual Domain Detail |
(Bigdom) | Domain Code | (Domain Names, in order) |
100 | 10, 20, 30, 40 | Galena Hill (GA4, GA3, GA1, GA2) |
200 | 50, 60 | VOK Domain 13 (DOM13, DOM13B) |
300 | 70, 80, 90 | VOK North (DOM38, DOM38B, NVOK) |
400 | 130, 140 | VOK/Bridge Zone P1 contact zone (P1, P2) |
500 | 110, 120 | Eastern Promises VOK (EVOK1, EVOK2) |
600 | 100, 150, 160, 170, 180 | Main VOK domains (ARG, DOM23, DOM8, DOM11, DOM17) |
700 | 190 | VOK Lateral (EW LATERAL) |
800 | 200 | Cleopatra structure south of 6257972 mN (CLEO) |
801 | 200 | Cleopatra structure north of 6257972 mN (CLEO) |
900 | 210 | Domain 20 normal fault – higher grade (DOM20) |
901 | 220 | Domain 20 normal fault – lower grade (DOM20D) |
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Figure 14-3: Plan View of Mineralized Domain triangulations used in the Generation of the January 2019 Mineral Resource
Note: | Numbers are domain codes |
Source: | Pretivm (2019) |
Figure 14-4: North-South Cross Section Along 426635 mE of Mineralized Domain Triangulations used in the Generation of the January 2019 Mineral Resource
Note: | Numbers are domain codes |
Source: | Pretivm (March 2019) |
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Figure 14-5: Plan View Showing the Main Grouped Valley of the Kings Mineralized Domains used in the Generation of the January 2019 Mineral Resource
Notes: | Domain 100 is included in grouped domain Bigdom 600, but not located in the updated area of this study, thus not seen in this figure. Grouped domain Bigdom 901 is included in the updated area but obscured by grouped domain Bigdom 900. |
Source: | Pretivm (2019) |
14.6 | Data Selection and Preparation |
14.6.1 | Update Area |
As noted in the introductory comments to Section 14.0 (Page 14-1), only a subset of the full Valley of the Kings Zone has been informed by sufficiently closely spaced new drilling to justify model updating. Additionally, there is a change in geology at depth and outside of the update area, where precious metal mineralization is predominantly hosted in carbonate-only (as opposed to quartz-carbonate) veining, and VSF and P1BZ become the dominant lithological units (as opposed to ANDX, TRANS, CONG, and SILCAP). Geostatistical parameters derived from tightly-spaced infill drilling in the update area were therefore not considered representative of the mineralization outside of this area, and the previous resource estimate (December 2013; Jones 2014) was retained. A model update solid was generated for the area informed by new conditioning data (Figure 14-1; Figure 14-6). The Valley of the Kings Zone resource estimate was updated inside this solid.
Drillhole data were selected inside the six grouped domains (Bigdom) that were present in the update area (Figure 14-1; Figure 14-5), resulting in a total of 156,837 gold and 152,537 silver assay data in 2,312 drillholes. Exploratory data statistical analyses were conducted on the selected data using Snowden’s Supervisor (v.8.9) geostatistical software.
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Figure 14-6: Plan View Showing Model Update Area Solid (blue) and Drillholes (red) from the 2017 – 2018 Infill Drill Campaign
Source: | Pretivm (2019) |
14.6.2 | Compositing |
All data was composited to the dominant sample length of 1.5 m prior to analysis and estimation. The composited data was then coded according to the relevant mineralized domain in preparation for modelling. Normally, compositing is done with respect to geological and/or domain boundaries. As the gold mineralization in the Brucejack Deposit overprints all lithological units, no geological control was used during compositing. Furthermore, as stockwork mineralization domain boundaries tend to be gradational rather than sharp, strict domain boundary control on composites was not necessary and likely represents false resolution, in light of the soft boundary nature of the mineralization. Consequently, normal composites of 1.5 m in length were generated from collar to end of drill string. The composites were then flagged as being in or out of the mineralization domain, depending on whether the composite centroid was inside or outside of the domain wireframe. A minimum composite length of 1.25 m was enforced, removing any short composite intervals from drillholes terminating in the mineralization domain wireframe.
A total of 130,484 gold and 127,256 silver domain-coded composite data were generated inside the Valley of the Kings grouped mineralized domains inside the update area. These composites were used in the generation of the grade estimates inside the update area.
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14.6.3 | Grade Populations |
Infill drilling conducted during the 2017 and 2018 programs confirmed the nature of the gold and silver grade distributions in the mineralized zones as defined by previous drilling programs (Figure 14-7). Comparing all drillhole composites constrained inside mineralized domains, as generated from the recent (2017-2018) and previous drilling programs, highlights both the similarity in grade distributions for gold and silver between drilling programs, and the mixed nature of the precious metal distributions. Log probability plots (cumulative distribution plots) of the 2017-2018 infill drillhole composite data for both gold and silver display a slightly higher proportion of samples in grades above the median grade to below the 90th percentile than the pre-2017 drillhole composite data, and a slightly lower proportion of grades above the 99.9th percentile (Figure 14-7).
The mixed nature of the precious metal gold distributions, as a function of the co-spatial nature of the overprinting mineralization systems (Section 7.0; Section 14.3), is readily evident on the log probability plots (Figure 14-7); there is a curved inflection zone between 1 g/t Au and 5 g/t Au on the gold log probability plot; and between 10 g/t Ag and 50 g/t Ag on the silver log probability plot. Physical separation of the two (or more) grade distributions into individual domains has been unsuccessful due to the overlapping nature of the two mineralizing systems. The composite data were therefore separated into low-grade (<3.5 g/t Au; <20 g/t Ag) and high-grade (≥3.5 g/t Au; ≥20 g/t Ag) populations for grade modelling and estimation (see Section 14.7).
The high-grade distributions for gold and silver remained strongly positively-skewed (CV at 23.9 for Au and 7.03 for Ag). The QP considers the continued use of a non-linear estimator for grade estimation appropriate, based on the similarity in precious metal grade distributions between the recent (2017-2018) infill drilling and previous drilling programs in the Valley of the Kings Zone.
The use of grade capping (top cutting) in conjunction with a linear estimator (e.g., OK, inverse distance) was considered in 2012, but was shown to produce some unrealistic results. This approach was therefore regarded as inappropriate in the modelling of the mineralization at Brucejack. There are several reasons:
■ | The challenge in selecting an appropriate top cut (grade cap).The positive tail of the grade distribution does not break down (tail decomposition method) until well into the multi-kilogram per tonne range, and even then, the more data that is collected, the higher the value before tail decomposition. Using a percentile-based approach results in an arbitrary and unjustifiable capping of extreme gold grades. |
■ | The appropriateness of grade capping. Consistency of intersecting high grade (gold and silver) throughout the Valley of the Kings Zone and the robust positive tail of the high-grade distributions, indicate that the high-grade intersections are an integral part of the grade distribution and therefore should be used for grade estimation. Selecting an arbitrary top cut value results in the artificial removal of high-grade values that are necessary to preserve the metal in the grade estimation (and value). Recent experience has shown that even with these values, the grades are under-estimated with respect to production. |
■ | Mixed grade populations that are impossible to separate.Geologically the low- and high-grade populations are co-spatial (Section 7.0) and cannot be separated by domaining alone. This requires the use of an estimation technique that models the grade distribution. Non-linear techniques like MIK were developed to deal with mixed populations (e.g., Glacken and Blackney 1998). |
■ | Block grade trends not matching input drilling data trends at Brucejack. Estimates made using linear estimation techniques with and without grade capping generally result in poor representation of input drilling data trends. This is a function of using a linear estimation technique for a highly skewed grade dataset characterized by mixed populations. |
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Figure 14-7: Log Probability Plots of A) Gold and B) Silver Composited Data Inside the Valley of the Kings Mineralization Domains
Source: | Pretivm (2019) |
Owing to the mixed nature of the grade distribution and the extremely positively skewed nature of the gold and silver data, a non-linear estimation technique was deemed necessary to model the Valley of the Kings Zone. MIK was selected because the method allows modelling of the actual grade distribution using a series of grade thresholds, as well as a mathematical model for the uppermost grade bin (or class), precluding the need for an arbitrary grade cap or top-cut. It also allows the practitioner to consider that samples with different grades have different levels of continuity, with higher grades having a lot lower continuity than the lower grades. Additional resolution on grade continuity across the distribution is provided by modelling of variograms at each grade threshold.
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14.6.4 | Summary Statistics |
Histograms for all composited data inside the Valley of the Kings Zone mineralized domains indicate that the gold and silver populations are extremely positively-skewed with a high CV and low mean grades (see Figure 14-8). Summary statistics for the domain-coded composited drillhole data for the 2019 updated area are presented in Table 14-2.
Ranking the data by gold grade shows that 88% of the metal in the Valley of the Kings Zone mineralization domain is represented by approximately 5% of the sample data, with 83% being represented by the top 1% of the sample data. Similarly, 50% of silver metal in the domain is represented by approximately 5% of the sample data, and 25% represented by the top 1% of the sample data. These statistics highlight that significant value in the Valley of the Kings Zone is associated with uppermost part of the relevant grade histogram. The ubiquitous presence of elevated gold intersections throughout the Valley of the Kings drilling and underground workings (visible gold) demonstrates that the grades are not anomalous, and that it is important that these high-grade samples are considered in the grade estimation process. The strong positive skewness, high CV, and low mean grades of the gold and silver grade distributions indicate that the mineralized domains contain a significant level of internal low grade. These features are in keeping with the geological interpretation (see Section 7.0) that a variable and disjunctive high-grade epithermal vein stockwork system was superimposed on a lower-grade porphyry-associated phyllic alteration system in such a way that the two systems are physically inseparable for modelling purposes.
Figure 14-8: Log-normal Histogram Plot of A) Gold and B) Silver Composited Data Inside the 2019 Updated Area Mineralization Domains
Source: | Pretivm (2019) |
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Table 14-2: | Summary Statistics of Gold and Silver Composited Data by Grouped Domain in 2019 Model Updated Area |
Grouped Domain (Bigdom) | ||||||||||
600 | 700 | 800/801 | 900 | 901 | ||||||
Au | Ag | Au | Ag | Au | Ag | Au | Ag | Au | Ag | |
Statistic | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) | (g/t) |
Number of Samples | 61,473 | 60,586 | 3,271 | 3,271 | 2,294 | 2,238 | 12,840 | 12,734 | 3,933 | 3,933 |
Minimum Grade | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Mean Grade | 4.46 | 7.92 | 10.13 | 11.45 | 24.33 | 19.52 | 5.68 | 19.73 | 1.05 | 6.57 |
Maximum | 12,375 | 7,105 | 3,618 | 1,941 | 14,746 | 9,934 | 3,568 | 1,889 | 287 | 466 |
Standard Deviation | 111.9 | 62.7 | 106.0 | 54.2 | 408.0 | 246.4 | 75.0 | 61.1 | 7.4 | 16.6 |
Variance | 12,515 | 3,933 | 11,235 | 2,934 | 166,432 | 60,724 | 5,631 | 3,730 | 54 | 214 |
CV | 25.09 | 7.92 | 10.46 | 4.73 | 16.77 | 12.62 | 13.22 | 3.10 | 7.05 | 2.23 |
HGT | 3.5 | 20.0 | 3.5 | 20.0 | 3.50 | 20.0 | 3.5 | 20.0 | 3.5 | 20.0 |
Percent ≥ HGT | 3.8% | 4.8% | 14.5% | 7.7% | 8.9% | 7.5% | 6.9% | 19.2% | 1.9% | 4.1% |
Mean Grade Above HGT (g/t) | 103.82 | 82.08 | 65.15 | 91.13 | 267.50 | 208.81 | 72.63 | 72.52 | 28.04 | 49.70 |
Note: | RC samples and blasthole samples are not included in these statistics; HGT – high-grade threshold. |
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14.7 | Estimation |
14.7.1 | Methodology |
Grade estimates were generated into grouped domains inside the update area using the domain-coded composite data. The overall approach is similar to that used in the generation of the December 2013 and July 2016 Mineral Resource estimates in that separate high-grade, low-grade, and probability of high-grade estimates are generated for each block using the split population non-linear estimation approach detailed in Jones (2014). Additional resolution provided by infill drilling and the evaluation of that data inside the update area has indicated that 3.5 g/t Au and 20 g/t Ag best distinguish between low- and high-grade populations for these two grade variables. The grade estimation workflow used to generate the January 2019 Mineral Resource is detailed below.
■ | A model was prepared at the parent block size (5 mE by 5 mN by 5 mZ) and coded by lithology and mineralized domain (individual and grouped) as the parent model. |
■ | A separate block model was set up with a 2.5 mE by 2.5 mN by 2.5 mZ block size and coded by mineralized domain (individual and grouped) for grade estimation. |
■ | Statistical analysis was conducted on the gold and silver grade distributions using Snowden’s Supervisor geostatistical software. The following was conducted: |
– | discretization of the high-grade gold (≥3.5 g/t) and silver (≥20 g/t) distributions using appropriate decluster-weighted grade thresholds |
– | lower and upper tail analysis of the high-grade gold and silver distributions and selection of appropriate mathematical models for these |
– | determination of the appropriate percentile for the threshold of the top class in the high-grade indicator thresholds using the decluster-weighted gold and silver data |
– | univariate statistical analysis of the low-grade population (<3.5 g/t Au, <20 g/t Ag). |
■ | Three-dimensional spatial analysis (variography). |
■ | Search, estimation, and variogram parameter sensitivity analyses. |
■ | Grade interpolation of each grade variable (i.e., low grade, high grade, probability of high grade for each of gold and silver) separately into 2.5 m by 2.5 m by 2.5 m blocks using: |
– | OK for grade of the low-grade mineralization (<3.5 g/t Au, <20 g/t Ag) |
– | MIK for grade of the high-grade mineralization (≥3.5 g/t Au and ≥20 g/t Ag) |
– | OK of the mineralization indicator for the proportion of high grade (i.e., probability of Au ≥3.5 g/t and Ag ≥20 g/t). |
■ | The 2.5 mE by 2.5 mN by 2.5 mZ estimates were post-processed to provide total gold and silver grades for each block (e-type estimates). The grade of the mineralization above 3.50 g/t Au and the grade of the mineralization below 3.50 g/t Au in the block were each multiplied by the relevant proportions to calculate the final grade estimate for each block. The same process was applied to the silver grades. Grade estimates were then re-blocked to 5 mE by 5 mN by 5 mZ blocks to provide an appropriate volume estimate. |
■ | The individual estimates were checked/validated against the relevant input composite data (see Section 14.8). |
■ | The validated block model inside the update area was then added to the July 2016 block model (Board et al. 2017) to generate the full Valley of the Kings Zone resource model. All blocks inside the update area effectively overprinted all blocks updated as part of the July 2016 resource estimate. All blocks outside the update area are the same as those generated as part of the December 2013 resource estimate (Jones 2014). |
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14.7.2 | Parameter Optimization |
Estimation parameter optimization through iterative model testing was conducted on several updated versions of the input drillhole database ahead of the January 7, 2019 database cut-off date (see Section 14.4.1). Iterative test work conducted ahead of final parameter selection included:
■ | Low-grade/high-grade population delimiter selection. Models run using 5.0 g/t Au as the population delimiter generated results that were not significantly different to those obtained using a 3.5 g/t Au delimiter. However, improved reconciliation between model and mill data was noted when using the 3.5 g/t Au delimiter, and moving window statistics indicated the 3.5 g/t Au delimiter provided better local accuracy when compared to the local data. Furthermore, mathematical models for the top-grade class (uppermost tail of the high-grade distribution) were easier to define using the 3.5 g/t Au delimiter than using the 5.0 g/t Au delimiter (see Section 14.7.5). Similar observations were made for silver using a 20 g/t Ag versus a 50 g/t Ag delimiter. |
■ | High-grade population threshold and tail modelling. The different thresholds, upper and lower tail models, and the use of grade capping (top cuts) were tested. Grade capping yielded unsatisfactory results (see Section 14.6.3 for a discussion on top cutting) where all models based on grade capping significantly under-called actual production. Increasing the number of thresholds, especially adding more thresholds above the 95th percentile (e.g., the 97.5th and 99th percentile) resulted in instability of the top class as a result of fewer data points in that class. The 95th percentile was selected as the uppermost percentile to model the high-grade gold and silver populations as it facilitated the most representative mathematical modelling of the upper class. |
■ | Parent block size. The possibility of increasing the parent block size to 10 mE by 5 mN by 10 mZ was investigated. Despite no significant differences in reported ounces between the 10 mE by 10 mN by 10 mZ and 5 mE by 5 mN by 5 mZ block sizes, the smaller block size was favoured in the update area due to the better definition available for detailed mine design. |
■ | Mineralized domain edge effects. The presence (if any), impact, and management of edge effects in blocks at the margins of the mineralized domain was tested. Edge effects, which had a significant impact on the resource estimate, were noted when using a hard boundary for the high-grade and probability of high-grade variable estimation. A soft boundary approach was deemed more appropriate for the estimation of these two variables, in light of the gradational nature between mineralized and unmineralized rock (high-grade epithermal veining cuts lower grade phyllically altered host rock throughout, with no distinct sharp boundaries between high- and low-grade parts of the system: indeed high-grade electrum can be found in contact with low-grade porphyry and porphyry-epithermal associated pyrite down to the microscale; McLeish et al. 2019; Board et al. in press). Improved validation to the processed material from the 2013 bulk sample (see Farley et al. 2014; Jones 2014) was obtained for those iterations employing a soft boundary approach (Board et al. 2017). |
14.7.3 | Variography |
Three-dimensional spatial analysis was conducted on composite data using Snowden’s Supervisor geostatistical software. Experimental variograms were generated for each of the grade estimation variables in the following way:
■ | Indicator semi-variograms were generated at each grade threshold discretizing the high-grade gold (≥3.5 g/t Au) and silver (≥20 g/t Ag) distributions by grouped domain inside the update area (Section 14.7.3.1). |
■ | Indicator semi-variograms were generated for thresholds set at the gold and silver delimiters (3.5 g/t Au; 20 g/t Ag) using full gold and silver grade distributions in the update area (Section 14.7.3.2). |
■ | Traditional semi-variograms were generated for low-grade gold (<3.5 g/t Au) and low-grade silver (<20 g/t Ag) inside the update area (Section14.7.3.3). |
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14.7.3.1 | High-grade Population Indicator Variograms |
Indicator variograms for the high-grade gold and silver populations were generated and modelled using domain-coded composite data for each of the grouped domains. Variogram orientations were primarily defined using dominant domain orientations (which, in turn, were based on dominant mineralized vein orientations). High-grade gold and silver grade distributions were discretized into 11 thresholds (20, 30, 40, 50, 60, 70, 75, 80, 85, 90, and 95th percentile; Table 14-3 and Table 14-1). Experimental variograms were generated and modelled at each grade threshold for both gold and silver by grouped domain. Variogram models for silver were adopted from the gold variograms by percentile threshold and Bigdom domain as the models were sufficiently similar, and the experimental variograms were better for gold. Example indicator variogram parameters generated for the largest grouped domain (Bigdom 600) are presented in Table 14-4.
Table 14-3: | Thresholds Discretizing High-grade Distribution by Grouped Domain |
Au (g/t) | Ag (g/t) | |||||||||
Threshold | Domain | Domain | Domain | Domain | Domain | Domain | Domain | Domain | Domain | Domain |
Percentile | 600 | 700 | 800/801 | 900 | 901 | 600 | 700 | 800/801 | 900 | 901 |
20 | 4.82 | 4.61 | 5.14 | 4.78 | 4.85 | 23.76 | 24.2 | 22.96 | 24.45 | 22.79 |
30 | 5.87 | 5.32 | 6.81 | 5.74 | 5.99 | 26.37 | 27.74 | 27.2 | 27.45 | 25.34 |
40 | 7.41 | 6.23 | 9.97 | 6.71 | 7.53 | 29.99 | 32.71 | 32.76 | 31.47 | 28.3 |
50 | 10.24 | 7.93 | 14.41 | 8.59 | 10.01 | 34.76 | 39.22 | 38.48 | 36.7 | 31.33 |
60 | 14.69 | 10.92 | 20.51 | 12.28 | 15.25 | 41.76 | 47.11 | 46.65 | 45.3 | 35.19 |
70 | 24.60 | 16.57 | 33.63 | 19.02 | 19.3 | 52.8 | 63.51 | 69.22 | 55.9 | 44.6 |
75 | 33.50 | 23.26 | 50.59 | 27.25 | 21.45 | 60.49 | 77.35 | 80.34 | 65.1 | 52.65 |
80 | 49.01 | 35.48 | 65.91 | 37.64 | 30.65 | 71.66 | 90.8 | 107.5 | 80.04 | 59.75 |
85 | 72.92 | 58.66 | 136.9 | 56.1 | 45.13 | 90.96 | 109 | 147.1 | 99 | 64.44 |
90 | 141.8 | 108.6 | 305.4 | 109.5 | 73.14 | 125.2 | 205.6 | 257.1 | 140.3 | 88.75 |
95 | 326.9 | 286.2 | 630.2 | 283.1 | 123.2 | 225.1 | 371.7 | 440.1 | 230.7 | 127.8 |
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Table 14-4: | Indicator Variogram Parameters for High-grade Gold in Grouped Domain Bigdom 600 |
Structure 1 | Structure 2 | |||||
Cut-off Grade | ||||||
Au g/t | Range | Range | ||||
(Percentile) | Orientation | Nugget | Sill | (m) | Sill | (m) |
4.82 (20) | D1:-90° →000° | 0.30 | 0.50 | 18 | 0.20 | 170 |
D2: 00° →290° | 18 | 170 | ||||
D3: 00° →020° | 12 | 16 | ||||
5.87 (30) | D1:-90° →000° | 0.30 | 0.55 | 9 | 0.15 | 140 |
D2: 00° →290° | 9 | 140 | ||||
D3: 00° →020° | 9 | 10 | ||||
7.41 (40) | D1:-90° →000° | 0.30 | 0.70 | 20 | - | - |
D2: 00° →290° | 15 | - | ||||
D3: 00° →020° | 12 | - | ||||
10.24 (50) | D1:-90° →000° | 0.30 | 0.70 | 12 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
14.69 (60) | D1:-90° →000° | 0.35 | 0.65 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
24.60 (70) | D1:-90° →000° | 0.40 | 0.60 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
33.50 (75) | D1:-90° →000° | 0.45 | 0.55 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
49.01 (80) | D1:-90° →000° | 0.50 | 0.50 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
72.92 (85) | D1:-90° →000° | 0.50 | 0.50 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 10 | - | ||||
141.80 (90) | D1:-90° →000° | 0.50 | 0.50 | 10 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 7 | - | ||||
326.90 (95) | D1:-90° →000° | 0.55 | 0.45 | 6 | - | - |
D2: 00° →290° | 10 | - | ||||
D3: 00° →020° | 5 | - |
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14.7.3.2 | Probability of High-grade Variograms |
Variogram models generated for the probability of high-grade gold and silver were generated using all drillhole composite data inside the update area and were not constrained by domain. This was done to mitigate against edge effects on the margins of the high-grade domains, and to better estimate the proportion of high-grade mineralization at domain edges. Variogram model parameters for the probability of high-grade are presented in Table 14-5 and Table 14-6. Note for all tables presenting variogram parameters that D1, D2, and D3 are the major, semi-major, and minor axes of the continuity ellipse and that xx° →yyy° means a dip of xx° on a bearing of yyy°.
Table 14-5: | Variogram Model for the Probability of High-grade Gold Indicator Variable at 3.5 g/t Au |
Structure 1 | Structure 2 | ||||||
Orientation | Range | Range | |||||
Domain | Vulcan (ZXY) | Axis | Nugget | Sill | (m) | Sill | (m) |
600 | (0,-90,-20) | Major | 0.50 | 0.28 | 3 | 0.34 | 12 |
Semi-major | 2 | 6 | |||||
Minor | 1 | 4 | |||||
700 | (0,-90,-10) | Major | 0.50 | 0.28 | 3 | 0.34 | 12 |
Semi-major | 2 | 6 | |||||
Minor | 1 | 4 | |||||
800 | (0,-90,-90) | Major | 0.50 | 0.46 | 7 | 0.18 | 22 |
Semi-major | 15 | 15 | |||||
Minor | 1 | 1 | |||||
801 | (0,-90,-110) | Major | 0.50 | 0.46 | 7 | 0.18 | 22 |
Semi-major | 15 | 15 | |||||
Minor | 1 | 1 | |||||
900 | (210, -65, -180) | Major | 0.40 | 0.37 | 5 | 0.23 | 40 |
Semi-major | 10 | 25 | |||||
Minor | 2 | 20 | |||||
901 | (210, -65, -180) | Major | 0.40 | 0.37 | 5 | 0.23 | 40 |
Semi-major | 10 | 25 | |||||
Minor | 2 | 20 |
Note: | Variograms modelled to experimental sill. |
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Table 14-6: | Variogram Model for the Probability of High-grade Silver Indicator Variable at 20 g/t Ag |
Structure 1 | Structure 2 | ||||||
Orientation | Range | Range | |||||
Domain | Vulcan (ZXY) | Axis | Nugget | Sill | (m) | Sill | (m) |
600 | (0,-90,-20) | Major | 0.40 | 0.38 | 5 | 0.22 | 13 |
Semi-major | 4 | 8 | |||||
Minor | 3 | 10 | |||||
700 | (0,-90,-10) | Major | 0.40 | 0.38 | 7 | 0.22 | 19 |
Semi-major | 3 | 3 | |||||
Minor | 5 | 10 | |||||
800 | (0,-90,-90) | Major | 0.40 | 0.38 | 5 | 0.22 | 12 |
Semi-major | 3 | 5 | |||||
Minor | 3 | 12 | |||||
801 | (0,-90,-110) | Major | 0.40 | 0.38 | 5 | 0.22 | 12 |
Semi-major | 3 | 5 | |||||
Minor | 3 | 12 | |||||
900 | (210, -65, -180) | Major | 0.40 | 0.38 | 5 | 0.22 | 12 |
Semi-major | 3 | 5 | |||||
Minor | 3 | 12 | |||||
901 | (210, -65, -180) | Major | 0.40 | 0.38 | 3 | 0.22 | 8 |
Semi-major | 4 | 6 | |||||
Minor | 5 | 20 |
Note: | Variograms modelled to experimental sill. |
14.7.3.3 | Low grade population variograms |
Traditional semi-variograms for low-grade gold and silver were generated and modelled using all composite data inside the update area. There was no need to subdivide the low-grade precious metal mineralization into individual or grouped domains as the mineralization is ubiquitous and statistically similar throughout the phyllically altered rocks in the update area. Variogram parameters generated for low-grade gold and silver populations are presented in Table 14-7.
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Table 14-7: | Variogram Model for Low-grade Gold and Silver Mineralization |
Structure 1 | Structure 2 | |||||
Range | Range | |||||
Indicator | Orientation | Nugget | Sill | (m) | Sill | (m) |
<3.50 g/t Au | D1:-90° →000° | 0.15 | 0.52 | 15 | 0.33 | 35 |
and | D2: 00° →290° | 12 | 32 | |||
<20 g/t Ag | D3: 00° →025° | 7 | 22 |
14.7.4 | Search Parameters |
Final search parameters used in the estimation of the January 2019 Mineral Resource were based on exhaustive iterative modelling, and are presented in Table 14-8 and Table 14-9. Search parameters were optimized to reduce excessive smearing while allowing sufficient data to be used to create a representative estimate. Whilst the maximum number of samples used in estimation appears low, it was noted that using more samples created excessive grade smearing, with increasing under-calling of high-grade areas, and over-calling of low-grade areas.
Table 14-8: | Search Parameters for High-grade and Probability of High-grade Variables for Gold and Silver by Grouped Domain Inside the Update Area |
First Search Pass | Second Search Pass | |||||||
Max. No. | Max. No. | |||||||
Orientation | Search | No. | Samples | Search | No. | Samples | ||
Grouped | Vulcan | Estimation | Ellipse | Samples | per | Ellipse | Samples | per |
Domain | (ZXY) | Variable | (m) | (Min,Max) | Drillhole | (m) | (Min,Max) | Drillhole |
600 | (0, -90, -20) | High grade | 50x30x20 | 2,6 | - | 70x45x30 | 2,6 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30 | 12,16 | 8 | ||
700 | (0, -90, -10) | High grade | 35x35x15 | 2,6 | - | 70x70x30 | 2,6 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30 | 2,6 | 8 | ||
800 | (0, -90, -90) | High grade | 25x25x10 | 2,6 | - | 50x50x20 | 2,6 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30 | 2,6 | 8 | ||
801 | (0, -90, -110) | High grade | 25x25x10 | 2,6 | - | 50x50x20 | 2,6 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30x | 2,6 | 8 | ||
900 | (210, -65, -180) | High grade | 40x30x15 | 2,6 | - | 80x60x30 | 2,16 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30 | 2,6 | 8 | ||
901 | (210, -65, -180) | High grade | 40x30x15 | 2,6 | - | 80x60x30 | 2,16 | - |
Probability | 35x35x15 | 12,16 | 8 | 70x70x30 | 2,6 | 8 |
Note: | Gold and silver search parameters are identical. |
The search strategy recognizes the variability of the local average grade, while attempting to minimize grade smearing. Search ellipse orientation was defined by trends in the domain wireframes based, in turn, on trends of major mineralized structures within the domains.
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Table 14-9: | Search Parameters for Low-grade Gold and Silver Inside the Update Area |
Orientation | Search | ||
Vulcan | Ellipse | No. Samples | Max. No. Samples |
(ZXY) | (m) | (Min, Max) | per Drillhole |
(0, -90, -25) | 50x50x20 | 8,20 | 6 |
Note: | Gold and silver search parameters are identical. |
14.7.5 | Upper Tail Modelling of High-grade Population in MIK Estimation |
Caution is required when estimating the grade of the upper bin (top class) for mixed positively-skewed distributions like that of the Brucejack Deposit. The use of median and mean grades to represent the grade of the top class was not considered suitable as these statistics could lead to gold and silver grade over-estimation due to the shape of the upper tails of the high grade gold and silver distributions (see Figure 14-9). The grade of the top class was therefore modelled using either a hyperbolic or a power model, depending on which best fit the upper tail of the high-grade gold and silver distributions for each of the grouped domains (Table 14-10).
Figure 14-9: Example of Modelling the Upper Tail of the A) High-grade Gold and B) High-grade Silver Populations using a Hyperbolic Model; Data Shown for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
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Table 14-10: | Mathematical Model Parameters for the Top MIK Threshold for Each Grouped Domain |
Grouped | Model Type | Model Parameter | Maximum Grade | |||
Domain | Au | Ag | ||||
(Bigdom) | Au | Ag | Au | Ag | (g/t) | (g/t) |
600 | Hyperbolic | Hyperbolic | 1.10 | 1.35 | 12,375 | 7,105 |
700 | Hyperbolic | Hyperbolic | 1.35 | 2.30 | 3,618 | 1,941 |
800 | Power | Hyperbolic | 0.28 | 0.95 | 14,746 | 9,934 |
900 | Power | Power | 0.22 | 1.80 | 3,586 | 1,889 |
901 | Hyperbolic | Hyperbolic | 3.40 | 2.15 | 287 | 466 |
14.7.6 | Specific Gravity and Bulk Density |
A total of 2,641 specific gravity and 405 bulk density measurements have been collected from the Valley of the Kings Zone of the Brucejack Deposit. No new specific gravity or bulk density data were collected subsequent to the December 2013 Mineral Resource. Specific gravity and bulk density data were treated in a similar way to Jones (2014), with some refinements, including the use of updated lithology wireframes. A total of 696 specific gravity and 276 bulk density data were relevant for the January 2019 Mineral Resource. Conversion factors between specific gravity and bulk density were determined by lithology (Table 14-11) and used in the block model.
Table 14-11: | Specific Gravity Values and Bulk Density Conversion Factors for Resource Modelling in the Update Area |
Rock | No. of | Average | Bulk Density | |
Type | Lithology | samples | Specific Gravity | Conversion Factor |
P2 | Two feldspar latite porphyritic flow | - | 2.82(2) | 0.9863(1) |
Silcap | Silicified conglomerate | 45 | 2.79 | 0.9813 |
Andx | Latite fragmental | 313 | 2.87 | 0.9756 |
Trans | Transitional unit | 64 | 2.88 | 0.9756 |
Cong | Polylithic conglomerate | 123 | 2.83 | 0.9755 |
VSF | Volcano-sedimentary facies rocks | 138 | 2.82 | 0.9873 |
Arg | Argillite | 11 | 2.70 | 0.9813 |
P1BZ | Bridge Zone latite porphyry | 2 | 2.85 | 0.98631 |
P1OF | Office latite porphyry | - | 2.822 | 0.98631 |
Note: | Bulk Density = Specific Gravity*Conversion Factor |
(1)Factor generated using all data due to limited bulk density data for the porphyry units. | |
(2)Lithologies with no measured specific gravity have been set to the default value of 2.82. The P1 and P2 lithological units are not present in the update area and have limited representation in the full Valley of the Kings model. |
14.7.7 | Other variables |
Block estimates were generated for arsenic (As), sulphur (S), and calcium (Ca) as part of the January 2019 Mineral Resource update. As and S are deleterious elements reporting to the flotation concentrate. Ca and S are used in the determination of the Neutralization Potential Ratio (NPR) of the mill feed in order to optimize tailings geochemistry (minimize acid generating potential) for disposal in the lake or as part of paste backfill, and do not constrain the Mineral Resource.
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All drillhole data were composited to 1.5 m length with no breaks for lithological or mineralization boundaries, however only those inside the 2019 resource update box were flagged for use in estimation. Following exploratory data analysis, variography, and parameter selection, the As, S, and Ca variables were estimated directly into the parent 5 mE by 5 mN by 5 mZ block model using OK. Model validation was carried out by comparing global statistics between composited data and estimated grades. Additionally, local accuracy was validated by comparing sectional grades using slice plots. Both validation techniques showed good reproduction of input data.
14.8 | Model Validation |
Validation of the final model represents only one part of the overall validation process conducted in the generation of the January 2019 resource estimate. Detailed validation was conducted at each step of the modelling process, from data collection to resource reporting. Model validation checks included checks on the physical generation of the model (e.g., correct block coding, block model regularization and addition processes), as well as checks on block model grade estimate data. In the final model, grade estimates were compared against input drillhole data to assess how well the average of modelled grades match the average of the input data grades, and how well the model honours grade trends in the input data.
Grade validation checks included:
■ | statistical checks of final grade, low-grade, high-grade, and probability estimates against input data by domain |
■ | swath plots for each of the estimated variables (final grade, low grade, high grade, and probability), by domain |
■ | visual checks comparing model grades against input drillhole data in plan, on section, and in three dimensions |
■ | visual checks of zones of estimated mineralization against actual underground exposures |
■ | production checks. |
The presence of high and extreme gold grades in the stockwork mineralization in the Brucejack Deposit makes for challenging model validation. The high to extreme grades distort the local statistics on the composite grades, yet they are not anomalies in the grade distribution (see Section 14.6). High-grade mineralization is often present in the mineralization in a given volume but not represented in samples collected from that volume (evidenced both in underground workings, processing of the bulk sample, and daily mill reporting). Alternatively, if a piece of gold is intersected in a sample, there is the possibility that the sample is not representative of the surrounding rock because of the infrequent, but significant nature of its occurrence. This results in challenges with respect to the accuracy of local grade estimates.
14.8.1 | Statistical Checks – Final Gold and Silver Grade Estimates |
Final gold and silver grade estimates in the resource model were compared against the undeclustered input domain-coded drillhole composite data (see Table 14-12). Overall the global average grade estimates for gold and silver honour the input drillhole composite data are considered globally unbiased. The variable differences between the estimated and input grades reflect variable degrees of clustering of the input data by domain: the estimated and input grades are close where the clustering effect is low; the grade estimates are generally lower where there is increased clustering of the drillhole data.
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Table 14-12: | Global Comparison of Mean Estimated and Input Composite Grade Data for Gold and Silver by Domain |
Bigdom Domain | ||||||||||
600 | 700 | 800/801 | 900 | 901 | ||||||
Statistic | Au | Ag | Au | Ag | Au | Ag | Au | Ag | Au | Ag |
Number of Samples | 61,473 | 60,586 | 3,271 | 3,271 | 2,294 | 2,238 | 12,840 | 12,734 | 3,933 | 3,933 |
Mean Grade – Composite (g/t) | 4.46 | 7.92 | 10.13 | 11.45 | 24.33 | 19.52 | 5.68 | 19.73 | 1.05 | 6.57 |
Mean Grade – Estimate (g/t) | 4.28 | 7.84 | 8.76 | 9.88 | 24.52 | 16.49 | 5.67 | 16.01 | 0.98 | 5.02 |
Note: | Comparisons were restricted to the 2019 updated area. |
14.8.2 | Grade Trend Plots |
Trend plots (or swath plots) comparing model estimates and decluster-weighted input drillhole composite data by easting, northing, and elevation were generated for each individual parameter (e.g., low-grade, high-grade, proportion above the grade population delimiter, and the final grade) as a primary validation tool. This was done to assess how well grade trends in the input data were being modelled in the resource estimate, a feature not apparent in univariate summary statistics. Difficulties in manually matching the declustering that occurs as part of the estimation process (see Section 14.8.1) necessitated the use of a spatially reasonable cell size to approximate declustering for comparative purposes. Example trend plots (for grouped domain Bigdom 600) are presented in Figure 14-10 to Figure 14-15.
Estimates of the individual variables (low grade, high grade, and proportion of high grade) showed a relatively good comparison to their respective input composite data for each domain. These estimates were therefore considered robust and suitable for being recombined to form the final gold and silver grade estimates (see Section 14.7.1).
Recombined final grade estimates displayed smoother (less spikey) trend lines than those generated for the input drilling composite data, for all three directions. This is due to the volume-variance effect evident between drillhole composites (point data) and block estimates. Block grade estimate data display similar trends to the input drillhole composite data, for all three directions, with a tendency towards being slightly lower grade than the input data (i.e., the trendline is not the exact mean of the input data). This is a function of the decluster-weighting of the input drillhole composite data and difficulties associated with it, as noted above. Grade trends in the input drillhole composite data are best honoured where the conditioning data is spaced at between 10 m and 15 m centres. In poorly informed areas (e.g., north of 6258080 mN and below approximately 1,100 m elevation), the plots show relatively poor correlation between model estimates and input data. Similar observations are developed in the silver trend plots.
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Figure 14-10: Example Gold Grade Trend Plots by Easting for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
Figure 14-11: Example Gold Grade Trend Plots by Northing for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
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Figure 14-12: Example Gold Grade Trend Plots by Elevation for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
Figure 14-13: Example Silver Grade Trend Plots by Easting for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
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Figure 14-14: Example Silver Grade Trend Plots by Northing for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
Figure 14-15: Example Silver Grade Trend Plots by Elevation for Grouped Domain Bigdom 600
Source: | Pretivm (2019) |
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14.8.3 | Visual Validation |
Visual validation of the block grade estimates for the January 2019 resource estimate was conducted in the update area to assess the validity of grade trends, identify potential grade blow-out zones, identify zones of high, medium, and low confidence in the block grade estimates, and to assess the edge of the modelled mineralized zone relative to actual epithermal veining. Visual model validation was done by comparing block grade estimates against input drillhole composites in the Maptek Vulcan software, and against geology in the underground mine exposures.
Block model grade estimates were compared against input drillhole composite grades in three dimensions (model rotation and iterative zoom-in, zoom-out), as well as on a section-by-section basis (along easting, northing, and in plan view). Incremental slicing tools in the Vulcan mining software, with variable viewing windows, were used for this check. Example section and plan views are shown in Figure 14-16 and Figure 14-17.
Overall, the visual validation check indicated that high-grade blocks were being informed by high- and extreme-grade mineralization, and that, in areas of higher infill drilling density, high-grade blocks were reasonably constrained by lower grade mineralization (i.e., no blow-outs). Mineralization trends in the input composite data appear to be reasonably represented in the block grade estimates. Underground geological exposures confirmed the presence of epithermal veining where mineralized blocks were estimated, including the presence of visible electrum in places. Estimates in mineralized domains showed reasonable boundary resolution relative to the edges of the mineralized epithermal vein system exposed in the underground workings, particularly in areas informed by tightly-spaced drilling.
Low- and medium-grade composite data are well represented by the model, although there are numerous places where high and extreme-grades are suppressed by lower grade composite data, with no significant expression in the block grade estimates. This is due to the low estimate of the proportion of high grade in areas dominated by lower grade intersections. Given the hit-and-miss nature of the high-grade data in the drilling (see Section 10.0) and the heterogeneous nature of the gold mineralization in the Valley of the Kings Zone (see Section 7.0), it is likely that the block model estimate is conservative in such areas.
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Figure 14-16: Plan View of the 1,290 m Level Showing Block Grade Estimates and Input Drillhole Composite Data Colour Coded by Gold Grade
Note: | Viewing window is ±30 m; drillhole composites shown as ’+’ markers |
Source: | Pretivm (2019) |
Figure 14-17: North-South Cross Section Along 426630E Showing Block Grade Estimates and Input Drillhole Composite Data Coloured by Gold Grade
Note: | Viewing window is ±30 m; drillhole composites shown as ’+’ markers |
Source: | Pretivm (2019) |
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14.8.4 | Reconciliation of the Resource Model with 2018 Production |
Additional validation checks were conducted by reconciling the January 2019 resource model to the mill grade and recovered ounces for 2018 production (see Table 14-13 and Figure 14-18). The reconciliation presented in this section compares the resource model to mill production prior to application of mill recovery factors. Two reconciliation approaches were used as a test to enhance confidence in the validity of the resource model:
■ | Model to mill reconciliation in as-mined shapes to provide a single annual production reconciliation. |
■ | Model to mill reconciliation using material movement tracking data to provide a time-based reconciliation. |
As-mined shapes are wireframe solids and included those from the Maptek Aegis mining software blast shapes for stope rings sent as ore or waste, surveyed underground development rounds sent as ore or waste, and stope CMS (underground cavity monitoring survey) scans. Assayed surface stockpile material sent to the mill was included, although this represented a very small portion (<1%) of the material mined. Aegis blast shapes for a given stope were compared against final surveyed CMS stope scans and found to be reasonably representative of the mined volume.
Material movement tracking was conducted by truck counting on a per shift basis, with an applied mass factor per truck and LHD (scoop) bucket. These factors were reconciled monthly against actual crusher weightometer data. Challenges associated with material movement tracking included variable residency times of mucked ore in remuck bays on mining levels, as well as in crusher feed remuck bays, and ore from different stopes being blended together in variable quantities as a function of mining exigencies. The nature of material movement and stope blending in the Brucejack Gold Mine therefore precluded exact reconciliation by source (i.e., on a stope-by-stope basis). Material movement tracking data did however facilitate approximation of model to mill reconciliation through the year for trend analysis.
Table 14-13: | January 2019 Model to 2018 Mill Gold Production Reconciliation |
Tonnage | Au | Contained Au | |
(’000 t) | (g/t) | (’000 oz) | |
Total Mined Wireframe Approach | 1,000 | 11.07 | 356 |
Total Mined Materials Movement Tracking Approach | 1,006 | 11.80 | 382 |
Mill Data | 1,006 | 11.90 | 385 |
Percentage Difference Mined to Mill Wireframe Approach | 0.6% | 7.0% | 7.6% |
Percentage Difference Mined to Mill Materials Movement Tracking | - | 0.9% | 0.9% |
Note: | Silver grades are not reported in daily figures by the mill |
Results of both reconciliation approaches show that the predicted grades and contained ounces in the January 2019 model are within 10% of the raw mill production data for 2018. This is well within acceptable limits for the mining of heterogeneous nuggety gold deposits on an annual production basis. The model to mill reconciliation data based on materials movement tracking shows an undulating trend in the model predicted cumulative ounces curve relative to the mill production contained ounces curve (Figure 14-18), with the two curves being relatively close from August 2018 to the end of the year. Undulations in model predicted ounces relative to mill produced ounces are expected to continue as the model remains an estimate with an associated variance. Undulations reflect local over- and under-estimation of grade for short-term mining volumes and are expected to average out over an annual production volume for an unbiased model.
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Figure 14-18: Cumulative Ounces Plot for the January 2019 Model Relative to 2018 Mill Production
Notes: | 2018 production data is shown as mill feed; cumulative ounces for the January 2019 resource model is based on material movement tracking data to approximate time-based reconciliation. Difficulties inherent in truck tracking preclude exact stope-by-stope reconciliation due to stope blending and variable underground muck residency times. |
Source: | Pretivm (2019) |
14.8.5 | Concluding Remarks: Model Validation |
Based on the various model validation checks presented above, the QP considers the January 2019 resource model as being a reasonable representation of the input drilling data at the block scale, particularly in well-drilled areas. In addition, he considers the January 2019 model to be a reasonable predictor of gold grade and contained metal in well-drilled areas.
14.9 | Mineral Resource Classification |
Additional data generated as part of the 2017-2018 infill drill campaign and from extensive underground development completed since the July 2016 resource estimate were incorporated into an updated resource classification for parts of the January 2019 Mineral Resource. Changes to the resource classification were limited to that part of the resource model updated in this study (see introductory comments to Section 14.0 and Section 14.6.1).
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Details of Measured, Indicated, and Inferred classification criteria pertaining to the December 2013 estimate outside of the update area are presented in Farley et al. (2014) and Jones (2014). Classification criteria pertaining to the July 2016 estimate are presented in Board et al. (2017). The Mineral Resource defined in Farley et al. (2014) and Jones (2014) was a global resource predicated on bulk mining, and included the classification of Indicated Resources where the drillholes were spaced up to 40 m apart.
The May 10 (2014) definition standards of the CIM (2014) were followed in the classification of the January 2019 Mineral Resource estimate, whereby:
AMeasured Mineral Resource is that part of a Mineral Resource for which quantity, grade or quality, densities, shape, and physical characteristics areestimated with confidence sufficient to allow the application of Modifying Factors to support detailed mine planning and final evaluation of the economic viability of the deposit. Geological evidence is derived from detailed and reliable exploration, sampling and testing and is sufficient to confirm geological and grade or quality continuity between points of observation. A Measured Mineral Resource has a higher level of confidence than that applying to either an Indicated Mineral Resource or an Inferred Mineral Resource. It may be converted to a Proven Mineral Reserve or to a Probable Mineral Reserve
AnIndicated Mineral Resource is that part of a Mineral Resource for which quantity, grade or quality, densities, shape and physical characteristics areestimated with sufficient confidence to allow the application of Modifying Factors in sufficient detail to support mine planning and evaluation of the economic viability of the deposit. Geological evidence is derived from adequately detailed and reliable exploration, sampling and testing and is sufficient to assume geological and grade or quality continuity between points of observation. An Indicated Mineral Resource has a lower level of confidence than that applying to a Measured Mineral Resource and may only be converted to a Probable Mineral Reserve.
AnInferred Mineral Resource is that part of a Mineral Resource for which quantity and grade or quality areestimated on the basis of limited geological evidence and sampling. Geological evidence is sufficient to imply but not verify geological and grade or quality continuity. An Inferred Mineral Resource has a lower level of confidence than that applying to an Indicated Mineral Resource and must not be converted to a Mineral Reserve. It is reasonably expected that the majority of Inferred Mineral Resources could be upgraded to Indicated Mineral Resources with continued exploration.
Drillhole spacing, geological maps of the extensive underground development, model validation (Section 14.8) results, and production reconciliation (Section 14.9) were reviewed in detail as part of the resource classification process. Existing wireframe solid interpretations for Measured and Indicated classifications were then refined and validated. Blocks in the 2019 resource model were coded according to resource classification using the revised wireframe solids, where:
■ | Measured Resources are those with infill drilling characterized by up to 15 m spacing in areas informed by new underground development. Measured Resources are expected to be within 10% of production on an annual basis. |
■ | Indicated Resources are those informed by appropriately spaced (up to 25 m centers) drilling and using information from a minimum of two drillholes. Indicated Mineral Resources using this classification scheme are expected to be within 15% of production on an annual basis. |
Indicated Resources outside of the update box include drilling between 25 to 40 m centers, originally considered appropriate for bulk mining of the deposit (Farley et al. 2014; Jones 2014). Additional infill drilling, ahead of mine scheduling, will be necessary in these areas to increase definition of high-grade corridors within the broader stockwork zones should more selective mining scenarios (e.g., longitudinal mining) be envisaged.
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It is the QPs opinion that the approach to resource classification is appropriate given the nature of the mineralization in the Brucejack Deposit. It is his opinion that the information used to define the Mineral Resource is of a high quality and suitable for the estimation and classification of resources with a high level of confidence.
14.10 | Mineral Resource Reporting |
14.10.1 | January 2019 Mineral Resource for the Brucejack Deposit |
The January 2019 Mineral Resource for the Brucejack Deposit (Valley of the Kings Zone and West Zone together) is presented in Table 14-14. Details of the Mineral Resource reported by zone are presented in Table 14-15 and Table 14-16. For comparative purposes, the January 2019 Mineral Resource is reported above a cut-off grade of 5 g/t AuEq in a manner consistent with the November 2012 (Jones 2012c), December 2013 (Jones 2014), and July 2016 (Board et al. 2017) Mineral Resources. The gold equivalent for each block was derived according to the same formula used for each Mineral Resource (AuEq = Au + Ag/53).
Table 14-14: | January 2019 Valley of the Kings and West Zone Mineral Resource(1,2,3,4,5,6) |
Tonnes | Au | Ag | Contained Au | Contained Ag | |
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) |
Measured | 4.2 | 10.71 | 204.8 | 1.5 | 27.8 |
Indicated | 14.4 | 15.19 | 45.6 | 7.1 | 21.0 |
Measured + Indicated | 18.7 | 14.18 | 81.6 | 8.5 | 48.7 |
Inferred | 7.8 | 12.0 | 51.3 | 3.0 | 13.0 |
Notes: | (1)Mineral Resources which are not Mineral Reserves do not have demonstrated economic viability. The estimate of Mineral Resources may be materially affected by environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant issues. The Mineral Resources in this Technical Report were estimated using the CIM Standards on Mineral Resources and Reserves, Definitions and Guidelines (CIM 2014) prepared by the CIM Standing Committee on Reserve Definitions and adopted by CIM Council. |
(2)The quantity and grade of reported Inferred resources in this estimation are uncertain in nature and there has been insufficient exploration to define these Inferred Resources as an Indicated or Measured Mineral Resource and it is uncertain if further exploration will result in upgrading them to an Indicated or Measured Mineral Resource category. | |
(3)Contained metal and tonnes figures in totals may differ due to rounding. | |
(4)Resources depleted for production to December 31, 2018. | |
(5)For comparative purposes only, the January 2019 Mineral Resource is reported above a gold equivalent cut-off grade of 5 g/t AuEq (where AuEq = Au + Ag/53 as per previous models). | |
(6)Mineral Resource is reported inclusive of Mineral Reserve. |
Table 14-15: | January 2019 Valley of the Kings Zone Mineral Resource(1) |
Tonnes | Au | Ag | Contained Au | Contained Ag | |
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) |
Measured | 1.8 | 17.15 | 16.4 | 1.0 | 1.0 |
Indicated | 11.9 | 17.15 | 15.4 | 6.6 | 5.9 |
Measured + Indicated | 13.7 | 17.15 | 15.5 | 7.6 | 6.8 |
Inferred | 3.8 | 17.7 | 19.4 | 2.2 | 2.4 |
Notes: | (1) Notes from Table 14-14 apply |
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Table 14-16: | West Zone Mineral Resource, April 2012(1) |
Tonnes | Au | Ag | Contained Au | Contained Ag | |
Category | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) |
Measured | 2.4 | 5.85 | 347 | 0.5 | 26.8 |
Indicated | 2.5 | 5.86 | 190 | 0.5 | 15.1 |
Measured + Indicated | 4.9 | 5.85 | 267 | 0.9 | 41.9 |
Inferred | 4.0 | 6.4 | 82 | 0.8 | 10.6 |
Notes: | (1)Notes from Table 14-14 apply (see Jones 2012a for more details) |
Source: | Jones (2012a) |
14.10.2 | Resource Sensitivity |
The January 2019 resource model coded as Measured or Indicated for the Valley of the Kings Zone (depleted for production up to December 31, 2018) is reported at a series of gold equivalent cut-off grades to demonstrate sensitivity (see Figure 14-19). Estimated gold grade decreases and tonnage increases at progressively lower gold equivalent cut-offs (and vice versa at higher cut-offs). Gold grade remains above 10 g/t Au at a cut-off of 2.5 g/t AuEq.
Figure 14-19: January 2019 Valley of the Kings Zone Measured + Indicated Mineral Resource Sensitivity
Note: | AuEq = Au + Ag/53 (as at March 2019) |
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14.11 | Comparison with the July 2016 Mineral Resource Estimate |
As there have been no changes to the West Zone Mineral Resource and the December 2013 Valley of the Kings Mineral Resource outside the update area (see introductory comments to Section 14.0 and Section 14.6.1), comparison between the January 2019 and July 2016 resource estimates is limited to the Valley of the Kings Zone inside the update area (see Table 14-17). The comparison focuses on resource estimates that have not been depleted for production as the July 2016 Mineral Resource was completed prior to commissioning of the mine.
Table 14-17: | Comparison Between January 2019 and July 2016 Resource Estimates for the Valley of the Kings Zone Inside the Update Area |
AuEq | ||||||
Resource | Cut-off | Tonnes | Au | Ag | Contained Au | Contained Ag |
Model | (g/t) | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) |
Measured | ||||||
January 2019 | 5 | 2.4 | 19.7 | 19.1 | 1.5 | 1.4 |
July 2016 | 5 | 3.5 | 17.0 | 15.3 | 1.9 | 1.7 |
Change | - | -1.1 | +2.7 | +3.8 | -0.4 | -0.3 |
Indicated | ||||||
January 2019 | 5 | 12.1 | 17.2 | 15.4 | 6.7 | 6.0 |
July 2016 | 5 | 13.0 | 17.3 | 15.0 | 7.2 | 6.2 |
Change | - | -0.9 | -0.1 | +0.4 | -0.5 | -0.2 |
Measured + Indicated | ||||||
January 2019 | 5 | 14.5 | 17.6 | 16.0 | 8.2 | 7.4 |
July 2016 | 5 | 16.4 | 17.2 | 15.0 | 9.1 | 7.9 |
Change | - | -1.9 | +0.4 | +1.0 | -0.9 | -0.5 |
Inferred | ||||||
January 2019 | 5 | 3.9 | 17.7 | 19.4 | 2.2 | 2.4 |
July 2016 | 5 | 4.6 | 21.0 | 26.9 | 3.1 | 4.0 |
Change | - | -0.7 | -3.3 | -7.5 | -0.9 | -1.6 |
Note: | These numbers have been reported for comparative purposes and have not been depleted to account for production. The reader should refer to Table 14-15 for the current January 2019 Valley of the Kings Mineral Resource, reported depleted of production as at December 31, 2018. |
There is a reduction from the July 2016 resource estimate to the January 2019 resource estimate (Measured + Indicated Mineral Resource) by approximately 1.9 Mt, 0.9 Moz contained gold, and 0.5 Moz contained silver at similar estimated gold and silver grades. Inferred Mineral Resources also decreased by approximately 0.7 Mt, 0.9 Moz contained gold, and 1.6 Moz contained silver, with a grade drop in both estimated gold and silver.
The differences between the two models are largely data-driven, but partly also due to a revision of some of the grade estimation parameters. Additional tightly-spaced conditioning data generated during infill drilling inside the update area since 2016, increased underground exposure of the mineralized system during mining, and over 1.5 Mt of actual production data have resulted in improved domain definition (tighter domains with better resolution on higher grade and lower grade mineralization) and improved local estimation parameter definition. This has resulted in more locally restricted high-grade corridors within the broader mineralized domains, resulting in an overall reduction in tonnes and ounces at the relevant cut-off grade. The average grade at the relevant cut-off is generally maintained. Additional drilling in the lower confidence parts of the deposit has also resulted in upgrading parts of the Inferred Mineral Resource to the Indicated Mineral Resource category; elsewhere the additional drilling has resulted in writing off material as uneconomic.
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15.0 | MINERAL RESERVE ESTIMATES |
15.1 | General |
The Mineral Reserves for the Brucejack Mine, stated herein, are considered economically feasible to mine based on the following:
■ | the completion of financial modelling based on Mineral Reserves |
■ | there are no known legal or political matters preclude continued mining |
■ | Pretivm holds the permits required to operate the Brucejack mine |
■ | the mining and processing operations are technical and economically feasible under current and foreseeable economic conditions |
■ | the Metallurgical recoveries from operating data and test work are understood |
■ | the Infrastructure required to continue operations is in place |
■ | there are no other know factors preclude continued mining and processing operations. |
The Mineral Reserve estimate stated herein is consistent with the CIM Standards on Mineral Resources and Mineral Reserves and is suitable for public reporting. As such, the Mineral Reserves are based on Measured and Indicated Mineral Resources and do not include any Inferred Mineral Resources. This Mineral Reserve estimate update only pertains to the Valley of the Kings mining area; no additional work has been completed on the West Zone since the 2014 FS (Ireland et al. 2014).
The Valley of the Kings Mineral Reserves were developed from the Mineral Resource model “res1901_finmod_20190115_v3”, which was created by Pretivm and provided in January 2019. These Mineral Reserves do not include the mined-out material up to year-end of 2018.
15.2 | Cut-off Grade |
A NSR cut-off grade of US$185/t or Cdn$237/t of ore was used to define the Mineral Reserves. This cut-off grade is based on a 3,800 t/d mining operation. This cut-off grade has increased from the previous cut-off grade of US$165/t from the 2014 FS (Ireland et al. 2014). Table 15-1 shows the average site operating cost estimates over the LOM.
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Table 15-1: | Cut-off Grade Costs |
Area | Cost |
Mining | Cdn$127.22/t |
Processing | Cdn$26.55/t |
Maintenance | Cdn$10.76/t |
G&A | Cdn$71.66/t |
Total (Cdn$) | Cdn$236.18/t |
Foreign Exchange Rate | Cdn$1.00:US$0.78 |
Total (US$) | US$184.22/t |
15.3 | NSR Model |
A NSR model was created for the Mineral Reserves and used the parameters summarized in Table 15-2. The NSR for each block in the Mineral Resource model was calculated as the payable revenue for gold and silver, less the costs of refining, treatment, transportation, assays, consultants, and penalties.
The metal price assumptions for delineation of the Mineral Reserves are US$1,200/oz Au and US$15.60/oz Ag. A foreign exchange rate of Cdn$1.00:US$0.78 was used.
The NSR contributions for both doré and floatation were calculated separately, then combined to create a total NSR for each block in the Mineral Resource model. The recovery and mass pull percentages were calculated using trends from mill data obtained throughout production.
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Table 15-2: | NSR Parameters |
Items | Units | Parameters | ||
Foreign Exchange Rate | Cdn$:US$ | - | 1:0.78 | |
Metal Prices | Gold | US$/oz | - | 1,200.00 |
Silver | US$/oz | - | 15.60 | |
Doré | ||||
Recoveries | Gold | % | Au/S <= 0.15 | 0 |
% | 0.15 < Au/S <= 5.02 | 19.778*ln(Au/S)+40.101 | ||
% | Au/S > 5.02 | 72 | ||
Silver | % | Ag/Au >= 4.03 | 0 | |
% | 4.03 > Ag/Au >= 0.11 | -27.41*ln(Ag/Au)+38.215 | ||
% | Ag/Au < 0.11 | 98 | ||
Selling Cost | Transport | US$/Au oz doré | - | 2.71 |
Assays | US$/Au oz doré | - | 0.36 | |
Consultants | US$/Au oz doré | - | 0.03 | |
Other | US$/Au oz doré | - | 0.12 | |
Treatment | US$/Au oz doré | - | 0.5 | |
Penalty | US$/Au oz doré | - | 1.2 | |
Metal Payable | Gold | % | - | 99.97 |
Silver | % | - | 99.6 | |
Flotation Concentration | ||||
Recoveries | Gold | % | Au/S <= 0.06 | 98 |
% | 0.06 < Au/S < 4.8 | -16.15*LN(Au/S)+52.343 | ||
% | Au/S >= 4.8 | 27 | ||
Silver | % | Ag/Au <= 4.7 | 12.811*Ag/Au+37.965 | |
% | Ag/Au > 4.7 | 98 | ||
Mass Pull | % | - | 0.005*(S/C)+0.0426 | |
Selling Cost | Treatment | US$/dmt | - | 240 |
Refining | US$/payable Au oz | - | 9 | |
Transport | US$/dmt | - | 269.95 | |
Assays | US$/dmt | - | 6.03 | |
Consulting | US$/dmt | - | 8.69 | |
Other | US$/dmt | - | 1.72 | |
Metal Payable | Gold | % | - | 97.5 |
Silver | % | - | 95 | |
Arsenic Recovery | % | - | 0.0439*(S/C)+0.4537 | |
Arsenic Penalty | US$/t concentrate | As <= 0.2% | 0 | |
US$/t concentrate | 0.5% > As > 0.2% | (As-0.2)*6.25 | ||
US$/t concentrate | 0.5% > As | (As-0.5)*7.5 + 18.75 |
Note: | All costs and metal prices were based upon conservative estimates and used solely for the generation of the NSR model and delineation of the Mineral Reserves. |
15.4 | Mining Shapes |
Pretivm used the Mineable Shape Optimizer (MSO) module from Vulcan v. 10.1.6 software to produce design excavations that met both the cut-off grade and operational design criteria.
The design criteria constrain the geometry of all planned excavations to mineable shapes through the planned mining methods. Section 16.0 provides further detail on mining shapes and design parameters.
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The preliminary shapes were individually refined where necessary to ensure stope geometry viability and to minimize the amount of sub-economic material within the shape volume that is inseparable from profitable material due to the practical constraints of mining.
The Mineral Reserve stope and development shapes were used as the basis for short-term mine planning by the Brucejack Gold Mine site mine planning department. Based on further grade control drilling and assaying work completed prior to mining, additional stope shape changes may occur to adjust mining to the results of grade control work.
15.5 | Dilution and Recovery Estimates |
In evaluating the Mineral Reserves, modifying factors were applied to the tonnage and grade of all mining shapes (both stoping and development) to account for the dilution and ore loss.
Ore dilution includes overbreak into the design hanging wall and design footwall, as well as into adjacent backfilled stopes. Diluting materials were assumed to carry no metal values in the estimation of Mineral Reserve grades.
The largest component of dilution at the Brucejack Gold Mine will be paste backfill due to its inherently weaker strength as compared to the hanging wall and footwall rock masses for any given dimensions of exposure. Ore loss (recovery factors) is related to the practicalities of extracting ore under varying conditions, including difficult mining geometry, problematic rock conditions, losses in fill, and blasting issues.
The dilution factors were estimated from standard overbreak assumptions based on Pretivm’s experience and benchmarking of similar long-hole open stope operations.
■ | Long-hole stopes (primary, secondary, and tertiary) carry 1.0 m of dilution from paste or country rock overbreak into the design hanging wall and design footwall and 0.3 m of backfill dilution from the floor. |
■ | Secondary or tertiary stopes carry an additional 1.0 m of backfill dilution on each wall that exposes a primary stope. |
■ | Sill pillar stopes are treated as secondary stopes, given the additional backfill dilution that can be expected from the roof. |
■ | Ore cross-cuts carry 0.5 m of dilution from rock overbreak into the design hanging wall and design footwall. |
■ | Production slashing of secondary stopes carries 0.5 m of backfill dilution on each wall that exposes a primary stope. |
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Figure 15-1 shows the typical sources of stope dilution.
Figure 15-1: Sources of Stope Dilution
The application of the above parameters yields an overall LOM ore recovery of 94% and an overall ore dilution of 12%. The use of parallel production drillholes in stoping operations at the Brucejack Gold Mine will provide improved dilution control in comparison to fan drilling (discussed further in Section 16.0).
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15.6 | Orebody Description |
Mineral Reserves delineated at the US$185/t NSR cut-off define an orebody consisting of numerous independent lenses in the Valley of the Kings Zone and two distinct lenses in the West Zone extending over a 570 m vertical distance from the 990 m elevation level to surface (approximately 1,560 m elevation level).
15.6.1 | Valley of the Kings Zone |
The Valley of the Kings Zone hosts multiple lenses that includes 13.1 Mt of Mineral Reserves. Mineral Reserves in the Galena Hill Zone are proximal to the Valley of the Kings Zone and have been considered as part of the Valley of the Kings Mineral Reserves.
Strike length varies considerably with elevation, but the core of the Valley of the Kings Zone has a strike length of approximately 330 m. The other main lens in the Valley of the Kings Zone has a strike of approximately 360 m. Orebody thickness varies with elevation. Table 15-3 shows a breakdown by mining block.
Table 15-3: | Main Valley of the Kings Mining Thickness by Mining Block |
Mining Thickness | |
Level | (m) |
990-1050 | 16 |
1080-1170 | 14 |
1200-1290 | 14 |
1320-1560 | 15 |
Narrow Mineral Reserves have been delineated down to a minimum 10 m mining thickness. The Valley of the Kings Zone has a slight plunge towards the east.
15.6.2 | West Zone |
Mineral Reserves for the West Zone remain unchanged from the 2014 FS (Ireland et al. 2014) as no new drilling has been completed and no new information has been obtained in this zone. Mineral Reserves within the West Zone are contained within four lenses, three of which host 90% of West Zone Mineral Reserves. Strike lengths vary considerably with elevation, averaging approximately 100 m in the larger lenses, while the smaller lenses are no more than 35 m along strike.
The average thickness is approximately 25 m, with the smaller lenses averaging only 15 m.
15.7 | Mineral Reserves |
Table 15-4 presents the Mineral Reserves tabulated by zone and by reserve category. All Mineral Reserves are scheduled in the LOM plan, presented in Section 16.0.
The mining blocks divide the Mineral Reserves into logical parcels consistent with the mining sequence and form the basis of the LOM development and production schedule also discussed in Section 16.0.
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Table 15-4: | Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Zone |
Grade | Contained Metal | |||||
Ore | ||||||
Tonnes | Au | Ag | Au | Ag | ||
Zone | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | |
Valley of the Kings Zone | Proven | 2.0 | 11.2 | 11.8 | 0.7 | 0.7 |
Probable | 11.1 | 14.3 | 10.5 | 5.1 | 3.8 | |
Total | 13.1 | 13.8 | 10.7 | 5.8 | 4.5 | |
West Zone | Proven | 1.4 | 7.2 | 383.0 | 0.3 | 17.4 |
Probable | 1.5 | 6.5 | 181.0 | 0.3 | 8.6 | |
Total | 2.9 | 6.9 | 278.5 | 0.6 | 26.0 | |
Total Mine | Proven | 3.4 | 9.5 | 166.5 | 1.0 | 18.1 |
Probable | 12.6 | 13.4 | 30.8 | 5.4 | 12.4 | |
Total | 16.0 | 12.6 | 59.3 | 6.4 | 30.5 |
Note: | (1)Rounding of some figures may lead to minor discrepancies in totals. |
(2)Based on US$185/t cut-off grade, US$1,200/oz Au price, US$15.6/oz Ag price, and a Cdn$1.00:US$0.78 foreign exchange rate. |
Table 15-5: | Brucejack Gold Mine Mineral Reserves(1)(2) by Mining Block |
Grade | Contained Metal | ||||||
Ore | |||||||
Tonnes | Au | Ag | Au | Ag | NSR | ||
Zone | (Mt) | (g/t) | (g/t) | (Moz) | (Moz) | ($/t) | |
Valley of the Kings Zone | 990-1050 | 0.8 | 10.3 | 3.9 | 0.2 | 0.1 | 384 |
1080-1170 | 2.6 | 10.7 | 8.8 | 0.9 | 0.7 | 395 | |
1200-1290 | 4.8 | 12.8 | 9.2 | 2.0 | 1.4 | 477 | |
1320-1560 | 5.0 | 16.9 | 14.1 | 2.7 | 2.3 | 629 | |
Total | 13.1 | 13.8 | 10.7 | 5.8 | 4.5 | 513 | |
West Zone | Upper West Zone | 0.6 | 4.2 | 407.0 | 0.1 | 8.0 | 304 |
Lower West Zone | 2.3 | 7.6 | 245.0 | 0.6 | 18.1 | 350 | |
Total | 2.9 | 6.9 | 278.5 | 0.7 | 26.1 | 340 | |
Mine | All Mining Blocks | 16.0 | 12.6 | 59.3 | 6.4 | 30.5 | 482 |
Note: | (1) Rounding of some figures may lead to minor discrepancies in totals. |
(2) Based on US$185/t cut-off grade, US$1,200/oz Au price, US$15.60/oz Ag price, an a Cdn$1.00:US$0.78 foreign exchange rate. |
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Figure 15-2: 2019 Reserve Shapes and Mining Blocks in the Main Valley of the Kings Zone
Source: | Pretivm (2019) |
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Figure 15-3: Reserve Shapes and Mining Blocks in the West Zone
Figure 15-4: Combined 2019 Reserves and LOM Development by Mining Blocks, Looking West
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15.8 | Mineral Reserve Validation |
In order to validate the methodology applied to the delineation of the 2019 Mineral Reserves the process used in the delineation of the 2019 Mineral Reserves was replicated on the depleted portions of the 2019 Mineral Resource model (in particular areas mined in 2018). These generated shapes, referred to as Reserve Validation Shapes, overlap with mined-out development and stopes from prior mining activities. The 2019 Mineral Resource model that was contained within the validation shapes that are broadly coincident with the 2018 actual stope and development ore positions were compared to the 2018 milled and mined results. Applicable validation shapes were determined using CMS scans of the mined material for 2018. Table 15-6 shows the comparison.
Table 15-6: | Comparison of 2018 Actuals vs. 2019 Reserve Validation Shapes |
Contained Gold | |||
Tonnes | Gold Grade | Ounces | |
Year | (’000 t) | (g/t) | (’000 oz) |
2018 Actuals | 1,006 | 11.9 | 385 |
2019 Reserve Validation Shapes | 801 | 15.4 | 397 |
Difference | 20% | 29% | 3% |
The tonnage from the validation shapes is 20% less than actual mined, while the ounces produced are comparable. The primary cause for this difference is the mining of material outside of the 2019 Mineral Reserve Validation Shapes that were originally part of the 2016 Mineral Reserves. This additional material is not encompassed within the validation shapes and therefore would not be a part of the 2019 Mineral Reserves if these areas were to be mined again. The inclusion of uneconomic material (waste) within the mined stopes resulted in mining more tonnage at a lower grade in 2018 than would have been mined based solely on the 2019 Mineral Reserve Validation Shapes.
The 2018 actuals are based upon reconciled month-end figures that were calculated from mill actuals (doré, gold in bagged concentrate, weightometer figures, tailings figures, and changes in gold in process). The 2019 Reserve Validation Shapes’ tonnes and grade were determined from the contained 2019 Mineral Resource model. For these validation shapes, 95% mining recovery and 12% dilution rates were applied; the same as the 2019 Mineral Reserves.
15.9 | Mineral Reserve Comparison |
As significant material has been mined between the 2019 Mineral Reserves and the 2016 Mineral Reserve update a direct comparison of reserves will not provide an accurate assessment of the changes made. To provide a valid comparison the inclusion of the mined-out material between these two time periods needs to be added. As the 2019 Mineral Reserves are exclusive of all material mined prior to January 1, 2019 and the 2016 Mineral Reserves were updated prior to the milling of any material, the 2019 Mineral Reserves in combination with the 2017 and 2018 milled actuals are a valid comparison to the 2016 Mineral Reserve update. Table 15-7 shows the comparison.
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Table 15-7: | Comparison of 2019 Mineral Reserves with Mined Actuals to Previous Reserve |
Ore | Contained | |||
Tonnes | Grade | Metal | ||
Reserves | (Mt) | Au (g/t) | Au (Moz) | |
2019 Mineral Reserves + Milled Actuals | Proven + Probable | 16 | 12.6 | 6.4 |
2017 Actuals | 0.5 | 9.4 | 0.2 | |
2018 Actuals | 1 | 11.9 | 0.4 | |
Total | 17.5 | 12.4 | 6.9 | |
2016 Mineral Reserves | Total | 18.5 | 14.4 | 8.7 |
2019 - 2016 | Difference | -1.0 | -2.0 | -1.7 |
Note: | * Rounding of some figures may lead to minor discrepancies in totals. |
All milled actuals based off of reconciled year end results. |
The 2019 Mineral Reserves contained metal has decreased from the 2016 Mineral Reserves as changes in the Mineral Resource model and cost increases have reduced the gold grade and overall tonnage. In addition to this, during initial mining of production stopes some additional material outside of the most recent Mineral Reserves were mined. These portions of the stopes were part of the 2016 Mineral Reserves; however, some of this material has now become uneconomic or of lower grade in the 2019 Mineral Reserve. This mined-out reserve material, in combination with a reduction in overall reserve grade and tonnage, results in lower contained metal when the 2019 Mineral Reserves are compared to the previously updated Mineral Reserves.
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16.0 | MINING METHODS |
16.1 | General |
Brucejack Gold Mine development has been ongoing since the start of commercial production in 2017. The execution of the mine plan closely matches the mine plan as disclosed in the 2014 FS (Ireland et al. 2014). Locations for some infrastructure items have been adjusted to improve practicality as the mine has developed. These changes include the location and type of the main dewatering system and the utilization of settling sumps to pump the sediment and slimes directly to the mill clarifier. The explosives magazine was moved to isolate the location from the main works and to allow direct ventilation exhaust to surface in the event of combustion or explosion. The layout for the underground service facilities was also modified.
The updated underground mine design supports the extraction of 3,800 t/d of ore through a combination of transverse and longitudinal LHOS. Paste backfill is integral to the mine plan to maximize both orebody recovery and mining productivity. Modern trackless mobile equipment is employed in the majority of mining activities.
A main decline, designated as the Valley of the Kings access, extends from the surface portal near the concentrator and is used to access the mine and as a conveyor way. The conveyors installed have a combined length of 800 m. The existing West Zone portal will continue to provide access (and egress) to the mine and serve as the main access for large underground equipment and waste haulage.
A fleet of LHD and underground trucks are used for material loading and transport from the underground working areas and through an internal ramp system that connects all levels to the centrally located crusher.
Permanent fans provide ventilation by forcing air down the declines through the internal ramps and exhausting to surface via dedicated raises that connect the working levels to surface in each zone. The primary fans are located at each of the main surface portals. An electric mine air heating system is used to take advantage of low electricity prices, with a propane system available as a back-up.
Ongoing development to sustain 3,800 t/d of ore production will average approximately 900 m/mo during the first two years of production ramp-up and will decrease to less than 90 m/mo in the latter years of the LOM following completion of West Zone infrastructure development.
Major underground infrastructure includes crusher, conveyors, ventilation raises, fans, heating system, pumping stations, electrical substations, explosives magazines, paste fill booster pump station, refuges, mine communications, and other ancillary installations that include an underground maintenance service facility and a fuelling facility
16.2 | Mine Design |
16.2.1 | Access and Ramp Infrastructure |
The Valley of the Kings Zone is currently accessible via internal ramps between the 1,080 m and 1,470 m elevation levels via both the Valley of the Kings ramp and the West Zone ramp from surface. The continued infrastructure development program will utilize this existing infrastructure.
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The Valley of the Kings access decline joins the main surface portal to the Valley of the Kings ramp at the 1,290 m and at the 1,320 m elevation levels on the West Zone access ramp. The West Zone will likewise be accessed from the existing bulk sample access drive during the latter half of the LOM. Figure 16-1 illustrates the general development arrangement.
Figure 16-1: Mine Access and Development Infrastructure
Source: | Pretivm (2019) |
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The internal ramp starts at the 1,335 m elevation level and proceeds up and down the Valley of the Kings deposit at ±15% gradient. At the 1,290 m elevation level the internal ramp connects with the bottom of the Valley of the Kings access ramp. The decline and incline have been developed in a race-track configuration.
An independent ramp for each zone—as opposed to a single ramp servicing both the Valley of the Kings Zone and the West Zone—was selected and developed in the interest of access and capital efficiency, given that the West Zone is mined later during the LOM.
For ease of entry and exit, ramps have been developed with a 25 m turning radius and a 15% gradient, levelling out to a 0% gradient in proximity to a level access intersection. Passing bays are incorporated where required in the main Valley of the Kings Zone and West Zone access ramps. Figure 16-2 shows the ramp system for both zones in perspective view.
Figure 16-2: Brucejack Ramp System – Perspective View
Source: | Pretivm (2019) |
16.2.2 | Level Development |
Sublevels are accessed from the ramps on 30 m vertical intervals that are defined by the planned stoping heights. Footwall and/or hanging wall drives are set back a minimum of 10 m from the ore contact, whereas ramp development is set back at a minimum of 50 m from the ore contact. This arrangement promotes long-term geotechnical stability and provides adequate space for the placement of a fresh air raise and other ancillary services between the ramp and level development.
Sublevels generally have a raise on one or both ends, permitting the exhaust of contaminated air from activity on the level. Figure 16-3 illustrates the Valley of the Kings Zone sublevel arrangement in long section.
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Figure 16-3: Valley of the Kings Zone Sublevel Arrangement – Long Section
Source: | Pretivm (2019) |
Level development follows the general strike of the various lenses of the Brucejack Deposit, providing access to the mineralized zones in a manner that allows for either transverse or lateral mining; whichever is more suitable for that zone of the deposit. Level development is generally in the footwall and includes excavations for sumps, refuges, transformers, remucks, paste fill line, and raise accesses.
Stope-access cross-cuts located outside of the Brucejack Fault Zone are on 15 m spacings for transverse stope blocks, while the multiple access configuration of lateral mining stopes is determined based on efficiency and mining sequence. This excludes those levels where sill extraction or near-surface weathered ore is recovered in smaller stopes that are designed to geotechnical criteria. Likewise, all Brucejack Fault Zone ore is developed on 10 m spacings to accommodate poorer ground conditions. These spacings are modified as geotechnical experience is gained.
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Figure 16-4 illustrates typical level development requirements from the LOM plan.
Figure 16-4: Typical Level Development – Valley of the Kings Zone
Source: | Pretivm (2019) |
Level development design considers equipment size, services, and required activity. Table 16-1 summarizes the design parameters and Figure 16-5 illustrates standard designs for development drives.
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Table 16-1: | Development Design Parameters |
Parameter | |||
Maximum | |||
Development | Width | Height/Length | Gradient |
Type | (m) | (m) | (%) |
Remuck | 5.5 | 5.5 | 2 |
Footwall Drives | 5.5 | 5.5 | 15 |
Access Drive | 5.5 | 5.5 | 2 |
Electric LHD Cut-out | 5.5 | 5.5 | 2 |
Conveyor Decline | 6.0 | 6.5 | 15 |
Main Access Decline | 6.0 | 5.5 | 15 |
Infrastructure Drive | 5.5 | 5.5 | 2 |
Drainage Cut-out | 5.5 | 5.5 | 2 |
Waste Cross-cut | 5.0 | 4.5 | 2 |
Refuge Bay Cut-out | 5.5 | 5.5 | 2 |
Ore Cross-cut | 5.0 | 4.5 | 2 |
Fresh Air Drive | 5.5 | 5.0 | 2 |
Return Air Drive | 5.5 | 5.0 | 2 |
Paste Fill Line Drive | 5.5 | 5.0 | 2 |
Vertical | |||
Alimak Raise | 3.0 | 3.0 | - |
Return Air Drive | 3.0 | 3.0 | - |
Fresh Air Raise | 3.0 | 3.0 | - |
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Figure 16-5: Standard Designs – General Layout for all
16.2.3 | Stope Design |
The Brucejack Gold Mine uses the MSO module from the Vulcan mine planning software package to produce conceptual stope shapes. Table 16-2 summarizes the key design parameters used in the MSO. The conceptual stope shapes are refined as necessary to minimize planned dilution and to meet practical mining constraints.
Table 16-2: | Stope Design Parameters |
Valley of the Kings Zone | West Zone | ||||||
Sill | Sill | ||||||
Parameter | Units | Standard | Weathered(1) | Pillar | Standard | Weathered(1) | Pillar |
NSR Cut-off | US$/t | 185 | 185 | 185 | 180 | 180 | 180 |
Level Spacing | m | 30 | 30 | 30 | 30 | 30 | 30 |
Stope Span | m | 10-15 | 10-15 | 10-15 | 15 | 10 | 10 |
Minimum Mining Width | m | 10 | 10 | 10 | 3 | 3 | 3 |
Minimum Waste Pillar Width | m | 5 | 5 | 5 | 5 | 5 | 5 |
Minimum Footwall Dip | degrees | 80 | 80 | 80 | 60 | 60 | 60 |
Minimum Hanging Wall Dip | degrees | 80 | 80 | 80 | 60 | 60 | 60 |
Note: | (1)Refers to stoping in weathered material immediately below the surface crown pillar. Weathered material extends 10 to 50 m below surface. |
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Individual areas meeting the cut-off grade are evaluated against access development costs to determine economic viability before including them in the mining plan. The LOM plan includes 822 stopes in the Valley of the Kings Zone and 135 stopes in the West Zone. Figure 16-6 and Figure 16-7 are long-section views showing stope shapes generated by the MSO process.
Figure 16-6: MSO Stope Shapes – VOK Zone
Source: | Pretivm (2019) |
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Figure 16-7: MSO Stope Shapes – West Zone
Source: | Pretivm (2019) |
16.3 | Mining Method and Sequence |
16.3.1 | Block Definition |
The orebody is divided into six blocks, defined by elevation and zone, that facilitate a total of 3,800 t/d of production from multiple working areas. Mining progresses upward from the lowest elevation in each block.
The general levels are defined in the long-term mine plan, but the selection has been redefined for operational considerations. The current block sill levels are located at the 990 m, 1,080 m, 1,200 m, and 1,320 m elevation levels for the Valley of the Kings Zone.
16.3.2 | Stope Cycle |
The predominant mining method is transverse LHOS and is based on a standard primary/secondary sequence. No permanent pillars are required, and maximum ore extraction is targeted.
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The footwall drives are completed, and a through ventilation circuit is established before mining begins between any two levels.
Cross-cuts are driven from the footwall drive, through the centre of the stope, to the far ore contact on the undercut and overcut levels.
Cross-cuts on both levels are supported by long support-system cables and Swellex from the central access to pre-support the roof prior to full-width slashing of the entire stope footprint. The secondary stopes are not slashed to full width for ground control considerations.
Long holes are drilled with parallel holes, or in fan configurations, depending on whether the stope can be safely slashed across the entire mineralized width.
Where ground conditions permit, full-width slashing allows parallel production hole drilling across the entire width of the stope. This in turn reduces the potential for ore in stope corners to fail due to inadequate free face or poor explosives distribution. Ore recovery with parallel hole drilling is typically higher than with fan drilling (in the absence of full-width slashing). In poor or difficult grounds and in secondary stopes, fan drilling is used due to geotechnical constraints, utilizing only the initial cross cut and a hammerhead as the drilling platform.
Once the stope footprint is slashed out, a 762 mm pilot hole is drilled in the slot raise location. Production drilling follows in the raise and slot area, followed by the production rings, as drilling progresses towards the end of the stope.
The raise and slot are generally opened in five shots or less. Production blasting and mucking proceed cyclically until the stope is depleted and all ore has been mucked out. LHOS is a non-entry method, with remote mucking of blasted ore required once the draw point brow is open to the extent where the operator may be exposed to uncontrolled sloughing from the stope cavity.
The empty stope is remotely surveyed with cavity monitoring equipment. A barricade is constructed in the draw point and the stope backfilled to just below the floor elevation of the top level. Crushed aggregate or run-of-mine (ROM) waste is spread over the fill surface to reduce backfill dilution and increase trafficability of mucking equipment for the next lift of the stope.
In sills and other areas where top access is not available, mining proceeds in a similar manner; however, raise development and production drilling is performed via drilling up holes from the bottom level. Figure 16-8 illustrates the typical LHOS design for these areas.
Longitudinal LHOS is also employed at the mine, where, in contrast to transverse LHOS, mining progresses along the strike of the orebody to a common access point.
Where applicable, the overcut and undercut are slashed to the footwall and hanging wall contacts, although in numerous longitudinal stopes no overcut is required, and ore is extracted via upwards drilling. In all other respects, the stope cycle is similar to transverse LHOS.
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Figure 16-8: Typical LHOS Design
16.3.3 | Stope Sequence |
The mining sequence in any area of a given block begins with the extraction of the primary stopes on the first (lowest) level. Wherever possible, the first primary stope is located near the middle of the lens to develop a pattern of stope extraction that moves outwards to the extremities of the lens while progressing upwards towards the top. This generally promotes a favourable redistribution of ground stress, although many smaller lenses in the Brucejack orebody are either irregular in shape or of insufficient dimensions to properly develop this sequence.
When the adjacent primary stopes from the level above have been filled and cured, secondary stoping commences. Figure 16-9 illustrates typical sequencing for the more massive lenses at the mine.
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Figure 16-9: Example of Primary/Secondary LHOS at Brucejack Gold Mine
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16.3.4 | Backfilling |
The primary means of backfilling is paste fill, generated from unclassified mill tailings mixed with adequate cementitious binder to meet the strength requirements of re-exposure. Regular strength paste fill is commonly required where there will be re-exposure of vertical stope walls.
Stopes that are planned to not be re-exposed by adjacent mining and are below the 1,350 m elevation level may be backfilled with unconsolidated waste and/or by paste fill with sufficient binder to remove any risk of future liquefaction (low-strength paste fill). High-strength paste fill will be required in the lower portion of all primary and secondary stopes that will be undercut by sill extraction from below. Table 16-3 tabulates the total projected paste fill volumes over the LOM by strength requirement and by binder dosage.
Table 16-3: | LOM Paste Fill Requirements |
Density | ||||||
LOM | 28-day | Binder | Dry | Mass Dry | Binder | |
Quantity | Strength | Dosage | Paste | Paste | Required | |
Paste Fill Type | (m3) | (kPa) | (%) | (t/m3) | (t) | (t) |
High-strength Paste Fill | 385,896 | 800 | 11.8% | 1.11 | 428,345 | 45,420 |
Regular Paste Fill | 2,468,555 | 300 | 6.8% | 1.11 | 2,740,096 | 169,047 |
Low-strength Paste Fill | 1,634,554 | 100 | 4.6% | 1.11 | 1,814,355 | 75,206 |
Total | 4,489,005 | - | - | - | 4,982,795 | 289,672 |
16.3.5 | Paste Backfill Test Work |
Pretivm engaged AMC Mining Consultants (Canada) Ltd. (AMC) to undertake the first stage of a high-level study on the suitability of using mill flotation tailings for paste fill at the Brucejack Gold Mine (AMC 2015). The results showed a higher-then-expected cement requirement for the range of determined paste fill strengths. The density of the paste fill was low and resulting strengths required higher-than-expected cement content to achieve the target strengths.
Pretivm also engaged AMC to undertake second-stage laboratory testing. Stage 2 test work aimed to identify other classes of binders that would achieve target strengths at lower dosing rates (AMC 2018). In particular, the Stage 2 test work investigated the use of blended blast furnace slag and fly-ash with cement as possibly better paste mix recipes.
The Stage 2 test work program included:
■ | material characterization tests in areas such as specific gravity and particle size distribution |
■ | determination of paste fill density at a yield stress of 250 Pa as the benchmark for the paste fill mix |
■ | UCS tests of mixes using General Purpose (GP) cement, slag, and fly-ash blend cements to look at the effect of adding fine-ground iron blast furnace slag and fly-ash to the GP cement binder; two slag blends were tested: MineCem (MC) containing 55% slag and Sunstate Slag Blend (SS) containing 35% slag; medium-size fly-ash (FA) was also used. |
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As shown in Table 16-4, the Brucejack Gold Mine tailings paste fill mixes responded very favourably to the slag-based and fly-ash binders. The test program demonstrated a significant difference in the strength values for the paste fill mix with GP cement compared to the slag-based (MC and SS) and FA mixes. The following differences were noted:
■ | At 6% and 10% addition, consistently using MC binder (slag content 55%) produced a paste fill strength of more than double that of the GP mix. |
■ | At 6% and 10% addition, the SS binder (slag content 35%) consistently increased paste fill strengths by over 50% compared to the GP mix. |
■ | Using FA in the paste fill mixes reflected the expected lower strength gain in the early curing time (14 days) typical of FA mixes. However, the 28-day and final 56-day strengths steadily gained higher strength levels, showing the benefit of the FA in partly replacing the GP cement. |
Table 16-4: | Summary of Stage 2 UCS Results |
Tailings | |||||
Batch | (%) | Cement/Binder | 14 days | 28 days | 56 days |
1 | 94 | 6% GP | 405 | 448 | 565 |
2 | 90 | 10% GP | 875 | 1,038 | 1,204 |
3 | 94 | 6% MC | 909 | 1,145 | 1,428 |
4 | 90 | 10% MC | 2,008 | 2,507 | 2,783 |
5 | 94 | 6% SS | 577 | 738 | 903 |
6 | 90 | 10% SS | 1,525 | 1,831 | 1,920 |
7 | 94 | 3% GP + 3% FA | 340 | 537 | 681 |
8 | 90 | 5% GP + 5% FA | 1,050 | 1,824 | 2,415 |
Stage 3 strength and rheology test work on bulk sample material is currently being completed to update paste recipes and binder dosages for the key strength targets. For this study, AMC is adopting industry standard dosages to achieve the required 28-day strengths, as outlined in Table 16-4.
Pasting operations at the Brucejack Gold Mine commenced in August 2017. AMC developed paste fill recipes for various scenarios to be encountered during stoping, like a requirement for a sill beam or backfilling of a secondary stope. AMC recommended that Pretivm begin pasting operations with increased binder addition (20% higher than recommended recipes) as a contingency while the paste plant and pasting operations overall were being commissioned. During this time, as site-specific, consistent paste quality control data was acquired and analyzed by AMC, the recommended recipes would then be the default recipes moving forward.
16.3.5.1 | Waste Management and Stope Filling |
Waste rock from mine development is generated on an ongoing basis throughout the LOM.
Stopes are filled with development waste wherever possible, with waste additionally hauled to surface for disposal in Brucejack Lake. The waste-backfilled stopes are mainly secondary stopes below the 1,350 m elevation level in the mine. Waste generated before the start of secondary mining is hauled to surface since it is unsuitable for backfilling primary voids without a cementitious binder.
In addition, disused headings in mined-out areas are used for development waste disposal, and an allowance has been made in the waste disposal profile in this respect.
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The disposal of waste rock in underground stopes has the effect of reducing the total void volume requiring paste backfill, and hence reduces the percentage of mill tailings that can be returned to underground. Table 16-5 tabulates the projected volumes of waste to be generated from milled ore and development headings and the destination of these volumes over time. Over the LOM, 62% of development waste and 33% of tailings generated from milled ore will be placed back underground; the balance will be disposed of in Brucejack Lake.
Table 16-5: | LOM Backfilling – Waste Rock and Mill Tailings |
Ore | Total | Waste | Waste Fill | Paste Fill | Tailings | Waste to | |
Tonnes | Tailings | Tonnes | Volume | Volume | Underground | Surface | |
Year | ('000 t) | ('000 t) | ('000 t) | ('000 m3) | ('000 m3) | ('000 t) | ('000 t) |
2019 | 1,235 | 1,167 | 583 | 33 | 349 | 387 | 500 |
2020 | 1,371 | 1,296 | 599 | 107 | 363 | 403 | 333 |
2021 | 1,383 | 1,308 | 475 | 115 | 351 | 390 | 189 |
2022 | 1,386 | 1,314 | 474 | 151 | 319 | 355 | 97 |
2023 | 1,387 | 1,311 | 440 | 153 | 325 | 361 | 57 |
2024 | 1,388 | 1,322 | 385 | 80 | 385 | 428 | 185 |
2025 | 1,388 | 1,318 | 335 | 125 | 328 | 365 | 23 |
2026 | 1,380 | 1,312 | 223 | 85 | 414 | 459 | 11 |
2027 | 1,180 | 1,122 | 140 | 49 | 366 | 407 | 18 |
2028 | 1,180 | 1,120 | 39 | 9 | 409 | 454 | 15 |
2029 | 902 | 857 | 46 | 15 | 304 | 337 | 8 |
2030 | 826 | 785 | 33 | 11 | 292 | 324 | 4 |
2031 | 571 | 537 | 7 | 2 | 203 | 225 | 2 |
2032 | 177 | 165 | 3 | 0 | 81 | 89 | 3 |
Total | 15,754 | 14,934 | 3,781 | 935 | 4,489 | 4,983 | 1,443 |
16.4 | Development and Production Schedule |
16.4.1 | Production Rate |
From the start of commercial production in July 2017, the mine has been operating at a rate of 2,700 t/d. In December 2018, Pretivm received a permit to allow a mining rate increase to 3800 t/d. The updated Measured and Indicated Mineral Reserves supports this increase.
A detailed mine design was subsequently completed for the new Mineral Resource model and scheduled to 3,800 t/d steady state ore production. There is a ramp-up period of identified in the production schedule, which is considered reasonable and achievable with respect to current development plans.
The final production schedule was constrained to reflect realistic mining practices and availability of equipment. The model limits the number of active stopes at any one time to four blasting and mucking, one backfilling, four drilling, and up to seven curing. The average number of active stopes at any one time is 12, with variations from 10 to 16. The number of available stopes could be higher.
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16.4.2 | Sustaining Development |
Development of the Valley of the Kings Zone Upper and Middle blocks alone is insufficient to sustain 3,800 t/d of ore production. The Lower blocks must also be developed as a critical path activity. The following development activities will run in parallel with the Upper block development and mining and will continue until the Lower block begins producing critical stope ore in the third year of activity:
■ | advancement of the Valley of the Kings ramp downward to the 990 m elevation level |
■ | development of the 1,080 m, 1,140 m, and 1,170 m elevation levels |
■ | continuation of VR1 from the 1,140 m elevation level to the 1,080 m elevation level |
■ | excavation of the fresh air raise system from the 1,080 m elevation level to the 990 m elevation level. |
The Valley of the Kings ramp development will advance to the bottom of the mine (990 m elevation level). Levels will continue to be developed and stoping will continue in all four blocks. Development to the West Zone will begin later in the LOM to allow production from the Lower and Upper West Zone blocks. This development will be timed such that the 3,800 t/d mining rate can continue for as long as possible without interruption. Table 16-6 shows the LOM development rates.
Table 16-6: | LOM Development Requirements |
Capital | Operational | Total | ||||
Lateral | Vertical | Ore | Waste | Lateral | Vertical | |
Year | (m) | (m) | (m) | (m) | (m) | (m) |
2019 | 467 | 107 | 1,944 | 8,405 | 10,816 | 107 |
2020 | 321 | 115 | 1,614 | 8,900 | 10,835 | 115 |
2021 | 199 | 90 | 1,577 | 6,684 | 8,460 | 90 |
2022 | 190 | 161 | 1,464 | 6,736 | 8,389 | 161 |
2023 | 906 | 136 | 1,856 | 5,653 | 8,414 | 136 |
2024 | 440 | 88 | 1,644 | 5,178 | 7,262 | 88 |
2025 | 522 | 77 | 2,038 | 4,604 | 7,164 | 77 |
2026 | 644 | 232 | 975 | 2,523 | 4,141 | 232 |
2027 | 46 | 206 | 1,317 | 1,961 | 3,323 | 206 |
2028 | 0 | 0 | 367 | 644 | 1,011 | 0 |
2029 | 0 | 0 | 555 | 768 | 1,322 | 0 |
2030 | 0 | 0 | 373 | 543 | 915 | 0 |
2031 | 0 | 0 | 135 | 114 | 249 | 0 |
2032 | 0 | 0 | 50 | 46 | 96 | 0 |
Total | 3,735 | 1,211 | 15,906 | 52,758 | 72,398 | 1,211 |
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16.4.3 | LOM Production Schedule |
Full 2,700 t/d production was effectively achieved in Year 1 (2017). In Year 3 (2019), the mine will ramp up to 3,800 t/d.
Figure 16-10 illustrates the ramp-up to full production and the phasing of the various blocks.
Figure 16-11 shows the LOM split of production by development and stoping.
Figure 16-10: LOM Production Schedule by Mining Horizon
Figure 16-11: LOM Production Schedule by Activity
Table 16-7 is a summary of projected LOM production tonnes and grade.
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Table 16-7: | LOM Tonnes and Grades |
Ore | Au | Ag | |
Year | (kt) | (g/t) | (g/t) |
2019 | 1,235 | 10.6 | 11.2 |
2020 | 1,371 | 12.0 | 11.3 |
2021 | 1,383 | 13.0 | 11.7 |
2022 | 1,386 | 13.6 | 10.2 |
2023 | 1,387 | 12.3 | 17.5 |
2024 | 1,388 | 13.5 | 20.7 |
2025 | 1,388 | 14.3 | 52.1 |
2026 | 1,380 | 13.9 | 93.7 |
2027 | 1,180 | 12.6 | 85.6 |
2028 | 1,180 | 12.0 | 130.3 |
2029 | 902 | 10.8 | 87.7 |
2030 | 826 | 14.4 | 119.3 |
2031 | 571 | 9.8 | 220.1 |
2032 | 177 | 7.4 | 269.4 |
Total | 15,754 | 12.6 | 58.4 |
16.5 | Geotechnical |
Geotechnical designs and recommendations contained in the 2013 FS (Ireland et al. 2013) are based on the results of site investigations and geotechnical assessments completed by BGC on behalf of Pretivm. The assessments included rock mass characterization tasks, structural geology interpretations, excavation and pillar stability analyses, and ground support design.
Geotechnical site investigations completed to support the 2013 FS assessments included: geotechnical drilling and logging, oriented drill core measurements, borehole televiewer surveys, laboratory testing of rock core samples, and installation of borehole instrumentation to measure groundwater pressures. Geotechnical mapping of the dewatered historic underground workings was completed to provide structural geology information. The geotechnical performance of excavations in the existing mine were also reviewed. The FS site investigations were supplemented by a review of historical reports and inclusion of data collected during previous site investigation programs.
For the 2014 FS update (Ireland et al. 2014), the proposed twin portal had moved approximately 60 m to the west, the elevation of the surface decline intersection with main mine development had risen by approximately 30 m, the infrastructure excavations (crusher, etc.) had moved approximately 250 m to the east, and the mine plan through the Brucejack Fault Zone had been modified. No new rock mechanics site investigations or analysis work was completed for the 2014 FS, although a stope design update and review of geotechnical data collected since the 2013 FS were completed by BGC (2018; 2019b). The effect of the above noted changes on the 2013 FS rock mechanics assessments are noted in the appropriate sections that follow.
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16.5.1 | Rock Mass Properties |
The rock mass of the Brucejack area is divided into eight geotechnical units based on characteristics of the rock mass.
The geotechnical units in the West Zone, in order of increasing competence, are as follows:
■ | The West Zone Fault Zone (WZ FZ) unit includes fault-disturbed rock. This unit is strong (according to the methods of ISRM (1978)) with fair rock RQD (Bieniawski 1976) and close to moderate discontinuity spacing. |
■ | The West Zone Weathered Rock Zone (WZ WRZ) unit includes weathered near-surface rock. It is medium strong with good RQD and moderate discontinuity spacing. |
■ | The West Zone Fresh Rock (WZ FR) unit comprises all remaining rock, which is very strong with excellent RQD and wide discontinuity spacing. |
The geotechnical units in the Valley of the Kings Zone, in order of increasing competence, are as follows:
■ | The Valley of the Kings Fault Zone (VOK FZ) unit includes fault-disturbed rock. The Fault Zone unit includes Brucejack Fault Zone rock and rock from all geologic units. It is strong with good RQD and close discontinuity spacing. |
■ | The Valley of the Kings Weathered Rock Zone (VOK WRZ) unit comprises near-surface weathered rock. This unit is strong with good RQD and close discontinuity spacing. |
■ | Rock mass Valley of the Kings Domain 1 (VOK D1) comprises the Argillite (ARG) geologic unit and is very strong with good RQD and moderate discontinuity spacing. |
■ | Rock mass Valley of the Kings Domain 2 (VOK D2) comprises the Bridge Zone Porphyry (BZP1), Office Porphyry (OFP1) and Silcap geologic units, which are strong with excellent RQD, and moderate discontinuity spacing. |
■ | Rock mass Valley of the Kings Domain 3 (VOK D3) comprises the Volcaniclastics, VSF, S3-Trans, and ANDX geologic units, which are very strong with excellent RQD and wide discontinuity spacing. |
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Table 16-8 summarizes the rock mass parameters used in the design.
Table16-8: | Rock Mass Properties |
Unit | |||||||
UCS(3) | Weight(2) | Erm | |||||
Unit | (MPa) | GSI(1) | (kN/m3) | mi | mb | S | (GPa) |
VOK FZ | 89 | 60 | 26.3 | 12 | 1.110 | 0.0023 | 5.13 |
VOK WRZ | 50 | 63 | 28.6 | 17 | 1.879 | 0.0037 | 0.77 |
VOK D1 | 116 | 72 | 27.2 | 17 | 3.211 | 0.0144 | 9.76 |
VOK D2 | 95 | 70 | 27.1 | 19 | 3.186 | 0.0106 | 9.02 |
VOK D3 | 73 | 85 | 27.3 | 26 | 10.647 | 0.1030 | 14.37 |
WZ FZ | 77 | 57 | 26.3 | 12 | 0.928 | 0.0015 | 4.27 |
WZ WRZ | 37 | 62 | 28.6 | 17 | 1.771 | 0.0032 | 0.73 |
WZ FR | 116 | 85 | 27.3 | 21 | 8.599 | 0.1030 | 16.77 |
Notes: | (1)GSI (Geologic Strength Index) are calculated from median rock mass parameters for each unit, where GSI = RMR ’76. |
(2)Unit weights are based on average results of specific gravity testing when possible. |
(3)UCS = intact unconfined compressive strength. |
The Hoek-Brown failure criteria (mi, mb, s) were estimated assuming a disturbance factor (‘D’) of 0.8 for all units. |
The Hoek-Brown curves were derived using a sigma 3 maximum for a tunnel depth of 650 m. |
16.5.2 | Mine-scale Fault Zones |
The three-dimensional major structures (fault) model developed by Pretivm shows that four large (i.e. mine-scale) fault zones are known to intersect the mining footprint: the Brucejack Fault Zone, the Rainy Fault, the Valley of the Kings Main Fault, and the Upper Thrust Fault.
The Brucejack Fault Zone is a northerly striking anastomosing fault zone located along the western margin of the study area and extends north to the Iskut River Fault. In places the lineament appears to be several sub-vertical to moderately (greater than 60°) dipping fault strands braided together. The zone has normal faulting with variable displacement estimated at 500 to 800 m (ERSi 2010). It is comprised of a core of highly fractured rock with a zone of less fractured, fault-disturbed rock mass on either side. The width of the fault zone varies with depth and along strike from approximately 5 to 40 m. It is considered to be continuous along strike, and dips slightly to the east above the 1,325 m elevation, and dips slightly west below the 1,325 m elevation. For design purposes, the median RQD, joint condition, and point lead index Is50 value (ISRM 1985) are 62%, 16, and 3.5 MPa, respectively, compared to the “excellent” median RQD value (91%) and median Is50 value of 6.5 MPa in the surrounding undisturbed VOK D2 rock mass.
The Rainy Fault is a gently dipping (10 to 30°) south-southwest striking (220 to 240°) fault. It was studied in detail as part of the geotechnical assessment for the underground crusher (BGC 2015). The fault has a thickness ranging between 0.5 and 15 m (average thickness: 2 m), with the thickness appearing to increase with depth. The rock mass within the fault zone is generally very blocky with very poor to poor RQD (less than 50%) and discontinuity spacing less than 0.20 m but varies from relatively unbroken rock to compact silty/clayey gouge zones up to 1.5 m thick. Often the fault zone is comprised of multiple gouge zones separated by more competent zones of very blocky rock mass. Seepage conditions within the zone vary significantly, from dry to dripping.
The Valley of the Kings Main Fault is gently-dipping and south-southwest striking, and was intercepted during the FS drilling program by drillhole DH-BGC12-23 at between approximately 210 to 250 m along hole. The fault zone resulted in locally reduced RQD (between 40 to 80%) and fracture spacing (between 0.06 to 0.50 m) compared to the fresh (unfaulted) rock.
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The Upper Thrust Fault is highest in the stratigraphic sequence of the three known faults in this package of gently-dipping south-southwest striking structures. DH-BGC12-23 also intercepted this fault, and although a small fault structure was logged, it did not cause a significant reduction in rock mass quality.
16.5.3 | Underground Rock Mechanics |
16.5.3.1 | Stope Design Criteria |
For the 2013 FS (Ireland et al. 2013), rock mechanics analyses were completed to estimate achievable spans for the planned mine openings. Stope stability analyses for the observed lower quartile (“conservative”, Q’ = 10) and median (“base case”, Q’ = 40) rock masses were completed. The recommended maximum unsupported hydraulic radii vary from 1.9 to 3.1 for the backs and from 6.2 to 11.0 for the hanging walls, for the conservative and base case designs, respectively. The recommended maximum supported hydraulic radii vary from 4.1 to 5.6 for the backs and from 10.0 to 14.5 for the hanging walls, for the conservative and base case designs, respectively.
Since that time, a stope design update was completed by BGC in 2018, and the geotechnical units and structural domains were reviewed by BGC (2019b). The most recent work by BGC, which compiled and reviewed geotechnical rock mass data collected at Brucejack since the 2013 FS, showed that although the new data suggest the FS design ranges are still valid (with 50% of the rock mass having Q’ >10), the Q’ medians are less than 40, and the higher quality rock may be less common than initially assumed during previous assessments. BGC continues to recommend that the Brucejack Gold Mine review stope designs on a case-by-case/package-by-package basis, particularly if optimized, larger, and less conservative stope dimensions (i.e. greater than “median” designs) are proposed to be implemented in the mine plan.
A preliminary MAP3D numerical model developed during the 2013 FS (Ireland et al. 2013) for the Valley of the Kings Zone showed stress concentration and yielding proximal to the dense stope clusters in the middle of the Valley of the Kings Zone, indicative of potential instability in the stope hanging walls and footwalls. This indicates some potential for increased dilution. If required, cable bolts will be installed into the hanging walls of dense stoping blocks to “tie” the hanging wall together until backfill is placed, to help reduce this dilution. BGC (2019a) advanced the FS modelling in 2019 using RS3 (Rocscience), as part of a geotechnical assessment of secondary stope stability. The results of the modelling supported the FS work, and showed areas within the mine where elevated but not un-manageable stress conditions are anticipated as a result of mining activities. These areas will be monitored as mining progresses, with step-wise increases to ground surveillance and monitoring programs as required. Note that currently, the numerical models are not considered sufficiently calibrated for quantitative design.
16.5.3.2 | Stand-off Distances |
Minimum stand-off distances between excavations of 10 m, 25 m, and 50 m are planned for the raises, ramps, and underground crusher, respectively. The stope stand-off distance from all hanging wall drives is 25 m.
16.5.3.3 | Rib Pillars |
The rib pillars between cross-cuts were designed to be in waste and will not be recovered, but are considered temporary based on the short-term lifespan required for access to a given stope. The minimum recommended pillar width to height ratio for cross-cut rib pillars for the “base case” stope design is 1.1:1.0. If cross-cuts are developed within the weathered zone, the recommended rib pillar width to height ratio is 1.7:1.
The rib pillars between the open stoping blocks are intended to give temporary support to the mining block until the primary stopes are backfilled and the pillar can be recovered in the form of a secondary stope. Using the pillar stability graph method developed by Hudyma (1988) and tributary loading theory, the minimum recommended secondary stope span (rib pillar thickness) to primary stope span for the “base case” stope design is 1:1 for sublevel intervals of 30 m.
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Analysis of the “conservative case” shows that high stresses may develop in the pillar core, and that some spalling and dynamic rockmass damage may be expected. This may result in spalling in 25% of rib pillars, and difficult drilling in approximately 25% of secondary stopes. If stopes are developed within the weathered zone, the minimum recommended secondary stope span (rib pillar thickness) to primary stope span is 1.5:1.
AMC estimated ore recovery in the weathered zone to be 75% in anticipation of stress-induced mining difficulties. Furthermore, the operational expenditure was escalated for ore in the weathered zone in consideration of the increased ground support requirements.
Analysis of the weathered zone stopes shows low confinement; ground support including resin-grouted rebar, mesh-reinforced shotcrete, and straps may be required to confine the pillar rock mass and prevent unravelling. Many of the near-surface stopes will actually extend below the weathered zone into the fresh rock, which will reduce the potential for rib pillar instability.
16.5.3.4 | Sill Pillars |
The current design sill pillar thickness is 30 m. The numerical modelling analysis shows some relaxation in larger stope hanging walls, and stress concentrations in sill pillars within areas of the mine with denser stoping. The model shows that the bottom-up sequence concentrates stress in both Valley of the Kings Zone sill pillars. Yielding is likely to occur prior to recovering the entire sill pillar, and therefore achievable sill pillar recovery may be less than 100%. The West Zone sill pillar is interpreted to be stable except for stress concentration in the sill pillar abutments. Stress concentration in pillar abutments is common in mines using centre-out sequencing, and does not necessarily indicate stability problems prior to full extraction of the sill pillar.
16.5.3.5 | Ground Support Requirements |
The structural stability of the excavations was analyzed using an empirical design chart after Grimstad and Barton (1993) and Unwedge©(Rocscience 2003) to develop minimum ground support recommendations. Ground support analyses for primary (permanent “man-entry”) and secondary (temporary “development”) headings were conducted in each structural domain. Ground support recommendations are provided in Table 16-9.
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Table 16-9: | Ground Support Recommendations |
Mesh | |||||||
Cross Section | Ground Support | Length | Spacing | Estimate | Additional | ||
Opening Type | (Width by Height, m) | Type | (m) | (m) | (%) | Notes | |
Main Access Decline, Ramps, and Other Haulage Routes | 6 by 5.5 | Back Walls | Fully-grouted #7 resin rebar Fully-grouted #7 resin rebar | 2.4 2.4 | 1.8 by 1.8 1.8 by 1.8 | 100 70 | Welded wire mesh will be installed in the back and extended to within 1.5 to 3.0 m of sill elevation down the walls, lagging minimum one round behind only. All active faces to be screened 1.2 m down from the back. |
Level Development | 5.5 by 5.5 | Back Walls | Fully-grouted #7 resin rebar Fully-grouted #7 resin rebar | 2.4 2.4 | 1.8 by 1.8 1.8 by 1.8 | 100 70 | Welded wire mesh will be installed in the back and extended to within 1.5 to 3.0 m of sill elevation down the walls, lagging minimum one round behind only. All active faces to be screened 1.2 m down from back. |
Intersections | Includes 6 by 5, 5 by 5, three-way, four-way, and herringbone layouts | Back | Pre-support: Fully- grouted #7 resin rebar Long support: Coupled fully-grouted #7 resin rebar or double strand 0.7 inch bulbed cable bolts Fully-grouted #7 resin rebar | 2.4 5.0 2.4 | 1.8 by 1.8 2.4 by 2.4 1.8 by 1.8 | 100 100 70 | Welded wire mesh should be installed on the back and upper portion of each wall for all intersections with an effective span greater than 6 m. Strap consumption estimate: 25% of pillars; three straps per pillar. |
Full-width Undercuts | 5 by 5 pilot | Back Back Walls | Pre-support: SS39 Split- Set Long support: Long support: Single strand 0.7 inch bulbed cable bolts, 1.0 m bulb spacing or 16 ft connectable Swellex - | 2.4 6.0 - | 1.8 by 1.8 2.4 by 2.4 - | 100 100 20 | All support must be installed prior to slashing. |
Full-width Undercuts (continued) | 15 m wide full undercut (primary stopes) (post-slash) | Back Back | SS39 Split-Set Long support: Single strand 0.7 inch bulbed cable bolts, 1.0 m bulb spacing, or 16 ft connectable Swellex as required | 2.4 6.0 | 1.8 by 1.8 2.4 by 2.4 | 100 | All support except for shotcrete must be installed as each lateral slash is developed (prior to full width exposure). Long support design to be modified as required if persistent geologic structure intersects the stope. |
Raises | 3 by 3 | Walls All | SS39 Split-Set Fully-grouted #7 resin rebar | 2.4 1.2 | 1.8 by 1.8 0.8 by 0.8 | 25 50 | Staggered spacing. Reduced support may be feasible if man- access is not permitted. |
Notes: | Design factor of safety is 1.3. |
Wall bolts and screen must extend down to within 1.5 m of sill (floor), with wall screen lagging no more than one round behind current face in all cases during development. |
Screen to be extended one screen width down from the back at all active headings for further loose retention at the face. |
Surface support is installed when excavation intersects relatively poorer ground, faults, more persistent joints or narrower joint spacing, soft joint walls, groundwater seepage points, or “dead” sounding difficult to scale material. |
Use mesh estimate percentage for shotcrete cost estimating if shotcrete is preferred surface support. |
Mesh and shotcrete will only be used in the exhaust raises if ground conditions require it, as there are no manways in these raises. The fresh air/scapeway raises will be bolted. |
All estimates are provided for cost estimating purposes only. |
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16.5.3.6 | Full Width Undercuts |
The mine plan incorporates full-width undercutting of select primary stopes. Ground support recommendations are provided in Table 16-10. Primary stopes will be tight- filled as best as possible.
16.5.3.7 | Mining Through Mine-scale Fault Zones |
All developments through large (mine-scale) fault zones will require support with fully grouted #7 resin grouted rebar bolts on a 1.2 m square pattern, full coverage (sill to sill) of welded wire mesh, and 50 mm of fiber-reinforced shotcrete. Long support (cable bolts or connectable Swellex) will be installed as required.
Stopes will be excavated in isolation and backfilled prior to any other production openings within the fault zone. The rock mass within the fault zone is not competent enough to form adequate rib or sill pillar strength between stopes. In each case, stopes will be constrained to either the host or fault disturbed rock. Excavations bridging the boundary will have unplanned dilution along the contact.
The preliminary recommendation for maximum supported back hydraulic radii is 2.5 (10 m by 10 m), and maximum unsupported hanging wall hydraulic radii is 3.75 (10 m by 30 m), for stopes within large fault zones. Ground support in the back of the stopes will consist of cable bolt support consisting of 6 m single or double strand bulbed cable bolts on a 2.5 m square spacing.
16.5.3.8 | Surface Raise Locations |
The finalized raise locations avoid fault-disturbed rock and minimize intersection of weathered rock. The recommended pillar thickness between a raise and nearby development or production openings, including the decline access ramp, is 10 m.
16.5.3.9 | Underground Crusher, Portal, and Other Mine Infrastructure |
The underground crusher, portal, and other mine infrastructure have been excavated as part of ongoing development of the mine. Ground support recommendations for future mine infrastructure developments are summarized in Table 16-10.
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Table 16-10: | Mine Infrastructure Excavations – Ground Support Recommendations |
Dimension | |||||
(height x | |||||
width | Trend/ | Design | |||
(along trend) | Plunge | Factor | |||
by length) | of | of | Life | ||
Area | (m) | Excavation | Safety | Span(1) | Support |
Cap Magazine | 3.05 by 6.1 by 3.05 | 152/21 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). |
Electricians and Millwrights Shop | 5.5 by 16.2 by 5.5 | 270/01 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). |
Fuel and Lube Station | 4.5 by 35 by 8.5 | 243/06 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). Cable bolts: Back: 5.0 m length, bulbed strand, 2.5 m square spacing |
Service Bay, Maintenance Bay, and Tire Bay | 11.5 by 42 by 10.0 | 005/00 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). Cable bolts: Walls: 5.0 m length, bulbed strand, 2.5 m square spacing Back: 5.0 m length, bulbed strand, 2.5 m square spacing |
Powder Magazine | 7.1 by 14.1 by 6.4 | 152/01 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). Cable bolts: Walls: 5.0 m length, bulbed strand, 2.5 m square spacing Back: 5.0 m length, bulbed strand, 2.5 m square spacing |
Refuge Station and Offices | 4.6 by 15 by 5.2 | 062/01 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2 inch SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). |
Warehouse | 5.5 by 27 by 5.5 | 270/01 | 2 | LOM | Galvanized, resin-grouted rebar (or equivalent); 1.8 m length; 1.75 m square spacing. Welded wire mesh, 100% coverage on back and walls, coated with minimum 2” SFRS (shotcrete only required if rehab will not be practical due to installed infrastructure). |
Notes: | (1)LOM assumed 20 to 25 years; SFRS – steel fiber reinforced shotcrete. |
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16.5.3.10 | Crown Pillar |
To maximize crown pillar recovery, the minimum crown pillar thickness for the West Zone and the Valley of the Kings Zone is 15 m, with a maximum stope span of 10 m for all stopes immediately below the crown pillar. As the recommended maximum span is narrower than the transverse width of the mineralized zones, transverse stopes immediately below the crown will be tight-filled as much as practicable to reduce the potential for crown pillar collapse. The crown pillar will be supported with 5.0 m long single strand bulbed cable bolts on 2.5 m spacing.
16.6 | Mobile Equipment Requirements |
16.6.1 | Production Phase |
The mining contractor supplies the bulk of the heavy equipment, with the exception of supplemental long-hole drills for production and sampling and some auxiliary vehicles. Table 16-11 lists the required equipment for development, stoping, and support activities.
Table 16-11: | Major Underground Development and Production Equipment List |
Total Number of | |
Description | Units Required |
6 yd Scoop | 1 |
8 yd Scoop | 5 |
10 yd Scoop | 3 |
30 t Trucks | 10 |
Development Jumbos | 3 |
Long-hole Drills | 5 |
RC Drills | 2 |
Bolters | 5 |
Emulsion Carrier | 2 |
Face Emulsion Loader | 2 |
Bulk Emulsion Loader/Carrier (LH) | 1 |
Shotcrete Machine | 1 |
Transmixer | 2 |
16.6.1.1 | Jumbos |
Development advance (in ore and waste) will average approximately 500 m/mo during the first 12 years of production. Two-boom units, capable of drilling holes 3.6 m deep, have been selected by the contractor to perform the work. Data from the first 18 months of operations show the jumbos averaged 780 m/mo, or approximately 390 m/mo per unit, exceeding the projected performance from the 2014 FS (Ireland et al. 2014). There is a single-boom jumbo on site that is used as a back up to the two-booms and for utility work where the two-boom is inefficient in smaller headings. The single boom is used sparingly.
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16.6.1.2 | LHDs |
On site there are three, 10 yd LHDs and five, 8 yd LHDs for production and development. This fleet is sufficient for the 3,800 t/d operation of the mine.
16.6.1.3 | Haulage Trucks |
The mine contractor has ten, 30 t trucks on site to support the development required to maintain current production. Later when the majority of ore hauled to the crusher is from the lower levels or the West Zone, one additional truck maybe required to support operations. The need for additional haulage capacity may be counteracted by the reduction of development needs at that same time, depending on the LOM schedule.
16.6.1.4 | Bolters |
The ground control management plan for pattern bolting development headings and stope backs utilizes bolters equipped for the installation of rebar and split set bolts. Currently, three Maclean bolters and a Robolter are on site, with one additional Maclean bolter added to the fleet for the 3800 t/d increase. The bolters are also used to assist in the installation of cable bolts.
16.6.1.5 | Long-hole Drills |
Production drilling is performed with top and bottom hammer drills. Slot raises are drilled with a V30 bit to allow void space in the slot. On site there are currently four drills; one additional drill will be added to the fleet for production drilling and an RC drill will be added for sampling.
16.6.1.6 | Explosive Loaders |
One face charger is on site and another one will be required for the 3,800 t/d production increase for development loading. For a period, there will be up to 9 rounds per day that will require loading. Each unit has pumps for face charging with emulsion. In addition to the face charges, there is one long-hole loading unit available for uphole and downhole emulsion loading in the stopes.
16.6.1.7 | Shotcrete Sprayers |
It was anticipated that 5 to 10% of development would require shotcrete; however, to date, shotcrete has primarily been required in areas near the Rainy Fault. Shotcrete is also required for paste fill exposures in stope development and barricade construction for backfilling and ventilation bulkheads. One unit is on site and provides adequate capacity for this activity. Wet, non-fiber-reinforced shotcrete is used as the standard.
16.6.1.8 | Transmixers |
Shotcrete is delivered from the underground batch plant. The contractor has two transmixers at the mine to support shotcrete operations on site. These are sufficient for the needs of the mine.
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16.6.2 | Support Equipment |
Table 16-12 presents the complete list of support equipment.
Table 16-12: | Support Equipment List |
Total Number of | |
Description | Units Required |
MT Truck | 1 |
Skid Steer | 1 |
Telehandler | 4 |
Shotcrete Machine | 1 |
Transmixer | 2 |
Boom Truck | 2 |
Scissorlift | 3 |
Kabota Tractor | 2 |
Jeffery Flatdeck/Boomtruck | 1 |
Jeffery Lube Truck | 1 |
Kabota RTV Personnel Carrier | 15 |
Four-man Jeffery Mancarrier Personnel Carrier | 1 |
Ten-person Jeffery Mancarrier Personnel Carrier | 3 |
16.6.2.1 | Personnel Carriers |
Personnel are transported in mancarriers. There are four carriers and 15 Kobotas to transport personnel through the mine. Technical services and Pretivm supervision use underground Toyota trucks of various configurations to access and work in the mine.
16.6.2.2 | Scissor Lift Trucks |
The contractor has three scissor lift trucks to support development and occasionally assist Pretivm maintenance crews.
16.6.2.3 | Lubrication Truck |
There is a lubrication truck on site to service underground equipment. The lubrication truck will be required to fuel and lubricate all equipment that is not likely to return to the shop area at frequent intervals. Down time can be reduced by keeping equipment near the working headings. This will also help improve traffic flow on the ramp. This equipment will include LHDs, jumbos, long-hole drills, and bolters. The service truck will travel between these equipment pieces to perform daily servicing.
16.6.2.4 | Boom Trucks |
A boom truck will be required for daily transport of materials from surface to underground and to facilitate loading and unloading. Material stockpiles will be set up throughout the mine for supplies such as rock bolts, screen, resin, vent duct, etc. One unit will provide adequate capacity.
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16.6.2.5 | Explosives Vehicles |
Explosives consumption is roughly 6.0 t/d of bulk emulsion per day and is delivered to the mine in three custom-made ISO-standard tanks, each with a capacity of 17,500 L.
A purpose-built truck transports the full tanks to the emulsion bays. Emulsion pumps are used to transfer emulsion from the full 17,500 L tank to 20,000 L ISO tanks in the emulsion bay. Consumption averages three ISO tanks per week. All other explosives are transported to the cap and powder magazines by the explosives handling truck. Approximately 272 to 610 caps and primers are required daily for development, depending on advance rates, with 60 caps and primers per day on average required for the long-hole production blasting.
16.6.2.6 | Water Truck |
A water truck will be on site to facilitate mine wall washing on an ongoing basis.
16.6.2.7 | Tractors, Telehandlers and Utility Vehicles |
Tractors are used for nipping materials and general transport through the mine. All tractors are equipped with a cargo/man carrying compartment in the back. Telehandlers are used for nipping materials and general transportation throughout the mine and are also capable of being fitted with man baskets for installing or maintenance of the services which are out of reach from the ground.
Utility vehicles are used by personnel for quick transport between headings and will be the preferred mode of transport for supervision and technical support staff.
The following crews will be issued utility vehicles for use during their shifts:
■ | development blasters |
■ | backfill crew |
■ | mechanics |
■ | electricians |
■ | production blasters |
■ | diamond drillers |
■ | warehouse |
■ | managers/shifters and technical support staff. |
16.7 | Ventilation |
The ventilation system was designed to meet the requirement of the Health, Safety and Reclamation Code for Mines in British Columbia (2008) (HSRCM), which requires a minimum of 0.06 m3/s of ventilating air for each kilowatt of power of diesel-powered equipment operating. The design is based on a “push” configuration, with permanent surface fans located at the portal of the twin declines.
The mining areas are supplied with fresh air from a connection to the twin declines and each area has at least one exhaust return-air raise (RAR) to surface.
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The underground crusher and workshop have a dedicated RAR to prevent the introduction of dust and other contaminants into production areas. The volume of air flowing through the crusher and workshop areas is controlled with a combination of fans and regulation.
Figure 16-12 shows an isometric view of the Brucejack Gold Mine ventilation system.
Figure 16-12: Brucejack Gold Mine Ventilation System (Looking West)
Source: | Pretivm (2019) |
16.7.1 | Design Criteria |
The ventilation system design has drawn information from the HSRCM. As stated in Part 4 of the HSRCM, Section 4.6.1: “a minimum of 0.06 m3/s of ventilating air for each kilowatt of power of the diesel-powered equipment operating shall be circulated by mechanical means through every workplace where diesel-powered equipment is operating”.
A diesel engine exhaust emissions dilution rate of 0.06 m3/s/kW is used in the ventilation system design.
16.7.2 | Total Airflow Requirements |
Total airflow requirements were determined based on the diesel equipment fleet and fixed facilities required to support steady state production and development activities. An airflow allowance was also determined for leakage and balancing inefficiencies.
The total airflow requirements for the Brucejack Gold Mine are:
■ | diesel equipment –272 m3/s |
■ | fixed facilities –55 m3/s |
■ | leakage and balancing (10%) –33 m3/s |
■ | total –360 m3/s. |
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16.7.3 | Auxiliary Ventilation |
Work areas in the mine not supplied with a split of fresh air are ventilated using auxiliary systems. The most effective means for providing airflow to areas without primary supply is typically with small diameter (up to 1,400 mm) axial fans combined with low leakage and flexible ducting.
16.7.3.1 | Development Ventilation |
During access and level development, distances up to 800 m are ventilated using auxiliary systems. The peak auxiliary airflow for development activity is required to dilute the emissions of one 30 t truck and one 12.5 t loader, amounting to 34 m³/s of auxiliary airflow.
Modelling indicates that a 150 kW fan with 1,500 mm in diameter ducting will supply 34 m3/s up to a distance of 850 m. This arrangement will allow for adequate overhead clearance for a fully-loaded 30 t truck.
16.7.3.2 | Drawpoint Ventilation |
An allowance of 18 m3/s was made for each active drawpoint for dust, blast fume, and diesel exhaust clearance. Modelling indicates that a single-stage 55 kW fan, with 1,200 mm diameter low-resistance, low-leakage ducting will supply the required airflow to a distance of at least 400 m.
Figure 16-13 shows a ventilation configuration for a typical production level.
Figure 16-13: Typical Production Level
Source: | Ireland et al (2014) |
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16.7.3.3 | Ventilation Modelling |
A ventilation model was developed (using Ventsim™) for the Brucejack Gold Mine for three primary purposes:
■ | to validate the operability of the ventilation circuit ensuring airflow can be provided to all the required areas |
■ | to ensure compliance with design criteria |
■ | to determine fan duties and energy requirements. |
Peak primary fan duties will occur at full production in conjunction with maximum development activities in the lowest levels of each ventilation district.
16.7.4 | Permanent Primary Fans |
Over the LOM, there will be a multitude of settings for the ventilation circuit, depending on the type of activities and their location throughout the mine. The modelled circuit reflects the peak primary fan duties that could be reasonably expected.
Table 16-13 summarizes the primary fan requirements.
Table 16-13: | Primary Fan Specifications |
Description | Specification |
Duty | Two each at 180 m3/s, at 1,200 Pa |
Fan Diameter | 2.84 m |
Type | Horizontal mount axial mine fan |
Configuration | Two forcing fans, each connected with ducting to the West Zone decline and conveyor decline |
Voltage | 4,160 V |
Fan Motor | 600 kW to 710 rpm, VFD capability |
16.7.5 | Mine Air Heating |
All intake air entering the mine is heated for the following reasons:
■ | protect the health and safety of personnel working or travelling in intake airways |
■ | prevent the freezing of service water and discharge lines |
■ | ensure reliable operation of conveying and other mechanical equipment in the decline |
■ | maintain ice-free and safely trafficable roadways |
■ | prevent rock surface (or shotcrete lining) expansion/contraction damage from freezing and thawing of rock joints in the upper parts of the intake airways. |
■ | prevent ice build-up in airways that would potentially lead to unsafe conditions. |
Discussion on the use of electric and propane mine air heating can be found in Section 16.8.13.
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16.7.6 | Conveyor Decline |
The conveyor decline is the main mine intake with dimensions of 6.0 m wide by 6.5 m high. Care is taken to ensure that the air speed in the conveyor decline is not too high to prevent the uptake of dust into the intake mine air.
Given that the conveyor is located in a primary air intake, the risk of the conveyor catching fire is also managed. The design includes the following:
■ | fire retardant belt |
■ | fire retardant grease and lubricants |
■ | ventilation controls to isolate the air in the conveyor decline in the event of a fire |
■ | regular inspection of the conveyor declines during operation in order to detect the development of faulty rollers or belt misalignment. |
In the unlikely event of a conveyor belt fire, fire doors placed in key areas would close and smoke would flow directly to the workshop/crusher exhaust raise. Figure 16-14 shows the isolation of conveyor fire contaminants from the ventilation circuit.
Figure 16-14: Conveyor Fire Isolation
Source: | Pretivm (2019) |
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16.7.7 | Emergency Preparedness |
In developing the ventilation strategy for the Brucejack Gold Mine, consideration was given to the potential for mine emergencies. As such, the following criteria was established:
■ | In general, ramps are in fresh air once developed. |
■ | On sublevels, escapeways are either to a ramp or to the escape ladderway. |
■ | The escape ladderways are located in the fresh air raises which were developed alongside the ramps. |
■ | In each ramp, escape may either be up the ramp or down the ramp to a safe area. |
■ | A permanent 40-person refuge station has been established at the 1,335 m elevation at the junction of the decline and incline of the Valley of the Kings Zone. |
■ | Other refuge chambers are portable for flexibility of location at the most appropriate points in the mine. |
■ | While the primary means of communication is by radio, a stench system is in place for introduction of ethyl mercaptan into both portals concurrently in the event of fire. |
■ | Fire doors are located in accordance with legislated requirements and to isolate areas of high fire potential to ensure noxious gases are not distributed through the mine workings. |
There are a variety of incidents that would trigger the emergency response plan and/or evacuation plan. Such events may be fire, rock fall, injured personnel, or major ventilation equipment breakdown. Emergency coordination occurs from the control room where all information and communications can be monitored.
The emergency response procedures incorporate trained on-site mine rescue teams made up of a cross section of the workforce and staff. These teams are trained in administration of first aid and firefighting procedures. As this site is remote, a first-aid facility run by a trained person, stocked with sufficient supplies, and provisions for an air ambulance landing pad have been taken into consideration.
For the two surface portals, both of which are supplied with fresh air, the West Zone portal is considered the primary escape and the conveyor portal the secondary escape.
For the production stoping blocks, a ladder-way is installed in each of the raises located next to main ramps. The raises are sized to afford easy passageway.
A static refuge station is established within the shop complex to service both the West Zone and the Valley of the Kings Zone. It is required to provide refuge for 40 persons during an emergency. This refuge station is designed to function independent of compressed air and provide refuge for personnel working predominantly in the workshop/crusher/mine offices area. In review of crew numbers during the LOM, it is estimated that the maximum number of personnel underground working during any shift will be 111; a typical underground workforce will be 580. Roughly 16 people work in the workshop/crusher area.
The remaining personnel working underground, namely the production development and service crews, are provided refuge by means of four, 16-person and one, 12-person mobile self-sufficient rescue chambers. These are supplied with compressed air from surface, with appropriate provisions for safe refuge. They are located in areas where a secondary egress is not, or has not yet been established and are sited relative to the active working areas in order to be within the average walking pace duration of a personal self-rescuer device. The MineARC system provides a supply of air as well as robust back-up systems.
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An automatic stench gas warning system is installed on the supply side of the surface vehicle portal and conveyor portal. When fired, this system will release stench gas into the main fresh air system allowing the gas to permeate rapidly throughout the mine workings. Once stench gas is released, underground mine personnel would report immediately to the nearest mine refuge station or surface, whichever is closer.
The primary purposes of fire doors are to prevent noxious gases from reaching workers should they be trapped underground and to prevent fire from spreading as much as possible.
Fire doors will isolate the conveyor decline in the event of fire. Portal doors are designed to meet fire door criteria.
16.8 | Underground Infrastructure |
16.8.1 | Mine Dewatering |
Mine dewatering is designed to accommodate groundwater inflows from the Valley of the Kings Zone workings, the West Zone workings, and inflows from drill and other operating equipment. Total inflows were estimated to be approximately 100 L/s (including service water); however, to accommodate for uncertainty in the water inflow model, the design capacity for the pumping system is based on maximum inflows of 139 L/s.
Brucejack Gold Mine dewatering is handled by a combination of submersible and horizontal centrifugal pumps located throughout the West Zone and Valley of the Kings Zone working levels. The pumps handle ground inflow and send drill water via multiple 30 m lifts throughout the mine.
The main sump consists of a single 30 m by 6 m wide sump with an outlet connected to the centrifugal pump system. The flow of underground water with slimes is pumped via four centrifugal pumps (two running, two backup) to the process plant on surface via a dedicated line up the Valley of the Kings conveyor way. Currently, there are sumps to the 1,110 m elevation level, with the remainder of sumps created as development advances.
To minimize up-front capital, pump procurement is staged such that pumps only arrive as their assigned sumps are excavated. Figure 16-15 is a line diagram of the current dewatering system.
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Figure 16-15: Dewatering Plan
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16.8.2 | Solids and Slimes Handling |
Solids and slimes entrained in water are pumped through the dewatering system to the main sump located at the 1,290 m elevation level. This main sump is described in Section 16.8.1.
16.8.3 | Materials Handling |
The crusher is located at the 1,300 m elevation level of the mine close to the Valley of the Kings Zone. The tipple for the ROM bin is located at the 1,335 m elevation level.
ROM material is transported underground by truck from the West Zone and the Valley of the Kings Zone and is preferentially dumped onto the ROM bin grizzly. If the ROM bin is full, or for other reasons the trucks cannot dump into the ROM bin, the trucks will dump into remucks near the ROM bin location. Material stockpiled in the remucks will be re-handled and deposited onto the grizzly by a LHD. At the grizzly, material smaller than 400 mm falls through to the ore bin and larger material is broken down by a hydraulic rock breaker stationed above the grizzly screen. Figure 16-16 shows a sectional projection through the coarse ore bin with the rock breaker and scalping grizzly.
Figure 16-16: Tipple and Ore Bin Sectional Projection
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The 750 t capacity ore bin feeds material down through a hopper at the bottom of the bin to a vibratory feeder. This vibratory feeder transports the ROM material to a jaw crusher and the crusher reduces the material down to 120 mm or finer in size and drops this product down the fines chute to the crusher belt conveyor. Figure 16-17 shows an isometric view of the crusher feed and crusher.
Figure 16-17: Crusher Feed and Crusher
The 1 m wide belting on the crusher conveyor carries material at a rate of approximately 225 t/h from the crushing area to the intermediate conveyor at a speed of 1 m/s. The ore on the crusher conveyor moves past a magnet that removes any tramp iron, depositing this iron into a waiting bin.
The intermediate conveyor also moves at a rate of 1 m/s, transporting the ore up the intermediate decline tunnel to the main conveyor. The main conveyor exits the decline tunnel into the portal structure. The ore is dropped onto the mill feed conveyor, which exits the portal structure and carries the ore to the mill through an enclosed, heated, rectangular gallery.
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16.8.4 | Power Requirements and Electrical Distribution |
BC Hydro indicated that the total electric power supply available for the Brucejack Gold Mine site is limited to a connected load of 20 MW. The maximum underground connected load to support full production and development activities is approximately 9 MW, inclusive of ventilation and heating.
Considering the other key consumers of mine power such as the mill and paste plant, the power available for mine air heating is limited to 4 MW. As the mine air heaters will at times require approximately 16 MW of power, a propane direct-fired system makes up the remaining heating requirement.
Figure 16-18 shows the growth of the power requirements over the LOM in relation to ore production. Ventilation and heating, mobile equipment, and dewatering are the main consumers of power. The maximum running load is estimated to be 4.8 MW and will occur when full production levels are achieved. As the mine is developed deeper, the dewatering power demand will increase due to a higher lifting head and increased inflows. As development activity and production decrease, the power requirements will also reduce.
Figure 16-18: Underground Power Requirement Profile
Electrical power is supplied to the mine three ways:
■ | through the Valley of The Kings portal into the underground electrical substation service (ESS) comprised of two, 500 MCM cables serviced at 4.16 kV |
■ | through the West Zone portal from the E4C e-house comprised of one, 500 MCM cable serviced at 4.16 kV |
■ | through a borehole from surface to the lower mine comprised of one, 500 MCM cable serviced at 4.16 kV. |
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The E4C e-house, which supplies power to the underground workings, is comprised of one 3,000 A breaker that is fed from the mill to supply transmission line power to the E4C bus. The E4C bus has a 3,000 A tie-breaker to facilitate splitting the bus if necessary. There are also additional loads that feed off the E4C e-house such as:
■ | underground ventilation fan house |
■ | camp services |
■ | underground workings through the West Zone portal |
■ | underground supply through a borehole. |
The system is comprised of two zig-zag transformers that supply a neutral grounding resistor on either side of the tie-breaker. Only one is on at any given time to supply the system with a ground reference. The E4C also has the breakers that tie the two 1,450 kW generators, six 1,850 kW generators, and transformer that feeds the bus via four 600 V generators.
The underground system is distributed via 4.16/0.6 kV portable transformers. The transformers are fed through load break switches which enable the transformers to be de-energized for maintenance purposes.
The additional feeds to the underground run via the West Zone portal, the Valley of the Kings portal and through a borehole fed via the E4C e-house. All the transformers are distributed as per the above configuration. These transformers feed mine development, pumps, fans, lights and all electrical workings underground.
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Figure 16-19 and Figure 16-20 show single-line electrical diagrams for the underground mine.
Figure 16-19: West Zone Portal Underground Single-line Diagram
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Figure 16-20: Borehole Underground Single-line Diagram
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16.8.5 | Compressed Air |
Compressed air is supplied by two compressors located near the West Zone portal and by three compressors spread through the Brucejack Gold Mine to reduce line loss in the system.
The in-the-hole drilling equipment has portable compressors close to the drill to meet their elevated pressure requirements.
16.8.6 | Service Water Supply |
Service water for drilling and dust control is supplied via a 100 mm (4 inch) steel line at the Valley of the Kings portal. The line continues through the Valley of the Kings decline ramp to the supply sump. The water supply sump is located at the 1,320 m elevation level in the West Zone area along the West Zone access. From this sump, the mine is supplied service water from which the pressure reducing valves (PRV) will be supplied at the 1,320 m, 1,230 m, 1,140 m and 1,050 m levels to reduce the supply pressure below 689 kPa (100 psig). Near the 1,380 m and 1,440 m elevation levels, a booster pump station is installed to supply operating pressure for the upper portion of the Valley of the Kings Zone.
Over the last year, the process water requirements for all the mine equipment jumbos, long-hole drills, bolters, diamond drills, and other equipment was approximately 1000 m3/d for development and stoping.
Figure 16-21 is a schematic of the main water distribution system.
Figure 16-21: Mine Service Water Distribution Schematic
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16.8.7 | Fueling and Lubrication |
Daily fuel consumption is estimated to be approximately 5,500 L. Currently, an underground fuel bay has not been excavated and facilities have not been installed. Large mine equipment haul trucks, LHDs, and vehicles that come to surface regularly fuel up on surface. Other equipment such as bolters, jumbos, and scissor decks are fueled by a lube truck. An underground fuel bay may be installed in the future.
16.8.8 | Workshop and Stores |
The main maintenance area is located on surface (covered in Section 18.0 of this report). All major scheduled planned maintenance and rebuilds take place in the surface shop. A smaller facility with two service bays, a warehouse, and a small office space is located along the West Zone access to the Valley of the Kings Zone. The service bays are located underground to complete low-level maintenance such as lubrication and small repairs. The service bays have finished concrete floors, tire storage, and lube storage.
The service area is equipped with a stationary compressor and airlines to power air tools and provide compressed air as needed. A welding plug is also sited in this area.
Figure 16-22 shows the layout of the underground equipment service facility.
Figure 16-22: Underground Equipment Service Facility
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16.8.9 | Explosives Magazine |
The entrance to the explosives magazine has rollup doors and man doors to allow access from both ends of the facility. Two bays provide storage of bulk emulsions, each containing one 20,000 L storage tank and a storage area. A powder bay is designated for the storage of all other explosive products (other than the bulk emulsion and the detonators) on wooden shelves. A fourth bay is designated for the storage of detonators on wooden shelves. A concrete wall with a steel door separates this bay from the rest of the mine works.
Figure 16-23 shows the underground magazine layout.
Figure 16-23: Bulk Emulsion/Powder Magazine Storage Plan
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Currently the bulk emulsion is transported by the explosives supplier directly from the manufacturing plant to the KM 48 explosive magazine/transfer in an ISO container containing ten 1,500 kg totes. The ISO container is then brought up to the Brucejack Gold Mine site, unloaded by the mining contractor, and the totes are transported underground to the emulsion storage area.
In the future, bulk emulsion will be transported by the explosives supplier directly from the manufacturing plant to the KM 48 explosive magazine/transfer. Each shipment will be delivered via transport trailer with one custom made 17 t (17,500 L) ISO tank per load. The ISO tank trailer will be transferred to the Brucejack Gold Mine site immediately upon arrival. Once the full ISO tank is offloaded from the transport trailer onto the special built emulsion hauler, the hauler will take the ISO tank to the emulsion storage area, where the emulsion will be pumped out of the tank into one of the two installed tanks. Once emptied, the ISO tank will be brought to surface, reloaded onto the surface transport trailer, and taken to the KM48 magazine area where it will wait for the next load to come in and the transport truck to take it to the manufacturer’s facility for refilling.
16.8.10 | Refuge Stations |
A refuge station (Figure 16-24) is located between the decline and incline drifts at the Valley of the Kings Zone. The station accommodates 40 people and is equipped with an airlock entrance, a battery back-up electrical system, an air conditioning unit, a carbon dioxide/carbon monoxide scrubbing unit, cache of oxygen-type cylinders, and emergency supply of first aid, food, water, and oxygen candles.
The refuge station is located in a bay off a drift and is separated from the drift by a concrete wall. Access to the station is through an airlock system.
This refuge station is also used as a lunchroom.
Figure 16-24: Permanent Refuge Station
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16.8.11 | Communications |
16.8.11.1 | Fiber Optics and Phone and Radio Communications |
The underground wireless network infrastructure consists of:
■ | voice over internet protocol (VoIP) mine phones – current |
■ | cap lamps – under review |
■ | asset and personnel tracking – under review |
Radio communications are through a leaky feeder system which links to the surface radio system. The radios are digital, allowing flexibility in the system as required. A secondary system using Wi-Fi is installed in other locations underground. This system covers most of the mine workings. The backbone of the network is comprised of a gigabit network where switches are installed throughout key areas to expand fiber services to the lateral drifts away from the main trunk area. Each switch also houses up to two wireless radios, giving pervasive wireless coverage along travel ways. This provides the ability to make continuous VoIP telephone calls from the portal to the face, and complete asset and personnel tracking. The system also has redundancy to keep it running in the event that the fiber gets damaged. Figure 16-25 shows a schematic of the typical underground communications system.
Figure 16-25 Underground Communications System Schematic
The network system “head end unit” resides in the switch room in the main camp. The two network backbone cables branch out through the portals into the underground access declines—one in the main access decline and one in the conveyor decline. Amplifiers are spaced out between ultra-high frequency (UHF) coax cable segments at no more than 350 m spacing. A communications cable branches out at drifts as necessary, with “end-of-line” termination antennas as required.
16.8.11.2 | Personnel and Equipment Tracking |
Personnel tracking will be accomplished via the wireless access point (WAP) installation throughout the mine and interrogating devices to allow location tracking of personnel and vehicles. The system will be integrated into a browser-based tracking and reporting application, allowing operators and mine controllers to monitor, track and allocate personnel and resources. Having the ability to ensure that mine staff are accounted for in an emergency increases safety and speeds up the provision of help to any potentially injured personnel. Tracking vehicles and assets also leads to increased productivity and efficiency by eliminating time wasted looking for equipment underground.
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16.8.11.3 | Fixed Plant Monitoring and Control |
A Delta-V distributed control system (DCS) is used for fixed plant monitoring and control. The DCS processor (main rack) resides in the mill switching room. Remote Delta-V charm racks placed near equipment (as necessary) monitor and control the underground systems, including, but not limited to:
■ | ROM bin levels |
■ | crusher |
■ | conveying equipment |
■ | magnet |
■ | substations |
■ | sumps and pumps |
■ | ventilation doors |
■ | fuel delivery |
■ | traffic control |
■ | air quality and quantity. |
The interface between fiber and copper is through the Delta-V charm system and can implement discreet input/output changes as well as dynamic changes such as 4-20 mA outputs.
The fiber optic backbone stemming from the main rack in the mill is used for remote input/output racks and Internet protocol network communications. Two independent fiber cables branch out through the portals into the underground access declines, one in the main access decline and one in the conveyor decline.
The DCS system controls the underground crushing, conveying, pumping, ventilation, air quality and quantity monitoring.
Camera systems are installed in key locations across the mine site. There are underground camera systems in the grizzly dump area, the crusher area, and along the conveyor up to the surge bin. These cameras access the fiber system via Internet protocol addressing and can be easily integrated into the DCS.
16.8.12 | Portal Structure |
The portal structure has been constructed at the access to the underground Valley of the Kings decline tunnel. The structure houses a mine air heater and ventilation fan, the top conveyor drive motor and structure, an electrical substation, and the access way for vehicles to enter the Valley of the Kings portal though the building. The main decline conveyor exits up from the portal and transfers ore to the mill feed conveyor. This transfer is located inside the portal structure. Access into the portal structure is via one of four overhead doors and man doors. The portal structure was built up against the mill site high wall and to resist roof snow loads with pressures up to 400 kg/m3.
A monorail located in the ceiling of the portal structure allows for removal of the mine air fan motor and components.
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16.8.13 | Heating System and Propane Storage |
The electrical energy is used to run mine air heaters, with propane supplementing the electric heater during colder ambient temperatures, when the electricals cannot maintain the temperature set point to provide above freezing air to the mine. The propane for the two heaters is stored in two vertical storage tanks in both the Valley of the Kings portal area and the West Zone area. The tanks are located in accordance with regulatory clearance requirements to the mine portals. Each of the two tank farms contains two tanks with a capacity of 68,180 L each or a total of 136,360 L per tank farm.
16.8.13.1 | Climatic Data |
In the 2014 FS (Ireland et al. 2014), climactic data from site was analyzed to quantify the amount of annual electric power and propane required for mine air heating. This established the operating parameters for the currently installed mine heaters. Reviewing the current year of data shows that the design parameters was within 10% of actual. The volumes will change depending on the severity of the temperature experienced at the mine site year to year.
16.8.14 | Propane Supply |
Mine air heating is the only consumer of propane for the underground operations. Surface infrastructure, including the camp, requires propane; however, storage of propane for this purpose is independent of mine air heating. Table 16-14 shows the first full-year monthly and annual propane consumption during steady state operations.
Table 16-14: | 2018 Propane Consumption |
Propane | |
Consumption | |
Month | (L) |
January | 115,226 |
February | 267,534 |
March | 147,316 |
April | 15,469 |
May | 8,122 |
June | 8,787 |
July | 0 |
August | 0 |
September | 961 |
October | 0 |
November | 0 |
December | 58,670 |
Total | 622,084 |
Propane for mine air heating is delivered to site approximately seven months of each year. The propane is delivered to site via the Brucejack Access Road.
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The propane supplier remotely monitors the levels in the propane farms and initiates a tank fill as required to ensure there are adequate supplies at the mine site at all times.
A 50,000 L propane delivery truck drives from Terrace, BC to the Brucejack Gold Mine site, and the delivery truck transfers propane into the various site tank farms. The site tanks supply propane to the heaters via a buried pipeline.
The frequency of propane delivery is dependent upon the air temperature and airflow volume required for the mine. During the coldest months of the year, January and February, at the maximum airflow volume, the mine air heaters consume approximately 5,500 L of propane each day of the month.
16.9 | Paste Fill Distribution |
Paste from the surface plant is fed to the underground stopes through a pipeline system. The paste was characterized through laboratory rheology testing on un-cemented paste samples.
The paste fill distribution requires a two-stage pumping system. A positive displacement pump in the paste fill plant provides paste to all of the West Zone (West Zone Upper and West Zone Lower) and the lower zones of the Valley of the Kings Zone (below the 1,350 m level). The paste plant pump also feeds a booster pump located near the ramp to Valley of the Kings Zone. This booster pump pumps paste up to the Upper Valley of the Kings Zone and Galena Hill (1,350 m level and above). Due to line resistance of longer pipelines to the stopes, the booster plant will be required to pump paste below the 1,350 m level.
The paste pumps are positive displacement piston pumps of 100 m3/h peak capacity with a pressure rating of 120 bar. The nominal flow rate for the system is 80 m3/h, with a nominal design supply rate of 112 dmt/h.
The underground booster pump station currently has one pump installed and includes a pump feed hopper, a water tank with a high-pressure pump for pipeline flushing, and a level platform for changing the distribution routing through the mine. A second pump is on order and will be installed as backup.
If there is an upset during pasting operations, there are two points that can be used to allow an emergency drain of the system to prevent the pipe system from plugging. The first point is located at the low point in the line between the mill and the 1,345-level booster station and the second point is located at the first low point after the booster station for the lines going into the upper part of the mine.
Instrumentation installed to ensure controlled operation includes pressure sensors on each operating level, cameras to allow the control room vision of conditions at the booster pump, power activated diversion valves and manual diversion stations, and integrated process control within the paste fill plant.
This paste fill distribution system provides paste to the stopes at a nominal yield stress of 250 Pa with a range of 100 to 375 Pa. This equates to cemented paste percent solids of 66.1% solids by weight (ranging from 62 to 69% solids by weight).
The piping specified for this distribution system is 8 in API 5L X52. The schedule of the pipe varies with the pressure rating of the area: borehole casing and loops in the Upper Valley of the Kings Zone levels are Schedule 120, while the Lower Valley of the Kings Zone and all the West Zone casing and loops are Schedule 80. The main drift piping (trunk) and level piping to the stopes is Schedule 80 and Schedule 40, respectively. Victaulic couplings are used as the connection method for the level distribution lines.
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16.9.1 | Distribution System Design |
The pipe routing for the underground distribution system (UDS) was developed taking into consideration site conditions, pipeline operation experience, and hydraulic modelling. Some of the conditions that were taken into account in the design include:
■ | the difficulty foreseen in accessing any trenched pipelines on surface due to site conditions, especially during winter months |
■ | the mining schedule, which defines that the Valley of the Kings Zone will be developed in the early years while the West Zone will only be developed in the second half of the LOM |
■ | the long distance from the paste fill plant to the underground workings (more than 800 m) |
■ | the location of the paste fill plant below the elevation of the top third of the Valley of the Kings Zone. |
The mining schedule breaks down the Brucejack orebody into six areas: VOK-990 to 1050, VOK-1080 to 1170, VOK- 1200 to 1290, VOK-1320 to 1560, WST-U, and WST-L, as shown with their respective elevations in Figure 16-26 and Figure 16-27. The first areas to be mined will be the VOK-1200 to 1290, and VOK- 1320 to 1560, which are currently being mined. Production in VOK-1080 to 1170 will start in Year 2 (2020), while the WST Zones will only come online after Year 8 (2026). The Valley of the Kings Zones have continuous production scheduled until end of mine life. The paste fill distribution system was designed with the schedule shown in Table 16-5 in mind.
The main challenge for the Brucejack paste fill distribution system is that a portion of the orebody is located above the elevation of the paste fill plant. A balance in strategy is required to ensure that paste can be pumped to this section of the orebody without compromising the quality and proper flow distribution to the rest of the mine.
16.9.2 | Distribution Approach |
The philosophy developed for the paste fill distribution system is a dual pumping system. This optimizes the pumping capacity and minimizes wear on the paste pumps. A positive displacement pump in the paste fill plant will provide paste to all of the West Zone (WST-U and WST-L) and the Lower Valley of the Kings Zone (below the 1,350 m level). The paste plant pump will also feed the booster pump located near to the main entrance to the Valley of the Kings Zone on the 1,345 m elevation level. This booster pump pumps paste up to the Upper Valley of the Kings Zone (1,350 m level and above). Figure 16-26 shows the breakdown of the Brucejack Deposit ore zones by the paste pumps feeding them: single pump zone and dual pump zone.
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Figure 16-26: Paste Fill Distribution System Schematic Showing Paste Pumping Zones
16.9.3 | Distribution System Layout |
The underground perspective view of the paste fill distribution system is provided in Figure 16-27.
Key points of the piping strategy are:
■ | one pump plus installed spare at the paste fill plant |
■ | one booster pump plus spare to be installed near the ramp to the Valley of the Kings Zone 1,345 m elevation |
■ | main distribution pipeline in the Valley of the Kings decline and then a bore to the West Zone Access Drift then to the Valley of the Kings Zone |
■ | one sump to divert paste from the pipeline during operation upsets. |
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Figure 16-27: Paste Fill Distribution System Schematic
Source: | Pretivm (2019) |
16.9.4 | Manpower Requirements |
16.9.5 | Schedule |
The mine is operated by a mining contractor with Pretivm supplying operational oversight and technical service support personnel.
As the Brucejack Gold Mine site is remote, a reasonable crew rotation is required to attract the skilled labour that will be necessary for operations. The Pretivm crews are on a two-week-in, two-week-out rotation, and the contractor crews operate on a three-week-in and three-week-out rotation. The working time per day is based on an 11-hour shift; allowing one hour for smoke to clear after end-of-shift blasting. However, the effective working time per day is less than 11 hours considering travel time, daily safety briefs, and pre-start safety checks. The effective working time per shift during production operations is nine hours.
To operate an 11-hour shift, a variance has been granted from the BC Government (to allow work over 8 hours per shift). The current mine contractor has obtained such a variance for the work at the mine.
16.9.6 | Organization and Manpower |
The underground mining group is organized into operational groups consisting of mining, logistics, maintenance, and technical support with mining logistics and maintenance under the contractor, and the operations contract management and technical support under Pretivm. Table 16-15 shows the total personnel required by operational group when the mine reaches full steady state production of 3,800 t/d.
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Initial loading will primarily be provided by the mining contractor, with technical support and operations contract supervision provided by Pretivm. Additional hires are personnel employed to compensate for shortages due to vacations, absenteeism, and turnover.
Table 16-15: | Manpower by Operational Group |
Head | Head | ||
Role | Count | Role | Count |
Mining Supervision (8) Pretivm | |||
Underground Superintendent | 1 | Mine Captain | 3 |
Safety/Training/First Aid | 4 | ||
Contractor Supervision and Support (16) | |||
Superintendent | 4 | Engineers /Technicians | 4 |
Administrator | 2 | Safety/Training | 4 |
Expeditors | 2 | ||
Development Crew (94) contractor | |||
Development Shift Boss | 4 | LHD Operators | 10 |
Jumbo Operators | 8 | Truck Operators | 10 |
Bolter Operators | 20 | Blasters | 12 |
Alimak Miners | 2 | Service Installers | 28 |
Production Crew (140) contractor | |||
Production Shift Boss | 8 | Crusher Operator | 6 |
Long Hole Drillers | 28 | Crusher Labourer | 4 |
Blasters | 12 | Backfill Leader | 4 |
LHD (Electric) Operators | 18 | Construction Crew | 32 |
Truck Operators | 10 | Backfill Operator | 8 |
General Labourers | 10 | ||
Raising (3) contractor | |||
Raise Leader (Contract) | 1 | Raise Mechanic (Contract) | 1 |
Raise Miner (Contract) | 1 | ||
Maintenance (79) contractor | |||
Maintenance Superintendent | 1 | Welders | 2 |
Master Mechanic | 2 | Warehouse | 4 |
Mechanics | 32 | Lead Electrician | 2 |
Mill Wrights | 8 | Electricians | 10 |
Tire Technician | 16 | Maintenance Planner | 2 |
Technical Services (40) Pretivm | |||
Technical Services Manager | 1 | Chief Engineer | 1 |
Senior Engineer | 3 | Planning /Ventilation /Drill Blast Engineer | 3 |
Chief Geologist | 2 | Mine Planning & Scheduling | 3 |
Senior Production Geologist | 2 | Surveyors | 8 |
Junior Production Geologist | 11 | Geotechnical Engineer | 6 |
Total Personnel | 380 |
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17.0 | RECOVERY METHODS |
17.1 | Mineral Processing |
17.1.1 | Introduction |
The Brucejack Deposit mineralization typically consists of quartz-carbonate-adularia, gold-silver bearing veins, stockwork and breccia zones, along with broad zones of disseminated mineralization. Gold and silver are the major economical metals contained in the mineralization. There is a significant portion of gold and silver present in the form of nugget or metallic gold and silver.
The concentrator was designed to process gold and silver ore at a nominal rate of 2,700 t/d with an equipment availability of 92% (365 d/a) using a combination of gravity concentration and conventional bulk sulphide flotation. The Brucejack Gold Mine was successfully commissioned from March to May of 2017, with the first gold pour on June 20, 2017. The process plant reached full operation in Q4 2017. Since then, new test programs have been conducted to further improve the mill operation. In 2018, further throughput increase reviews and test work were conducted by mill metallurgists and engineers, equipment suppliers, and independent consultants to improve the mill operation in an effort to increase the mill throughput to 3,800 t/d.
17.1.2 | Mill Operation Data |
The process flowsheet originally developed for the Brucejack Gold Mine uses a combination of conventional bulk gravity concentration and sulphide flotation. The gravity concentrate is refined in the gold room on site to produce gold-silver doré by directly smelting the upgraded gravity concentrate. The doré is shipped by air to precious metal refineries located worldwide for further processing to produce refined metals for sale. The final flotation concentrate is dewatered, loaded into customized bulk containers and trucked to the transload facility in Stewart, BC. From there, the concentrates are loaded in bulk form and shipped to international smelters or traders.
A portion of the flotation tailings is used to make paste to backfill excavated stopes in the underground mine, and the balance is stored in Brucejack Lake. Water from the concentrate and tailings thickener overflows is recycled as process make-up water. Treated water from the water treatment plant is used for mill cooling, gland seal service, reagent preparation, and make-up water.
In May 2017, ore was first introduced to the mill from the low-grade ore stockpiles with a focus on ramping up tonnage throughout to design capacity. The first gold was poured on June 20, 2017 and during commissioning 8,510 oz of gold were produced in June. On July 1, 2017, Pretivm declared commercial production at the Brucejack Gold Mine. Table 17-1 lists the production data from July 2017 to the end of 2018.
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Table 17-1: | Brucejack Mill Production Data 2017-2018 |
Mill Feed | Mill Feed | Total | ||||
Time | Tonnage | Grade | Recovery | |||
Tonne | t/d | (g/t Au) | (g/t Ag) | (% Au) | (%Ag) | |
Q3 2017 | 261,262 | 2,840 | 10.5 | n/a | 96.5 | n/a |
Q4 2017 | 271,501 | 2,951 | 8.2 | 13.8 | 95.8 | 80.8 |
Total 2017 | 532,763 | 2,895 | 9.4 | 13.8 | 96.2 | 80.8 |
Q1 2018 | 261,443 | 2,905 | 9.1 | 13.0 | 96.8 | 85.7 |
Q2 2018 | 236,990 | 2,604 | 14.9 | 17.1 | 97.7 | 88.3 |
Q3 2018 | 240,122 | 2,610 | 12.4 | 14.1 | 97.4 | 88.1 |
Q4 2018 | 267,048 | 2,903 | 11.5 | 15.8 | 97.0 | 85.6 |
Total 2018 | 1,005,603 | 2,755 | 11.9 | 15.0 | 97.3 | 87.0 |
Notes: | *Excluding gold from pre-commercial production. |
17.1.3 | Flowsheet Development |
The process flowsheet for the expanded mill (3,800 t/d throughput) is based on the existing operation, new test work and simulations, as well as Tetra Tech’s engineering experience.
In 2018, mill throughput increase reviews were conducted by Pretivm’s metallurgists and engineers, equipment suppliers, and independent consultants through various supporting test work and simulations. The upgraded flowsheet is identical to the existing operation flowsheet, as shown in Figure 17-1. The operation units include:
■ | one stage of crushing located underground |
■ | a mill feed surge bin with a live capacity of 2,500 t located on surface |
■ | a SABC primary grinding circuit integrated with a gravity concentration circuit |
■ | rougher flotation and scavenger flotation of the hydrocyclone overflow (gravity separation tailings) |
■ | cleaner flotation on combined rougher and scavenger concentrates |
■ | flotation concentrate dewatering |
■ | flotation tailings dewatering circuits. |
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Figure 17-1: Simplified Process Flowsheet
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17.1.4 | Plant Design |
17.1.4.1 | Major Design Criteria |
The upgraded process plant will process 3,800 t/d of ore at a mill availability of 92%. Table 17-2 outlines the major criteria used to upgrade the process flowsheet.
Table 17-2: | Major Design Criteria |
Criteria | Unit | Value |
Daily Processing Rate | t/d | 3,800 |
Operating Days per Year | d/a | 365 |
Operating Schedule | - | two shifts/day; 12 hours/shift |
Mill Feed Grades – Average | g/t Au | 5 to 20 |
g/t Ag | 5 to 200 | |
% S | 2.85 | |
Primary Crushing (Underground) | ||
Crushing Availability | % | 60 |
Crushing Product Particle Size, 80% passing | mm | 120 or finer |
Grinding/Flotation/ Gravity Concentration | ||
Availability | % | 92 |
Milling and Flotation Process Rate | t/h | 172 |
SAG Mill Feed Size, 80% passing | mm | 120 or finer |
SAG Mill Grind Size, 80% passing | µm | 800 to 1,000 |
Drop Weight Breakage Parameter | A x b | 41.4 (ranging 29.1 to 78.7) |
Ball Mill Grind Size, 80% passing | µm | 90 |
Ball Mill Circulating Load | % | 300 |
Bond Ball Mill Work Index – Average | kWh/t | 14.0 |
Bond Ball Mill Work Index – Design | kWh/t | 16.6 |
Nugget Gold Recovery from Primary Grinding Circuit | - | Centrifugal and Tabling Gravity Concentration |
17.1.4.2 | Operating Schedule and Availability |
The upgraded process plant will continue to operate on two, 12-hour shifts per day, 365 d/a. The overall availability of the underground primary crusher circuit will be 60%. The grinding, flotation, and gravity concentration availability will be 92%. The gold room will operate during the day shift only. These availabilities will allow for a potential increase in crushing rate, downtime for scheduled and unscheduled maintenance of the crushing and process plant equipment, and potential weather interruptions.
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17.1.5 | Process Plant Description |
17.1.5.1 | Primary Crushing (Underground) |
The primary crushing facility will have an average process rate of 264 t/h at a crushing availability of 60% to meet the increased mill throughput of 3,800 t/d at a closed-side setting of approximately four inches.
The current primary crushing unit is located underground and includes the following major units:
■ | hydraulic rock breaker |
■ | stationary grizzly |
■ | jaw crusher (150 kW) |
■ | vibrating grizzly feeder |
■ | associated dump pocket and belt conveyor |
■ | belt scales |
■ | a dust collection system. |
The ROM ore is trucked from the underground mine to the underground primary crushing facility. The particle size of the jaw crusher feed is typically less than 700 mm. The jaw crusher reduces the ROM material to 80% passing 120 mm or finer.
The crusher product is transported by a conveyor system from the underground primary crushing facility to the SAG mill feed surge bin located on surface. The primary crushing and conveying facilities are equipped with a spray water dust suppression system to control fugitive dust generated during crushing and conveyor loading. The crushing and conveying system are monitored through closed-circuit television (CCTV) and can be controlled by the local control system or from the process central control room located in the process plant.
17.1.5.2 | Mill Feed Surge Bin |
The SAG mill feed surge bin was designed to have a live capacity of 2,500 t and this will remain the same for the 3,800 t/d mill scenario. The crushed product from the underground primary crushing facility is first conveyed to the transfer tower, which is part of the portal building on the surface. From there, it is further transported to the SAG mill feed surge bin.
The ore from the mill feed surge bin is reclaimed by two 1,067 mm wide by 15,000 mm long apron feeders onto the SAG mill feed conveyor at a nominal rate of 172 t/h.
The stocking and re-handling system for the crushed ore includes the following major components:
■ | one jaw crusher discharge belt conveyor |
■ | two belt conveyors located in the underground and one conveyor located at surface to feed the SAG mill feed surge bin |
■ | one SAG mill feed surge bin with a live capacity of 2,500 t |
■ | two apron feeders, 1,067 mm wide by 15,000 mm |
■ | local dust collection systems. |
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The crushed ore conveyor transfer points at the portal and at the SAG mill surge bin are equipped with a dust collection system to control fugitive dust generated while transporting the crushed material.
17.1.5.3 | Grinding, Classification and Gravity Concentration |
A SABC grinding circuit has been installed at the mine site and incorporated with two centrifugal gravity concentrators to recover gold/silver nugget grains that are liberated or partially liberated from their host minerals.
The upgraded primary grinding circuit will have an average feed rate of 172 t/h at a 92% availability to meet the increased mill throughput of 3,800 t/d and maintain a target product size of 80% passing 90 to 100 µm. According to the new comminution tests and simulation results (Section 13.0), the capacity should be readily achieved within the current circuit by:
■ | increasing the SAG mill critical speed |
■ | increasing the SAG mill charge loading |
■ | placing one of the two stand-by cyclones into operation. |
According to the simulations, the grinding mills should be able to achieve approximately 4,240 t/d before the grind size needs to increase to coarser than 80% passing 90 µm.
The two gravity concentrators (Model QS40) have a design unit capacity of 250 t/h. This arrangement also allows the two units to treat 100% of the ball discharge at the increased operating rate.
The grinding/gravity concentration circuit includes:
■ | one SAG mill, 6,096 mm diameter by 3,048 mm long (20 ft by 10 ft) (effective grinding length [EGL]), driven by a 2,013 kW VFD |
■ | one ball mill, 3,960 mm diameter by 7,260 mm long (13 ft by 23.8 ft) (EGL), powered by a 2,013 kW VFD |
■ | one HP 100 cone crusher |
■ | one 1.83 m wide by 3.66 m long vibrating screen |
■ | two 10-inch x 8-inch hydrocyclone feed slurry pumps, each with an installed power of 250 hp |
■ | six 381 mm hydrocyclones (gMax15-3123), with five in operation and one on standby |
■ | two QS40 centrifugal gravity concentrators and ancillary screens |
■ | two shaking tables, one secondary Knelson concentrator (CD12), one melting furnace, and related ancillary equipment in the secured gold room |
■ | one particle size analyzer |
■ | one online sampler. |
The crushed ore from the surge bin is reclaimed onto the belt conveyor that feeds the ore to the SAG mill. The SAG mill is equipped with 40 mm pebble ports to discharge the fine fraction from the SAG mill. The SAG mill discharge is screened by a vibrating screen, which has an opening of 8.0 mm (slot wide). The oversize from the screen is transported by conveyor to the HP100 pebble crusher. The screen undersize is discharged by gravity to the hydrocyclone feed pump box in the grinding circuit.
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The ball mill is operated in closed circuit with hydrocyclones and two centrifugal gravity concentrators. The product from the ball mill is discharged into the gravity concentrator feed pump box. The entire ball mill discharges report to the gravity concentration circuit. The stream is then split into two and each stream feeds to a safety screen with the undersize reporting to one of the centrifugal gravity concentrators. The gravity concentrator tailings, together with the safety screen oversize, flow by gravity to the hydrocyclone feed pump box where the gravity separation tailings join with the SAG mill trommel screen undersize slurry.
The blended slurry in the pump box is pumped to the hydrocyclones for classification. The hydrocyclone underflow returns by gravity to the ball mill. The circulating load to the ball mill is approximately 300%. The particle size of the hydrocyclone overflow, or the product of the primary grind circuit, is 80% passing 90 to 100 µm. The pulp density of the hydrocyclone overflow slurry is approximately 33% w/w solids. Steel balls are manually added into the mills on a batch basis as grinding media.
Dilution water is added to the grinding circuit as required. A particle size analyzer is installed to monitor and optimize the operating efficiency, in conjunction with an automatic sampling system and the required instrumentation such as solid density, pressure, and flow rate meters.
17.1.5.4 | Rougher and Scavenger Flotation |
The pulp from the primary grinding circuit is subjected to conventional flotation to recover the free gold, silver, and their bearing minerals from the hydrocyclone overflow. Flotation reagents are added to the flotation circuits as defined through testing and the existing operation. The flotation reagents include PAX as the collector and D250 as the frother. The mass recovery of the rougher concentrate is approximately 15% of the flotation feed. The concentrates produced from the rougher flotation circuit are sent to the cleaner flotation circuit. The rougher flotation tailings are further floated by scavenger flotation, along with the tailings from the first cleaner flotation circuit. The scavenger concentrate returns to the head of rougher flotation for re-processing or to the first cleaner circuit for upgrading. Rougher and scavenger flotation are carried out at the natural pH level (without slurry pH adjustment).
The upgraded feed rate of the rougher flotation circuit will be 172 t/h. Based on the new test work and simulations completed by Metso (Section 13.0), the current rougher/scavenger flotation cells can provide sufficient flotation retention time. No upgrade is required for the rougher/scavenger flotation circuit, which includes:
■ | four 100 m3 rougher flotation tank cells |
■ | two 100 m3 scavenger flotation tank cells |
The tailings from the rougher scavenger flotation circuit are discharged to the tailings thickener. The tailings pumps will be upgraded to handle the increased tonnage. Depending upon the mining operation requirements, the thickener underflow will be pumped either to the paste backfill surge tank for excavated stope backfilling and/or to the tailings disposal surge tank prior to being pumped Brucejack Lake for storage.
Automatic sampling systems have been installed for the circuit, including the flotation feed; rougher scavenger tailings; and final flotation concentrate produced, to collect the samples required for process optimization and metallurgical accounting.
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17.1.5.5 | Cleaner Flotation |
In the current operation, the rougher and scavenger flotation concentrates undergo three stages of cleaning by flotation in order to produce the final gold-silver bearing concentrate.
The upgraded feed rate of the cleaner flotation circuit will be approximately 44 t/h. Based on the new test work and simulations (Section 13.0), the current first cleaner/scavenger flotation cells can provide the required flotation retention time for the increased feed rate.
The existing second cleaner flotation cell will not be able to handle the increased feed rate, lacking approximately 35% of the required capacity. Therefore, one additional flotation cell is required.
To meet the increased mill feed rate, the existing second and third cleaner cells will be converted for the second cleaner flotation and operate in series. A new 30 m3 flotation cell will be installed for the third cleaner flotation.
The upgraded rougher/scavenger flotation circuit will include:
■ | four 15 m3 tank cells for the first cleaner flotation |
■ | two 15 m3 tank cells for the first cleaner/scavenger flotation |
■ | two 15 m3 tank cells for the second cleaner flotation |
■ | one 30 m3 tank cell for the third cleaner flotation. |
The rougher concentrate together with the scavenger concentrate are initially upgraded in the first cleaner tank cells. As an option, the current operation can also direct the rougher-scavenger concentrate to the rougher flotation head depending on the flotation feed mineralogy. Also, based on concentrate grade of the first rougher flotation cell, the rougher concentrate can bypass the first cleaner flotation and report to the second cleaner flotation directly.
The first cleaner concentrate is pumped to the second cleaner circuit, while the first cleaner tailings passes to the first cleaner scavenger flotation cells for further concentration. The first cleaner scavenger flotation concentrate is returned to the head of the first cleaner flotation cell bank, joined with the rougher and scavenger flotation concentrates and the second cleaner tailings. The first cleaner scavenger flotation tailings are pumped back to the rougher scavenger flotation feed box.
The concentrate from the second cleaner flotation stage is further upgraded by the third cleaner flotation with the new 30 m3flotation cell; the second cleaner tailings will be pumped to back the first cleaner flotation. The concentrate from the third cleaner flotation cell, the final concentrate product, is pumped to the concentrate thickener. The third cleaner tailings are recycled back to the head of the second cleaner flotation circuit.
The reagents used in the primary bulk flotation circuits will also be added to the three stages of cleaner flotation to float the target minerals. The cleaner flotation processes are carried out at the natural slurry pH level.
17.1.5.6 | Gravity Concentrate Upgrading/Refining |
The primary gravity concentrate is further upgraded and refined in the gold room, which is located within a security room and has 24-hour CCTV surveillance. The access to the gold room is only for authorized personnel.
For the increased plant feed throughput of 3,800 t/d, it is anticipated that the gold room treatment capacity will be able to meet the increased gravity concentrate production by extending the operating time.
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Key equipment remains as for the current operation, which includes:
■ | one 1.8 m wide by 4.9 m primary gravity concentration table |
■ | one Knelson CD-12 centrifugal gravity concentrator |
■ | one 1.7 m wide by 2.7 m secondary gravity concentration table |
■ | one table concentrate dryer |
■ | flux reagent storage |
■ | one flux mixer |
■ | one 138 kW induction melting furnace |
■ | one vault for storing doré and table concentrate |
■ | one electrostatic dust collector |
■ | one off-gas and dust scrubbing system |
■ | ancillary equipment, including slag treatment devices. |
The primary gravity concentrate is pumped to the gold room for further upgrading by tabling on the 1,800 mm wide by 4,900 mm long shaking table. The tailings from the primary tabling is further processed by the CD12 centrifugal concentrator and the table middlings is recycled back to the table feed surge bin. The concentrate produced from the secondary centrifugal concentrator is upgraded using a 1,700 mm wide by 2,700 mm long shaking table while the centrifugal concentrator tailings are pumped to the hydrocyclone feed pump box. The secondary table tailings are pumped to the primary table feed surge bin. The concentrates from both the primary and secondary tables, which are the final products, are dried and melted in the induction furnace to produce gold-silver doré. The discharge from the furnace is poured into bar molds in a cascade-casting arrangement. The gold doré bars are weighed, sampled, and stored in the vault prior to shipping to refineries.
The concentrates from both the tables are dewatered, dried in a dryer, then weighed and stored in the vault prior to smelting.
The existing wet scrubbing system is used to clean the off-gas generated during the drying, calcination, mixing, melting, and slag crushing operations. The equipment used for these processes are equipped with hoods. Sufficient ventilation is provided in the gold room to protect the operators. All clothes, gloves, and other safety equipment necessary for high-temperature protection is provided to the operators working in the secure area.
17.1.5.7 | Concentrate Handling |
The concentrate from the third cleaner flotation is thickened, filtered, and loaded into customized bulk containers prior to being transported to off-site smelter(s).
When the process plant throughput increases to 3,800 t/d, the current concentrate dewatering system should be able to handle the increased tonnage according to the test results and simulations completed by suppliers. For the concentrate thickener, proper thickener feed conditioning will be required, including feed dilution to 15 % w/w, and use of a more efficient flocculant at recommended dosages. For concentrate filtration, two additional filter plates and the associated auxiliaries will be required to increase the filtration capacity from the current 22 to 25 m2. Also, one additional thickener underflow pump will be installed to handle the increased concentrate production.
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The concentrate handling facility will have the following equipment:
■ | one 5 m diameter high-rate thickener |
■ | three thickener underflow slurry pumps, two in operation and one on standby |
■ | one concentrate filter feed stock tank (5,000 mm diameter by 6,000 mm high) |
■ | one tower-type pressure filter (filtration area increased from 22 to 25 m2 by adding two additional plates) |
■ | one concentrate cake handling system. |
The final flotation concentrate is pumped to the concentrate thickener. Flocculant is added to the thickener feed well to aid the settling process. The thickened concentrate is pumped to the concentrate stock tank. The underflow density of the thickener is approximately 70% solids. The concentrate stock tank is an agitated tank, which serves as the feed tank for the concentrate filter. A tower-type press filter is used for further concentrate dewatering. The filter press reduces the moisture content of the thickener underflow to approximately 8%. The filter press solids are discharged into a bulk container. The loaded containers are stacked in the concentrate loading area prior to being loaded into vehicles with chained tires and transported to the Knipple Transfer Station, then to Stewart, BC. The concentrate is then transported in bulk by sea to international smelters or traders. The process plant provides sufficient on-site storage capacity for up to 10 days of production in the event of unexpected transportation disruption. Additional secured storage is also provided at the Knipple Transfer Station.
The filtrate from the pressure filter is circulated back to the concentrate thickener feed well as dilution water. The overflow from the thickener is pumped to the process water tank or to the grinding circuit for re-use as process water.
17.1.5.8 | Tailings Disposal |
The final tailings are pumped to an 18 m deep cone thickener where most of water is removed as thickener overflow and re-used in operation. Part of the thickened tailings, approximately 30 to 40% of the overall tailings, is pumped to the paste backfill feed surge tank prior to feeding the paste plant for underground mine backfilling. The remaining thickened tailings are pumped to Brucejack Lake for storage.
At an increased process plant feed rate of 3,800 t/d, based on the completed test results and simulations, the existing 18 m tailings thickener is capable of handling the capacity by using proper feed conditioning, including feed dilution and the use of the optimum flocculant type at recommended dosages. The projected solids density of the tailings thickener underflow is approximately 65% by weight.
The existing tailings handling facility has the following equipment:
■ | one 18 m diameter deep cone thickener |
■ | one 4 m diameter by 5 m high disposal surge tank for the tailings that is discharged to Brucejack Lake |
■ | one 11.0 m diameter by 11.6 m high thickener underflow stock tank |
■ | two thickener underflow positive displacement (PD) pumps, each with an installed power of 20 hp |
■ | two thickener underflow recycle PD pumps, each with an installed power of 20 hp |
■ | two tailings disposal pumps, each 4 inches by 3 inches and an installed power of 75 hp. |
The flotation tailings are pumped directly from the pump box in the flotation circuit to the tailings thickener feed well where the tailings are diluted in an inner dilution launder and flocculant is added to improve settling efficiency. The thickener underflow is pumped to a 11 m diameter by 11.6 m high thickener tailings stock tank. The thickened tailings are pumped to the tailings disposal tank and then pumped to Brucejack Lake for storage. When the backfill plant is in operation, the tailings are also pumped to the paste plant fully or partially based on the paste plant requirement. The thickener overflow is sent to the process water tank for re-use as process water.
When the tailings are backfilled to the excavated underground stopes, the water from the water treatment plant or from Brucejack Lake is sent to the mixing tank. The thickener overflow is sent to process water tank.
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17.1.5.9 | Reagent Handling and Storage |
PAX and D250 are added to the flotation process slurry stream to modify the chemical and physical characteristics of mineral particle surfaces, and to enhance the floatability of the valuable mineral particles into the concentrate products.
PAX is shipped to the mine site in solid form. A 20% reagent solution is made by mixing PAX with fresh water in a mixing tank. The reagent solution is stored in a 1.50 m diameter by 1.50 m high holding tank and added to the various addition points through metering pumps. The PAX consumption is in the range of approximately 50 to 80 g/t milled.
D250 in liquid form is added directly into the flotation cells without dilution through metering pumps. The dosage applied is approximately 20 g/t milled.
Flocculant is used as a settling aid for the flotation concentrate and tailings thickening. The existing flocculant system will be replaced with a larger unit for the higher process rate requirement. Solid flocculant is prepared in the standard manner in a wetting and mixing system to a dilute solution of less than 0.2% solution strength. The solution is stored a holding tank prior to being pumped to the thickener feed wells. The flocculant dosages added to the concentrate and tailings thickeners are approximately 15 to 20 g/t concentrate and 60 to 80 g/t milled, respectively.
Hydrated lime is used to prepare an alkaline solution for scrubbing.
Anti-scalant chemicals are delivered in liquid form and added to the process water tank as required to minimize scale build-up in the water pipelines and process equipment. This reagent is added in undiluted form.
17.1.5.10 | Assay and Metallurgical Laboratory |
The assay laboratory, located at the Knipple Transfer Station, is equipped with the necessary analytical instruments to provide all routine assays for the mine, process plant, and environmental department.
A metallurgical laboratory is located in the mill to undertake the necessary test work to monitor metallurgical performance and, more importantly, to improve process flowsheet unit operations and efficiencies.
17.1.5.11 | Water Supply |
Two separate water supply systems are provided to support the operations for the process plant: one fresh water supply system and one process water supply system.
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Fresh Water Supply System
Fresh water is supplied to a fresh/fire water storage tank (10 m diameter by 11 m high) from the water treatment plant or from Brucejack Lake. Fresh water is primarily be used for:
■ | fire water for emergency use |
■ | cooling water for mill motor and mill lubrication systems |
■ | gland water for the slurry pumps |
■ | reagent make-up |
■ | process water make-up. |
The fresh/fire water tank is equipped with a standpipe for fire water requirements.
Wells supply water to the mine site potable water supply system. The water is sanitized and stored in potable water storage tanks prior to delivery to various service points within the mill and camp.
Process Water Supply System
The overflow solution from the tailings thickener is pumped to the process tank (8,000 mm diameter by 8,000 mm high) and re-used in the process circuit. The water treatment plant, which treats water from the mine (underground water), water collected from the plant site, or from Brucejack Lake, as required, provides the balance of the process water.
17.1.5.12 | Air Supply |
Existing air service systems should be able to meet the increased tonnage requirement. The air system supplies air to the following service areas:
■ | Crushing circuit – an air supply system located underground supplies high-pressure air for dust suppression and equipment services. |
■ | Flotation – air blowers provide low-pressure air for flotation cells. |
■ | Filtration circuit – dedicated air compressors provide high-pressure air for filtration and drying. |
■ | Plant air service – dedicated air compressors provide high-pressure air for various services. |
■ | Instrumentation – plant air compressors provide service air that is dried and stored in a dedicated air receiver. |
17.1.5.13 | Process Control and Instrumentation |
At the increased plant throughput of 3,800 t/d, the process control system will remain the same as the current system installed for the current production rate of 2,700 t/d. There is central control room in the mill office complex that can monitor and control plant operations, including the underground crushing and conveying systems. CCTV cameras are installed at various locations throughout the plant.
Sampling and Inline Analysis
The process plant relies on the on-stream or in-stream particle size analyzer and various flow rate and solid density meters for process control. The analyzer and meters examine the various slurry streams in the circuit. The on-stream particle size monitor determines the particle sizes of the hydrocyclone overflows in the primary grinding circuit. Required samples are taken in order to control hydrocyclone overflow particle size and optimize the grinding circuit operations. Specific samples taken for metallurgical accounting purposes include the flotation feed to the circuit, the final tailings, the final concentrate sample, and occasionally the middling products. These samples are collected on a shift-basis and assayed in the assay laboratory.
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17.2 | Annual Production Estimate |
The upgraded process plant will continue to generate two products: gold-silver doré and gold-silver bearing concentrate for the expected remaining LOM of 14 years. Table 17-3 shows the annual metal production, which has been projected based on the mining production plan outlined in Section 16.0 and the operation data and metallurgical results outlined in Section 13.0. Based on the annual average and excluding the last year of operation, the process plant is estimated to produce approximately 8,490 kg Au and 4,740 kg Ag contained in doré, and 62,330 t Au-Ag bearing flotation concentrate with average grades of approximately 99 g/t Au and 869 g/t Ag. The arsenic content of the flotation concentrates to be shipped to the smelter(s) is expected to be marginally higher than the penalty thresholds outlined by most smelters and will require further review.
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Table 17-3: | Projected Gold and Silver Production |
Mill Feed | Metal Recovery to Doré and Flotation Concentrate | Flotation Concentrate | ||||||||||
Tonnage | Grade | Doré | Concentrate | Total | Tonnage | Grade | ||||||
Year | (kt) | (g/t Au) | (g/t Ag) | (% Au) | (% Ag) | (% Au) | (% Ag) | (% Au) | (% Ag) | (dmt) | (g/t Au) | (g/t Ag) |
2019 | 1,235 | 10.6 | 11.2 | 64.2 | 36.5 | 32.3 | 51.6 | 96.4 | 88.1 | 68,379 | 61.9 | 104.2 |
2020 | 1,371 | 12.0 | 11.3 | 66.6 | 38.9 | 30.2 | 50.1 | 96.8 | 89.0 | 75,302 | 66.0 | 103.4 |
2021 | 1,383 | 13.0 | 11.7 | 68.5 | 39.6 | 28.6 | 49.4 | 97.1 | 89.0 | 74,694 | 69.0 | 106.9 |
2022 | 1,386 | 13.6 | 10.2 | 70.1 | 41.5 | 27.2 | 47.5 | 97.3 | 89.0 | 71,728 | 71.7 | 93.5 |
2023 | 1,387 | 12.3 | 17.5 | 67.2 | 28.6 | 29.7 | 56.2 | 96.9 | 84.7 | 75,890 | 67.0 | 180.0 |
2024 | 1,388 | 13.5 | 20.7 | 71.2 | 26.4 | 26.3 | 57.7 | 97.5 | 84.1 | 66,646 | 73.8 | 249.3 |
2025 | 1,388 | 14.3 | 52.1 | 43.5 | 5.2 | 52.6 | 80.5 | 96.1 | 85.7 | 70,159 | 148.8 | 830.2 |
2026 | 1,380 | 13.9 | 93.7 | 43.3 | 3.9 | 52.8 | 83.5 | 96.1 | 87.5 | 68,590 | 148.1 | 1,575.4 |
2027 | 1,180 | 12.6 | 85.6 | 42.5 | 4.1 | 53.4 | 83.1 | 96.0 | 87.2 | 58,159 | 136.1 | 1,443.3 |
2028 | 1,180 | 12.0 | 130.3 | 42.2 | 1.5 | 53.7 | 86.9 | 95.9 | 88.4 | 60,538 | 125.5 | 2,207.5 |
2029 | 902 | 10.8 | 87.7 | 41.4 | 4.0 | 54.4 | 83.2 | 95.8 | 87.3 | 45,346 | 116.3 | 1,452.0 |
2030 | 826 | 14.4 | 119.3 | 43.5 | 3.5 | 52.6 | 84.7 | 96.1 | 88.2 | 41,278 | 151.1 | 2,021.2 |
2031 | 571 | 9.8 | 220.1 | 40.2 | 1.5 | 55.3 | 88.5 | 95.6 | 90.0 | 33,635 | 91.7 | 3,304.7 |
2032 | 177 | 7.4 | 269.4 | 32.8 | 1.5 | 62.4 | 89.1 | 95.2 | 90.6 | 11,453 | 71.4 | 3,703.8 |
Total | 15,754 | 12.6 | 58.4 | 55.8 | 6.8 | 40.8 | 81.2 | 96.5 | 87.9 | 821,796 | 98.6 | 908.5 |
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18.0 | PROJECT INFRASTRUCTURE |
18.1 | Overview |
The Brucejack Gold Mine is situated approximately 65 km north-northwest of Stewart, BC. During construction from 2015 to 2017, a number of on-site and off-site infrastructure were built to support the mining operation (Figure 18-1, Figure 18-2, and Figure 18-3). The locations of operation and supporting facilities and infrastructure were selected to take advantage of local topography, accommodate environmental considerations, avoid avalanche hazards, and ensure efficient and convenient underground crew shift change.
The Brucejack Gold Mine is accessed via a 73.5 km access road that intersects Highway 37 at km 215, some 60 km north of Meziadin Junction. Electrical power is supplied from the BC Hydro grid via a 57 km transmission line constructed in 2016/2017, from the Long Lake Substation located 13 km north of Stewart, BC. The transmission line is a 138 kV power supply line from the Long Lake Hydro Substation to the Knipple Substation, with a 69 kV power supply line from the Knipple Substation to the mine distribution centre.
Facilities and infrastructure are split between those at the Brucejack Gold Mine site and those along the Brucejack Access Road. Infrastructure at the mine site includes mill; camp; fire hall; warehouse; transmission power line power distribution; emergency diesel power station (DPS); fuel farm; waste management facilities including incinerator, mobile equipment maintenance shops, underground miners support facility, explosives storage, mine ventilation and heating equipment, water management facilities, potable and waste water treatment facilities, ore storage and waste rock/tailings storage facility (WRTSF).
Support facilities along the Brucejack Access Road are located at the Knipple Transfer Station, Bowser Aerodrome, and Wildfire Camp. The Knipple Transfer Station is the main hub for materials staging and transfer to suitable vehicles for delivery to the Brucejack Gold Mine. Facilities at the Knipple Transfer Station include the transmission line stepdown substation, camp, cold storage building, potable water supply and treatment, waste materials handling facility with incinerator, fuel storage and distribution facility, paste binder silos, assay laboratory, emergency vehicle storage, first aid facility, and sewage disposal system.
The Bowser Aerodrome is a 5,000 ft long by 75 ft wide gravel airstrip suitable for such aircraft as a Beechcraft 1900, or similar speed and weight category aircraft, or Twin-Otter type aircraft. Adjacent to Bowser Aerodrome were Bowser Temporary Construction and Bowser West camps. Bowser Camp originally housed mineral exploration crews and then construction crews. The general site was used for extensive laydown of equipment for mine and transmission line construction. Following closure of Bowser and temporary construction camps, Bowser West Camp was used for road maintenance and exploration crews. Currently, Bowser West Camp is used as a laydown yard and core logging facility; bunkhouses and kitchen are being decommissioned and personnel housed at Knipple Camp.
Wildfire Camp is at km 1 on the Brucejack Access Road. Wildfire Camp comprises a gate at the highway intersection to screen access, a security building with gate for access control, camp, potable water well with water treatment, sewage disposal system, and large laydown yard for incoming and outgoing freight. Just west of Wildfire Camp (at km 1.5), there is an area designated for paste binder storage and transfer.
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Figure 18-1: Brucejack Gold Mine General Arrangement
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Figure 18-2: Brucejack Gold Mine On-site Infrastructure Layout
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Figure 18-3: Brucejack Gold Mine Off-site Infrastructure Layout
Source: | Pretivm (2019) |
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18.2 | Mine Site Surface Infrastructure |
Mine site infrastructure (Figure 18-1) covers a compact area due to the nature of the site terrain. Facilities are localized to three general locations all in close proximity. Underground mine related facilities are located along the south side of Brucejack Creek in proximity to the West Zone portal, the main access for personnel and vehicles. Also located along the south side of Brucejack Creek are the fuel farm, emergency DPS, and associated DPS pond/sump. Centrally located on the mine site are the mill, fire hall, emergency vehicles, two phases of camp buildings, truck shop, and the Valley of the Kings portal. East of the mill area waste handling, warehouse and miscellaneous buildings, ore storage and overburden storage, and waste rock dump are all located along the southwest shore of Brucejack Lake. Outlier facilities include the potable water well and incinerator located northwest of the main site, and the Valley of the Kings weather station located south of the main site. Water collection and diversion infrastructure (e.g., collection ponds and ditches, diversion channels, high-density polyethylene (HDPE) pipelines, sumps, weirs, etc.) are present throughout the mine site to appropriately manage water.
18.2.1 | Mill Facility Description |
The mill building houses equipment for the entire process following delivery of ore from underground. The 2,700 t/d process flowsheet (Section 17.0, Figure 17-1) outlines the following sequence: ore delivery from the Valley of the Kings Zone via the conveyor system to the surge bin located at the surface. The main surface processing circuits include:
■ | primary grinding circuit consisting of a SAG mill, a ball mill, a pebble crusher, and a related cyclone pack |
■ | gravity concentration and refining circuit consisting of two centrifugal concentrators, two shaking tables, and one centrifugal concentrator for recovering the gold and silver grains from the tabling tailings; and one smelting furnace for production of doré |
■ | rougher and scavenger flotation followed by three stages of cleaner flotation to produce gold-silver concentrate |
■ | concentrate dewatering system using one high rate thickener and one tower-type filter press to dewater concentrate to less than 10% w/w moisture; flotation concentrate is loaded into customized containers prior to being shipped offsite; the bulk containers replaced the previous bagging system in April 2019; concentrate in bulk containers is trucked to Stewart, BC for transshipment by ocean freight to smelter(s) |
■ | flotation tailings dewatering and management system consisting of one deep cone tailings thickener, one thickened tailings surge tank, and one tailings disposal surge tank; thickened tailings is sent either to the tailings surge tank and then to backfill paste preparation system prior to the underground mine or to the disposal surge tank prior to being pumped to Brucejack Lake for deposition on the lake bottom |
■ | process water recirculation system; both the overflows from the tailings thickener and the flotation concentrate thickener are reused as process water. |
The planned 3,800 t/d production, to be instituted in 2019, follows the same flowsheet (Section 17.0, Figure 17-1) for the current process, but with some modifications to piping, pump and motor upgrades, and second and third cleaner flotation cell upgrades. Engineering and modifications for the process changes are ongoing.
18.2.1.1 | Process Plant Control |
A control system provides equipment interlocking, process monitoring and control functions, supervisory control, and an expert control system. The control system generates production reports and provides data and malfunction analyses, including a log of all process upsets. All process alarms and events are logged by the control system.
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Operator interface to the DCS is via PC-based operator workstations located in the underground crushing, process plant, water treatment, and paste plant area control rooms. Control rooms are staffed by trained personnel 24 h/d.
Operator workstations can monitor the entire plant site process operations, viewing alarms, and controlling equipment within the plant. Supervisory workstations are provided in the offices of the senior metallurgists, as well as in the mine operations hallway. An additional operator interface is located in the main camp boardroom and is used in emergency situations.
Field instruments used in the mill process include microprocessor-based “smart” type devices. Instruments are grouped by process area and wired to local field instrument junction boxes in each respective area. Signal trunk cables connect the field instrument junction boxes to the control system input/output cabinets.
Intelligent-type MCCs are located in electrical rooms throughout the plant. A serial interface to the control system facilitates the MCCs remote operation and monitoring. Control systems philosophy is primarily focused on crushing, concentrator, and remote monitoring.
For site-wide infrastructure (i.e. telephone, Internet, security, fire alarm, and control systems), a fiber optic backbone is installed throughout the plant site.
A PC workstation is installed in the main control room to monitor the underground and crushing operations and conveying operations to the surge bin. The information is provided to the mill process control system via serial or Ethernet gateway. System controls include SAG feed conveyors (zero speed switches, side travel switches, emergency pull cords, and plugged chute detection) and surge bin levels (radar level, plug chute detection).
To control and monitor all mill building concentrator processes, three PC workstations are installed in the mill building’s central control room. They control and monitor the following: grinding conveyors (zero speed switches, side travel switches, emergency pull cords, and plugged chute detection), SAG and ball grinding mills (mill speed, bearing temperatures, lubrication systems, clutches, motors, and feed rates), particle size monitors (for grinding optimization and cyclone feed), pump boxes, tanks, and bin levels, variable speed pumps, cyclone feed density, thickeners (drives, slurry interface levels, underflow density, and flocculent addition), flotation cells (level controls, reagent addition, and airflow rates), samplers (for flotation optimization), gravity concentrators, pressure filter, and load out, reagent handling and distribution systems, tailings disposal to paste backfill or tailings storage, water treatment, water storage (including underground sumps and Contact Water Pond [CWP]) and reclamation/distribution (including tank level automatic control), air compressors, paste plant (vendor control system), fuel storage, and vendors’ instrumentation packages.
An automatic sampling system collects samples from various product streams for online analysis and daily metallurgical balance. Composite samples are generated for each 12-hour shift and are sent for assay at the Knipple assay laboratory.
A particle-size-based computer control system is used to maintain the optimum grind sizes for the primary grinding circuits. The particle-size analyzer provides main inputs to the control system.
Remote monitoring is achieved through CCTV cameras installed at various locations throughout the plant, such as the crusher conveyor discharge point, the SAG surge feed conveyer, the SAG and ball mill grinding area, the flotation area, the paste plant, the gold room, the concentrate handling area, and the tailings handling facilities. The cameras are monitored from the plant control room.
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18.2.1.2 | Water Treatment Plants |
Water treatment is undertaken in three separate facilities: operations water treatment plant (WTP), potable WTP, and waste water (sewage) treatment plant.
18.2.1.3 | Operations Water Treatment Plant |
The operations WTP, located in the mill building, treats underground inflows and surface water from the contact water collection system, process water, and water from Brucejack Lake.
The operations WTP is capable of treating up to 10,000 m3/d. The treatment process consists of the following steps: suspended solids removal (via clarification, coagulation using ferric sulphate and flocculation using silica sand and anionic flocculants), dissolved metal precipitation and total metals removal (through hydrated lime precipitation and ferric sulphate co-precipitation), fine solids filtration (via 10 µm disc filters), and pH adjustment (using sulphuric acid or hydrated lime). Sludge from this water treatment is mixed with tailings and deposited in Brucejack Lake.
Under the 3,800 t/d production plan, it is estimated that following cessation of mining, projected to be in 14 years, the operations WTP will continue to operate for less than a year to achieve acceptable discharge water quality.
18.2.1.4 | Potable Water Treatment Plant |
The Brucejack Gold Mine site potable WTP is located adjacent to the Phase 2 Camp. Raw water is pumped from a groundwater well located approximately 1.5 km northwest of the camp site to two raw water storage tanks. A booster pumping system withdraws raw water from the storage tanks and pumps it through green sand filters, woven canister filters (down to 1 µ) and through ultraviolet (UV) disinfection. Distribution pumps transport the water to both the Phase 1 and 2 camps, as well as the mill building.
Potable water within the mill building is treated in a similar manner (cartridge filters and UV disinfection) and is used to supply the lunchroom, bathrooms, and safety shower/eye wash stations through the mill.
The Brucejack Gold Mine potable WTP currently supplies approximately 75 m3/d based on an average usage rate of 200 L/d per person and a camp population of 360 persons. The facility is sized to treat water sufficient for a camp population of at least 720 persons. The potable water well has more than enough capacity to provide 150 m3/d.
18.2.1.5 | Sewage Treatment Plant |
The Brucejack Gold Mine site sewage treatment plant consists of two packaged C-75 Filterboxx treatment plant units, each designed to treat up to 75 m3/d of wastewater, for a total current treatment capacity of 150 m3/d. The current treatment rate is an average of approximately 75 m3/d, sufficient for 360 persons. The total treatment capacity is capable of treatment for approximately double the current camp population. Sewage is piped from the two camps and mine dry to the sewage treatment plant. Portable bathrooms at the mine site that are not plumbed into the sewage lines are regularly pumped out with a vacuum truck that offloads the raw sewage into the main lift station which feeds the treatment plant. Raw sewage is treated via primary screens, biological aeration reactors, and biological membrane filtration. The sludge from the sewage treatment plant is dewatered using a rotary vane filter and dried prior to final disposal by incineration at the on-site incinerator.
The mine is authorized via its Effluent Permit for an additional 25 m3/d treatment unit and can add this if required. Effluent from these treatment plants is discharged into Brucejack Lake in accordance with the mine’s Effluent Permit.
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18.2.1.6 | Non-potable Water |
Mill non-potable water requirements are supplied from the operations WTP and the reclaim pump house located at Brucejack Lake. The operations WTP treats underground mine water, surface contact water (via the CWP, and process water from within the mill. The treated effluent is then pumped into the fresh/fire water tank located in the mill. The fresh/fire water tank is also supplied by the reclaim pump house. The operations WTP supplies approximately 70% of the fresh water for the mill and the reclaim pump house supplies 30% of the mill’s fresh non-potable water needs. Water is pumped from the fresh/fire water tank through a distribution manifold within the mill which supplies water for use in gravity recovery, flotation, paste plant, reagent preparation, gland seal water, and wash down hoses.
The fresh/fire water tank is approximately 785 m3 in volume and only the top 30% is used for fresh water within the mill. The lower 70% of the tank volume is used for fire protection water within the mill and camp buildings.
18.2.2 | Mine Waste Management |
18.2.2.1 | Waste Rock and Tailings Storage Facility |
Waste rock and tailings deposition entails depositing tailings and potentially acid generating (PAG) waste rock into Brucejack Lake, or as underground mine backfill. Brucejack Lake is a deep natural glacier and snow meltwater lake allowing for LOM subaqueous waste rock and tailings deposition without the need for any engineered containment structures.
Most of the lake-deposited waste rock is deposited 1 m or more below the lake surface elevation via excavator (“bailing”) or tele-stacker (“stacking”) soon after being temporarily stockpiled on the waste rock dump. Waste rock deposited into the lake via these methods builds up and eventually forms the waste rock dump platform, where some waste rock extends above the normal lake level. This subaerially exposed PAG waste rock is replaced with either non-PAG (NPAG) material or freshly excavated PAG waste rock such that all PAG waste rock is ultimately subaqueously deposited within the allowable two-year subaerial exposure period. Tailings are NPAG and deposited in the deepest part of the lake via tailings discharge line or used for paste backfill in underground mined stopes.
The initial WRTSF design is documented in SRK (2016). This report includes the WRTSF stability and settlement analysis (SRK 2014, Appendix C) which takes into consideration site specific physical characterization of the lake bed sediments, the lake bathymetry, and measured lake bed sediment thickness. The design includes measured tailings rheological properties (SRK 2015, Appendix A), which confirms similarity between lake bed sediments and tailings.
SRK (2018b) contains an updated WRTSF design triggered by the requirement for increased waste rock and tailings volumes to be deposited into Brucejack Lake. This updated design includes comprehensive stability analysis of a critical section of the WRTSF considering leanings from monitoring data collected since the start of dump construction. It therefore represents an up to date evaluation of all site-specific data and confirms that actual dump behavior is representative of the numerical analysis completed.
Prescribed stability requirements are not available for subaqueous waste rock deposition in BC (or globally). However, theMined Rock and Overburden Piles Investigation and Design Manual (BCMWRP 1991) can be used as a starting point to inform a possible minimum acceptable factor of safety (FOS).
The WRTSF design (SRK 2018b) confirmed that physical stability of the Brucejack waste rock dump results in inherently low FOS when compared to the British Columbia Mine Waste Rock Pile Research Committee (BCMWRP) (1991). Fundamentally, it was determined that the active dumping face of the Brucejack WRTSF remains in a quasi-stable state with a FOS near unity for a period of weeks to months depending on the thickness of the unconsolidated undrained and highly variable lake bed sediments (and tailings), until enough pore pressure dissipation has occurred to allow the WRTSF foundation to carry the load of the waste rock and remain stable.
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Because the design analysis confirmed that a conventional FOS approach, based on numerical analysis would not allow for construction of the WRTSF, the observational method (Terzaghi and Peck 1967; Peck 1969) was adopted as the design approach for the WRTSF. This method was developed from the need to avoid highly conservative assumptions about ground properties in geotechnical design when faced with unavoidable uncertainties of natural ground conditions. It takes advantage of observations and data gathered during construction to adapt the design to actual ground conditions in an orderly and planned way. Implementation of this approach in the context of the WRTSF requires the following:
■ | conduct numerical analysis to establish behavioral bookends |
■ | develop monitoring requirements to allow behavioral tracking |
■ | develop and implement safe operating procedures for WRTSF construction |
■ | develop Quantifiable Performance Objectives (QPOs) to inform safe operating procedures |
■ | conduct ongoing monitoring and reanalysis as necessary |
■ | continuously revisit and update safe operating procedures as necessary. |
As a result, strict operational controls were set to ensure safe WRTSF construction. This rigorous dumping procedure allows for enough safe preloading of the foundation, subject to continuous monitoring and review by a qualified geotechnical site engineer, with ongoing oversight by the engineer of record (EOR).
This dumping procedure is independent of the lake bed sediment (and tailings) thickness or strength, because it assumes that the foundation cannot initially carry the load whether it is due to sediment (and tailings) thickness or strength (or both).
Waste rock and tailings deposition is governed by the Operations, Maintenance and Surveillance (OMS) Manual, the last version having been updated in October 2018 (SRK 2018a). Specifically, waste rock dumping is done in accordance with a standard operating procedure (Brucejack Lake Waste Rock Disposal, Standard Operating procedure [SOP] 011), which is an appendix to the OMS Manual. Pretivm’s engineering team manages the day-today waste rock deposition, and follow-up monitoring and surveillance following procedures outlined in the OMS
Manual. The OMS Manual has been developed in accordance with SRK’s design recommendations and undergoes updates as necessary. All employees working on the WRTSF are provided training on the OMS Manual, specifically the WRTSF SOP.
The required surveillance procedures for waste rock and tailings deposition is explicitly outlined in the OMS Manual, as are the QPO’s.
A daily report is produced by the Pretivm on-site geotechnical engineers that outlines all activities pertaining the waste rock dumping. This report is circulated internally to Pretivm staff including senior management, all off-shift geotechnical personnel to ensure continuity, as well as to the EOR. If the EOR identifies any anomalies or areas of concern based on the daily report, he reaches out to the on-site geotechnical engineers.
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18.2.2.2 | Tailings Delivery |
The tailings delivery system discharges thickened tailings slurry to the bottom of Brucejack Lake (80 m deep) when not used for paste backfill (approximately 40 to 50% of the time). For discharge to the lake, the tailings slurry is pumped to an agitated slurry mixing tank at approximately 65% w/w solids and then diluted with water to a maximum 55% w/w at the nominal solids throughput rate of approximately 180 t/h. The diluted slurry is pumped overland through one of two 8 inch HDPE DR 6.3 pipelines from the mill building to Brucejack Lake, a distance of approximately 900 m and then underwater along the suspended discharge lines another 400 m to the discharge point.
There is one duty pump and one standby pump to permit an immediate switch over when necessary. The pumps discharge the diluted slurry at a variable flow rate of varying concentration, which depend upon the throughput and concentration of tailings slurry entering the mixing tank. The mixing tank is typically maintained at a constant level through the addition of water through a control valve. There is a constant flow through the pipeline to prevent blockage of the pipe through tailings deposition within the pipe. When the thickened tailings are used in the backfill plant, flow is maintained with water.
Portions of the pipeline alignment are subject to avalanches and those sections of the pipeline are placed in a trench and backfilled to protect the pipe. The pipeline is heat traced to prevent freezing in winter and has a continuous downward slope from the mill building to the lake shore to ensure that the line drains during shutdowns.
The pipelines discharge a maximum of 7 m above the lake bottom, a Discharge Permit condition. The pipelines are switched if the active pipe become unusable, such as if the back-pressure approaches the upper operating range of the discharge pump, or if bathymetric surveys indicate excessive accumulations at the pipe discharge site. Both pipes are suspended on cables to allow for vertical and horizontal repositioning over the LOM to ensure the pipe is not covered by tailings and to meet permit conditions for vertical positioning above the lake bottom.
There are air/vacuum valves at the lake shore to prevent the possibility of air entering the underwater section. A large volume of air entering the underwater section could potentially float sections of the pipeline. The valves function primarily during start up and shut down.
18.2.3 | Mine Site Ancillary Facilities |
18.2.3.1 | Accommodations |
There are two accommodation complexes at the mine site: Phase 1 and Phase 2 camp complexes. The main (Phase 2) camp complex is located approximately 100 m southwest of the mill and can accommodate up to 330 persons. The Phase 2 camp complex features common facilities such as kitchens, mess halls, recreation rooms, common rooms, and offices. The older (Phase 1) camp complex is located 200 m south of the mill and can accommodate up to 212 persons. Each dormitory module contains dormitory rooms, washrooms with showers, and laundry rooms. The older Phase 1 camp kitchen has been repurposed as a training center with safety offices.
18.2.3.2 | Solid Waste Handling and Domestic Waste Incineration |
Camp and facilities waste are managed following the Waste Management Plan and, with respect to incineration, the Refuse Incinerator Management Plan and the Air Discharge Permit. Wastes are initially separated and disposed into receptacles appropriate to each waste stream and further sorted at the mine’s waste handling and sorting facility.
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A batch-fed containerized incinerator system is designed to process up to 1,800 kg of mixed solid waste material generated at the mine site per day. Solid waste includes mixed camp waste, non-hazardous solid waste consisting of food-waste, kitchen waste including packaging, cardboard, wood waste, kitchen grease, and general refuse.
Clean or untreated wood waste is burned at approved burn pits at the mine site following requirements specified in the Waste Management Plan and the Air Discharge Permit. Recyclables are separated at the time of disposal, further sorted as appropriate, then transported to off-site recycling facilities. Hazardous wastes are deposited in dedicated receptacles and taken to off-site licensed facilities for disposal. Remaining materials requiring landfilling are transported to local regional landfills as needed.
18.2.3.3 | Power Supply and Distribution |
At the Brucejack Gold Mine, 69 kV electrical power enters the mill via the transmission line from the Knipple Substation. There, the voltage is further stepped down from 69 to 4.16 kV via two 15/20/25 MVA oil-filled transformers and distributed to the site via 4.16 kV rated switchgear. The rating for site on a distribution end is 4.16 kV and further transformed to 0.6 kV for smaller loads.
The main mill and underground loads are fed via power cables in cable tray. The main substation is located inside the mill. Power feeds to the mill building, camps, truck shop, and underground are all underground buried services.
Within the mill, large loads are powered at 4.16 kV. Smaller loads are powered at 600 V via switchgear and MCCs. VFDs and soft starters are employed strategically to optimize process and energy performance.
Underground buried services provide power to outlying buildings.
18.2.3.4 | Emergency Power Generating Facility |
Emergency power is supplied from four 500 kW, 600 V generators, located at the DPS, that supply a step-up transformer and feed the E4C e-house. Additionally, there are two 1,450 kW, 4.16 kV diesel generators that are also directly interconnected to the E4C bus. As well, there are six 1,825 kW, 4.16 kV diesel generators that are interconnected into the E4C e-house. The total emergency power for the mine site is 15.85 MW, which can adequately supply the mill, underground, and camp facilities with sufficient power if the transmission line sourced power is interrupted.
A dedicated power system programmable logic controller (PLC) is included in the E4C e-house. This PLC controls the breakers for system synchronization of the generators. An uninterruptable power supply (UPS) backs up the PLC and communications to ensure reliable operations under all circumstances. The power system PLC performs two important functions: load optimization/load shedding to ensure line limits are not exceeded, while maximizing electricity use and power control during emergency power operations to ensure correct sequencing and operations of critical loads.
The controls for the power house can be activated via fiber optic through the mill electrical supervisory control and data acquisition (SCADA) system, as well as through a local SCADA system. If there is a loss of power the system will automatically start the generators to achieve operating temperature and the E4C bus will be energized.
Extensive bedrock exposures and extremely thin and spotty soils result in very poor resistivity. As a result, remote grounds have been constructed in addition to substation yard grounding.
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18.2.3.5 | Fuel Supply and Distribution |
Diesel fuel, primarily for mobile equipment, is stored in four 50,000 L double-walled tanks and one 45,000 L double-walled tank located at the mill site. The storage has approximately six to seven days capacity, including allowance for auxiliary equipment. The fueling station includes loading/unloading pumps and filters.
Aviation fuel is delivered in totes and barrels to both Brucejack and Knipple camp sites. Gasoline for mobile equipment is stored in one 5,000 L double-walled fuel tank located adjacent to the diesel fuel tanks.
Two 18,000 gal propane tanks are located adjacent to the camp facilities. Two additional 18,000 gal propane tanks are located near the West Zone area.
18.2.3.6 | Water Management System |
Surface water management is accomplished through a system of diversion ditches to direct non-contact fresh water around the core of the mine site area. The Johnson Creek (East) Diversion directs water to Brucejack Lake, while the Camp Creek (West) Diversion directs water to Brucejack Creek. Camp Creek naturally contains elevated metal concentrations. Contact water from within the mill and camp pads area is directed to the CWP via collection weirs, ditches, sumps and HDPE pipelines. The CWP is primarily a management tool to store water should there be a heavy rain event that would uncontrollably wash sediment with high metal or suspended solids into Brucejack Creek and acts as a reservoir for retreatment of off-specification water from the operations WTP. If there is insufficient process water available from dewatering the mine or the CWP pond, then process water is pumped from Brucejack Lake.
18.2.3.7 | Telecommunications |
A complete site-wide telecommunications system has been installed comprising four relay microwave stations and one backup microwave system, which include:
■ | VoIP telephone system for buildings, camps, and offices |
■ | emergency Satellite communications for critical voice and data needs |
■ | ethernet cabling for site infrastructure and wireless internet access |
■ | very-high frequency (VHF) two-way radio system with eight public channels |
■ | four remotely located VHF repeaters |
■ | satellite TV and Internet for employees at all camps |
■ | wireless access tower for communications at the towers |
■ | satellite phones available for remote work or communications outside the normal area limitations. |
A pre-manufactured trailer is used as an information management center (IMC) to house all communications equipment. The IMC includes all heating, ventilation and air conditioning (HVAC) equipment and an UPS.
The site telecommunications are linked to the site fiber optic backbone via the IMC. A separate emergency satellite communications system is provided and is isolated in the main camp building. This system handles emergency off-site contact in the unlikely event that the IMC and its vital equipment are compromised, or the main microwave system is interrupted.
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The microwave network towers are powered by multiple redundant power sources of: EFOY fuel cell, solar energy and propane power generation. Power and network traffic are also continually monitored to ensure proper maintenance routines. Internal facilities/information technology (IT) and specialized vendor support are contracted for the microwave system technical support.
18.2.3.8 | Miscellaneous Buildings |
A metallurgical laboratory, located on two 20 ft containers inside the mill building, houses all necessary laboratory equipment for metallurgical testing and control. The laboratory is equipped with all appropriate HVAC and chemical disposal equipment as needed.
The warehouse facility, including cold storage, located at the mine site houses consumable parts storage and conducts logistic support for inbound and outbound freight.
A medical clinic is located within the main camp and provides routine and emergency first aid services.
A fire hall houses emergency vehicles, including ambulance, fire trucks, and rescue equipment.
The mine dry is part of the camp and can accommodate up to 350 people, each with individual lockers and hanging baskets. The wicket and lamp rooms are located in the main camp adjacent to the dry where underground personnel are picked up by underground vehicles and transported to and from the underground mine.
In 2019, a mill dry will be constructed between the mill building and main camp. The facility will accommodate 100 persons.
A light vehicle/heavy equipment maintenance shop is located along the road immediately east of the mill building. The shop includes an oil water separator located on the north side of the building.
18.2.4 | Km 72 NPAG Quarry |
Construction aggregate for the mine was sourced from the NPAG quarry located at km 72 on the access road near the southeast corner of Brucejack Lake. Site investigations, which began in 2013, determined that the porphyry rock mass was NPAG and subsequent sampling each year of quarrying has confirmed that determination. Quarry material is used for road capping, both on surface and in the mine, and to provide a working surface on the waste rock dump for that portion of the waste rock dump above the lake surface level. There is sufficient quarriable material for all foreseeable mine needs.
18.3 | Off-site Infrastructure |
Off-site infrastructure (Figure 18-3) comprises the Brucejack Access Road from Highway 37, transmission line, Bowser Aerodrome, Knipple Transfer Station Camp, and Wildfire Camp. During construction other camp infrastructure was located at the Bowser site, but the accommodation and kitchen facilities are currently being decommissioned. For the time being the exploration geological core logging/sampling facilities remain in operation.
18.3.1 | Transmission Line |
Electricity for the Brucejack Gold Mine and Knipple Camp is provided from the BC Hydro network. An interconnection to the provincial grid is located at the Long Lake Hydro Substation, approximately 13 km north of Stewart. From the Long Lake Substation, the 138 kV line proceeds northward for 1.5 km to a control station, Brucejack Terminal, and then continues a further 42 km to the Knipple Substation. The Knipple Substation reduces the voltage from 138 to 69 kV; the transmission line then carries on to Brucejack Camp and is introduced into the mill where the main Brucejack distribution transformers are located. The 57 km line was completed on March 31, 2017.
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18.3.1.1 | Transmission Line Operations, Maintenance, and Emergency Response |
The transmission line is controlled via the main incoming breaker located at the control station, Brucejack Terminal, 1.5 km north of Long Lake Substation. The line section from Long Lake Substation to the control station is under control of BC Hydro. The Brucejack Transmission Line, past Brucejack Terminal, is controlled either through the Brucejack Camp control station or the Knipple Substation. An operating procedure establishes the procedures and communication protocols for operation of the transmission line to protect any transmission line workers and the integrity of the BC Hydro system.
Maintenance of the Brucejack Transmission Line consists of visual inspections along the transmission line, as well as periodic infrared surveys to look for potential deterioration in splices or other energized components. This is complemented with a periodic inspection of the transmission line towers, with climbing inspections to ensure the functionality of all conductors, guy wires, cross arms, and other transmission tower components. Emergency response is also important to manage the risk to the transmission line, with spare tower sections and other parts kept at Bowser Aerodrome to facilitate rapid response and restoration in the event of extreme weather damaging the transmission line.
18.3.2 | Access Road |
The Brucejack Access Road is an all-season, two-way gravel surfaced road that commences at Highway 37 at km 215 and travels generally westward to Brucejack Lake, a distance of 73.5 km.
The Brucejack Access Road is maintained throughout the year by maintenance crews stationed at Knipple Transfer Station. Aggregate materials for road maintenance are sourced from quarries located at km 10 and km 58. Regular patrols are conducted in potential avalanche areas with avalanche control measures in place.
A 12 km section of road, from km 59 to km 71, traverses the main arm of Knipple Glacier. The glacier toe has receded about 1 km and melted at least 100 m vertically since the route was pioneered by Newhawk in the 1980s. In 2012, when Pretivm reactivated the route, a new ramp was developed onto the ice but continued melting has required further road development off the glacier. A new 600 m section of road will be activated on the south side of the glacier in 2019 to bypass the lowermost portion of the glacier road.
Unlike other glaciers in the area, the Knipple Glacier is generally free from large crevasse fields that would present a difficult and hazardous route to vehicles and equipment. It does contain crevasses and mill holes (moulins) large enough to present hazards to all-terrain vehicles or personnel on foot. These hazardous crevasses and mill holes become increasingly visible throughout the summer as winter snows melt. Seracs, or ice cliffs, are not present along the immediate travel route.
Glacier travel guidelines and glacier emergency response plans have been developed and implemented by Pretivm. Personnel on foot are not allowed to traverse the glacier unless for a specific task related to road maintenance or monitoring. Only specially trained persons are allowed to exit vehicles on the ice. These personnel operating on the glacier receive additional safety training and are issued additional personal protective equipment such as rescue harnesses, avalanche beacons, rope rescue equipment, and avalanche rescue equipment.
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18.3.3 | Knipple Transfer Station Facilities |
The Knipple Transfer Station facilities include a camp with offices; potable water well with treatment system; maintenance and emergency vehicle building; covered storage facility including cold storage, fuel storage and dispensing system; helipad; waste handling facility with an incinerator, assay laboratory, paste binder silos, sewage treatment by septic systems; transmission line substation; and laydown area as shown in Figure 18-4. All deliveries to and from the mill site report to this facility for intermediate storage or transfer to a different vehicle before delivery to the mine or off site.
Figure 18-4: Knipple Transfer Station
18.3.3.1 | Camp |
The camp is sized to accommodate 120 people, complete with kitchen, recreation, dormitories, potable water treatment system, and a sewage treatment system. Offices are included in the camp to manage the shipping and receiving of goods. An emergency diesel generator provides power to the camp in case of transmission line power interruption. A wireless system provides communications.
Knipple Camp facilities include a first aid/emergency vehicle parking building, a cold storage/maintenance building, storage in sea can containers, and a waste handling facility with incinerator.
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18.3.3.2 | Fuel Storage |
Fuel is delivered to the Knipple Transfer Station and then stored in tanks before transshipment to the mine, except for propane which is delivered directly to the mine. Storage facilities comprise one 150,000 L and one 10,000 L diesel storage tanks, one 10,000 L gasoline tank, and propane in 30,000 L, two 8,000 L and two 4,000 L tanks. Diesel fuel, primarily for mobile equipment, is stored in one 150,000 L double-walled tank located at the laydown area. Aviation fuel is stored in barrels and in one 5,000 L tank. The fueling station lies on a lined pad and includes an oil water separator, a receiving pump, a strainer, and delivery pumps and filters.
18.3.4 | Bowser Aerodrome |
Bowser Aerodrome comprises a 5,000 ft long by 75 ft wide gravel airstrip with an apron for aircraft parking. The aerodrome is located 2 km east of Knipple Lake at 1,424 ft elevation. The airstrip is shown in Figure 18-5.
Figure 18-5: Bowser Aerodrome
The airstrip was constructed at the site by expanding and improving an existing gravel airstrip to provide a safe and maintainable facility for chartered air traffic. It is available to provide air service by chartered flights to and from the mine. Currently, the personnel transportation between Brucejack Gold Mine and Smithers/Terrace, BC is facilitated by chartered bus service. However, routine crew changes by chartered air service is under study. Personnel would be transported from the aerodrome to the mine camp by bus.
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The passenger aircraft used in the initial design of the aerodrome was the Beechcraft 1900; however, the design width has not been completed nor have all approach/departure obstacle clearing requirements been met. Larger aircraft such as the DE Havilland Dash 8 turboprops or C-130 Hercules could use the aerodrome if the full design criteria are built.
Regular maintenance, provided by road maintenance personnel and equipment, permit year-round operation.
18.3.4.1 | Maneuvering and Movement Surfaces (Runway and Apron) |
The runway and apron surface are granular and suitable for turbo-prop aircraft. The runway surface is 1,643 m (5,392 ft) long and 23 m (75 ft) wide and oriented magnetically to correspond to the runway designations 06-24. Runway 06 (western approach direction) has a displaced threshold, elevation 1,445 ft, that is 364 m (1,195 ft) from the west end of the airstrip. Runway 24 (eastern approach direction) threshold, elevation 1,440 ft, is located 60 m (198 ft) from the runway’s eastern end. The runway includes a 7.5 m (25 ft) graded area along each runway edge. The aircraft parking apron is located on the south side of the runway at runway 06 displaced threshold and has been sized to allow two Beach 1900 sized aircraft to maneuver and park.
All granular surfaces are treated with water for dust reduction.
18.3.4.2 | Aerodrome Equipment Requirements |
A weather station is located just east of the aerodrome and a ceilometer and altimeter are located at the aerodrome. A trained radio operator at site communicates with aircraft prior to arrival and is available after the flights have departed. This allows the operator to relay weather and altimeter information to the pilots prior to, during, and after departure (in case an emergency return is required).
18.3.5 | Wildfire Security and Camp |
The Wildfire Camp (Figure 18-6) is located at km 1 on the Brucejack Access Road. Facilities include a gate at the Highway 37 junction to screen access and a security building with a gate at the eastern side of Wildfire Camp to control access and importation of banned substances and fishing and hunting equipment. The security screening is to prevent unauthorized departure with gold. Screening of vehicles and equipment for invasive plant species is also undertaken at Wildfire Camp. All traffic entering or exiting the Brucejack Access Road must report to this facility. Access to/from the mine is controlled by the security personnel at site. The camp area includes a large laydown area for incoming and outgoing freight vehicles.
Wildifire Camp is sized to accommodate 27 people, complete with kitchen, dormitories, potable water well and pumphouse, potable WTP, and a septic field for sewage disposal. For bear protection the camp dormitories, dry, and kitchen buildings are enclosed with an electric fence with gates for pedestrians and service vehicles.
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Figure 18-6: Wildfire Camp
18.4 | Site Geotechnical Assessment |
The geotechnical engineering assessment for the Brucejack Gold Mine site has included several subsurface investigation programs completed over the past decade. The regional and local geologic conditions near the plant site are well understood based on surface mapping and sampling of overburden soils and bedrock. The geotechnical engineering parameters that were recommended for inclusion in the earthworks design and foundation analysis at the Brucejack, proved satisfactory in the preparation of Issued for Construction documents in 2016-17. Construction Record Reports for earthworks documented that the design intent of the drawings and specifications were met at the Brucejack Gold Mine. Further expansion will require only site-specific recommendations for any proposed expansion facilities as there is a large volume of site investigation and construction records from the main plant available.
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18.5 | Avalanche Hazard Assessment |
An avalanche hazard assessment of the mine site, Brucejack Access Road, and transmission line route was presented in the 2014 FS (Ireland et al. 2014). Generally, this hazard assessment remains unchanged.
In summary:
■ | The avalanche season for infrastructure below 1,000 m elevation is generally from November to May, while for elevations above 1,200 m the season is from October to June, or if cool, wet conditions persist avalanches can occur in summer months. Snow avalanches generally occur in areas where there are steep open slopes or gullies, and deep (more than 50 cm) mountain snow packs. Risks associated with avalanches are normally due to exposure to the high-impact forces that occur, as well as the effects of extended burial for any person caught in an avalanche. Avalanches may reach speeds up to 60 m/s (200 km/h). Impact pressures from dense flows are much greater than the powder component due to the density of the snow. |
■ | An avalanche path generally consists of a starting zone, a track, and a runout zone. Avalanches start and accelerate in the starting zone, which typically has a slope incline greater than 30°. Downslope of the starting zone, most large avalanche paths have a distinct track in which the slope angle is typically in the range of 15 to 30°. Large avalanches decelerate and stop in the runout zone where the incline is usually less than 15°. Smaller avalanches may decelerate and even stop on steeper slopes (15 to 24°). |
■ | Avalanche frequency is the reciprocal of avalanche return period and is typically referred to as an order of magnitude ranging from 1:1 (annual) up to 1:300 (1 in 300) years. Each winter the probability of an avalanche with a specified return period is constant; however, the frequency depends upon snow supply, decreases with distance downslope in the track, and runout zone and varies from year to year. |
■ | Destructive potential of an avalanche relates to the magnitude of an avalanche. In general, large destructive avalanches occur less frequently, while smaller ones occur on a more regular basis. The spacial relationship of infrastructure to the location along an avalanche path will affect the destructive potential. A further distance from the toe of an avalanche will result in less risk and frequency of that risk. |
■ | Prior to construction, 15 avalanche paths or hazard areas were estimted that potentially could reach infrastructure or access roads, and many of those on an annual basis. These avalanche hazards were avoided wherever possible. At the mine site there remains a risk of avalanches along the Brucejack Access Road between the NPAG quarry and the waste management facility on the eastern side of the mine site. There are also avalanche hazard zones along the Brucejack Access Road, particularly at km 44 and between Knipple Transfer Station and the ramp onto Knipple Glacier. In the km 44 area, remote avalanche control systems have been installed to trigger avalanches at controlled times in order to avoid significant likelihood of large avalanche development. Similar remote avalanche control systems are planned for the new section of Brucejack Access Road and ramp onto Knipple Glacier. |
■ | Pretivm has full time mountain safety technicians who monitor avalanche risk, develop hazard ratings for the Brucejack Access Road by specific sections, and release hazard bulletins with avalanche ratings for those road sections and glacier hazard ratings for travel on the glacier. The mountain safety technicians regularly survey the ice road and work with road maintenance to ensure safe travel on the ice. |
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19.0 | MARKET STUDIES AND CONTRACTS |
19.1 | Markets |
The Brucejack Gold Mine produces doré and flotation concentrate, which contain both gold and silver. The doré will be shipped to precious metal refineries located worldwide for further processing to produce refined metals for sale. The concentrate will be sold to international smelters or traders in concentrate form. The concentrates will be exported out of Stewart, BC in bulk form. With regards to the sale of gold, Pretivm is obligated to deliver refined gold up to 7,067,000 oz to Offtakers, under the Offtake Agreement entered in September 2015 as part of Brucejack Gold Mine construction financing.
Gold and silver prices have fluctuated significantly. Table 19-1 shows the current gold and silver prices (as of April 3rd, 2019) together with the last two-year and the last five-year average prices.
Table 19-1: | Gold and Silver Prices |
Metal | Unit | Spot(1) | Two Years | Five Years |
Gold | US$/oz | 1,290 | 1,274 | 1,241 |
Silver | US$/oz | 15.1 | 16.1 | 16.7 |
Note: | (1)Gold price on April 3rd, 2019 |
19.2 | Smelter Terms |
The terms reflected in the doré refinery and/or concentrate sales contracts that Pretivm currently holds at the time of this Technical Report. The related charge rates are within the industry normal rates. The terms are summarized as follows:
■ | Gold-silver doré: |
– | Gold and silver – pay 99. 97% of gold and 99.6% of silver content. Gold is refined and delivered to Offtakers’ accounts and treatment charge of US$0.50/troy oz and other agreed deleterious charges are deducted from the proceeds of silver sales. |
■ | Gold-silver concentrate: |
– | Gold and silver – pay 97.5% of gold depending on the gold contents, and 95% of silver content. An average treatment charge of US$240.00/dmt of concentrate is applied. Refining charges for payable metals are an average of US$9.00/troy oz for gold and US$1.15/troy oz for silver respectively. A penalty charge for arsenic in the concentrate is an average of US$6.25 per each 0.1% of arsenic if the arsenic concentration is above 0.2%. |
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19.3 | Concentrate Transportation |
Concentrate will be transported to the Stewart Bulk Terminal (SBT) in customized bulk containers (maximum capacity of approximately 23 t). The containers are designed to have an openable lid on top and hinged doors on the side. Containers will be loaded at the Brucejack Gold Mine site and trucked down to the Knipple Transfer Station, where a third-party trucking company will further transport them down to the SBT. From the SBT, the concentrate will be exported to international customers in bulk vessels.
The estimated concentrate transportation cost is U$163.75/wmt of concentrate, including ocean freight to Asian destinations at current market.
19.4 | Mining Development Contracts |
Underground mining at the Brucejack Mine is currently completed by Procon. This work includes lateral and ramp development, long hole drilling and blasting, mucking, hauling to the underground crusher, and backfilling. Mine planning is conducted by Pretivm employees who oversee the execution of the mining done by Procon.
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20.0 | ENVIRONMENTAL STUDIES, PERMITTING AND SOCIAL OR COMMUNITY IMPACT |
20.1 | Environment, Social and Sustainability |
20.1.1 | Corporate Policies, Guiding Principles and Criteria |
20.1.1.1 | Mine Operations Philosophy |
Pretivm is committed to continuing to operate the Brucejack Gold Mine in a sustainable manner and according to the guiding principles in its corporate Social, Environmental, and Health and Safety policies. Every reasonable effort has and will continue to be made to minimize or prevent potential long-term adverse environmental effects, and to ensure that the mine provides lasting benefits to local Indigenous and other communities while generating substantial economic and social advantages for shareholders, employees, and the broader community. Pretivm is focused on ensuring that the safe, successful operation of the Brucejack Gold Mine benefits the Province of British Columbia, and in particular the Nisga’a Nation, Tsetsaut Skii km Lax Ha First Nation, Tahltan Nation, and the communities of Gitlaxt’aamiks, Gitwinksihlkw, Laxgalts’ap, Gingolx, Dease Lake, Telegraph Creek, Iskut, Stewart, Terrace, Smithers, Hazelton and New Hazelton.
Pretivm is committed to sustainable resource development which balances environmental, social, and economic interests. Pretivm will continue to comply with regulatory requirements and to apply technically proven and economically feasible methodologies to protect the environment throughout mining, processing, and closure activities.
20.1.1.2 | Environmental Management Plan |
Environmental management is a corporate priority. Pretivm developed a comprehensive Environmental Management Plan (EMP) as part of its environmental assessment certification and major permits applications, implemented this during construction, and will continue to do so during mine operations and closure. The Brucejack Gold Mine approved EMP, including 20 component plans under the mine’s Environmental Assessment Certificate (EAC #M15-01) and additional plans approved via other mine authorizations, is integrated into all aspects of mine operations.
Environmental management is implemented on a basis of continual improvement. All of the component plans are considered to be live documents and undergo internal review a minimum of annually in accordance with regulatory requirements. Component plans are modified as appropriate based on these reviews and as required based on approved mine plan or environmental program modifications. Revised component EMPs are included in the mine’s annual report for its BCMines Act (M-243) andEnvironmental Management Act Permits (PE-107835 and PA-107025) and distributed to applicable BC provincial regulatory agencies; the Nisga’a Nation through the Nisga’a Lisims Government, the Tsetsaut Skii km Lax Ha First Nation; the Tahltan Nation (as represented by the Tahltan Central Government); and to the State of Alaska Department of Natural Resources. Updated versions of the EMP are also provided to BC EAO.
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Component plans of the EAC approved EMP are as follows:
■ | Aboriginal Consultation Plan |
■ | Air Quality Management Plan |
■ | Ancillary Infrastructure Decommissioning and Reclamation Plan |
■ | Aquatic Effects Monitoring Plan |
■ | Avalanche Safety Plan |
■ | Chemicals and Materials Storage and Handling Plan |
■ | Economic and Social Effects Mitigation Plan |
■ | Heritage Management Plan |
■ | Health Services Monitoring Plan |
■ | Invasive Plants Management Plan |
■ | Metal Leaching/Acid Rock Drainage (ML/ARD) Management Plan |
■ | Mine Emergency Response Plan |
■ | Reclamation and Closure Plan |
■ | Soils Management Plan |
■ | Spill Response Plan |
■ | Tailings and Subaqueous Waste Rock Deposition Management Plan (OMS: Brucejack Gold Mine Subaqueous Waste Rock and Tailings Deposition) |
■ | Traffic and Access Management Plan |
■ | Vegetation Management Plan |
■ | Waste Management Plan |
■ | Water Management Plan, OMS Manual |
■ | Wildlife Management Plan |
Additional management plans required for other authorizations or completed internally include:
■ | Geohazards Management Plan |
■ | Chromium Management Plan |
■ | Ground Control Management Plan |
■ | Health and Medical Services Plan |
■ | Mountain Goat Management Plan |
■ | Nitrogen Management Plan |
■ | Refuse Incinerator Management Plan |
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■ | Surface Erosion Prevention and Sediment Control Plan |
■ | Potable Water Management Plan |
■ | Construction Environmental Management Plan (applied to Construction phase only) |
Pretivm’s team of Environmental Department and Permitting personnel implement and/or direct, provide training as appropriate, and monitor the implementation of federal and provincial environmental requirements under the mine’s authorizations (BC EAC, Environmental Impact Statement [EIS] Decision Statement, permits, licenses, tenures) and EMP. Health and safety (including medical, security, and avalanche safety) requirements of applicable component plans are implemented and/or directed by the mine’s Health and Safety Department. Engineering related requirements, including geotechnical and geohazards, are led by the Technical Services Department. All of these personnel work closely with and/or are accountable to the mine manager, general manager, vice-president operations, director permitting, and environmental manager. SOPs have been developed as appropriate for the various plans and are implemented by personnel trained in their use.
20.1.1.3 | Traditional Knowledge |
Pretivm respects the traditional knowledge of the Indigenous peoples who have historically occupied or used the Project area. Pretivm recognizes that it has significant opportunity to learn from people who have generations of accumulated experience regarding the character of the plants and animals, and the spiritual significance of the area. Traditional knowledge informs planning for various aspects of the mine, including planning and design for future changes to the mine plan as may be applicable.
Pretivm is committed to an engagement process that continues to invite and consider input from people with traditional knowledge of the Brucejack Project area.
20.1.1.4 | Ecosystem Integrity |
Prior to about 1980, the local ecosystem was relatively undisturbed by human activities, although it was not static. Glacier retreat and relatively recent volcanic activity (within the last 10,000 years), along with landslides, debris flows, and snow avalanches, have and continue to modify the landscape. In the 1980s and through the 1990s, Newhawk completed mineral exploration, including advanced underground exploration, at Brucejack. In 2008, Silver Standard began surface exploration of Brucejack. Pretivm began major exploration programs starting in 2011, leading to mine construction in 2015.
The Brucejack Gold Mine was designed and constructed with a minimal disturbance area (surface disturbance of approximately 30 ha for core infrastructure at the mine site). Pretivm is committed to retaining current ecosystem integrity as much as possible during mine operations and closure. This objective is being met by:
■ | minimizing the mine infrastructure development footprint, and reclaiming areas that are no longer required for mine operations |
■ | avoiding adverse effects, where feasible |
■ | minimizing and/or mitigating unavoidable adverse effects. |
Following completion of operations, the mine and its supporting infrastructure will be closed and reclaimed to the approved end land uses in accordance with the Reclamation and Closure Plan. Objectives of the Reclamation and Closure Plan include returning disturbed areas to a land use meeting the average level of capability that existed prior to project development, where practical, and for the end configuration to be consistent with pre-existing ecosystems to the extent feasible.
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20.1.1.5 | Biodiversity and Protected Species |
Pretivm remains committed to making every reasonable effort toward maintaining biodiversity in the Brucejack Project area. Biodiversity is defined by the BC Ministry of Forests, Lands and Natural Resource Operations and Rural Development (MFLNRORD) as “the diversity of plants, animals, and other living organisms in all their forms and levels of organization, and includes the diversity of genes, species, and ecosystems, as well as the evolutionary and functional processes that link them” (BC MFLNRORD 1995).
Maintenance of biodiversity is not an isolated effort, but an integral part of project planning (mitigation and monitoring), environmental effects analyses, and achievement of sustainability goals. This approach was implemented throughout the mine’s environmental assessment and permits applications processes and subsequent development, and will continue to be implemented through operations.
20.1.2 | Social Setting |
20.1.2.1 | Socio-economic Setting |
Northwest BC is a sparsely populated and relatively undeveloped region of the province. Many of the smaller communities have predominantly Indigenous populations that are distant from one another as well as from the main regional centers of Smithers and Terrace. Nationally, the Indigenous population is one of the fastest growing populations, increasing at four times the rate of the non-Indigenous population since 2006. This suggests that the Indigenous population in this region will continue to represent a significant segment of the regional population into the future.
The Brucejack Gold Mine is located in the Regional District of Kitimat-Stikine. The mine’s area of influence is generally considered to be Northwest BC inclusive of communities from the Nass Valley and Terrace to Smithers, Stewart, and as far north as Dease Lake.
Primary resource industries, principally mining and forestry, are the mainstay of the regional economy. The forest industry declined in recent decades, which has significantly affected the economy and led to a steady decline in the regional population. As is typical of resource-dependent economies, communities in the region have experienced multiple cycles of “boom and bust” associated with mining and resource extraction, with the attendant population peaks and troughs. However, announcements of major projects (including mining and liquefied natural gas [LNG]) are expected to draw workers to the region, potentially leading to population growth in communities such as Smithers and Terrace.
Transportation infrastructure in northwest BC is limited. The primary transportation corridors are Highway 37 (north to south) and Highway 16 (east to west). Air transportation hubs include the Northwest Regional Airport in Terrace, which serves the communities of Terrace and Kitimat (including daily flights to Kelowna, Vancouver, Victoria and Prince George), the Smithers Regional Airport in Smithers (with flights to Vancouver, Dease Lake, Prince George, and other communities), and the Prince Rupert Airport in Prince Rupert (with scheduled flights to Vancouver).
Community and socio-economic impacts of the Brucejack Gold Mine are generally very favourable for the region, with many long-term opportunities created for local and regional workers. Pretivm is committed to hiring workers from northwest BC; as of December 2018, 58% of Pretivm’s direct workforce of 619 employees were residents of the region and 34% self-identified as Indigenous. These rotational jobs allow workers to continue living in their home communities, and have likely helped to reduce and possibly reverse the out-migration to larger centers. Pretivm has and continues to work actively with Indigenous groups (including the Nisga’a Nation, Tsetsaut Skii km Lax Ha First Nation, Tahltan Nation, and Gitanyow Hereditary Chiefs) and representatives of local communities to maximize benefits through employment and business opportunities, training, and skills development programs. Through multiple initiatives including working with local training organizations and holding career fairs throughout the region, Pretivm is committed to enhancing local benefits and improving economic growth in the region. Pretivm also owns a warehouse and office in Smithers, where it bases its off-site supply chain management, warehousing, travel, and some senior environmental and permitting personnel; approximately 20 employees work at this location.
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Pretivm reached a Cooperation and Impacts Benefits Agreement with Nisga’a Nation in April 2015, with Gitanyow Hereditary Chiefs in June 2016, and with the Tahltan Central Government in October 2017.
The following subsections profile northwest BC focusing on the Highway 16 and Highway 37 corridors with reference to population data from Statistics Canada’s 2016Census of Canada.
Highway 16 Corridor
From the deepwater port at the City of Prince Rupert on the west coast, Highway 16 extends eastward to Terrace, the Hazeltons, Smithers, and Prince George; the Canadian National Railway also follows this route. Rural settlements and Indigenous reserves are interspersed throughout the region. With a strong history in forestry, mining and rail transport, these communities have shown business growth and development of a wide array of goods and service contractors related to mineral exploration and mining. In 2016, Terrace was home to more than 11,000 residents and Smithers had a population of 5,350; further east, the northern service center of Prince George has a population of more than 86,000 people.
Highway 37 Corridor
Highway 37 connects with Highway 16 at Kitwanga and extends northward to the Yukon border. At Meziadin Junction, a secondary route (Highway 37A) branches west and connects to the deep-water port in the community of Stewart. The Brucejack Access Road intersects Highway 37 60 km north of Meziadin Junction at km 215 of Highway 37. Mining and forestry industries use the Stewart World Port and the SBT to ship products from northern BC and Yukon to international destinations, taking advantage of Canada’s most northerly ice-free port. Further north, the communities along this corridor include Iskut, Dease Lake, and Good Hope Lake.
With the exception of Stewart, most communities in this area are Indigenous. Indigenous communities include the Nisga’a Nation communities of Gitlaxt’aamiks, Gitwinksihlkw, Laxgalts’ap and Gingolx and the Tahltan Nation’s communities of Iskut, Telegraph Creek, and Dease Lake. These communities rely heavily on public sector employment, with growing involvement in the mining industry. They are distant from larger service centers and Dease Lake and Telegraph Creek are not connected to the provincial electricity network. Dease Lake, with a population of approximately 400 people (on- and off-reserve) in 2016, is the main center for goods and services (including a small airstrip), and is located approximately an eight-hour drive to either Smithers or Whitehorse.
Stewart, BC was established in 1902, and following an influx of gold seekers beginning in 1906 had a population of approximately 10,000 by 1910. Its population has subsequently fluctuated in response to mining (primarily) and forestry cycles, with many of the current structures constructed for development of the Granduc Mine in the 1960s. Since the Granduc Mine’s closure in the 1980s, the town’s population declined dramatically from nearly 1,500 in 1981 to approximately 500 people between 2006 and 2011. This was followed by a further 19% decline to 400 residents in 2016. Possible mine developments in the Highway 37A corridor have the potential to reverse the decline in population.
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As mentioned above, announcements of mining and LNG investments in recent years have created renewed optimism for opportunities in the shipping and LNG industries and the potential for increased jobs and investment to the region.
20.1.2.2 | Traditional Knowledge and Traditional Use |
The Brucejack Gold Mine is located on Crown land in an area historically used by several Indigenous groups. A desk-based ethnographic overview for the potentially affected Indigenous groups was undertaken in 2012 and 2013. In addition, a Traditional Knowledge/Traditional Use (TK/TU) study was completed for the Tsetsaut Skii km Lax Ha. These studies identify areas and seasons where Indigenous groups have engaged in traditional interests and activities including hunting, fishing, gathering, and spiritual activities.
As described further below, part of the Project area is covered by the Cassiar-Iskut Stikine LRMP which was developed by the province of BC resource agencies, in consultation with Indigenous partners, communities and other stakeholders. When the LRMP was approved in 2000, the Tahltan Nation became the first Indigenous group in BC to have participated in a LRMP process.
20.1.2.3 | Non-Indigenous Land Use |
The mine site portion of the Brucejack Project area is included in the Cassiar Iskut-Stikine LRMP, which was approved by the province in 2000 and encompasses 5.2 million hectares of northwestern BC. The LRMP is a subregional integrated resource plan that establishes the framework for land use and resource management objectives and strategies and provides a basis for detailed management planning. The LRMP outlines the management direction, research and inventory priorities, and economic strategies for the Cassiar Iskut-Stikine area, and presents an implementation and monitoring plan to reach the established objectives.
The Brucejack Access Road and transmission line east of the head of Knipple Glacier portions of the Brucejack Project area lie within the boundaries of the South Nass Sustainable Resource Management Plan (SRMP) area, finalized in June 2012. The SRMP is a landscape-level plan that addresses the sustainable management of land, water, and resources while considering economic interests.
The area surrounding the Brucejack Gold Mine has been the focus of mineral exploration for many years. There are indications that prospectors explored the area for placer gold in the late 1800s and early 1900s. Placer gold production has been reported for Sulphurets Creek in the 1930s, and a large log cabin near the confluence of Mitchell and Sulphurets Creeks was reportedly used by placer miners until the late 1960s. The region surrounding the mine is extensively staked with mineral claims and several other mining companies have active exploration programs nearby.
The mineral deposits in and adjacent to the Brucejack Gold Mine area have been extensively explored on an intermittent basis since the 1960s. Intensive underground exploration adjacent to Brucejack Lake in the 1980s by Newhawk was supported by an exploration road from Bowser Lake over Knipple Glacier.
Results of the 2012 non-traditional land use baseline research program indicate that a limited number of people access the Stewart to Bell II general area. Those known to access the broader general area include those with specific licenses and tenures for land and resource use, such as trappers, guide outfitters, hunters, and those who participate in commercial recreation activities such as heli-skiing, guided freshwater recreation, and guided mountaineering. Other individuals with interests in the general area include those who hold forestry licenses, mineral claims, and placer claims, all linked to resource development and industry, as well as water licenses, which may be linked to commercial recreation businesses. Overall, land use in the area is of low intensity and activities are often seasonal in nature.
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20.1.2.4 | Archaeology and Heritage Resources |
Archaeological assessments were conducted in accordance with approved methodologies of permits issued under theHeritage Conservation Actaround the mine site and along the access and transmission corridors. Two small prehistoric archaeological sites were identified in proximity (within 1 km) to mine related infrastructure and were avoided during construction.
20.1.2.5 | Social and Community Management Systems |
Pretivm developed an ESEMP as a requirement of its EAC. The ESEMP comprises specific strategies to minimize, mitigate and/or manage potential adverse effects while enhancing positive impacts of the Brucejack Gold Mine on surrounding local and Indigenous communities. These communities comprise the Local Study Area (LSA) and include the Nisga’a villages (Gitlaxt’aamiks, Gitwinksihlkw, Laxgalts’ap and Gingolx), Telegraph Creek, Dease Lake,
Iskut, Hazelton, New Hazelton, Stewart, Terrace and Smithers. Strategies relate to local employment, procurement, training, transportation and communications protocols, including reporting and feedback. The ESEMP was first drafted in August 2015 and provided to the Nisga’a Lisims Government, Tahltan Central Government, and Tsetsaut Skii km Lax Ha First Nation for review and comments. An updated version the ESEMP was issued in March 2019 inclusive of minor updates to reflect the changes required during full-time commercial mine operations.
Pretivm prepares an annual report on the outcomes and achievements related to the ESEMP each year (latest issued January 2019) and circulates it to the BC EAO, Indigenous groups and LSA communities. This report documents the following:
■ | engagement with, and feedback from, local and regional residents |
■ | employment, hiring, and recruitment statistics, including efforts for local and Indigenous hiring |
■ | summary of education and training initiatives |
■ | procurement initiatives including local and Indigenous contracts |
■ | changes or updates to the workforce transportation strategy. |
20.1.3 | Consultation |
Pretivm recognizes the importance of carrying out consultation and will continue to meet all regulatory requirements to conduct consultation. Pretivm regularly engages with Indigenous groups, community residents, local governments, and educational institutions in northwest BC in order to provide information and seek feedback about the Brucejack Gold Mine.
20.1.3.1 | Consultation Policy Requirements |
Provincial and federal regulations, various permit requirements, best practices, and internal company policies contain provisions for consultation with Nisga’a Nation, Tsetsaut Skii km Lax Ha, Tahltan Nation, and various communities, both Indigenous and non-Indigenous.
20.1.3.2 | Consultation |
Community engagement and consultation are fundamental to the success of the Brucejack Gold Mine. Since 2011, Pretivm has regularly consulted with the Nisga’a Nation, Tahltan Nation, Tsetsaut Skii km Lax Ha, as well as other Indigenous groups. As part of the environmental assessment process, Pretivm participated in all BC EAO technical working group meetings, which involved engagement with all relevant government agencies, and Indigenous representatives. Through this process, Pretivm developed a specific consultation plan for engagement with Indigenous groups, spanning from the environmental assessment pre-application through to the post-application periods. Indigenous, public, and government consultation activities, such as private and community meetings, open houses, information distribution activities and site tours, all informed the EAC application process and subsequent permitting processes. In recent years, engagement has focused on permit amendments and local hiring to fill positions at the mine (including Pretivm and contractor workers) and opportunities for education, training, procurement, and addressing barriers to employment.
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Pretivm employs a full-time community relations manager, based at the company’s office in Smithers. The community relations manager is responsible for engagement with Indigenous groups and other local stakeholders, and works with Pretivm’s staff and contractors to ensure that the company’s commitments for engagement, communication, and local recruitment are addressed. Consultation activities are tracked and recorded using an online database and are regularly reviewed to promote and strengthen continual relationship building and issues tracking. A summary of engagement is provided in Pretivm’s annual ESEMP reports.
Ongoing consultation efforts aim to engage both the leadership and community membership and attempt to resolve potential issues and concerns as they arise, with a focus on proactive inclusion and increased supplier development within the Brucejack supply chain for local and Indigenous businesses. No substantive issues have been raised to date regarding the mine.
Pretivm has and continues to engage and collaborate with the federal, provincial, regional, and municipal government agencies and representatives as required with respect to topics such as: permit compliance, land and resource management, and environmental and social studies.
Pretivm consults with the public and relevant stakeholder groups, including land tenure holders, businesses, economic development organizations, businesses and contractors (e.g., suppliers and service providers), education and training providers, and special interest groups (e.g., environmental, labour, social, health, and recreation groups), as appropriate.
20.2 | Environmental Assessment Certifications and Permitting |
Mining projects in BC are subject to regulation under federal and provincial legislation to protect workers and the environment. This section discusses the principal licenses and permits acquired for the Brucejack Project.
20.2.1 | Environmental Assessment Certifications |
Major mining projects in BC are subject to environmental assessment and review prior to certification and issuance of permits to authorize construction and operations. Environmental assessment is a means of ensuring the potential for adverse environmental, social, economic, health, and heritage effects or the potential for adverse effects on Aboriginal interests or rights are addressed prior to project approval. Brucejack was subject to both the BCEnvironmental Assessment Act (BCEAA) and CanadianEnvironmental Assessment Act (CEAA) 2012 review processes. The design production rate of 2,700 t/d exceeded the BC provincial threshold criterion for requirement of an environmental assessment as specified in the BC Reviewable Project Regulations [75,000 t/a (or 205 t/d)], and the federal threshold criterion for gold mine developments of 600 t/d, as specified under the Regulations Designating Physical Activities. On March 26th, 2015, BC EAC #M15-01 was awarded and on July 27th, 2015, a federal project approval was issued in a Decision Statement under Section 54 of the CEAA, 2012.
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Following issuance of the BCMines Act Permit M-243 andEnvironmental Management Act permits PE 107835 and PA 107025 in July and August, 2015 respectively, the Brucejack EAC #M15-01 was amended five times. These amendments were to bring the EAC into conformance with changes to infrastructure and design that resulted both during the initialMines Act andEnvironmental Management Act permits application and review process and later due to facility refinements during subsequent detailed design and construction. The fifth EAC amendment included increasing the total tonnage to be mined and increased the daily/annual mining rate. The federal Decision Statement is not subject to amendments and the increase in production rate was not sufficient to require a new federal environmental review.
Table 20-1: | List of Amendments to EAC #M-15-01 |
Amendment | Date | Purpose |
1 | 10 March 2016 | Add NPAG rock quarry, set time limit for PAG rock storage, remove borrow source component, amend layout figures and maps. |
2 | 12 August 2016 | Add electric fencing to Wildfire Camp, revise Schedule A and figures. |
3 | 23 November 2016 | Add aviation beacons and revise layout figures and maps. |
4 | 13 March 2017 | Changed time limit for PAG rock storage in amendment #1. |
5 | 15 November 2018 | Changed maximum production to 18.5 Mt of ore, added snow melter and |
process water pumping system, and changed wording related to waste rock and tailings storage. |
On December 21, 2017 the EAO issued a determination that the project has been substantially started, which has the effect that the EAC remains in effect for the life of the project, subject to the Minister’s power to cancel and suspend a certificate under Section 37 of the BCEAA.
20.2.2 | Permits and Other Authorizations |
A variety of applicable BC and Canadian environmental, safety standards and practices required permits and other authorizations for Brucejack Gold Mine construction and operations. Pertinent provincial and federal legislation and/or under which authorizations have been obtained include:
■ | Environmental Assessment Act(BC) |
■ | Environmental Management Act(BC) |
■ | Forest Act(BC) |
■ | Forest and Range Practices Act(BC) |
■ | Forest Practices Code of British Columbia Act(BC) |
■ | Health Act(BC) |
■ | Health, Safety and Reclamation Code for Mines in British Columbia(BC) |
■ | Industrial Roads Act(BC) |
■ | Land Act(BC) |
■ | Mineral Tenure Act(BC) |
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■ | Mines Act(BC) |
■ | Mining Right of Way Act(BC) |
■ | Motor Vehicle Act(BC) |
■ | Nisga’a Final Agreement Act(BC) |
■ | Safety Act(BC) |
■ | Transportation Act(BC) |
■ | Water Sustainability Act(BC) |
■ | Wildlife Act(BC) |
■ | Canadian Environmental Protection Act(Canada) |
■ | Canada Transportation Act(Canada) |
■ | Transportation of Dangerous Goods Act(Canada) |
■ | Canada Explosives Act(Canada) |
■ | Nuclear Safety and Control Act(Canada) |
■ | Navigation Protection Act (formerly Navigable Waters Protection Act)(Canada) |
■ | Fisheries Act(Canada) |
■ | International Rivers Improvement Act(Canada) |
Major federal and provincial licenses, permits, and approvals that were obtained to construct and operate the Brucejack Project are summarized in the following sections. This summary cannot be considered final for the LOM due to the complexity of government regulatory processes, which evolve over time, and the large number of minor permits, licenses, approvals, consents, authorizations, and potential amendments that are required from time to time. More than 100 authorizations have been issued to date for construction and operation of the Brucejack Gold Mine and its supporting infrastructure. A compliance tracking system is used.
20.2.2.1 | British Columbia Authorizations, Licenses and Permits |
While major statutory permits for provincial permitting, licensing, and approval processes proceeded concurrently with the BCEAA review, no statutory permit approvals can be issued before the EAC is issued. As well, through mine life when significant changes to provincial permits are requested, the EAC must be amended before those permit amendments can be approved. BrucejackMines Act Permit M-243 has been amended seven times to accommodate mine plan changes, including the increase in production rate to 1,387,000 t/a (3,800 t/d). TheEnvironmental Management Act discharge permits for waste discharges to both water and air have been amended four times. The Brucejack Access Road, initially permitted under a BCMines Act exploration permit, was re-permitted as a Special Use Permit S25923 and has been amended once.
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Table 20-2: | List of BC Major Authorizations, Licenses, and Permits Obtained to Develop and Operate the Brucejack Project |
BC Government Agency - Permits and Licenses | Enabling Legislation and Authorization |
Environmental Assessment Office | Environmental Assessment Act EAC #M15-01 issued 26 March 2015; amended 10 March 2016, 12 August 2016, 23 November 2016, 31 March 2017, and 15 November 2018 |
Ministry of Energy, Mines and Petroleum Resources, Approving Mine Plan and Reclamation Program, including the northern one-third of the transmission line on Pretivm mineral tenures. | Mines Act Permit M-243 issued 22 July 2015; amended 26 August 2015, 9 September 2015, 17 March 2016, 4 August 2016, 3 April 2017 and 14 December 2018. |
Ministry of Energy, Mines and Petroleum Resources Issuance of Mining Leases | Mineral Tenure Ac Tenures 1038597, 1038598, 1038599 and 1038600 issued 17 September 2015 |
Ministry of Environment and Climate Change Strategy Discharge Mine Related Contaminants and Effluent to Water Permit | Environmental Management Act Permit 107835 issued 31 August 2015; amended 4 February 2016, 12 July 2016, 31 March 2017 and 14 December 2018. |
Ministry of Environment and Climate Change Strategy Discharge Mine Related Contaminants to Air and Ash to Ground Permit | Environmental Management Act Permit 107025 issued 9 January 2014; amended 22 July 2015, 12 July 2016, 8 September 2017 (temporary item that was included in next amendment), and 27 March 2018. |
Ministry of Forests, Lands, Natural Resource Operations and Rural Development Access Road | Forest Practices Code of British Columbia ActandMining Right of Way Act Special Use Permit S25923 issued 23 July 2015; amended 7 June 2016 |
Ministry of Forests, Lands, Natural Resource Operations and Rural Development Occupant License to Cut | Forest Act Licenses to cut to clear timber along the transmission line and access road route and other infrastructure sites, OLTC L48433 and L50280 issued 1 May 2015 and 23 July 2015, respectively. |
Ministry of Forests, Lands, Natural Resource Operations and Rural Development Water License – Use | Water Sustainability Act Process water withdrawal license 500684 issued 26 November 2018 (replaces prior license) |
Ministry of Forests, Lands, Natural Resource Operations and Rural Development
| Water Sustainability Act Diversion of surface waters around site and withdrawal from mine. Licences C132076 and C132077. |
Safety Authority | Incinerators and southern two-thirds of transmission line |
Ministry of Forests, Lands, Natural Resource Operations and Rural Development Licenses of Occupation (a total of 20 sites) Transmission Line (southern two-thirds), Wildfire Camp / Laydown, Bowser Aerodrome / Camp / Laydown, Explosives Storage Areas, Knipple Transfer Station, Scott Weather Station, Communication Tower Sites, Aviation Beacon Sites | Land Act Most issued in 2015 with additions in 2016. |
Ministry of Environment and Climate Change Strategy Hazardous Waste | Hazardous Waste Regulation Provincial identification number BCG 10829 issued 6 September 2013. |
Northern Health Camp Operation Permits (potable water system (including wells), sewage systems, camp operations, camp food services) | Drinking Water Protection Act/Health Act/Municipal Wastewater Act All issued by Northern Health starting in 2013, ongoing as annual updates for changes in design and operations. |
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20.2.2.2 | Federal Approvals and Authorizations |
Applications for federal approvals can be completed concurrently with or following the provincial environmental assessment process, but permits and authorizations cannot be obtained until federal approval of the EIS. Table 20-3 lists federal approvals obtained for the Brucejack Gold Mine.
Table 20-3: | List of Federal Approvals and Licenses Obtained to Develop and Operate the Brucejack Project |
Federal Government Approvals and Licenses | Enabling Legislation and Authorization |
Canadian Environmental Assessment Agency EIS | CEAA 2012 Decision Statement issued 27 July 2015. |
Environment Canada Alteration of flow on an international river | International Rivers Improvement Act Exception received 26 November 2015. |
Environment Canada MDMER | Fisheries Act/Metal and Diamond Mining Effluent Regulation (MDMER) The mine became subject to MDMER on 12 January 2016. |
Transport Canada, Navigable Waters Protection Program Stream crossings authorization | Navigation Protection Act Issued 10 December 2012; not subject to the act as of 6 July 2016. |
Natural Resources Canada Explosives Storage Facilities | Explosives Act |
Innovation, Science and Economic Development Canada Radio Licenses | Radio Communication Act |
Canadian Nuclear Safety Commission Radioisotope License (nuclear density gauges) | Nuclear Safety and Control Act |
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20.2.3 | Financial Assurance |
The Reclamation Security for activities within the area covered byMines Act Permit M-243 (primarily the area within the Mining Leases) totals $31,700,000. This reclamation security is reviewed annually as part of the annual MEMPR reporting requirements and is also subject to major review every five years to reflect changes in mine plans and anticipated reclamation costing rate changes. The next five-year review is due in 2020. The Brucejack Access Road reclamation security held under the Special Use Permit totals $2,000,000. This security is subject to annual changes based upon Canadian Consumer Price Indices. A number of smaller reclamation securities are established under each license agreement for facilities built on Licenses of Occupation.
20.3 | Environment |
20.3.1 | Environmental Setting |
20.3.1.1 | Introduction |
The Brucejack Gold Mine is located at km 73 of the Brucejack Access Road, in an alpine area along the southwest shore of Brucejack Lake (Figure 4-2). The mine site elevation is approximately 1,400 masl; treeline is at approximately 1,200 masl. Elevations of the Knipple Camp (km 56), Bowser Aerodrome (km 51), and Wildfire Camp and Security (km 1) areas are approximately 470, 444, and 453 masl, respectively. The 73 km Brucejack Access Road climbs to an elevation of approximately 1,000 masl at the summit of Scott Pass, near km 17 between Wildfire Camp and Bowser Aerodrome.
This topographic and spatial variation results in significant temperature, precipitation, and wind differences between these project infrastructure areas and along the Brucejack Access Road. The mine and its supporting infrastructure lie in a transition zone between the very wet coastal and drier interior regions of BC. This part of northwestern BC is dominated by weather systems generated from the Pacific Ocean, but is also strongly influenced by orographic effects caused by the local mountain topography that produces high spatial variability in snowfall and precipitation, and in temperatures and snowmelt. In addition, the large glacial areas around the mine site can impact snowmelt rates and produce high runoff volumes during the summer months. The humid climate and physical characteristics of the region result in dynamic streams and rivers with high annual runoff rates and high average stream flows.
The Brucejack Gold Mine and its supporting infrastructure are located in a rugged area with elevations ranging from approximately 500 masl at the lower elevations along parts of the Brucejack Access Road and the transmission line to 1,400 m at the mine site. Peaks surrounding the mine site and for the northernmost part of the transmission line reach elevations of up to approximately 2,200 masl. Glaciers and icefields surround the mine site to the west, south, and east.
Recent and rapid deglaciation has resulted in over-steepened and unstable slopes in many areas. Recently deglaciated areas typically have limited soil development, consisting of glacial till and colluvium. Lower elevation areas with mature vegetation may have a well-developed organic soil layer. Avalanche chutes are common throughout the area, and management of avalanche hazards is a key aspect of mine and access road operations. Avalanche and glacier access hazards are actively monitored and managed by mountain safety personnel within the mine’s health and safety department, in accordance with the Avalanche Safety Plan (ASP).
The mine site area (all mine infrastructure west of the upper Knipple Glacier, km 71) is situated within the Brucejack Creek watershed, which is a small headwater sub-basin within the Sulphurets Creek watershed (drainage area 299 km2). Sulphurets Creek is a tributary of the Unuk River that flows southwest, eventually discharging to the Pacific Ocean northeast of Ketchikan, Alaska (drainage area 2,577 km2 at the mouth). Brucejack Access Road km 0 to 71.5 and the infrastructure areas along the road are located within the Bell-Irving River watershed, which drains to the Nass River. The Nass River discharges into the Pacific Ocean in Canada.
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There are no fish present within Brucejack Lake or Creek, or in most of Sulphurets Creek downstream of the mine. The nearest recorded fish presence is more than 20 km downstream of the mine, approximately 300 m upstream of the confluence of Suphurets Creek with the Unuk River. The Bowser and Bell-Irving rivers are both fish-bearing, including by anadromous salmonids and resident Dolly Varden char. Wildlife species present in the area include black and grizzly bears, moose, and mountain goats.
Pretivm undertook extensive environmental baseline studies in support of its EAC/EIS Decision Statement and subsequent major provincial permit applications (Mines Act Permit,Environmental Management Act permits and other authorizations). These included atmosphere/climate, surface and subsurface hydrology, aquatics, geochemistry, hydrogeology, surface water and sediment quality, limnology, fish habitat, soils, vegetation and wildlife studies to characterize the local and regional ecosystem prior to major disturbances. Archaeology, heritage, land use, cultural, Traditional Knowledge, and socio-economic baseline studies were also carried out to characterize the regional human environment. An extensive environmental monitoring program was implemented through mine construction and is being continued through mine operations in accordance with the mine’s authorizations.
20.3.1.2 | Climate |
The climate of the Iskut region is relatively extreme and daily weather patterns are unpredictable. Prolonged clear sunny days can prevail during the summers. Precipitation in the region is approximately 1,600 to 2,100 mm annually. The majority of precipitation falls during the autumn and winter months, from October to April. Records show that Brucejack Lake receives approximately 70% of its annual precipitation on average during this period. The months of October through to January typically have the highest monthly precipitation amounts, while late spring or early summer months are typically much drier. Snowpack typically ranges from 1 to 2 m deep, but high winds can create snowdrifts up to 15 m deep. Permanent icefields are present in the upper reaches of the Brucejack Lake watershed.
A full meteorological station was established west of the Brucejack Camp in mid-October 2009 to collect site-specific weather data. The station measures wind speed and direction, air temperature and pressure, rainfall, snowfall, relative humidity, solar radiation, net radiation, and snow depth. The Brucejack Lake station operated from October 2009 to August 2014. The tower and instrumentation were relocated to a site in the Valley of the Kings valley, more proximal to the Brucejack Camp, in September 2014.
Table 20-4 presents the estimated average monthly climate data for the Brucejack Project site (BGC 2017).
Average monthly temperature data used at the Brucejack Project site are based on temperature data collected at site for the 2013-2016 period.
Annual evaporation at the site was estimated using local climate data from the on-site climate station for the period 2010 to 2012, and Reference Evapotranspiration (REF-ET) calculation software (Version 3.1.14). Climate inputs required for the model include air temperature, wind speed, incoming solar radiation (or sunshine hours), relative humidity, dew point temperature, and atmospheric pressure. Monthly evaporation and sublimation totals are summarized in Table 20-4.
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Table 20-4: | Average Monthly Climate Data for the Brucejack Gold Mine Site |
Average | |||
Average | Average | Evaporation/ | |
Temperature | Precipitation | Sublimation | |
Month | (°C) | (mm) | (mm) |
January | -5.0 | 269 | 2 |
February | -6.9 | 231 | 2 |
March | -5.8 | 196 | 2 |
April | -2.6 | 105 | 4 |
May | 3.8 | 95 | 10 |
June | 5.8 | 72 | 23 |
July | 8.1 | 90 | 46 |
August | 8.5 | 150 | 41 |
September | 4.5 | 224 | 25 |
October | -0.1 | 267 | 8 |
November | -5.2 | 233 | 2 |
December | -7.7 | 267 | 2 |
Average/Total | -0.2 | 2,200 | 167 |
Source: | BGC (2017). |
20.3.1.3 | Ecosystems |
The mine site is situated in a gossanous area above the treeline. Prior to construction it was dominated by unvegetated and sparsely vegetated terrain, with limited areas of alpine ecosystems within the gossan itself. Alpine ecosystems, including tundra, heather, and fellfield classes, are common in the area surrounding the mine site. The The Brucejack Access Road traverses valley bottom forests, subalpine stands of subalpine fir and Engelmann spruce in higher elevation sections, particularly through Scott Pass. Dry glaciofluvial terraces supporting early seral pioneer ecosystems are present within the lower elevation portions of the Bowser River valley. The transmission line from the mine site to its intertie at the Long Lake Hydro substation traverses both mature forest and recently deglaciated terrain, dominated by scoured rock, eroding moraine, and glaciofluvial deposits. The northernmost segment extending from Knipple Camp to the mine site traverses mountain ridges and tops and includes several large glacier spans.
Wetlands are very limited in extent in the vicinity of the Mine and along the Brucejack Access Road. There are several wetlands along or near to the Brucejack Access Road in the Scott Pass area between km 15 and 30, and along the Bowser River floodplain section of the road. Wetlands are valued ecosystem components (VECs) and were assessed as part of the Brucejack Gold Mine environmental assessment process. Wetlands are conserved and managed through federal initiatives, such as the Federal Policy on Wetland Conservation. Baseline studies were conducted to map and classify wetlands, and to identify the primary wetland functions. These baseline data were used to identify areas where toad tunnels were installed along the Brucejack Access Road to provide safe access to wetlands for migrating Western toads.
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The region surrounding the Brucejack Gold Mine and its supporting infrastructure is home to many terrestrial and aquatic wildlife species including black and grizzly bears, mountain goats, moose, bats, furbearers, small mammals, birds of prey, migratory songbirds, waterfowl, and herptiles. These include several species at risk as well as species of cultural and economic importance. Prior to the environmental assessment process, Pretivm evaluated the potential for adverse effects on representative species that were identified as being at risk or of concern within the area through baseline surveys. Species at risk that were encountered during baseline studies included wolverine, fisher, grizzly bear, western toad, barn swallow, rusty blackbird, olive sided fly catcher, and little brown Myotis. While no little brown Myotis bat habitat was identified as disturbed, bat houses were installed along the Brucejack Access Road and along the transmission line. Species of concern include those that may not be of conservation concern but are of regional importance for other reasons, or are identified in the Cassiar Iskut-Stikine LRMP, and include moose, mountain goat, black bear, and American marten.
Wildlife monitoring is conducted, and additional mountain goat and moose surveys will be conducted for these species at five-year intervals throughout mine life. Wildlife observations at mine infrastructure areas are recorded and helicopter pilots are required to implement measures to minimize or prevent disturbance of mountain goats and other species. The mine implements a rigorous waste management program and other measures to prevent wildlife access to food or other potential mine-related attractants. A Wildlife Advisory Committee (WAC), which includes representatives of the Nisga’a Nation, Tahltan Central Government, Tsetsaut/Skii km Lax Ha and BC MFLNRORD, was established at the beginning of mine construction and will continue to meet during mine operations.
The Brucejack Gold Mine is situated in the headwaters of the Brucejack Lake watershed; Brucejack Creek drains Brucejack Lake and enters the subglacial flow of Sulphurets Creek approximately 3.1 km downstream of the Brucejack Lake outlet. Sulphurets Creek flows approximately 20 km downstream of the Brucejack/Sulphurets Creek confluence to its confluence with the Unuk River. Fish are absent within and downstream of Brucejack Lake in all waterbodies, including Sulphurets Creek, upstream of a barrier located 300 m upstream of the confluence of Sulphurets Creek and the Unuk River. The Unuk River is a large river system that provides important habitat for the five species of Pacific salmon, as well as habitat for resident trout (cutthroat, rainbow), and resident Dolly Varden.
The Brucejack Access Road traverses the watershed of the Bell-Irving River, including its tributaries Wildfire Creek, Todedada Creek (tributary to Treaty Creek which is tributary to the Bell-Irving River) and the Bowser River. The Bell-Irving River in turn drains to the Nass River. The Bell-Irving River system provides habitat for sockeye, Coho, and Chinook salmon; resident and anadromous trout (rainbow and steelhead); resident char (Dolly Varden and bull trout); mountain whitefish; and coarse fish species. The fisheries resources and fish habitat of potentially affected rivers and their tributaries were assessed as part of the baseline program for the Brucejack Gold Mine.
20.3.2 | Geochemistry |
20.3.2.1 | Introduction |
The geochemistry of rock that has been or will be disturbed, excavated or exposed at the Brucejack Gold Mine has been characterized through static and kinetic test programs. The characterization programs have also evaluated the water quality impacts of explosives used for blasting and cement products used in shotcrete and paste backfill. Static tests include acid base accounting (ABA) analyses to evaluate whether material is PAG, elemental analyses to identify parameters which are elevated and of potential concern, and shake flask extraction tests to provide an indication of soluble loads and drainage chemistry. Kinetic tests including field bins (n=14), humidity cells (n=69) and saturated columns (n=22) have been carried out to assess the long-term behaviour of materials under site-specific conditions. Baseline studies and confirmatory sampling programs have been carried out for the following:
■ | waste rock |
■ | ore, tailings and paste backfill |
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■ | quarry rock |
■ | underground mine water |
■ | water treatment plant effluent and associated treatment residues (i.e., sludge) |
■ | excavated surface rock exposures and runoff contacting these exposures |
■ | explosives-related residues. |
The results of these characterization studies have informed management and monitoring plans designed to prevent or minimize potential geochemistry and chemistry related adverse environmental effects associated with development, operation and closure/reclamation of the Brucejack Gold Mine. The following sections summarize the geochemical characteristics of the above referenced rock, mine wastes and contact waters, and describe the associated management strategies.
20.3.2.2 | Waste Rock |
Waste rock generated at the Brucejack Gold Mine is predominantly PAG and is managed following best practices to minimize the oxidation of sulphide minerals (i.e., pyrite). All waste rock is managed as PAG and has and will continue to be either deposited subaqueously in Brucejack Lake or placed as backfill in the underground mine below the post-closure final water table elevation. Surface waste rock excavated to support development of the mine site during construction was placed subaqueously in Brucejack Lake. Excavation of underground mine waste rock is ongoing, with this waste rock placed both in Brucejack Lake and in the underground mine as backfill. There are no permanent surface subaerial waste rock dumps at the mine site, however theMines Act Permit (M-243) authorizes temporary subaerial storage of waste rock for up to two years prior to subaqueous deposition in Brucejack Lake. Geochemical studies have been carried out to assess the behaviour of waste rock in both saturated and unsaturated conditions.
Static characterization studies (ABA and total elemental analyses) carried out on a total of 160 surface waste rock samples from five different lithologic units (Fragmental Andesite (ANDX), VSF, Porphyry 2 (P2), Conglomerate, and Porphyry 1 (P1)) indicated that 78 samples (49%) were characterized as PAG (Pretivm 2017; Pretivm 2018a). Surface waste rock characterization studies identified enrichments (greater than 10x average continental crust) in silver, arsenic, manganese, antimony and selenium (Pretivm 2016; Pretivm 2017). Kinetic tests (field bins and saturated columns) were initiated on the four rock units comprising 95% of surface waste rock excavated, and results confirm that permanent subaqueous waste rock storage will minimize potential metal leaching. The test data also indicate that subaerial exposure of waste rock for two years prior to permanent subaqueous storage will not result in any significant changes to Brucejack Lake water quality (Lorax 2016a; Lorax 2017).
Underground waste rock samples (n=568) from six lithologic units (VSF, Fragmental, Conglomerate, P1, P2, and Silicified Cap) have been characterized through static and kinetic test work. The results indicate that rocks from all units are dominantly PAG (n=472; 83.1%) with elevated concentrations of metals (e.g., silver, cadmium, zinc) and metalloids (arsenic, antimony) compared to continental crust. The data also show that many of the PAG samples contain significant amounts of carbonate minerals (mostly calcite) that will neutralize acidity generated and prolong the onset to acid generation (Pretivm 2016). Under oxidizing unsaturated conditions, waste rock and associated wall rock exposures have the potential to leach metals into mine water. During mine operations, the underground mine and surface contact water has and will continue to be treated by the WTP, which has been designed to treat and manage metals of potential concern. The mine will be flooded at closure, at which point saturated conditions are expected to limit acid generating reactions (as supported by saturated column test results), thereby minimizing potential adverse effects on water quality of the aquatic receiving environment. Similarly, saturated column tests simulating underground mine waste rock leaching behaviour in Brucejack Lake, as well as onsite water quality monitoring data, indicate that permanent subaqueous storage of waste rock deposited in Brucejack Lake will not result in exceedances of regulated discharge concentrations at the outlet of Brucejack Lake.
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20.3.2.3 | Ore, Tailings and Paste Backfill |
The Brucejack Gold Mine mill began operating in July 2017; tailings generated by milling have and will continue to be placed as thickened tailings in Brucejack Lake and as cemented paste backfill in mined out stopes. The Brucejack Gold Mine ore is characterized as PAG with elevated concentrations of silver, arsenic, cadmium, manganese, and selenium, compared to continental crust (BGC 2014). Characterization studies carried out on thickened tailings generated from the mill (n=38) show the same metal enrichments, but samples are predominantly NPAG, with a median NPR of 3.1 (Pretivm 2018a; Pretivm 2019). Paste samples (n=23) are similar in composition to thickened tailings, but with a slightly higher median NPR (4.8). Kinetic tests have been carried out to assess the behaviour of tailings deposited in Brucejack Lake, as well as the behaviour of cemented paste in unsaturated and saturated conditions within the underground mine.
Saturated column tests comprised of tailings flushed with lake water were carried out under both oxidizing and reducing conditions to estimate potential leaching rates and changes to Brucejack Lake water quality following deposition. The results of the study (Lorax 2016b) indicated that chemical loads released into the lake from tailings would not result in significant changes to Brucejack Lake water quality.
Kinetic test work to assess chemical loads released from paste backfill during mine operations indicates that chemical loads from paste backfill are minor compared to other mine-related sources. Some potential concerns with chromium were raised based on early-stage test work, with an off-shore sourced binder, however follow-up kinetic test work, using binder sourced for use at the mine, and updated water quality modeling (Pretivm 2018b) do not predict any exceedances of chromium water quality guidelines in the aquatic receiving environment. No exceedances of chromium have been reported since paste backfilling commenced (Pretivm 2019).
Saturated column tests carried out on paste backfill are used to predict underground mine water quality for the post-closure flooded mine condition. The results of these tests (Pretivm 2019) do not identify backfilled tailings as the dominant source of any parameters of potential concern.
20.3.2.4 | Quarry Rock |
Rock excavated from the Brucejack Gold Mine NPAG Quarry located at km 72 of the Brucejack Access Road was used to construct the mill and Phase 2 camp pads, and for various building foundations, roads and other construction activities at the mine site. It continues to be used for road surfacing and other maintenance requirements. The NPAG Quarry is located near the southeast end of Brucejack Lake; quarry runoff flows into Brucejack Lake. The NPAG Quarry is comprised predominantly of volcanic (plagioclase-hornblende) porphyry, with lesser amounts of conglomerate, and has negligible sulfide mineralization. Characterization studies of 70 NPAG Quarry rock samples have confirmed that rock excavated from the NPAG Quarry is consistently NPAG, with low neutral metal leaching potential.
20.3.2.5 | Mine Water |
Underground mine water at the Brucejack Gold Mine is dominantly comprised of groundwater with added geochemical loads from blasted rock, wall rock, waste rock backfill, and paste backfill. Underground mine water chemistry is monitored twice a month, and results indicate that the water quality has been within the range predicted by the water quality model. Despite the prevalence of PAG waste rock, mine water has alkaline pH levels, supporting the assertion that neutralization afforded by carbonate minerals will buffer any acid generated from sulphide oxidation reactions for several decades or more (Pretivm 2015). Similarly, there is no indication of increasing concentrations of dissolved metals associated with the onset of ML/ARD as predicted by kinetic tests (e.g., cadmium, cobalt, copper, iron, zinc) since gold production commenced in June 2017. Mine water will be treated throughout mine operations and into the closure phase.
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20.3.2.6 | Water Treatment Plant Effluent and Sludge |
The WTP receives and treats underground mine water from mine dewatering, surface contact water from with the surface contact water collection system, WTP effluent collected in the CWP, and recycled process water from the mill. The WTP is designed to chemically precipitate targeted dissolved metals and remove resultant chemical precipitates and influent TSS. The WTP effluent has consistently met design specifications. The water treatment design, metals and solids removal process, and effluent design criteria are described in the 2015Mining Act-Environmental Management Act Permits Application (Pretivm 2015).
The WTP generates a solid waste product (sludge) that requires management and disposal. Sludge generated from the WTP is currently being co-deposited with thickened tailings into Brucejack Lake. Static test results indicate that the sludge is NPAG with elevated concentrations (greater than 10x average continental crust) of several metals (e.g., silver, arsenic, cadmium, manganese, molybdenum, antimony, and selenium). However, the results also show that the sludge is stable under a range of pH and redox conditions. Kinetic tests have been carried out to evaluate potential chemical loads that may leach into Brucejack Lake under both oxidizing and reducing conditions. The studies predict low metal leaching rates for the co-deposited tailings and sludge and thus no long-term effects to Brucejack Lake water quality are anticipated.
20.3.2.7 | Surface Rock Exposures and Runoff |
The contact water collection system collects contact water from within the main Mine Site areas of excavated bedrock exposures, particularly the mill, Phase 2 Camp, and Valley of the Kings portal pads. The contact water collection system directs water to the WTP via the CWP. Non-contact surface runoff from areas immediately surrounding the mine site are directed to Brucejack Lake via the East (Johnson Creek) Diversion Channel, and to Camp Creek via the West (Camp Creek) Diversion Channel. Camp Creek runoff is naturally acidic, with elevated metal concentrations (e.g., silver, cadmium, copper, and zinc). Mine Site contact water system runoff has been assessed based on direct CWP samples (n=3) and shake flask experiments carried out on all surface exposed rock units (n=92). Results of ongoing monitoring are presented in the Annual Reclamation reports. During the operations phase, all surface runoff within the contact water collection system has and will continue to be treated by the WTP. At closure, the mine site will be reclaimed and surface runoff will follow natural pathways to the receiving environment. The potential effects of this drainage on the receiving environment will continue to be assessed as monitoring data are collected. Based on the SFE data and water quality predictions, no significant impacts to water quality in the receiving environment are anticipated.
20.3.2.8 | Explosives-related Residues |
Water quality model predictions presented in theMining Act/Environmental Management Act Permits Application (Pretivm 2015) identified nitrite as a parameter of potential concern. The main source of nitrite in Brucejack Gold Mine related discharge is from explosives used to blast waste rock and ore. Explosives-related residues contain water soluble nitrogen compounds that can affect water quality in the receiving environment. Site monitoring data have been used to derive and refine water quality predictions with respect to these compounds (Pretivm 2018b). Pretivm implements a Nitrogen Management Plan that was developed for the Brucejack Gold Mine and includes monitoring requirements, source control measures and management triggers for mitigation. The water quality model was updated based on the latest data sets and no exceedances of the current discharge limits for nitrogen compounds are predicted, nor have any been observed since gold production commenced (Pretivm 2018a and 2019).
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20.3.3 | Hydrogeology |
20.3.3.1 | Overview |
The groundwater flow system at the Brucejack Gold Mine has been conceptualized to provide estimates of groundwater inflow to the existing and future underground mine workings during operations and closure, and of groundwater flow paths at post-closure. The time periods and general conditions covered by this work originated in 2010, when initial investigations were conducted by BGC at the mine site. Data available through late 2014 were used in conceptual and numerical model development, calibration, and benchmarking. Site investigations were completed to evaluate the hydrogeologic conditions (e.g. hydraulic parameters of the bedrock, hydrostratigraphic units, and hydraulic gradients) in the vicinity of the underground mine workings, and included hydraulic response testing (e.g. packer testing, slug testing) and the installation of groundwater monitoring wells and vibrating wire piezometers. Data collected during site investigations are supplemented by ongoing monitoring of groundwater elevations and collection of water quality samples, and by data collected from ongoing dewatering activities at the mine.
Groundwater quantity monitoring has been ongoing at the Brucejack Gold Mine site since 2011. The data collected generally indicate the effects of underground dewatering are consistent with predictive simulations (BGC 2015). These effects include declining groundwater levels, increasingly negative vertical hydraulic gradients, and the depression of the groundwater table near the underground workings forming a drawdown cone (BGC 2018).
Conceptual and numerical hydrogeologic models were used to evaluate inflow rates to the mine and the extent of mine influence on the groundwater system at the Brucejack Gold Mine. Details of the models and investigations and data used to develop them are summarized in the numerical hydrogeologic model report entitledBrucejack Project MA/EMA Permitting Phase - Numerical Hydrogeologic Model Update Report (BGC 2015).
20.3.3.2 | Conceptual Hydrogeologic Model |
Surface topography has a pervasive influence on the groundwater flow system at the Brucejack Gold Mine. The elevation within the immediate mine area ranges in elevation from approximately 1,350 masl at the outlet of Brucejack Lake to over 2,000 masl at the highest peaks. Measured groundwater elevations suggest that the water table is a subdued replica of topography, with depths to groundwater typically greater in the uplands relative to the valley bottoms. Groundwater enters the flow system from infiltrating precipitation and snowmelt, with lesser components supplied by surface water infiltration in lakes. Groundwater discharge zones are generally restricted to lakes, creeks, gullies, and breaks in slope.
The hydrostratigraphy of the mine site is comprised of a thin, discontinuous layer of glacial till or colluvium underlain by bedrock. Thicker unconsolidated deposits are confined to local sections of the valley bottom and are not present near the mine.
The bedrock at the mine site can be broadly divided as follows:
■ | Triassic marine sedimentary and volcanic rocks of the Stuhini Group |
■ | Jurassic sediments and volcanics of the Hazelton Group |
■ | Early Jurassic dikes, sills, and plugs of diorite, monzonite, syenite, and granite, the most common of which are grouped as the “Sulphurets Intrusions”. |
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There is a general site-wide trend of decreasing bedrock hydraulic conductivity, K, with depth, although K varies across at least two to three orders of magnitude at any given depth. Based on available data, there is no apparent relationship between hydraulic conductivity and the major structure in the immediate vicinity of the mine site (the Brucejack Fault). However, the structure referred to as the Bruce Fault, a westward trending feature occupying Brucejack Creek at the outlet of Brucejack Lake, appears to act as a control on groundwater flow in that area.
20.3.3.3 | Numerical Hydrogeologic Model |
The conceptual model described in Section 20.3.3.2 was used as the basis for the development of a numerical hydrogeologic model. The numerical model was initially developed in 2013 (BGC 2013), and was subsequently refined in 2014 (BGC 2014) and again in 2015 (BGC 2015) for theMining Act/Environmental Management Act Permits Application (Pretivm 2015). The model was built using the graphical user interface Groundwater Vistas (Environmental Simulations Inc. 2011), and MODFLOW-Surfact code (Harbaugh et al. 2000; HydroGeoLogic 2012). The numerical model was calibrated in stages to available hydrogeologic data collected within the study area, including steady-state and transient hydraulic head targets, vertical hydraulic head gradients, streamflow data and winter low-flow estimates for the period 2008 to 2014, and volumetric discharge data available from mine dewatering activities for the period 2011 to late-2014. The results of model calibration to pre-disturbance and post-disturbance conditions, and benchmarking to transient adit dewatering data indicated that the numerical representation of the hydrogeological system was suitable for predictive analyses.
20.3.3.4 | Predictive Simulations and Inflow Estimates |
Predictive simulations were based on the 18-year underground mine plan with a throughput of 2700 t/d as presented in the 2014 FS (Ireland et al. 2014). The underground mining stopes and associated developments were simulated using head-dependent boundaries constrained to only represent outflow (i.e. drain boundary conditions). Drains representing the development (i.e. underground workings, access and egress ramps, and declines) were activated according to the annual schedule in the mine plan, and remained active throughout mining operations, while mining stopes were deactivated after a period of one year, at which point the stopes were assumed to be backfilled with paste. The conductance of Brucejack Lake was adjusted throughout the simulated operations to reflect tailings deposition.
The base case (i.e., best calibrated parameter set or “best estimate”) average annual rate of groundwater inflow to the underground workings was predicted to remain relatively stable throughout the development of the Valley of the Kings resource during years 1 to 9 of mine life, ranging between 2,500 and 2,900 m3/d. With initiation of mining in the West Zone (years 9 to 12), predicted annual average inflows increased from 2,900 to 3,500 m3/d, and then remained stable at 3,500 m3/d for the remainder of mine life (i.e., years 12 through 18). The overall average inflow for the simulated mining period was 2,900 m3/d. Groundwater inflow to the underground workings for the base case was predicted to vary seasonally by about 2,000 m3/d; estimated inflows varied from approximately 1,400 to 3,400 m3/d (58 to 141 m3/h) over the first half of mine life and from approximately 2,400 to 4,400 m3/d (100 to 183 m3/h) later in mine life. Simulated groundwater inflow to the underground workings is illustrated in Figure 20-1, for the base case, high K + high recharge and the low K modeling scenarios. These results bracket the uncertainty associated with inflow rates to the underground.
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Figure 20-1: Estimated Inflow to Underground Workings for Base Case Predictive Simulation and Selected Sensitivity Scenarios
20.3.4 | Water Management |
20.3.4.1 | General |
Water management is a critical component of Brucejack Gold Mine design and environmental protection in this high runoff environment. As such, through its consultants and in accordance with its regulatory requirements, Pretivm developed a Water Management Plan that applies throughout the LOM. The Water Management Plan was prepared prior to mine construction as part of the EMP; was updated as appropriate during construction; and following completion of the contact water management system (infrastructure) was expanded to an OMS Manual (Surface Water Management Facilities OMS Manual) that includes both the Water Management Plan component and other details such as specifics of procedures, roles and responsibilities. The goals of the Water Management Plan are to:
■ | provide a basis for management of surface fresh water within the core infrastructure area of the mine site, where significant PAG bedrock excavation was necessary as part of site preparation and where construction also resulted in significant changes to local flow pathways and drainage areas |
■ | related to the preceding point, direct the management of water to help ensure that the mine’s surface water discharge is in compliance with regulatory water quality requirements (i.e. to protect the water quality of the aquatic receiving environment downstream of the mine) |
■ | provide and retain water for mine operations |
■ | define water management control structures. |
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Strategies for water management that were applied as part of mine design and construction and remain in effect through operations include:
■ | separation of non-contact water (from the area surrounding the mine site) from contact water via non-contact diversion channels (Camp Creek and Johnson Creek diversion channels), and directing the undisturbed runoff away from mining related activities |
■ | minimizing the size of the mine site development area and minimizing surface PAG rock excavation by adjusting the elevations of the mill and Phase 2 Camp pads |
■ | collecting water within the surface contact water management system area and groundwater from the underground mine, and treating it to meet discharge standards prior to release |
■ | minimizing the use of fresh water through recycling of water to the extent feasible. |
20.3.4.2 | Water Management Overview |
Contact Water
Contact water in the context of the Brucejack Gold Mine site is defined as water contacting PAG rock exposed through mining or mine related rock excavation (i.e. the latter occurring during site preparation for mine surface infrastructure construction).
There are three sources of contact water during operations:
■ | waste rock deposited in Brucejack Lake |
■ | surface contact water from PAG bedrock excavations that occurred during site preparation for infrastructure construction, the largest of these being rock excavation to create the pad areas for the mill and the Phase 2 Camp |
■ | groundwater seepage to the underground mine. |
Runoff from the latter two sources is managed by collection and treatment. All runoff within the mine site contact water management system is collected in the CWP. This pond has been sized to contain the runoff volume (50,000 m3) associated with the 24-hour, 200-year return period rain on snow event (220 mm). The CWP is located near the southwest shore of Brucejack Lake. Runoff is directed to the facility through a series of contact water ditches, pipes and sump collection areas. From the CWP, contact water is pumped to the WTP, located within the mill building. Treatment of collected surface contact water began part way through mine construction and will continue throughout the LOM. The treated water is either used in process or discharged to Brucejack Lake at depth. The WTP has been designed with a nominal capacity of 9,600 m3/d. The system is scalable such that additional units can be added if required.
Average annual groundwater seepage into the underground workings is expected to vary from approximately 2,500 to 3,500 m3/d throughout the remaining LOM. This water is initially sent to the WTP for treatment before being sent to the process plant, where its use is maximized in process. Excess treated groundwater is discharged to Brucejack Lake at depth.
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Diversion Channels
Two fresh water (non-contact) diversion channels divert non-contact water around the core mine site surface infrastructure area. The Johnson Creek (East) Diversion Channel drains into Brucejack Lake, while the Camp Creek (West) Diversion Channel discharges to Brucejack Creek.
Process Water Requirements
The average water requirement for the Brucejack process plant is 2,847 m3/d, based on a mill throughput of 3,800 t/d. This water is required for the tailings slurry to the lake, the underground paste backfill, the concentrate slurry, and underground mine supply. Process water is sourced from:
■ | treated underground seepage water |
■ | treated contact water from the CWP |
■ | ore moisture (approximately 3% by weight) |
■ | water withdrawal from Brucejack Lake at its outlet. |
Water withdrawal from Brucejack Lake is required because there are periods in the winter when groundwater inflows are less than the process requirement.
Details of subaqueous tailings deposition are provided in Chapter 18.0. Tailings are either directed to the paste backfill plant or diluted and sent to Brucejack Lake, but never concurrently. A constant flow (either tailings or water) is required through the tailings pipeline at all times to prevent a buildup of tailings and blockage of the pipelines; however, the tailings line to the lake will be operational approximately 60 to 70% of the time. Therefore, when the thickened tailings are being directed to the paste plant for underground mine paste backfill, fluidizing water is discharged via the tailings pipeline.
20.3.4.3 | Water Balance Model |
A water balance model for the Brucejack Gold Mine site was constructed using a monthly time-step (BGC 2017). The following assumptions were used as input to the water balance model:
■ | a final tailings settled dry density of 1.68 t/m3 for the lake deposition |
■ | a solids specific gravity of 2.68 is assumed for the tailings |
■ | a nominal mill throughput of 3,800 t/d with: |
– | 177 t/d (5% of total production) sent to an off-site facility as concentrate for secondary processing in a slurry of 93% solids by weight (13 m3/d of slurry water) |
– | 1,812 t/d (46% of total production) will be deposited at depth in Brucejack Lake in a slurry of 62% solids by weight (1,110 m3/d of slurry water) |
– | 1,920 t/d (40% of total production including 5 to 6% bonder) will be deposited in the underground mine in a backfill paste of 61% solids by weight (1,233 m3/d of slurry water) |
■ | an average underground evaporation loss of about 168 m3/d |
■ | an average annual precipitation of 2,200 mm and potential lake evaporation and sublimation losses of 167 mm. |
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A water balance schematic for the mine during operations is shown in Figure 20-2. Values shown are average flows (m3/h) over the LOM and account for the annual variations in ore production. The following items should also be noted in Figure 20-2:
■ | The model accounts for the displacement of lake water resulting from tailings and waste rock deposition. |
■ | Numerical groundwater modelling of the site indicates that during mine operations, the natural groundwater flow pattern will be altered and a cone of depression will form around the underground workings, as seepage water is pumped from the underground and used in process. In response, the baseflow inputs to Brucejack Lake will also be altered during this period. The undisturbed runoff value in the flow schematic accounts for these reduced baseflows. |
The paste backfill will exude some water during the curing phase (approximately 2.5% of the paste tailings water). It is assumed that this additional water is pumped out with the seepage water and sent to treatment.
An average annual outflow of 2,012 m3/h from Brucejack Lake has been estimated for the LOM, which is an average decrease of approximately 2% above existing conditions (2,059 m3/h).
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Figure 20-2: Brucejack Lake Water Balance Model Schematic – Operations (Average Conditions)
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20.3.5 | Water Quality |
Effluent Permit 107835 (PE-107835), most recently amended December 14th, 2018, authorizes the Brucejack Gold Mine to discharge specified effluents under the conditions of the permit. PE-107835 specifies maximum concentrations for certain parameters in WTP effluent discharged to Brucejack Lake (TSS, pH, aluminum, arsenic, cadmium, cobalt, chromium, copper, iron, lead, manganese, silver, and zinc) and for the discharge from Brucejack Lake to Brucejack Creek at the lake outlet (TSS, pH, nitrite, nitrate, ammonia, antimony, arsenic, iron, and silver). The permit specifies that other parameters should meet BC Water Quality Guidelines (WQGs) for protection of aquatic life at the Brucejack Lake outlet. Effluent quality at the Brucejack Lake outlet is also required to meet federal MDMER. Water quality results from 2018 did not exceed any current (December 14th, 2018) effluent permit discharge limits or MDMER limits, and all other parameters that were monitored were below BC WQGs.
Water quality has been modeled at the Brucejack Lake outlet and at locations in Brucejack Creek downstream of the lake outlet to provide estimates of water quality during the mine operations, closure, and post-closure phases. The GoldSim water quality model derives estimates of contaminant loadings from mine sources (water from the underground mine, WTP effluent, WTP sludge, sewage treatment plant effluent, mine tailings, surface runoff from the NPAG Quarry, waste rock) and combines these with background loadings to derive water quality predictions. Background water quality is derived from pre-construction monitoring (ERM Rescan 2014), while mine-related water quality signatures are based on geochemical source terms developed from geochemical characterization studies and monitoring data sets reported in the annual reports. Modeled flows are assigned based on the water balance model (Pretivm 2018b, Appendix C). The predicted monthly flows in the water balance model vary throughout the year, reflecting site hydrology and hydrogeology.
Water quality predictions were most recently generated for a Base Case and an Upper Case scenario for the 3800 t/dMines Act and Effluent permits amendment application (Appendix A of Pretivm, 2018b). These model results are also considered to be representative of the 2019 updated mine plan, since waste rock volumes have not increased significantly compared to the 3800 t/d model. The Base Case represents an expected condition, whereas the Upper Case applies upper case geochemical source terms to all mine-related inputs to the model. The Upper Case scenario, while not the expected case, was conservatively used for water quality management planning, such as the design of the WTP. Water quality monitoring results from the lake outlet are compared to water quality model results in the Brucejack Gold Mine annual reports. This comparison has shown that measured concentrations have been well represented by the Base Case model. The Base Case model predicts that concentrations at the lake outlet will continue to meet discharge limits or water quality guidelines throughout the operations, closure, and post-closure phases.
At closure, the Brucejack Gold Mine will be flooded and most of the flow from the underground mine is modeled to report directly to Brucejack Creek via subsurface pathways. The Base Case model predicts that Brucejack Creek will experience periods during closure when arsenic and zinc are slightly above discharge limits or water quality guidelines, but even if the maximum predicted concentrations are realized, they are not expected to have a significant effect on aquatic life (Pretivm 2018b). Iron concentrations are also predicted to be higher than water quality guidelines in groundwater flowing to Brucejack Creek from the underground mine. However, it is expected that ferrous iron in groundwater will oxidize to relatively insoluble ferric iron after entering Brucejack Creek and form iron-oxyhydroxide precipitates. This precipitation process will lower the iron concentration in water to concentrations that are below BC WQGs. Potential effects to aquatic life in Brucejack Creek from iron precipitates were assessed as having low significance (Pretivm 2015). All other parameters modeled for Closure and Post-closure are predicted to have concentrations that are below discharge limits or BC WQGs.
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20.3.6 | Waste Management |
20.3.6.1 | Mine Wastes |
Mine wastes, including waste rock and tailings, are backfilled in the underground mine workings and deposited subaqueously into Brucejack Lake as approved under the mine’s authorizations. Additional details of the mine waste handling and associated rationale are provided in Sections 16.3, 16.5, 18.2.2 and 20.3.2. As described in Section 20.3.2, all waste rock is assumed to be PAG and is deposited either below the ultimate flooding elevation of the underground mine or under water in Brucejack Lake to prevent ARD. Subaqueous deposition of waste rock into Brucejack Lake was previously conducted by Newhawk in 1999, following underground development by Newhawk. As noted in section 20.3.1.3, Brucejack Lake and its downstream drainage are not fish-bearing for more than 20 km.
20.3.6.2 | Non-hazardous Waste |
Waste handling facilities located at the Brucejack Gold Mine Site and Knipple Transfer Area are the primary facilities used for temporarily storing and separating waste. All non-hazardous industrial and domestic solid wastes are managed in accordance with the mine’s approved Waste Management Plan and Refuse Incinerator Management Plan to minimize potential adverse effects to the environment, wildlife and mine personnel. Non-hazardous waste is separated for recycling or disposal.
On-site disposal of non-hazardous waste consists of incineration, recycling, and open pit burning. Incineration of non-hazardous products includes the operation of two authorized high temperature incinerators located at the Brucejack Gold Mine site and Knipple Transfer Area. Open pit burning of non-hazardous waste is conducted at permitted locations at the mine site and at the Knipple and Wildlife camps.
Recycling of non-hazardous material is an important component of waste management and environmental protection. Personnel at all Brucejack Gold Mine infrastructure areas participate in the mine’s recycling program, which reduces the amount of garbage shipped off-site and thereby reduces the quantity of waste disposed at regional landfills. Recycling of various materials is implemented at mine facilities, including: recyclable containers, tin cans, batteries, e-waste, cardboard, light bulbs, heavy plastics, metal, aerosol cans and electrical wire. Recyclable waste generated on site is transported off site to local recycling facilities.
20.3.6.3 | Hazardous Waste |
Hazardous waste generated at the Brucejack Gold Mine is managed in accordance with the approved Waste Management Plan and the Refuse Incinerator Management Plan, theEnvironmental Management Act Hazardous Waste Regulations and the Transportation of Dangerous Goods Regulations to protect mine personnel and the environment. Hazardous wastes generated at the mine site and supporting infrastructure are temporarily stored in the mine’s waste handling facilities prior to transport and disposal at licensed off-site disposal facilities.
On-site disposal of hazardous waste is limited but does occur in the form of incineration of some items and waste oil heat production; both of these are conducted in accordance with the approved Waste Management Plan and other applicable requirements under theEnvironmental Management Act.
20.3.7 | Air Emission Control |
Since mining occurs underground and mine wastes (tailings and waste rock) are ultimately stored either subaqueously within Brucejack Lake or backfilled into the underground mine, combined with the use of electricity as the primary source of power during operations, rather than on-site generators using diesel, air emissions are not significant. There is some fugitive dust from waste rock handling on the waste rock dump, and seasonally from road use, and there are minor emissions from the mill and assay lab.
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Pretivm implements its approved Air Quality Management Plan to mitigate air emissions. Key mitigations for fugitive dust from roads include road watering and application of dust control solution. Emission controls were designed and implemented for mill and assay lab emission sources and include various enclosures, ventilation systems, dust collectors, wet scrubbers, fans, and related appurtenances. These emission controls are also regulated under the mine’s Air Permit (PA-107025); Pretivm conducts monitoring and maintenance in accordance with the permit. The Air Permit also regulates operations of the mine’s incinerators and has conditions specific to fugitive dust, the underground mine, and the burn pits.
20.3.8 | Closure Plan and Costs |
Following completion of mining, the Brucejack Gold Mine will be closed, reclaimed and monitored in accordance with its authorizations and its Mine Site Reclamation and Closure Plan, Ancillary Infrastructure Decommissioning and Reclamation Plan, and other applicable EMP component plans. Closure of the mine site at the end of operations will include flooding of the underground mine to the Brucejack Lake elevation, with continued water treatment during flooding; removal of all structures and equipment, closure of the mine portals, and rehabilitation of site disturbances. The mine has been planned and designed to operate and be closed and reclaimed in a manner that achieves the approved end land use objectives, returns the site to as close to its pre-disturbance condition as practical, and minimizes the potential for long-term adverse effects on the environment.
Closure of the underground facilities will include the removal of material supplies and mobile equipment such as ventilation fans and safety equipment. These will be removed from the site for reuse or will be recycled. Hydrocarbons will be drained from all equipment and from underground storage and the distribution system and disposed in an approved manner.
The underground mine workings will be progressively backfilled with tailings and waste rock throughout mine operations, to the level of expected water table rebound, and once mining is completed, the underground will be allowed to flood. The ventilation shafts and underground portals will be sealed with concrete plugs. The water table is not expected to reach higher than the elevation of Brucejack Lake.
Closure of the above-ground facilities will include the removal of all buildings and structures at the mine site and along the Brucejack Access Road. Buildings will be dismantled, and removable materials will be taken off-site for reuse or recycling. Concrete pads (mill, Valley of the Kings Zone and West Zone portal buildings and West Zone shop) will remain in place, and the Phase 2 Camp supporting pedestals will be cut off at ground level. Oil, fuels, and processing fluids will be drained from equipment before the equipment is removed, and disposed of in an approved manner. Processing equipment will be removed from site and sold or recycled. Above-ground pipes and sediment curtains in Brucejack Lake and Creek will be removed and disposed in accordance with the Reclamation and Closure Plan.
Post-closure water management features will be constructed and pad and road surfaces will be recontoured, decompacted, and revegetated as applicable in accordance with the reclamation plans. The transmission line will be dismantled. The steel poles and the conductors will be removed off-site and sold, or recycled, or disposed in an approved manner.
The reclamation security for all infrastructure authorized underMines Act Permit M-243, including the mine site, is $31.7 million. An additional reclamation security of $2 million is held for the Brucejack Access Road under Special Use Permit S25923. There are other reclamation securities, totaling $70,000, for infrastructure located on Licenses of Occupation. As the Brucejack Gold Mine site covers a very small surface footprint, there are not anticipated to be opportunities to partially reclaim disturbances and reduce theMines Act reclamation security prior to closure.
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21.0 | CAPITAL AND OPERATING COST ESTIMATES |
21.1 | Capital Cost Estimate |
21.1.1 | Summary |
The total estimated initial capital cost to upgrade the Brucejack Gold Mine mill capacity from 2,700 to 3,800 t/d is US$22.5 million, excluding the costs related to the mining operation capacity increase, which is included in the sustaining capital cost. Table 21-1 shows a summary breakdown of the initial capital costs required to expand the operating mine. This estimated cost includes design, construction, installation, and commissioning.
Together with other consultants and potential suppliers, Tetra Tech reviewed the mill processing capacity by circuit. In general, most of the circuits have sufficient capacity available for the increased throughput. However, some pumps, the second cleaner flotation, and the third cleaner flotation circuits will need some modifications and upgrades.
The mining capital cost for the increased mining rate was estimated as an ongoing sustaining capital cost, which is based on ongoing underground development, additional mining equipment purchases, and underground infrastructure upgrades.
The total estimated LOM sustaining capital cost is US$207 million and a summary breakdown of the sustaining capital costs is shown in Table 21-2.
The key inputs to this cost estimate include equipment quotations from vendors and construction cost data estimated by Pretivm and Tetra Tech.
Table 21-1: | Summary of Initial Capital Costs |
Capital Cost | ||
Major Area | Area Description | (US$ 000) |
Direct Costs | ||
11 | Mine Site (included in ongoing sustaining capital cost) | - |
21 | Process – Underground | 3,256 |
31 | Process – Surface | 4,620 |
33 | Mine Site Additional Facilities | 7,889 |
35 | Mine Site Temporary Facilities | 542 |
Subtotal Direct Costs | 16,306 | |
91 | Indirect Costs | 2,446 |
99 | Contingency | 3,751 |
Total Initial Capital Cost | 22,503 |
Note: | Numbers may not total due to rounding. |
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Table 21-2: | Summary of LOM Sustaining Capital Costs |
Capital Cost | |
Area Description | (US$million) |
Mining | 51.6 |
Processing | 33.5 |
Site Infrastructure and Services | 115.7 |
Total LOM Sustaining Capital Cost | 200.7 |
Note: | Numbers may not total due to rounding. |
21.1.2 | Initial Capital Cost Estimate |
21.1.2.1 | Purpose and Class of Estimate |
Purpose
The purpose of this capital cost estimate is to provide an update to the 2014 FS estimate (Ireland et al. 2014) for use as input to the Brucejack Gold Mine financial model for this Technical Report.
Class of Estimate, Degree of Project Definition and Accuracy
This estimate is a Class 4 feasibility cost estimate update prepared in accordance with the Recommended Practice No. 18R-97: Cost Estimate Classification System - AACE. According to AACE, the accuracy of a Class 4 estimate is expected to be in the range of -15%/+20%.
21.1.2.2 | Estimate Base Date and Validity Period |
This estimate was prepared on with a base date of Q1 2019 and does not include any escalation beyond this quarter. The quotations used for this estimate were obtained in Q4 2018 and Q1 2019 with a validity period of 90 days.
21.1.2.3 | Estimate Approach |
Currency and Foreign Exchange
The capital cost estimate uses US dollars as the base currency. All costs presented in this section are in US dollars unless otherwise stated. All costs, including quotations received from vendors, were converted to US dollars using the foreign exchange rate listed in Table 21-3.
Table 21-3: | Foreign Exchange Rates |
Base Currency | Foreign Currency |
Cdn$1.00 | US$0.775 |
Duties and Taxes
Duties and taxes are not included in this estimate.
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Measurement System
This estimate uses the International System of Units (SI), unless otherwise noted.
21.1.2.4 | Work Breakdown Structure |
The estimate is organized according to the following hierarchical work breakdown structure (WBS):
■ | Level 1 = Major Area |
■ | Level 2 = Area |
■ | Level 3 = Sub-Area. |
21.1.2.5 | Elements of Cost |
This capital cost estimate consists of the following four main parts.
Direct Costs
AACE defines direct costs as:
…costs of completing work that areand aredirectlynecessaryforits completionattributable.In construction, (it is considered to be) the cost of installed equipment, material, labor and supervision directly or immediately involved in the physical construction of the permanent facility.
Examples of direct costs include mining equipment, process equipment, mills, and permanent buildings.
The total estimated direct cost is US$16.3 million.
Indirect Project Costs
AACE defines indirect costs as:
…costs not directly attributable to the completion of an activity, which are typically allocated or spread across all activities on a predetermined basis. In construction, (field) indirects are costs which do not become a final part of the installation, but which are required for the orderly completion of the installation and may include, but are not limited to, field administration, direct supervision, capital tools, startup costs, contractor’s fees, insurance, taxes, etc.
The total estimated indirect cost is US$2.4 million.
Contingency
When estimating costs for a project, there is always uncertainty as to the precise content of all items in the estimate, how work will be performed, what work conditions will be like when the project is executed, etc. These uncertainties are risks to a project. These risks are often referred to as “unknown-unknowns” and are referred to by cost estimators as “cost contingency”.
Tetra Tech estimated a contingency for each activity or discipline based on the level of engineering effort as well as experience on past projects.
The total estimated contingency is US$3.8 million.
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Mine Site Processing and Off-Site Infrastructures Capital Cost Estimate
Major mechanical costs are based on quotations from equipment manufacturers and were consolidated and provided to Tetra Tech by Pretivm. All equipment and material costs are included as free carrier (FCA) or free on board (FOB) manufacturer plants and are exclusive of spare parts, taxes, duties, freight, and packaging. These costs, if appropriate, are covered in the indirect cost section of the estimate. Equipment upgrade costs are also based on quotations from equipment manufacturers.
Costs for the mill dry complex upgrade are based on information from the recently constructed Brucejack Gold Mine.
Project Indirect Costs
Construction indirect costs are based on a percentage of direct costs. Spare parts and freight costs are based on quotations from equipment manufactures and Owner’s experience.
21.1.2.6 | Capital Cost Exclusions |
The following items are excluded from this capital cost estimate:
■ | working or deferred capital |
■ | financing costs |
■ | refundable taxes and duties |
■ | land acquisition |
■ | currency fluctuations |
■ | lost time due to severe weather conditions |
■ | lost time due to force majeure |
■ | additional costs for accelerated or decelerated deliveries of equipment, materials, labor or services resultant from a change in project schedule |
■ | warehouse inventories |
■ | any project sunk costs (studies, exploration programs, etc.) |
■ | sustaining capital costs (included in the sustaining capital cost estimate) |
■ | mine reclamation costs (included in financial model) |
■ | mine closure costs (included in financial model) |
■ | escalation costs |
■ | additional permitting costs not identified in the estimate |
■ | community relations. |
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21.1.3 | Sustaining Capital Cost Estimates |
21.1.3.1 | Mining Sustaining Capital Costs |
Mining sustaining capital cost estimates are based on ongoing underground development, additional mining equipment purchases, and underground infrastructure. Underground development includes ramp and raise development, whereas lateral and stope development are considered operating costs.
Underground development is conducted by a contractor with roughly three quarters of development consisting of underground ramps and one quarter vertical development.
Table 21-4 shows the breakdown of the mining sustaining capital costs over the LOM.
Table 21-4: | Mining Sustaining Capital Costs over the LOM |
Capital Cost | |
Area | (US$ million) |
Underground Development Capitalized | 25.1 |
Underground Equipment | 8.1 |
Underground Infrastructure | 18.3 |
Total Mining Sustaining Capital Cost | 51.6 |
Note: | Numbers may not total due to rounding. |
Table 21-5 shows a detailed breakdown of the mining sustaining capital costs by year.
Table 21-5: | Mining Sustaining Capital Costs by Year (US$000) |
Area | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 | 2026 | 2027 | 2028 |
Capitalized Development | 4,040 | 2,105 | 1,395 | 1,693 | 5,024 | 2,547 | 2,891 | 4,225 | 1,212 | - |
Underground Infrastructure | 1,988 | - | - | 500 | 500 | 500 | 500 | 500 | 500 | 500 |
Mechanical Controlled Vent Regulators | 327 | 300 | 300 | 300 | 300 | 300 | 300 | 300 | 300 | 300 |
Backfill Piping | 387 | 350 | 350 | 700 | 700 | 700 | 700 | 700 | 700 | 700 |
Sump Pumps | 233 | 200 | 200 | 200 | 200 | 200 | 200 | 200 | 200 | 200 |
Escape Way Construction | 171 | 150 | 150 | 300 | 300 | 300 | 300 | 300 | 300 | 300 |
Miscellaneous | 804 | - | - | - | - | - | - | - | - | - |
Ventilation Infrastructure | 399 | 400 | 400 | 650 | 650 | 650 | 650 | 650 | 650 | 650 |
Mining Equipment Purchases | 769 | - | - | - | - | - | - | - | - | - |
Total Mining Sustaining Capital Costs | 9,118 | 3,505 | 2,795 | 4,343 | 7,674 | 5,197 | 5,541 | 6,875 | 3,862 | 2,650 |
Note: | Numbers may not total due to rounding. |
21.1.3.2 | Process Sustaining Capital Costs |
The estimated LOM total sustaining capital cost for process-related operations is US$33.5 million. Table 21-6 summarizes the annual process sustaining capital cost estimates.
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Table 21-6: | Process Sustaining Capital Costs Over the LOM (US$ million) |
Year | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 | 2026 | 2027 | 2028 | 2029 | 2030 |
Process Sustaining Capital Costs | 3.5 | 3.0 | 2.5 | 3.0 | 5.0 | 3.0 | 2.5 | 3.0 | 5.0 | 1.0 | 1.0 | 1.0 |
21.1.3.3 | Site Services/Infrastructure Sustaining Capital Costs |
The total estimated LOM sustaining capital cost for site services and infrastructure is based on operation information from the Brucejack Gold Mine. The total estimated sustaining site services and infrastructure cost is US$115.7 million. Table 21-7 summarizes the estimated LOM site service and infrastructure maintenance related sustaining capital costs.
Table 21-7: | Site Services and Infrastructure Sustaining Capital Costs Over the LOM (US$ million) |
Year | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 | 2026 | 2027 | 2028 | 2029 | 2030 |
Site Services and Infrastructure Sustaining Capital Costs | 16.8 | 15.0 | 16.3 | 8.5 | 8.5 | 8.5 | 8.5 | 8.5 | 8.5 | 5.5 | 5.5 | 5.5 |
21.2 | Operating Cost Estimate |
21.2.1 | Summary |
The estimated LOM average operating cost is US$168.02/t milled. Operating costs are defined as the direct operational costs, which include mining, processing, water treatment, tailings storage, site services, and G&A costs, excluding product freight costs, sale related costs, and royalties, which are included in the economic analysis (Section 22.0). The estimate is based on an average annual plant feed rate of approximately 1.387 Mt of ore processed (3,800 t/d milled). Table 21-8 shows the cost breakdown for each area and Figure 21-1 shows the cost distribution.
Table 21-8: | LOM Average Operating Cost Summary |
Unit Operating Cost | |
Area | (US$/t milled) |
Mining | 74.42 |
Processing | 21.87 |
Overall Site Services, including Off-site/Satellite Offices(1) | 36.19 |
G&A | 35.54 |
Total Operating Cost | 168.02 |
Note: | (1)Includes costs for off-site and satellite offices. |
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Figure 21-1: Overall Operating Cost Distribution by Area
The operating cost estimates are based on the Brucejack Gold Mine operating experience, and include consumable supplies, power supply, contractor services, camp services, worker transportation and labour salaries/wages for Q4 2018 and Q1 2019. The expected accuracy range of the operating cost estimate is +15%/-15%. All costs are estimated in US dollars, unless otherwise specified. Table 21-3 shows the foreign exchange rates used for the estimate.
The operating costs exclude shipping charges and sale costs for the gold-silver doré and gold-silver concentrate, as well as royalties, which are included in economic analysis (Section 22.0).
All operating cost estimates exclude taxes unless otherwise specified.
21.2.2 | Mining Operating Cost Estimate |
Mining operating costs include production costs such as drilling, blasting, explosives, mucking, backfill, and support costs. Non-capitalized underground development (lateral development and stope development) are considered operating costs. The estimated LOM average mining cost is US$74.42/t milled, with a high of US$113/t milled forecast for Q2 of 2019.
The estimated mining operating costs are based on current and forecast contractor rates. Figure 21-2 illustrates the cost distribution.
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Figure 21-2: Mining Operating Cost Distribution by Area
21.2.3 | Process Operating Cost Estimate |
The estimated LOM average unit process operating cost is US$21.87/t milled at an average annual plant feed rate of approximately 1.387 Mt of ore processed, or a nominal plant feed rate of 3,800 t/d, including tailings delivery. The estimate is based on 12-hour shifts per day, 24 h/d and 365 d/a.
The process operating cost estimate includes:
■ | personnel requirements, including supervision, operation and maintenance; and salary/wage levels, including burdens, based on Q4 2018/Q1 2019 labour rates |
■ | SAG mill and ball mill liner and grinding media consumption |
■ | maintenance supplies |
■ | reagent consumptions |
■ | other operation supplies |
■ | power consumption for the processing plant |
■ | other process related costs, such as mobile equipment, consulting, and general expenses. |
Figure 21-3 shows the process operating cost distribution.
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Figure 21-3: Process Operating Cost Distribution by Area
21.2.4 | G&A and Site Services Operating Cost Estimate |
G&A and site services costs include expenditures that do not relate directly to mining or process operating costs. The estimated LOM average unit operating cost is US$35.54/t milled for G&A and US$36.19/t milled for site services, based on a nominal daily ore plant feed rate of 3,800 t.
The G&A and site service costs include costs related to the satellite site operations at the Knipple Transfer Station and the mine access security station. In addition, G&A costs include operation-related costs for the off-site office in Smithers, BC.
Site services costs include:
■ | manpower related costs, including supervision, operation and maintenance; and salary/wage levels, including burdens, based on Q4 2018/Q1 2019 labour rates |
■ | energy |
■ | operating supplies and consumables |
■ | maintenance supplies |
■ | rental and lease |
■ | other related costs. |
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G&A costs include:
■ | manpower related costs, including supervision, operation and maintenance; and salary/wage levels, including burdens, based on Q4 2018/Q1 2019 labour rates |
■ | various general operating management and services related costs, mainly for the following main areas: |
− | general mine administration |
− | environmental and permitting |
− | procurement and supply chain |
− | camp services |
− | health and safety |
− | accounting and financial services |
− | human resources |
− | IT related various services |
− | worker transportation services. |
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22.0 | ECONOMIC ANALYSIS |
22.1 | Introduction |
Tetra Tech prepared an economic evaluation of the Brucejack Gold Mine based on a discounted cash flow model for the remaining 14-year LOM and 15.74 Mt of mine plan tonnage. The current forecast for the remaining Brucejack Gold Mine LOM shows a post-tax NPV of US$2.59 billion, at a 5% discount rate, and US$2.23 billion at an 8% discount rate. Internal rate of return and payback period results as referenced by NI 43-101F1 are not relevant to this Technical Report as mine revenues provide sufficient cash flow to cover expansion capital and no negative cashflow periods are expected.
Table 22-1 shows a summary of the economic analysis results.
Table 22-1: | Cash Flow Results Summary (including Discounted Post-tax NPV) |
Unit | Amount | |
Tonnes Mined and Processed | kt | 15,754,279 |
Gold Head Grade | g/t | 12.6 |
Silver Head Grade | g/t | 58.4 |
Doré Production | ||
Gold Ounces Produced | ’000 oz | 3,564,103 |
Silver Ounces Produced | ’000 oz | 2,005,871 |
Concentrate Production | ||
Concentrate Sold | dmt | 821,796 |
Gold Contained in Concentrate | ’000 oz | 2,540,002 |
Silver Contained in Concentrate | ’000 oz | 22,804,234 |
Total Project Revenue | US$ million | $7,911 |
Operating Costs | US$ million | (2,647) |
Royalties | US$ million | (139) |
EBITDA | US$ million | 5,125 |
Sustaining Capital Costs | US$ million | (223) |
Other Expenses | US$ million | (29) |
Pre-tax Cash Flow | US$ million | 4,873 |
Allowable Tax Deductions | US$ million | (1,272) |
Taxable Income | US$ million | 3,601 |
Taxes Payable | US$ million | (1,445) |
Post-tax Cash Flow | US$ million | 3,428 |
Post-tax NPV (5% Discount Rate) | US$ million | 2,587 |
Post-tax NPV (8% Discount Rate) | US$ million | 2,225 |
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The Brucejack Gold Mine economic model is based on the following assumptions:
■ | gold price of US$1,300/oz |
■ | silver price of US$16.90/oz |
■ | foreign exchange rate of Cdn$1.00:US$0.778. |
Note that the metal prices listed above differ from metal pricing used for Mineral Reserve delineation. Gold price for financial modelling is based on the median of consensus economic pricing through 2020 (US$1,330/oz) and three-year trailing average (US$1,270/oz). Silver price is based solely on the three-year trailing average.
Pretium provided doré and concentrate payment terms, smelting and refining charges, transportation costs, and insurance costs. Gold and silver recoveries are based on the Brucejack Gold Mine operational data and metallurgical test results as discussed in Section 13.0 of this Technical Report.
22.2 | Pre-tax Model |
The production schedule has been incorporated into the pre-tax financial model to develop annual recovered metal production. The annual at-mine revenue contribution of each metal was determined by deducting the applicable treatment, refining, and transportation charges (from mine site to market) from gross revenue.
Sustaining capital costs have been incorporated on a year-by-year basis over the LOM and operating costs were deducted from gross revenue to estimate annual mine operating earnings. Capital expenditures include mill feed throughput expansion capital costs to increase mining and mill capacity from 2,700 to 3,800 t/d and ongoing sustaining capital costs for mining and milling additions and equipment replacement. The total LOM capital cost is US$223.2 million, including US$22.5 million in expansion capital.
The mine closure and reclamation cost of US$28.62 million has been included in the financial model.
Working capital has not been included in the model, as the Brucejack Gold Mine is currently in operation and generating positive cash flow.
NPV has been estimated at the beginning of the mining schedule and therefore has an effective date of January 1st, 2019.
Table 22-2 shows the metal production quantities and Figure 22-1 shows the annual pre-tax net cash flows (NCFs) and cumulative net cash flows (CNCFs).
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Table 22-2: | Metal Production Quantities |
Units | First Five Years | LOM | |
Total Tonnes Milled | Mt | 6.76 | 15.75 |
Average Annual Tonnes Milled | Mt | 1.35 | 1.125 |
Average Grade | |||
Gold | g/t | 12.37 | 12.62 |
Silver | g/t | 12.42 | 58.4 |
Total Production | |||
Gold | ’000 oz | 2,688 | 6,392 |
Silver | ’000 oz | 2,699 | 29,579 |
Average Annual Production | |||
Gold | ’000 oz | 537.68 | 456.57 |
Silver | ’000 oz | 539.82 | 2,112.82 |
Figure 22-1: Pre-tax Cash Flow
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22.2.1 | Metal Price Scenarios |
Table 22-3 tabulates the economic results at different metal price scenarios.
Table 22-3: | Economic Results Summary for Different Metal Price Scenarios |
Economic | Gold Price (US$/oz) | |||
Parameter | Unit | 1,100 | 1,300 | 1,500 |
Silver Price | US$/oz | 14.30 | 16.90 | 19.50 |
Net Cash Flow | US$ | 3.62 (pre-tax) | 4.87 (pre-tax) | 6.13 (pre-tax) |
billion | 2.63 (post-tax) | 3.43 (post-tax) | 4.22 (post-tax) | |
NPV(1) | US$ | 2.67 (pre-tax) | 3.60 (pre-tax) | 4.54 (pre-tax) |
(at a 5.0% discount rate) | billion | 1.98 (post-tax) | 2.59 (post-tax) | 3.18 (post-tax) |
Exchange Rate | Cdn$:US$ | 0.775 | 0.775 | 0.775 |
Note: | (1)The NPV is discounted to January 2019. |
22.3 | Smelter Terms |
As referenced in Section 19.0 of this report, Table 22-4 shows the payment, smelting, and refining terms that have been applied in the economic analysis.
Table 22-4: | Payment, Smelting and Refining Terms |
Term | Unit | Amount |
Doré | ||
Gold Payable | % | 99.97 |
Silver Payable | % | 99.60 |
Transport | US$/oz | 2.90 |
Assays | US$/oz | 0.40 |
Treatment | US$/oz | 0.50 |
Penalty | US$/oz | 1.20 |
Concentrate | ||
Gold Payable | % | 97.50 |
Silver Payable | % | 95.00 |
Transport | US$/wmt | 163.75 |
Assays | US$/oz Au | 6.80 |
Treatment | US$/dmt | 240.00 |
Penalty | US$/dmt | 18.75 |
Refining – Gold | US$/oz | 9.00 |
Refining – Silver | US$/oz | 1.15 |
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22.4 | Markets and Contracts |
The Brucejack Gold Mine produces gold and silver doré and concentrates. Doré is transported to the smelter by air. Concentrate is loaded in customized bulk containers and transported from the mill site to Knipple Transfer Station and then to SBT by a third-party party trucking company. The bulk concentrate is then loaded into ocean vessels to international customers.
22.5 | Taxation and Royalty Considerations |
Pretivm completed the post-tax economic evaluation of the Brucejack Gold Mine, including applicable income and mining taxes.
Based on the metal prices used for this Technical Report, the total estimated taxes payable on Brucejack Gold Mine profits are US$3,427 million over the 14-year LOM. Table 22-5 shows the various payable tax components.
The Brucejack Gold Mine was evaluated on an after-tax basis levied as three separate tax contributions at the federal, provincial, and provincial-mining level (BC Mineral Tax). Table 22-5 shows the pre- and post-tax breakdowns for these cash flows and the allowable tax deductions.
Table | 22-5: LOM Taxes Summary |
Cash | LOM Total |
Costs | (US$million) |
Pre-tax NCF | 4,873 |
Taxable Income | 3,601 |
Federal Taxes | 532 |
Provincial Taxes | 432 |
BC Mineral Tax | 482 |
Post-tax NCF | 3,427 |
Post-tax NPV (at a 5% Discount Rate) | 2,587 |
Post-tax NPV (at an 8% Discount Rate) | 2,225 |
The following general tax regime is recognized as applicable, as of the effective date of this Technical Report.
22.5.1 | Canadian Income Tax System |
The Canadian federal income tax rate is 15%.
22.5.1.1 | Machinery and Equipment |
Prior to 2021, assets purchased prior to commercial production are added to a Class 41(a) pool and are deducted at an accelerated rate, at up to 100% of the balance, to the extent of taxable income from the mine.
Changes from the 2013 federal budget phases out the accelerated deduction over the years 2017 to 2020. One hundred percent of the accelerated rate will be permitted from 2013 to 2016, 90% in 2017, 80% in 2018, 60% in 2019, and 30% in 2020.
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Assets purchased after the start of production are added to a Class 41(b) pool and are deducted at up to 25% of the balance.
22.5.1.2 | Mine Acquisition Costs |
Mine acquisition costs include costs of land, exploration and mining rights, licenses, permits, and leases.
These costs are added to a Canadian Development Expense (CDE) pool and can be deducted at up to 30% of the balance in a year.
22.5.1.3 | Pre-production Mine Expenditures |
Pre-production mine expenditures include both exploration and mine development costs.
Prior to 2015, exploration and mine development are added to a Canadian Exploration Expense (CEE) pool. One hundred percent of the balance can be deducted in a year, but the deduction is also limited to the income from the mine.
Pre-production mine development costs incurred subsequent to 2017 are treated as CDE instead of CEE. The transition started to be phased-in beginning in 2015, with 20% of costs being allocated proportionately to CDE and 80% to CEE in 2015, 40% to CDE and 60% to CEE in 2016, and 70% to CDE in 2017 and 30% to CEE in 2017.
22.5.2 | Provincial (BC) Mining Tax System |
The BC provincial income tax rate is 12%.
22.5.2.1 | Net Current Proceeds Tax |
A 2% tax is levied on an amount by which gross revenues exceed current operating costs.
Hedging income and losses, royalties, and financing costs are excluded. Capital costs including exploration, pre-production development, and leasing are excluded. Capital costs are relevant for Net Revenue Tax.
The net current proceeds tax is added to a cumulative tax credit account (CTCA) and is available to offset net revenue tax payable.
22.5.2.2 | Net Revenue (13%) Tax |
Tax is levied at 13% of net revenue. All capital expenditures, both mine development costs and fixed asset purchases, are accumulated in a cumulative expenditure account (CEA). Net revenue is defined as 13% of gross revenues less the current operating costs for the year, less any accumulated CEA balance. Therefore, for net revenue tax, all current and capital expenditures are fully deductible in the year they are incurred or in the following year. Net revenue does not become assessable until the costs of all preproduction capital expenditures have been recovered. A “new mine allowance” is also provided to encourage new mine development in BC. The allowance allows a mine operator to add 133% of its capital expenditures incurred prior to commencing production to the CEA account if the mine began producing minerals in reasonable commercial quantities before January 1, 2016.
BC mineral taxes are deductible for federal and provincial income tax purposes.
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22.6 | Royalties |
The Brucejack Gold Mine was evaluated under the assumption of the following royalties:
■ | First Nations royalty |
■ | Mineral royalty. |
The First Nations royalty is calculated at a rate of 9% of the BC Mineral Tax. The estimated value of the LOM royalty cost for the First Nation groups is US$44.5 million.
22.7 | Sensitivity Analysis |
A sensitivity analysis was performed on the financial model considering variations in:
■ | metal prices |
■ | mining, processing, and site services operating costs. |
The analysis shows that the Brucejack Gold Mine NPM is most sensitive to changes in gold price and less sensitive to changes in silver price. The Brucejack Gold Mine has similar sensitivity to grade as to metal pricing.
Figure 22-2 illustrates the sensitivity of the Brucejack Gold Mine economics to metal price fluctuations and Figure 22-3 illustrates the sensitivity to operating costs. The economics are most sensitive to operating costs.
Figure 22-2: Post-tax NPV Sensitivity to Metal Prices
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Figure 22-3: Post-tax NPV Sensitivity to Operating Costs
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23.0 | ADJACENT PROPERTIES |
The following subsections describing adjacent properties are based on information publicly disclosed by the Owner or Operator of the adjacent property and were sourced as per the notes in the relevant sections.
The QP has been unable to verify the information for any of the described adjacent properties except against what has been publicly reported, and the information is not necessarily indicative of the mineralization at Brucejack.
23.1 | Snowfield Property |
The Snowfield Property, held by Pretivm for future development of the Snowfield Deposit, is considered a separate property to the Brucejack Property. It was 100% owned by Newhawk and was not part of the joint venture that explored the Brucejack Property prior to the purchase of Newhawk by Silver Standard. The Snowfield Deposit is located approximately seven kilometers north of the Brucejack Deposit. This is reported to be a near surface, bulk tonnage gold-copper porphyry deposit with significant credits in silver, molybdenum, and rhenium. Mineral Resources are estimated at 1,370.1 Mt Measured and Indicated with a further 833.2 Mt in the Inferred category (Table 23-1). (Puritch at al. 2011)
Table 23-1: | February 2011 Snowfield Mineral Resource |
Average Grades | Contained Metal | ||||||||||
Resource | Tonnes | Au | Ag | Cu | Mo | Re | Au | Ag | Cu | No | Re |
Category | (Mt) | (g/t) | (g/t) | (%) | (ppm) | (ppm) | (Moz) | (Moz) | (Blb) | (Mlb) | (Moz) |
Measured | 189.8 | 0.82 | 1.69 | 0.09 | 97.4 | 0.57 | 4.983 | 10.332 | 0.38 | 40.8 | 3.5 |
Indicated | 1,180.3 | 0.55 | 1.73 | 0.10 | 83.6 | 0.50 | 20.934 | 65.444 | 2.60 | 217.5 | 19.0 |
Measured & Indicated | 1,370.1 | 0.59 | 1.73 | 0.10 | 85.5 | 0.51 | 25.917 | 75.776 | 2.98 | 258.3 | 22.5 |
Inferred | 833.2 | 0.34 | 1.90 | 0.06 | 69.5 | 0.43 | 9.029 | 50.964 | 1.10 | 127.7 | 11.5 |
Source: | Puritch et al. (2011) |
23.2 | Bowser Property |
The Bowser Property is a group of Pretivm mineral claims covering approximately 1,200 km2 that extend from the eastern boundary of Brucejack Property to east of Highway 37 and south from Treaty Creek to Long Lake. Exploration by Pretivm has included airborne electromagnetic, magnetic, hyperspectral, and radiometric geophysical surveys, ground geophysical surveys, extensive sampling, prospecting, and geological mapping over much of the property and diamond drilling on select mineralized zones.
Exploration results have highlighted four distinct areas for focused exploration. Several gold and silver epithermal targets have been identified in the American Creek Zone located approximately 25 km southeast of the Brucejack Gold Mine. The American Creek valley is dominated by kilometer-scale north-south structures and localized east-west stockworks, which host elevated gold values in rocks of the Lower Hazelton Group, Unuk River Formation, the same formation that hosts the Brucejack Gold Mine. The Koopa Zone, located approximately 30 km east-southeast of the Brucejack Gold Mine, is dominated by intensely quartz-sericite pyrite altered Salmon River Formation volcanics and Quock Formation sediments of the Upper Hazelton Group. The Bluffy Zone, located 30 km south-southeast of Brucejack Gold Mine, contains broad zones of low-grade gold hosted in shear zones, which contain narrow veins of high-grade gold and base metal values. The Upper Kirkham Zone is located 4 km southwest of Bowser Camp. Epithermal-style polymetallic veins with gold-silver-copper-lead-zinc mineralization and strong quartz-sericite pyrite halos are recently exposed by a receding glacier.
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Figure 23-1: Detailed Geological Map of KSM-Brucejack Area and McTagg Anticlinorium and Section Locations
Note: | The legend can be found in Figure 23-2. |
Source: | Nelson and Kyba (2014) |
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Figure 23-2: Legend for Detailed Geological Map of KSM-Brucejack Area and McTagg Anticlinorium and Section Locations
Source: | Nelson and Kyba (2014) |
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23.3 | Kerr-Sulphurets-Mitchell Property |
Adjacent to the west and north of Brucejack/Snowfield Properties lies the Seabridge Gold Inc. (Seabridge Gold) KSM Property. The KSM Property hosts four copper-gold mineral deposits: Kerr, Mitchell, Sulphurets, and Iron Cap. All of these deposits are situated within the KSM mining lease and claim holdings that are reported to be, at the time of writing this report, 100% owned and operated by Seabridge Gold.
Seabridge Gold acquired the KSM Property from Placer Dome in June 2000.
In March 2019, Seabridge Gold published an updated NI 43-101 Technical Report detailing- estimated Mineral Proven and Probable Reserves of 2.2 Bt of gold, copper, silver, and molybdenum ore. Table 23-2 is the published Proven and Probable Reserve Estimate, Table 23-3 is the published Measured plus Indicated Mineral Resource (http://seabridgegold.net). The resource estimate is based upon a combination of open pit and block caving mining methods. Over the entire LOM, ore will be fed to a flotation mill, which will produce a combined gold/copper/silver concentrate. The concentrate will be transported by truck to the nearby deep-water sea port at Stewart, BC, for shipment to a Pacific Rim smelter. Extensive metallurgical testing confirmed that KSM could produce a clean concentrate with an average copper grade of 25%, making it readily saleable. Separate molybdenum concentrate and gold-silver doré will be produced at the KSM processing facility. (http://seabridgegold.net).
Table 23-2: | March 2019 KSM Property Mineral Reserve |
Average Grades | Contained Metal | ||||||||
Reserve | Au | Cu | Ag | Mo | Au | Cu | Ag | Mo | |
Zone | Category | (g/t) | (%) | (g/t) | (ppm) | (Moz) | (Mlb) | (Moz) | (Mlb) |
Mitchell | Proven | 0.68 | 0.17 | 3.1 | 59.2 | 10.1 | 1,767 | 45 | 60 |
Probable | 0.58 | 0.16 | 3.1 | 50.2 | 17.4 | 3,325 | 95 | 104 | |
Iron Cap | Probable | 0.49 | 0.20 | 3.6 | 13.0 | 3.5 | 983 | 26 | 6 |
Sulphurets | Probable | 0.59 | 0.22 | 0.8 | 51.6 | 5.8 | 1,495 | 8 | 35 |
Kerr | Probable | 0.22 | 0.43 | 1.0 | 3.4 | 2.0 | 2,586 | 9 | 2 |
Total | 0.55 | 0.21 | 2.6 | 42.6 | 38.8 | 10,155 | 183 | 207 |
Note: | Cut-off values and mining methods used to report the Mineral Reserve Figures were defined based as Cdn$9 NSR for open pits and Cdn$16 NSR for underground. The reader should refer to the information provided by Seabridge Gold to get an accurate appreciation of the definition of the cut-off values for reporting. |
Source: | http://www.seabridgegold.net/resources.php. |
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Table 23-3: | March 2019 KSM Property Measured and Indicated Mineral Resources |
Average Grades | Contained Metal | ||||||||
Tonnes | Au | Cu | Ag | Mo | Au | Cu | Ag | Mo | |
Zone | (Mt) | (g/t) | (%) | (g/t) | (ppm) | (Moz) | (Mlb) | (Moz) | (Mlb) |
Mitchell | 1,794.7 | 0.57 | 0.16 | 3.1 | 58 | 34.31 | 6,638 | 179.053 | 230 |
Iron Cap | 422.6 | 0.41 | 0.22 | 4.6 | 41.0 | 5.576 | 2,051 | 62.559 | 38 |
Sulphurets | 381.6 | 0.58 | 0.21 | 0.8 | 48 | 7.116 | 1,766 | 9.815 | 40 |
Kerr | 378.4 | 0.22 | 0.41 | 1.1 | 5 | 2.692 | 3,445 | 13.909 | 4 |
KSM Total | 2,977.3 | 0.52 | 0.21 | 2.8 | 54 | 49.694 | 13,900 | 265.336 | 312 |
Note: | Cut-off values and mining methods used to report the Mineral Reserve Figures were defined based as Cdn $9 NSR for open pits and Cdn$16 NSR for underground. The reader should refer to the information provided by Seabridge Gold to get an accurate appreciation of the definition of the cut-off values for reporting. |
Source: | http://www.seabridgegold.net/resources.php. |
23.4 | Treaty Creek Property |
Tudor Gold Corp. owns a 60% interest in the Treaty Creek Property, with American Creek Resources Ltd. owning a 20% carried interest, and Teuton Resources Corp. owning a 20% carried interest with a 0.98% royalty interest in the core portion of the property and a 0.49% royalty interest in the periphery claims (http://www.teuton.com;http://www.americancreek.com). The Treaty Creek Property adjoins directly northeast of the Seabridge Gold’s KSM gold-copper property and is underlain by a similar geology. The Treaty Creek area has a long history of exploration, including extensive sampling and diamond drilling, dating back to its discovery in 1928 (Pardoe 2016). Exploration work uncovered several zones, the most promising of which are the Copper Belle (porphyry-style), GR2 (feeder zone to a VMS), Eureka (porphyry-style with a gold-silver epithermal overprint), and Treaty Ridge (VMS/Sedex?) zones. There are no public reports of Mineral Resources or Mineral Reserves.
23.5 | Catear |
Catear (Goldwedge) is a small 8.7 ha mining lease, mineral tenure 301579, held by Goldwedge Mines Inc. It is located 2.2 km northwest of Brucejack Gold Mine. Discovered in 1978, gold mineralization is hosted in a quartz vein and veinlet stockwork within andesite tuffs and lapilli tuffs of the Lower to Middle Jurassic Lower Hazelton Group. Although estimates of the contained mineralization are reported for two zones, these have not been prepared in accordance with NI 43-101 guidelines and are therefore not considered as current estimates for Catear. The estimates are presented here for information purposes only, and the reader is cautioned not to rely on them: Discovery Zone 34,451 t, grading 37.0 g/t Ag and 21.5 g/t Au; and Golden Rocket Zone 289,500 t, grading 38.3 g/t Ag and 27.4 g/t Au. Mining of the Golden Rocket Vein reportedly was undertaken in 1988 with ore processing through an on-site mill.
No records of production are available. (http://minfile.gov.bc.ca/Summary.aspx?minfilno=104B%20%20105)
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24.0 | OTHER RELEVANT DATA AND INFORMATION |
24.1 | Health, Safety, Environmental and Security |
A fully-integrated health, safety and environmental (HSE) program has been implemented to help achieve a “zero-harm” goal by Brucejack Gold Mine. To achieve this goal, all key project stakeholders have been responsible for providing leadership and committing to the highest HSE standards and values.
The development of HSE practices has required a high level of communication, motivation, and involvement including alignment with site contractors on topics such as safety training, hygiene, ergonomics, hazard awareness and risk assessment. Tools have been implemented for performance tracking and accountability, including procedures for incident management.
Established capture and containment guidelines are followed for the responsible management of process flows, effluent, and waste products. Environmental protection is incorporated in the operation of the main processes of the plant as well as in the transportation, storage, and disposal of materials within and outside of the boundaries of the Brucejack Gold Mine.
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25.0 | INTERPRETATIONS AND CONCLUSIONS |
25.1 | Geology |
The Brucejack Deposit is interpreted to be a deformed, porphyry-related transitional to intermediate sulphidation epithermal high-grade gold-silver deposit that was formed between 184 and 183 Ma in an active island arc setting similar to the modern-day Philippines. The Brucejack Deposit has many characteristics in common with carbonate-base metal gold deposits from the southwest Pacific Rim. Intermediate sulphidation epithermal deposits are considered to be a sulphide-rich sub-type of carbonate-base metal gold deposits by workers in the southwest Pacific Rim region.
High-grade gold-silver mineralization was formed in association with a telescoped, multi-pulsed magmatic-hydrothermal system beneath an active local volcanic center. This resulted in the overprinting of earlier porphyry alteration and mineralization, which includes low-grade gold mineralization, by later co-spatial epithermal veining and mineralization, including the high-grade gold mineralization. As a result, the precious metal grade distributions at the Brucejack Deposit are inherently mixed and unresolvable by domain generation alone.
Electrum occurs as clots and dendritic aggregates hosted in sub-vertical, nominally east-west trending quartz-carbonate and carbonate vein stockwork. Infill drilling and mine development have shown that there are corridors of higher-grade east-west trending electrum mineralization within the broader stockwork zones. This represents an opportunity for selectively using longitudinal mining.
Recent research has shown that precious metal mineralization was predominantly transported as colloidal suspensions, with transportation as dissolved metal complexes likely accounting for only a small component of the metal flux. Controls on electrum precipitation appear to be fluid mixing, decreasing temperature, local boiling, and local colloidal aggregate destabilization near pyrite-rich zones. Colloidal flocculation as a function of these controls appears to be concentrated along faults, fractures, pre-existing foliation planes, and along lithological contacts. This explains the lack of a geochemical proxy for precious metal mineralization at the Brucejack Deposit.
Brownfields exploration work has indicated the presence of at least two porphyry mineralization targets on the Brucejack Property: the Bridge Zone and the Flow Dome Zone. Recent work suggests that the Flow Dome Zone may be the surface expression of the porphyry system that drove the development of the epithermal mineralization in the Brucejack Deposit. The Bridge Zone porphyry system is older (approximately 191 to 189 Ma) and is similar to the Snowfield-Mitchell system. Additional exploration is currently targeting the Flow Dome Zone.
The Brucejack Deposit is currently focused on the Valley of the Kings Zone and the West Zone. Similar epithermal vein-hosted precious metal mineralization is present throughout the 5 km by 1.5 km wide arcuate band of phyllic alteration on the Brucejack Property (e.g., Gossan Hill Zone, Shore Zone, SG Zone, Golden Marmot Zone, and Hanging Glacier Zone). This alteration and mineralization band has yet to be explored in sufficient detail for resource estimation, and represents upside potential on the property.
25.2 | Mineral Resource |
An updated Mineral Resource, effective date January 1, 2019, has been prepared for the Brucejack Deposit, incorporating information from additional tightly-spaced infill drilling, mapping of underground geological exposures, and mine production. The new resource estimate comprises that part of the Valley of the Kings Zone updated where new information was available, the December 2013 resource estimates for the Valley of the Kings Zone outside the update area, and the April 2012 resource estimate for the West Zone. The January 2019 Mineral Resource inside the update area is reported inclusive of Mineral Reserves and exclusive of material mined to December 31, 2018.
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Data verification by the QP for the Mineral Resource confirmed that the drilling data were of suitable quality for use in resource estimation. Furthermore, the QP has confirmed that the geological and domain interpretations were representative of the nature and style of mineralization in the deposit, and were appropriate for the estimation of mineral resources.
The same estimation methodology used in the preparation of previous resource estimates for the Brucejack Deposit was followed in the generation of the January 2019 Mineral Resource. The non-linear split population-based approach, which separately estimates high grade, low grade, and probability of high-grade variables using a combination of multiple indicator and ordinary kriging, prior to recombining these into final gold and silver grades, is currently considered the most appropriate method for estimating the mixed and positively-skewed precious metal mineralization at Brucejack. Alternative techniques are continually evaluated as more information becomes available.
The model was validated against input drillhole data and mine production for the year 2018 and found to provide a reasonable to good representation of the input data and production information. The resource model was classified as Measured, Indicated, and Inferred in accordance with CIM (2014) Definition Standards. Measured Resources are expected to be within 10% and Indicated Resources are expected to be within 15% of mine production on an annual production basis. Shorter-term reconciliation is not considered appropriate given the highly variable and nuggety nature of the precious metal mineralization at Brucejack. Inferred Resources cannot be converted to Mineral Reserves as there is insufficient confidence in the estimate to support mine planning. They are, however, useful for resource definition drill targeting. Looking at the 2019 resource model retrospectively, the tonnes and grade reported from production in 2018 were within 10% of those reported from the 2019 resource model from within the mined outlines.
The January 2019 Mineral Resource effectively overwrites the July 2016 Mineral Resource inside the update area. Comparisons between these models (inclusive of mine production) show that the new estimate is lower by approximately 1.9 Mt, 0.9 Moz Au, and 0.5 Moz Ag in the Measured + Indicated Resource at similar estimated gold and silver grades, using the same cut-off grade. Inferred Resources also decreased by approximately 0.7 Mt, 0.9 Moz Au, and 1.6 Moz Ag, with a grade drop in both estimated gold and silver, using the same cut-off grade. The differences between the two models are largely data-driven. Additional tightly-spaced infill drilling, increased exposure of the mineralized system during mining, and over 1.5 Mt of actual production since mine commissioning have resulted in improved domain and local estimation parameter definition. Additional infill drilling in areas outside of the update area could result in similar changes in future resource updates.
25.3 | Mining |
25.3.1 | Underground Mine Geotechnical |
BGC has identified the following key risks and opportunities with regards to the rock mechanics assessment:
■ | The lack of in situ stress data limits the potential of the MAP3D model. Additional refinement of inputs, and calibration to underground observations, are required before quantitative characterization of the rock mass response is possible. This would allow optimization of excavation and pillar dimensions and associated ground support. |
■ | The stope dimensions provided in this Technical Report assume stope-scale geologic structures are present sub-parallel to the stope walls. As additional exploration drillholes are drilled, a structural model is developed for the Brucejack Property, and particularly as additional underground developments are exposed, the structural database and subsequent structural domains should be reviewed to refine the assumptions inherent in the stope span recommendations. Tighter definition of structural domains may allow less-conservative assumptions with respect to stope-scale structure, with a subsequent increase in recommended maximum stope spans. |
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25.3.2 | Mining Methods |
The current mining operation has proven mining performance at 3,800 t/d. The mine is equipped and staffed to continue mining of the reserves as planned. Ongoing reconciliation, cavity monitoring, and data collection provide feedback to the geology, mine planning, and operational teams to improve mining performance. The current mine plan includes accelerated development in order to sustain sufficient working areas for the target production.
The nature of the mineralization results in a degree of variance between planned tonnes and grade over short time periods. As mining continues, the nature of the mineralization and degree of variance will be better understood which will enable better forecasting of short- and long-term production.
25.3.3 | Waste Rock |
Bathymetric surveys, geotechnical site characterization, numerical assessment, back analysis, and continuous observation has been used to design the waste rock dump, including deposition on tailings. The observational method (Terzaghi and Peck 1967; Peck 1969) coupled with rigorous SPOs and QPOs documented in a comprehensive OMS Manual ensures continued safe operation of the dump.
This dumping procedure is independent of the Brucejack Lake bed sediment (and tailings) thickness or strength, because it assumes that the foundation cannot initially carry the load whether it is due to sediment (and tailings) thickness or strength (or both).
Four annual geotechnical inspections have been carried out on the waste rock dump (and tailings deposition) between 2015 and 2018 (Knight Piésold 2016; 2017; 2018a; SRK 2019). In addition, an Independent Tailings Review Board (ITRB) has been appointed by Pretivm and has completed annual inspections in 2017 and 2018 (Knight Piésold 2018b; 2019). All these inspections have consistently confirmed that the operational practices by Pretivm was appropriate for the site conditions, and that Pretivm staff was well informed of the procedures necessary to continue safe waste rock dumping.
25.4 | Mineral Processing and Metallurgical Testing |
25.4.1 | Metallurgical Testing |
The Brucejack Deposit mineralization typically consists of a significant portion of gold and silver present in the form of nugget or metallic gold and silver. Extensive metallurgical testing programs have been conducted on the Property since 1988, with major metallurgical test work performed between 2009 and 2014 to support the design and construction of the 2,700 t/d process plant for the Brucejack Gold Mine. The mill began commercial operation at the designed capacity in Q4 2017. In general, the mill feed is amenable to the process flowsheet designed, including gravity concentration and flotation concentration to produce a doré product and a flotation concentrate. On average, the gravity concentration circuit produced a much better gold recovery, compared to the results produced from the laboratory trials.
To increase the mill feed rate to 3,800 t/d, various test work, circuit simulations and review work were conducted in 2018 to assess the opportunities and bottlenecks for further improvement of the mill performance and throughput. The test and review work indicated that the process flowsheet currently used for recovery of the gold and silver values is feasible for the mineralization.
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25.4.2 | Mineral Processing |
The process plant was designed to process gold and silver ore at a nominal rate of 2,700 t/d to produce gold doré and gold flotation concentrate. The mill was successfully commissioned between March and May of 2017 and began commercial operation at the designed capacity in Q4 2017.
In 2018 various review and assessment work was conducted to assess potential of increasing mill throughput to 3,800 t/d and potential bottleneck that may limit for the increase in the mill feed rate. The review work was conducted by Brucejack Gold Mine’s engineers and metallurgists, equipment suppliers, and independent consultants with various supporting test work and simulations. The review work indicated that with some minor modifications, such as increasing some of the slurry pump sizing and increasing second and third flotation cleaner capacities, the process plant will be able to handle the increased throughput. The mill has partially started the modification work. The upgraded flowsheet is same as the existing operation, including the following components:
■ | one stage of crushing in underground |
■ | a 2,500 t SAG mill feed surge bin on surface |
■ | a SABC primary grinding circuit equipped with a gravity concentration circuit |
■ | rougher flotation and scavenger flotation of hydrocyclone overflow |
■ | three stages of cleaner flotation on combined rougher and scavenger concentrates |
■ | flotation concentrate dewatering |
■ | flotation tailings dewatering circuits. |
The mill feed ore is crushed and ground to the particle size of 80% passing approximately 90 to 100 µm. Two gravity centrifugal concentrators, together with two upgrading tables and associated one gravity centrifugal concentrator, recover the free nugget gold grains from the ball mill discharge. The resulting gravity concentrate is further refined in the gold room on site to produce gold-silver doré.
The hydrocyclone overflow, containing gold and silver bearing sulfide minerals, from the primary grinding circuit is floated by rougher and scavenger flotation. The resulting rougher flotation concentrate and scavenger flotation concentrate are further upgraded in three stages of cleaner flotation. The first cleaner scavenger flotation tailings report to the rougher scavenger flotation for further recovering the residual gold and silver bearing sulphides. The third cleaner concentrate, or the final flotation concentrate, is dewatered by a high-rate thickener and a tower-type filter press prior to being loaded in customized bulk containers for shipping.
The final rougher scavenger flotation tailings are dewatered in a deep cone thickener. Approximately 30 to 40% of the flotation tailings is used to make paste for backfilling the excavated stopes in the underground mine, and the balance is pumped to Brucejack Lake where the tailings is stored under water. The concentrate and tailings thickener overflows are recycled as process make-up water.
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25.5 | Environmental |
25.5.1 | Geochemistry |
The geochemistry of Brucejack Gold Mine rocks has been and continues to be assessed through comprehensive characterization studies (refer to Section 20.5.1) and ongoing monitoring programs. The geochemical data sets have been used to inform waste management plans and to predict associated water quality. The main conclusions of the geochemistry assessment are summarized as follows:
■ | A significant portion (49%) of surface waste rock samples are characterized as PAG with enrichments (greater than 10x average continental crust) in silver, gold, manganese, antimony, and selenium. Saturated column tests indicate that subaqueous storage of surface waste rock in Brucejack Lake will minimize any potential leaching and changes to Brucejack Lake water quality. |
■ | The majority of underground waste rock samples (83%) at the Brucejack Gold Mine are PAG; however, most of the rocks have considerable neutralization potential, which is predicted to delay the onset of ARD for decades or more. This is supported by the observation of alkaline mine waters and no indication of increasing concentrations of dissolved metals associated with the onset of ARD (e.g., cadmium, cobalt, copper, iron, zinc, as predicted by kinetic tests) since gold production commenced in June 2017. |
■ | The Brucejack Gold Mine ore is characterized as PAG, whereas tailings generated from the mill are generally characterized as NPAG. The tailings samples have elevated concentrations of silver, arsenic, cadmium, manganese, and selenium, compared to continental crust; however, saturated column test results indicate that subaqueous storage of tailings in Brucejack Lake or in the underground mine below the post-closure final water table elevation will minimize metal leaching. |
■ | NPAG quarry rock samples are consistently NPAG with low metal leaching potential. |
■ | WTP sludge is characterized as NPAG with elevated concentrations (greater than 10× average continental crust) of silver, arsenic, cadmium, manganese, molybdenum, antimony, and selenium. Based on static and kinetic tests, WTP sludge is predicted to be stable under a range of pH and redox conditions. |
The results of the geochemistry assessment indicate that water, waste rock, and tailings are being managed appropriately to minimize environmental risk.
25.5.2 | Hydrogelogy |
A calibrated three-dimensional numerical hydrogeologic model was used to estimate the inflow of groundwater to the Brucejack Gold Mine underground mine workings. The average annual rate of groundwater inflow to the underground workings was predicted to vary between 2,500 and 2,900 m3/d and to increase to between 2,900 to 3,500 m3/d with initiation of mining in the West Zone (Section 20.3.3). However, the observed average annual underground dewatering rate (a proxy for measuring groundwater inflow rate to the mine) from 2013 to 2017 was 1,300 m3/d, which suggests that actual inflow rates may remain between the simulated base case and the low K scenarios (Figure 25-1).
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Figure 25-1: Simulated vs. Observed Inflow Rates
Potential factors causing this difference between the calibrated base case and observed inflows include: the bulk rock mass hydraulic conductivity is lower than simulated for the base case; the rate and depth of mine development is different than that simulated in the model; seepage mitigation measures employed during mining (e.g., installing packers in exploration boreholes or grouting of higher producing zones); or some combination of these factors. It should also be noted that, due to the anisotropic and heterogeneous nature of fractured rock groundwater flow systems, higher inflow rates closer to the base case or the high K + high recharge scenario (Figure 20-1, Section 20.3.3) may still be observed as mining advances. This will be considered in the next update to the groundwater flow model.
25.5.3 | Water Management |
There are three sources of contact runoff during operations:
■ | waste rock deposited in Brucejack Lake |
■ | surface contact water from PAG bedrock excavations that occurred during site preparation for infrastructure construction, the largest of these being rock excavation to create the pad areas for the mill and the Phase 2 camp |
■ | groundwater seepage to the underground mine. |
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Runoff from the latter two sources is managed by storage and treatment. All runoff within the Brucejack Gold Mine site contact water management system is collected in the CWP. This pond has been sized to contain the runoff volume (50,000 m3) associated with the 24-hour, 200-year return period rain on snow event (220 mm). The contact water pond runoff is pumped to the mine WTP for treatment prior to use in process or for discharge to Brucejack Lake.
The average water requirement for the Brucejack Gold Mine process plant is 2,847 m3/d based on a mill throughput of 3,800 t/d. This water is required for the tailings slurry to the lake, the underground paste backfill, the concentrate slurry, and the underground mine supply. Process water is sourced from:
■ | treated underground seepage water |
■ | treated contact water from the CWP |
■ | ore moisture (approximately 3% by weight) |
■ | water withdrawal from Brucejack Lake at its outlet. |
Average annual groundwater seepage into the underground workings is expected to vary from approximately 2,500 to 3,500 m3/d throughout the remaining LOM. Seepage water is sent to the WTP, and then the process plant, where its use is maximized in process. The paste backfill will exude a minor amount of water (2.5% of the total paste backfill water volume) during the curing phase. This additional water is assumed to be pumped out with the seepage water and sent to treatment.
An average annual outflow of 2,012 m3/h from Brucejack Lake has been estimated for the LOM, an average decrease of 2% above existing conditions (2,059 m3/h). The decrease in flow results from slurry water being entrained in the voids of the deposited tailings, which offsets the displacement of water by the deposition of tailings and waste rock.
The water management assessment indicates that Brucejack Gold Mine surface and underground contact and non-contact waters are being managed appropriately, and that water inputs, including fresh water supplies, are adequate to support milling operations and other mine requirements.
25.5.4 | Water Quality |
Key mitigation measures to minimize Brucejack Gold Mine effects on water quality include collection of underground mine and surface waters that contact disturbed PAG surface and treatment of this collected water in the mine WTP; a sewage treatment plant to treat domestic wastewater; and subaqueous deposition of waste rock. Discharge of mine contact water to the aquatic receiving environment is regulated under the conditions in Effluent Permit 107835 (PE-107835), most recently amended on December 14th, 2018. Effluent permits in British Columbia are issued pursuant to the provisions in British Columbia’sEnvironmental Management Actfor the protection of the environment.
Water quality monitoring results have shown that water has and is continuing to be managed to meet the requirements of PE-107835, including with respect to water quality limits for the mine effluent discharge. Concentrations of metals and other parameters monitored at the outlet of Brucejack Lake are below the current limits in PE-107835 and/or below BC water quality guidelines for the protection of aquatic life. The Brucejack Gold Mine water quality model was updated in 2018 (Pretivm 2018b) and incorporated monitoring results from construction and operation phases of the mine, as well as recent geochemical test results. The updated model predicts that water quality will continue to meet the discharge limits and other conditions set out in PE-107835.
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25.6 | Capital Cost and Operating Cost Estimates |
The total estimated capital cost to upgrade the Brucejack Gold Mine mill capacity to 3,800 t/d, including design, construction, installation, and commissioning, is US$22.5 million, excluding cost related to mining operations which are included in the sustaining capital cost. The total sustaining capital cost was estimated to be US$200.7 million, including related costs for mining, processing and site infrastructure and services. A foreign exchange rate of Cdn$1.00:US$0.775 was used for the cost estimate.
The estimated LOM average operating cost for the Brucejack Gold Mine is US$168.02/t milled. Table 25-1 shows the cost breakdown for each area.
Table 25-1: | LOM Average Operating Cost Summary |
Unit Operating Cost | |
Area | (US$/t milled) |
Mining | 74.42 |
Processing | 21.87 |
Overall Site Services, including Office(1) | 36.19 |
G&A(2) | 35.54 |
Total Operating Cost | 168.02 |
Note: | (1)Including the costs for off-site and satellite offices. |
The operating costs exclude shipping charges and sale costs for the gold-silver doré and gold-silver concentrate and royalties, which are included in financial analysis.
All operating cost estimates exclude taxes unless otherwise specified.
25.7 | Economic Analysis |
Tetra Tech prepared an economic evaluation of the Brucejack Gold Mine based on a discounted cash flow model for the remaining 14-year LOM and 15.74 Mt of ore included in the mine plan. For this mine plan, a post-tax NPV of US$2,225 million, at a discount rate of 8%, was calculated based on the following assumptions:
■ | gold price of US$1,300/oz |
■ | silver price of US$16.90/oz |
■ | foreign exchange rate of Cdn$1.00:US$0.778 |
The production schedule was incorporated into the pre-tax financial model to develop annual recovered metal production. Capital expenditures include mill feed throughput expansion capital costs to increase mining and mill capacity from 2,700 to 3,800 t/d and ongoing sustaining capital costs for mining and milling additions and equipment replacement.
The NPV was estimated at the beginning of the mining schedule and therefore has an effective date of January 1st, 2019.
Table 25-2 summarizes the forecast for economic performance for the Brucejack Gold Mine operation for the remaining LOM.
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Table 25-2: | Brucejack Gold Mine Economic Performance Forecast |
Unit | Amount | |
Tonnes Mined and Processed | kt | 15,754,279 |
Gold Head Grade | g/t | 12.6 |
Silver Head Grade | g/t | 58.4 |
Total Project Revenue | US$ million | 7,911 |
Operating Costs | US$ million | (2,647) |
Royalties | US$ million | (139) |
Sustaining Capital Costs | US$ million | (223) |
Other Expenses | US$ million | (29) |
Taxes Payable | US$ million | (1,445) |
Post-tax NPV (5% Discount Rate) | US$ million | 2,587 |
Post-tax NPV (8% Discount Rate) | US$ million | 2,225 |
The year of operations that has been completed at the Brucejack Gold Mine provides confidence in the project economics, especially with regard to understanding operating costs. The Brucejack Gold Mine is most sensitive to metal prices, with opportunities to improve profitability through cost management.
25.8 | Mineral Reserves |
The revision to Mineral Reserves is driven by the updated Mineral Resources. Measured and Indicated Mineral Resources that fall within planned mining shapes have been converted to Mineral Reserves. Adjustment factors applied to the Mineral Resources to convert to Mineral Reserves include estimation of mineable shapes, dilution, and mining losses. Mineral Reserves are delineated using a cut-off grade of $185/t, which is in excess of forecasted all-in sustaining costs per tonne milled for the remaining LOM.
Reconciliation of 2018 mined-out shapes has enabled validation of the process for estimating Mineral Reserves.
The following opportunities exist for continuous improvements with respect to Mineral Reserves:
■ | ongoing reconciliation to improve the understanding of dilution and mining recovery |
■ | optimization of cut-off grades; Pretivm should re-evaluate operating costs for the expanded throughput, which may allow for reduction in the cut-off grade and expansion of Mineral Reserves. |
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26.0 | RECOMMENDATIONS |
26.1 | Introduction |
This Technical Report indicates that the mine expansion plan is considered to be economically viable. The process plant is anticipated to be capable of processing 3,800 t/d of ore, or higher, with minor modifications on some existing circuits.
26.2 | Geology |
Faults, fractures, foliation planes, and lithological contact structures are considered key features controlling the distribution of electrum within the Brucejack Deposit. It is therefore recommended that all occurrences of visible electrum in the underground workings are calibrated to, and combined with drillhole data to create a predictive tool to assist in delineating more detailed corridors of higher-grade mineralization within the broader stockwork zones. This will assist in improved local resolution of high-grade zones for resource estimation and complement studies assessing longitudinal mining potential. This should be completed as a part of the standard underground geological mapping and other observations, and as such, does not need a separate budget.
Fluid mixing, utilizing various structural elements, appears to have been the primary cause of colloidal suspension destabilization and electrum precipitation. The presence of numerous phreatomagmatic breccia bodies, immature volcaniclastic lithological units, and carbonate-dominated veins, vein stockwork, and vein breccia, opens up the possibility of caldera collapse and seawater ingress as being a trigger for ubiquitous fluid mixing. It is recommended that a surface mapping campaign be conducted across the Flow Dome Zone, eastern parts of the Valley of the Kings Zone, as well as to the north and east of Brucejack Lake to test this possibility. Available drillhole logs, core, and core photos should be reviewed to augment this process. This should be completed as a part of the on-going exploration process, and as such, it is not expected that this needs a separate budget.
The geology at depth, to the west, and to the east of the Valley of the Kings Zone appears different to the part currently being mined: VSF volcanosedimentary rocks become the primary host, being replaced by P1 latite flows at depth and to the east; veins, vein breccia, and vein stockwork change from quartz-carbonate to carbonate only veining (at least three generations of calcite, including manganoan). Recent research has shown, through the use of Transmission Electron Microscopy, that all of the electrum is hosted in carbonate as opposed to quartz. The changing geology needs to be characterized to assess the significance of these changes and to characterize appropriate structural-lithological mineralization traps. Revisions to the existing mine stratigraphy and mineralized vein classification scheme will be required for these areas as drilling and mining expand into them. It is understood that this work is being completed as a part of the on-going near-mine exploration process, and as such, it is not expected that this needs a separate budget to the existing near-mine exploration budget.
Additional geophysical and drill exploration of the Flow Dome Zone should be reviewed in light of the results of the current deep drilling program and surface exploration. Additional near-mine exploration, including targeted surface drilling and geophysics, is warranted on the mineralized zones closest to the current mine to test the potential for additional high-grade precious metal resources proximal to the mill. The presence of phyllic alteration and precious metal mineralization on the northwest shore of Brucejack Lake (e.g., Windy Point) indicates that precious metal mineralization may continue under the lake. This possibility should be tested in future near-mine exploration drilling programs, and as such, it is not expected that this needs a separate budget to the existing near-mine exploration budget.
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26.3 | Mineral Resource |
Reconciliation of the January 2019 Mineral Resource to the 2018 mill production was within 10% on an annual production volume. Areas mined during this period were generally informed by drilling on up to 15 m centers. It is therefore recommended, going forward, that resource definition (infill) drilling be conducted at 15 m centers or tighter. This should be budgeted within the mine grade control process on an as-needed basis.
All future drilling to be conducted on the Valley of the Kings Zone and the West Zone should be as close to perpendicular to the main mineralized trend as possible. This includes drilling for exploration, resource definition drilling, and drilling for grade control purposes. All efforts should be made to avoid drilling parallel to the main mineralized trend.
Although it is impractical not to drill in fan patterns from underground drill bays, efforts should be made to minimize excessive clustering at resource definition drillhole collars in drill fans. This has the effect of locally suppressing estimation of higher-grade mineralization where the clustering occurs in interpreted mineralized domains. Drilling parallel fans from spaced drill bays versus multiple oriented fans from the same collar location is recommended to mitigate against the fan collar clustering effect.
Additional infill drilling should be conducted in zones of interest, particularly the Indicated Mineral Resource outside of the 2019 update area, where it is based on a drill spacing of between 25 m and 40 m to improve the confidence in the resource model. A budget for this will need to be determined on an as needs basis, as the needs of the mine change.
An updated simulation-based drillhole spacing study is recommended for the Valley of the Kings Zone considering the quantity of new drilling and mining information that has been generated subsequent to the previous study, conducted in 2016. No separate budget is required as the work should be completed internally by Pretivm’s Resource Geologist.
The current Mineral Resource is, in practical terms, a bulk mining model. This is particularly the case for that part of the Mineral Resource outside of the update area. In order to improve model selectivity and enhance local estimation resolution, in conjunction with infill drilling, alternative approaches to volume-variance adjustments are recommended. In addition to the current re-blocking-based approach as part of MIK post-processing, other techniques like Localized Uniform Conditioning and generating re-blocked local simulations should be tested.
An updated simulation-based stope risk assessment study is recommended. This will establish within-stope grade uncertainty to inform and improve mine scheduling, as well as highlight areas that require additional information. No separate budget is required as the work should be completed internally by Pretivm’s Resource Geologist.
Improved material tracking techniques should be investigated to enhance annual reconciliation. It is recommended that the mine source commercial software for the development of tracking requirements. The cost of the software and its set-up should be budgeted accordingly.
Near-mine Inferred Mineral Resources in the eastern parts of the Valley of the Kings Zone represent a proximal target for adding to the existing Measured + Indicated Mineral Resource base. Additional infill drilling is recommended for the near term. The appeal of this area is underlined by the results from the deep underground exploration drilling conducted in 2018, which demonstrated the continuation of Valley of the Kings Zone style mineralization towards the east and under the Flow Dome Zone. It is expected that this would be included in the exploration and near-mine exploration budgets as the company sees fit, and as such, it is not expected that this needs an additional budget.
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In 2011, Pretivm produced a Mineral Resource, in support of testing the open pit potential of other zones at Brucejack, including Shore Zone, Bridge Zone and the Galena Hill Zone. As open pit mining is currently not considered an option at Brucejack, that Mineral Resource is no longer current. It is recommended that Pretivm revisit these zones to examine the potential for estimating a Mineral Resource suitable for underground extraction. No separate budget is required as the work should be completed internally by Pretivm’s Resource Geologist.
26.4 | Mining |
26.4.1 | Underground Mine Geotechnical |
BGC makes the following recommendations for additional rock mechanics assessment work:
■ | Further work should be completed on the interpretation and modelling of large and intermediate scale faults. The presence of unknown major structures or splays off known faults have the potential to significantly affect rock mass stability. The updated model should be reviewed to determine if updates to the geotechnical assessments are required. |
■ | Numerical stress modeling has identified potential instability zones in stope clusters around the sill pillars and the crown pillar. The model should be updated with the West Zone geology model, in situ stress measurements, and a detailed stope-by-stope extraction plan. The updated model should be calibrated using any ground deformation observations recorded during development and production. The calibration data can then be used to increase confidence in the modelling results. This will facilitate a more detailed study of the mine sequencing effects on the rock mass stability, including pillars, stope hanging walls, mine abutments, and excavations through the Brucejack Fault Zone. |
The estimated cost for the above-mentioned recommended work is $300,000.
26.4.2 | Mining Methods |
Currently, Brucejack Gold Mine geology and mine planning teams conduct extensive assaying of drill cuttings but do not assay blasted muck from stoping. While Tetra Tech understands that the decision point for mill feed occurs prior to blasting in the stopes, there is a lost opportunity to provide reconciliation data on dilution and mining recovery to the mine planning team. Tetra Tech recommends conducting spot assaying to better calibrate dilution and mining recovery data for mine planning. A brief study can be conducted by in-house staff, and the cost is estimated to be less than $10,000.
Tetra Tech recommends the Brucejack Gold Mine build a comprehensive LOM production and cost model. This will enable better optimization of cut-off grades against target cash flow or project economic performance. This can be conducted by in-house employees at no additional cost.
26.4.3 | Waste Rock |
Waste rock and tailings deposition is governed by the OMS Manual, the last version having been updated in October 2018 (SRK 2018a). Specifically, waste rock dumping is done in accordance with a standard operating procedure (Brucejack Lake Waste Rock Disposal, SOP 011), which is an appendix to the OMS Manual. Pretivm’s engineering team manages the day-to-day waste rock deposition and follow-up monitoring and surveillance following procedures outlined in the OMS Manual. The OMS Manual has been developed in accordance with SRKs design recommendations and undergoes updates as necessary. All employees working on the WRTSF are provided training on the OMS Manual, specifically the WRTSF SOP.
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The required surveillance procedures for waste rock and tailings deposition is explicitly outlined in the OMS Manual, as are the QPOs.
A daily report is produced by the Pretivm on-site geotechnical engineers that outlines all activities pertaining the waste rock dumping. This report is circulated internally to Pretivm staff including senior management, all off-shift geotechnical personnel to ensure continuity, as well as to the EOR. If the EOR identifies any anomalies or areas of concern based on the daily report, they reach out to the on-site geotechnical engineers.
It is recommended that Pretivm continue to operate in accordance with these procedures outlined as it has been demonstrated to ensure safe waste rock and tailings deposition.
26.5 | Mineral Processing and Metallurgical Testing |
Further metallurgical tests are commended to optimize metallurgical performances and support the operations.
Installation of a regrinding and gravity concentration circuit to recover fine gravity recoverable gold and silver from the rougher flotation concentrate should be investigated to further improve gold and silver recoveries to the doré. The concentrate should be reground to release locked fine gold and silver grains. However, a comprehensive technical and economic review should be conducted, including investigating the effects of the additional gold and silver recovery to doré on capital costs, operating costs, and gold and silver payment of the flotation concentrate.
Tailings and flotation concentrate thickener performances should be further assessed, in particular at the increased mill feed rate. The review work should include further flocculant type and dosage evaluation and bypassing the coarse fraction of the final flotation tailings to the tailings surge tank by cycloning to reduce the tailings thickener loads. Also, the cyclone classification arrangement may increase solid density of the paste plant feed which may save paste binder material consumption.
Further optimization of crushing and grinding circuits should be conducted in an effort to reduce comminution circuit energy consumption and steel ball consumption, including better utilizing the installed pebble crusher.
The mill optimization is a part of daily process operation improvements. The costs associated with these optimizations have been included in the mill operating costs.
26.6 | Environmental |
26.6.1 | Geochemistry |
The geochemistry of Brucejack Gold Mine waste rock, ore, and tailings has been well characterized through baseline studies and ongoing confirmatory sampling programs. The environmental management plans in effect outline sampling recommendations, management triggers, and corrective actions that are expected to minimize potential adverse effects on water quality. It is recommended that, as planned, confirmatory sampling and ongoing site monitoring data for waste rock, NPAG quarry rock, tailings, paste backfill, and mine water continue to be evaluated on an ongoing basis to identify potential environmental issues, to improve understanding of site-specific geochemical behaviour, and to verify the site-wide water quality model.
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Recommendations for future geochemical studies at Brucejack Gold Mine include the following:
■ | additional saturated column tests on WTP sludge if the chemistry of mine water changes significantly or if modifications are made to the water treatment process |
■ | additional kinetic tests on tailings if changes are made to the milling process such that the chemistry of the tailings changes significantly |
■ | continued geochemical and mineralogical studies to predict mine water quality during closure when the mine is flooded. |
The estimated cost for this recommended work is $300,000.
26.6.2 | Hydrogelogy |
An update of the groundwater flow model to reflect the change in mining rate from 2,700 to the 3,800 t/d approved in late 2018, or for the 2019 mine plan changes, was not considered necessary because:
■ | The observed inflow rate is within the sensitivity bracket (i.e., between the low K and base case inflow estimates). |
■ | The dominant controls on predicted inflow rates to the underground in any year are the amount of open space underground at any given time and seasonal influences on infiltration rates. The amount of open space in the underground at any time does not change meaningfully as a result of the throughput increase (i.e., open space in any year in the model is adequately represented in the existing groundwater flow model) and the simulated seasonal variation on inflow rates is a good match to observed inflow rates. |
However, the conceptual hydrogeologic model and the numerical groundwater flow model should be revised and predicted inflow rates revisited if there are significant changes to the mine plan, particularly any resulting in significant development outside of the current underground mine “envelope”, or if there are other changes potentially impacting the hydrogeologic response of the system (e.g., changes to portal locations or surface layouts, waste deposition or backfill plans, or intersection of major fault(s) or hydraulically conductive structural geologic feature(s), etc.).
BGC makes the following hydrogeological recommendations:
■ | As planned, supplement the existing hydrogeologic monitoring record in 2019 and beyond with data from the seven additional pairs of nested (shallow and deep) groundwater monitoring wells installed during 2018 in accordance with PE-107835 andMines ActPermit M-243 requirements. |
■ | Further investigation of hydraulic conductivities (K) in the area of the Brucejack Fault or other large faults or geologic structures that may be encountered is recommended to support the distribution of K in the model and to inform fault-related sensitivity analyses. |
■ | Additional packer testing is recommended in any additional geotechnical or environmental boreholes that may need to be drilled to support ongoing development of the mine. |
It will be important to continue the collection of hydraulic head data and pumping rate data from underground dewatering operations on a year-round basis at the Brucejack Gold Mine site, as these data will be important for ongoing refinement of the conceptual and numerical hydrogeologic models.
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26.6.3 | Water Management |
Water management is a critical component of the Brucejack Gold Mine design in this high precipitation environment. As such, Pretivm has established a site-wide water management plan that includes monitoring of climate, streamflows, CWP levels, and flows being pumped around the mine site or discharged to the environment. This monitoring allows Pretivm to provide and retain water for mine operations; manage water to ensure that any discharges are in compliance with the applicable water quality levels and guidelines; and minimize the use of fresh water through recycling of water whenever possible. To ensure these goals continue to be met during future mine operations:
■ | Existing climate and hydrometric stations must continue to be monitored and maintained with an appropriate level of quality control. |
■ | The following levels/flows must also continue to be monitored and maintained with an appropriate level of quality control: |
– | CWP levels |
– | CWP water pumped to the plant site |
– | effluent discharged from the WTP to the CWP that does not meet the WTP water quality limits for discharge to Brucejack Gold Lake |
– | fresh water pumped from the low-level weir to the plant site |
– | water pumped from the fresh water tank to underground |
– | underground water pumped to the WTP |
– | treated effluent from the WTP discharged to Brucejack Lake. |
26.6.4 | Water Quality |
Water quality should continue to be monitored in compliance with mine authorizations and environmental management plans to verify that water is being managed to meet regulatory conditions for the protection of the environment. The Brucejack water quality model provides estimates of water quality through the operations, closure, and post-closure phases of the Brucejack Gold Mine. This model will be updated in 2020 as part of the five-year mine plan and reclamation program update. It is recommended that, as planned, this update incorporate the latest water quality monitoring data, geochemical test results, water balance, and mine plan.
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27.0 | REFERENCES |
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Tuncer, V., 2014b. Spartan Magnetotelluric Survey Geophysical Report – Addendum (Topography included 3D Inversion): Snowfield and Brucejack Projects, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by Quantec Geoscience Ltd. Dated December 12, 2014. 182 p.
Turkoglu, E., Young, C., and Gregory, W., 2011. Spartan Magnetotelluric Survey Geophysical Report: Snowfield & Brucejack Project, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by Quantec Geoscience Ltd. Dated December 14, 2011. 223 p.
Vallat, C., 2009. Quality Assurance and Quality Control Report on Brucejack pre-Silver Standard Resources Inc. Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Silver Standard Resources Inc. by GeoSpark Consulting Inc. Dated October 7, 2009. 142p.
Vallat, C., 2011. Quality Assurance and Quality Control Report on Brucejack 2011 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. Dated December 22, 2011. 53p.
Vallat, C., 2012. Quality Assurance and Quality Control Report on Brucejack 2012 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. Dated September 13, 2012. 39p.
Vallat, C., 2013. Quality Assurance and Quality Control Report on Brucejack 2012 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. Dated January 4, 2013. 60p.
Vallat, C., 2014. Quality Assurance and Quality Control Report on Brucejack 2013 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. Dated April 9, 2014. 74p.
Vallat, C., 2015. Quality Assurance and Quality Control Report on Brucejack 2014 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. January 21, 2015. 60p.
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Vallat, C., 2016a. Quality Assurance and Quality Control Report on Brucejack 2015 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. Dated March 24, 2016. 72p.
Vallat, C., 2016b. Quality Assurance and Quality Control Report on Brucejack 2016 Analytical Results, Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretium Resources Inc. by GeoSpark Consulting Inc. August 12, 2016. 41p.
Vallat, C., 2018. Quality Assurance and Quality Control Report on Brucejack 2017 and 2018 Analytical Results: Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished report prepared for Pretivm Resources Inc. by GeoSpark Consulting Inc. Dated September 21, 2018. 77 p.
Vallat, C., 2019. Quality Assurance and Quality Control Report on Brucejack 2018 Analytical Results: Brucejack Project, Skeena Mining Division, British Columbia, Canada. Unpublished draft report prepared for Pretivm Resources Inc. by GeoSpark Consulting Inc. Dated February 15, 2019. 67 p.
Wafforn, S.R., 2018a. Geological, Geochemical and Prospecting Program on the Bowser Property. BC Geological Survey Assessment Report No. 37435. Prepared for Pretium Resources Inc. Dated February 1, 2018. 514 p.
Wafforn, S.R., 2018b. Geological, Geochemical and Prospecting Program on the Bowser Property. BC Geological Survey Assessment Report No. 37443. Prepared for Pretium Resources Inc. Dated February 5, 2018. 1238 p.
27.2 | Metallurgy and Recovery Methods |
ALS Metallurgy-Kamloops, 2018. Metallurgical Testing for the Brucejack Project. June 18, 2018.
Bureau Veritas Commodities Canada Ltd. BC Minerals – Metallurgical Division, 2017. Mineralogical Assessment of Two Concentrate Samples. August 31, 2017
Bureau Veritas Commodities Canada Ltd. BC Minerals – Metallurgical Division, 2016. Metallurgical Testing for Concentrate Production. March 3, 2016.
Cominco Engineering Services Ltd., 1990. Feasibility Study Sulphurets Property Newhawk Gold Mines Ltd. March 1990
Contract Support Services, Inc., 2012. JK Simulation Results for Brucejack Project. November 29, 2012.
Dawson Metallurgical Laboratories, FLSmidth Ltd., 2014. Letter Report - Brucejack Tabling and Smelting. May 29, 2014.
F. Wright Consulting Inc., 2013. Gravity/Flotation Response - Valley of the Kings, Brucejack Project. May 7, 2013.
F. Wright Consulting Inc., 2013. Metallurgical Data - Brucejack Gold Silver Project. February 08, 2013.
F. Wright Consulting Inc., 2014. Low Grade Response - Valley of the Kings, Brucejack Project. June 10, 2014.
FLSmidth Knelson, A Division of FLSmidth Ltd., 2012a. Gravity Modeling Report. July 11, 2012.
FLSmidth Knelson, A Division of FLSmidth Ltd., 2012b. Gravity Test Work Report. August 09, 2012.
FLSmidth Ltd., 2018. Gravity Circuit Modeling Report. April 20, 2018.
Gekko Metallurgical Laboratory, 2017. Intensive Cyanidation of Knelson Concentrate Testwork Report. August 31, 2017
Gekko Systems Pty Ltd., 2014. Brucejack Python Study Update. May 06, 2014.
Gekko Systems Pty Ltd., 2014. Metallurgical Testwork Reports (Low Grade, Medium and High Grade Samples). April 28, 2014.
Hazen Research Inc., 2012. Comminution Testing with SMC Results. July 13, 2012
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Joe Zhou Mineralogy Ltd., 2012. Deportment Study of Gold and Silver in Cyanide Leach Residues from Brucejack Lake Project, Part I, Part II and Part III. February 20, 2012.
Metallurgical Division at Inspectorate America Corp., December 2009 to July 2010. Data Reports.
Metallurgical Division at Inspectorate America Corp., September 2010 to April 2011. Data Reports.
Metallurgical Division at Inspectorate Exploration and Mining Services Ltd., 2014. Mineralogical Assessments on the Process Stream Samples. May 15, 2014
Met-Solve Laboratories Inc., 2012. Gravity Test Report - MS1399. July 10, 2012.
Met-Solve Laboratories Inc., 2013. Gravity Circuit Modeling - MS1418. March 14, 2013. Met-Solve Laboratories Inc., 2014b. Letter Report - MS1542. June 02, 2014.
Met-Solve Laboratories Inc.,2014a. Letter Report - MS1542. May 21, 2014.
Pocock Industrial Inc., 2019. Solids-Liquid Separation Testing Report. January 2019.
Pocock Industrial, Inc., 2012. Sample Characterization, Particle Size Analysis, Flocculant Screening, Gravity Sedimentation, Pulp Rheology/Paste Vacuum Filtration and Pressure Filtration Studies. November 2012
Process Mineralogical Consulting Ltd., 2012. A Mineralogical Description of Six Samples from the Brucejack Project, Northwestern British Columbia. June 01, 2012
Process Mineralogical Consulting Ltd., 2018. A Mineralogical Description and Gold Deportment Analysis of One Concentrate Sample. October 01, 2018.
SNF Canada, 2016. Polymer cylinder Test Report. November 18, 2016.
SNF Canada, 2017a. Site Service Visit Report. October 19, 2017.
SNF Canada, 2017b. Tailings Thickener Polymer Treatment Review. December 20, 2017.
27.3 | Mining |
Ghaffari, H., Huang, J, Pelletier, P., Armstrong, T., Brown, F.H., Newcomen, H.W., Weatherly, H., Logue, C., Mokos, P., 2011: Technical Report and Preliminary Economic Assessment of the Brucejack Project. NI43-101 Technical Report prepared for Pretium Resources Inc., by Tetra Tech, Wardrop, P&E Mining Consultants Inc., BGC Engineering Inc., Rescan Environmental Services Ltd., AMC Mining Consultants (Canada) Ltd. 309pp. Effective Date 3 Jun 2011.
Ghaffari, H., Huang, J., Hafez, S. A., Pelletier, P., Armstrong, T., Brown, F.H., Vallat, C.J., Newcomen, H.W., Weatherly, H., Wilchek, L., Mokos, P., 2012: Technical Report and Updated Preliminary Economic Assessment of the Brucejack Project. NI43-101 Technical Report prepared for Pretium Resources Inc., by Tetra Tech, Wardrop, Rescan Environmental Services Ltd., P&E Mining Consultants Inc., Geospark Consulting Inc., BGC Engineering Inc., AMC Mining Consultants (Canada) Ltd. 328pp. Effective Date 20 Feb 2012.
Ireland, D., Olssen, L., Huang, J., Pelletier, P., Weatherly, H., Stoyko, H.W., Hafez, S.A., Keogh, C., Schmid, C., McAfee, B., Chin, M., Gould, B., Wise, M., Greisman, P., Scott, W.E., Farah, A., Zazzi, G., Crozier, T., and Blackmore, S., 2014. Feasibility Study and Technical Report Update on the Brucejack Project, Stewart, BC. Tetra Tech NI 43-101 Technical Report for Pretium Resources Inc. Effective Date June 19, 2014. 460 p.
AMC Mining Consultants (Canada) Ltd., 2015. Brucejack Underground Feasibility Study Update; Backfill Design and Test Work Report. May 5, 2015.
AMC Mining Consultants (Canada) Ltd., 2018. Brucejack Backfill Management Plan. October 8, 2018.
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27.4 | Mining Geotechnical |
BGC Engineering Inc., 2018. Brucejack Project – Review and Update of Stope Designs. Letter report issued to Pretium Resources Inc.January 30, 2018.
BGC Engineering Inc., 2019. Brucejack Project – Geotechnical Assessment of Secondary Stopes [presentation]. Presented to Pretium Resources, dated February 21, 2019.
BGC Engineering Inc., 2019b, February 22. Review of underground geotechnical units and structural domains for 2019 NI 43-101 update. Memorandum issued to Pretium Resources Inc.
Bieniawski, Z.T., 1976. Rock mass classification in rock engineering. In Exploration for rock engineering, proc. of the symp., (ed. Z.T. Bieniawski) 1, 97-106. Cape Town: Balkema.
ERSi (Earth Resource Surveys Inc.), 2010. KSM Project Area Structural Geology Assessment - Draft.
Grimstad, E. and Barton, N., 1993. Updating of the Q-system for NMT. Proceedings of the International Symposium on Sprayed Concrete. Modern Use of Wet Mix Sprayed Concrete for Underground Support, Fagemes. Norwegian Concrete Association, Oslo.
Hudyma, M.R., 1988. Development of Empirical Rib Pillar Design Criterion for Open Stope Mining. M.A.Sc. Thesis, University of British Columbia.
International Society of Rock Mechanics (ISRM), 1985. Suggested Method for Determining Point Load Strength.
Ireland, D., Jones, I.W.O., Huang, J., Pelletier, P., Weatherly, H., Stoyko, H.W., Hafez, S.A., Keogh, C., Schmid, C., Cullen, V., McGuiness, M., McAfee, B., Chin, M., Gould, B., Wise, M., Greisman, P., Richards, C., Scott, W.E., Farah, A., Halisheff, K., Sriskandafumar, S., and Molavi, M., 2013. Feasibility Study and Technical Report on the Brucejack Project, Stewart, BC. Tetra Tech NI 43-101 Technical Report for Pretium Resources. Effective Date June 21, 2013. 492 pp.
Ireland, D., Olssen, L., Huang, J., Pelletier, P., Weatherly, H., Stoyko, H.W., Hafez, S.A., Keogh, C., Schmid, C., McAfee, B., Chin, M., Gould, B., Wise, M., Greisman, P., Scott, W.E., Farah, A., Zazzi, G., Crozier, T., and Blackmore, S., 2014. Feasibility Study and Technical Report Update on the Brucejack Project, Stewart, BC. Tetra Tech NI 43-101 Technical Report for Pretium Resources Inc. Effective Date June 19, 2014. 460 p.
Rocscience Inc., 2003. Unwedge Version 3.0 – Underground Wedge Stability Analysis. www.rocscience.com, Toronto, Ontario, Canada.
27.5 | Waste Rock Disposal |
British Columbia Mine Waste Rock Pile Research Committee (BCMWRP), 1991. Mined Rock and Overburden Piles Investigation and Design Manual. Interim Guidelines. May.
Knight Piesold Ltd., 2016. Waste Rock Subaqueous Storage Area Third Party Review. Report prepared for Pretium Resources Inc., May 30.
Knight Piesold Ltd., 2017. Waste Rock Subaqueous Storage Area Third Party Review. Report prepared for Pretium Resources Inc., March 1.
Knight Piesold Ltd., 2018a. Waste Rock Subaqueous Storage Area Third Party Review. Report prepared for Pretium Resources Inc., March 12.
Knight Piesold Ltd., 2018b. Brucejack Gold Mine Independent Tailings Review Board (ITRB) Report #1. Letter report prepared for Pretium Resources Inc., March 12.
Knight Piesold Ltd., 2019. Brucejack Gold Mine, Waste Rock and Tailings Storage Facility (WRTSF) Independent Tailings Review Board (ITRB) 2018 Annual Report. Report prepared for Pretium Resources Inc., February 27.
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Peck, R. B., 1969. Advantages and limitations of the observational method in applied soil mechanics. Geotechnique 19.2: 171-187.
SRK Consulting (Canada) Inc., 2014. Brucejack Gold Mine Project – Waste Rock Stability and Settlement Analysis – UPDATED. Technical memo prepared for Pretium Resources Inc. December 23.
SRK Consulting (Canada) Inc., 2015. Brucejack Gold Mine Project – Waste Rock and Tailings Data Review – UPDATED. Technical memo prepared for Pretium Resources Inc. January 8.
SRK Consulting (Canada) Inc., 2016. Tailings and Waste Rock Subaqueous Deposition Management Plan Design Report, Brucejack Project, British Columbia. Report prepared for Pretium Resources Inc. February.
SRK Consulting (Canada) Inc., 2018a. Operation, Maintenance and Surveillance Manual: Brucejack Gold Mine Subaqueous Waste Rock and Tailings Deposition. Version 6. Report prepared for Pretium Resources Inc. October.
SRK Consulting (Canada) Inc., 2018b. Brucejack Gold Mine: Updated Subaqueous Waste Rock Dump Design. Report prepared for Pretium Resources Inc., October
SRK Consulting (Canada) Inc., 2019. Brucejack Gold Mine: 2018 EOR inspection of the WRSF. Report prepared for Pretivm Resources Inc. March.
Terzaghi, K. and Peck, R. B., 1967. Soil mechanics in engineering practice. 566-566.
27.6 | Environmental |
2006.pdf (accessed December 2014).
2006/dp-pd/prof/92-594/Index.cfm?Lang=E (accessed February 2014).
BC ILMB, 2000. Cassiar Iskut-Stikine Land and Resource Management Plan Prepared by the BritishBC ILMB, 2009. Nass South Sustainable Resource Management Plan: Draft.BC MFLNRO, 1995. Forest Practices Code Biodiversity Guidebook.
BC MFLNRO, 2012. Nass South Sustainable Resource Management PlanBC Ministry of Environment and BC Ministry of Energy and Mines, 2015. Environmental Assessment Certificate #M15-01 – Brucejack Gold Mine.
Business Corporations Act, SBC., 2002a. C. 57.
Canada Ltd.: Vancouver, BC.
Canadian Environmental Assessment Act, SC, 2012. C. 19. s. 52.
Columbia Integrated Land Management Bureau.Concurrent Approval Regulation, BC Reg. 371/2002.
Environmental Assessment Act, SBC, 2002b. C. 43.
Environmental Impact Assessment. Prepared for Pretium Resources Inc. by ERM Consultants Environmental Management Act, SBC., 2003. C. 53.
ERM Rescan, 2014. Brucejack Gold Mine Project: Application for an Environmental Assessment Certificate/Forest Act, RSBC., 1996a. C. 157.
Health Act, RSBC., 1996b. C. 179.
http://www.for.gov.bc.ca/tasb/slrp/lrmp/smithers/cassiar/plan/files/CIS-LRMP-November-http://www.ilmb.gov.bc.ca/slrp/srmp/south/nass/index.html (accessed September, 2009).
http://www.ilmb.gov.bc.ca/slrp/srmp/south/nass/index.html (accessed November 2012).
Land Act, RSBC., 1996c. C. 245.
Mines Act, RSBC., 1996d. C. 293.
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Regulations Designating Physical Activities, SOR/2012-147.
Reviewable Project Regulation, BC Reg. 370/2002.
Statistics Canada, 2007. 2006 Aboriginal Population Profile. http://www12.statcan.gc.ca/censusrecensement/Water Act, RSBC., 1996e. C. 483.
27.7 | Water Management |
BGC Engineering Inc. and Pretium Resources Inc., 2018. Brucejack Gold Mine – Operation, Maintenance & Surveillance Manual. Water Management Plan. Version 004, December 15, 2018.
BGC Engineering Inc., 2017. Water Balance Model 3800 tpd Permit Amendment Applications [Report]. Prepared for Pretium Resources Inc. Doc. No. BJ-2017-57, December 13, 2017.
27.8 | Water Quality |
ERM Rescan, 2014. Brucejack Gold Mine Project: Cumulative Water Quality Baseline Report. Prepared for Pretivm Resources Inc. by ERM Consultants Canada Ltd. Vancouver, BC. January 2014.
Pretium Resources Inc. (Pretivm), 2015. Applications for Mines Act and Environmental Management Act Permits. Submitted May 2015.
Pretivm Resources Inc. (Pretivm), 2018b. 3800 tpd Amendment Application for Permits M-243 and PE-107835. April 2018.
27.9 | Geochemistry |
BGC Engineering Inc., 2014b. Brucejack Environmental Assessment – ML/ARD Baseline Report. Prepared for Pretivm Resouces Inc. June 2014.
Lorax Environmental Service Ltd. (Lorax), 2016b. Brucejack Gold Mine: Assessment of Long-Term Sludge Stability for In-lake and Underground Deposition, Report submitted to Pretium Resources Inc., December 19, 2016.
Lorax Environmental Services Ltd. (Lorax), 2016a. Brucejack Mine: Proposed Extension for Waste Rock Storage on Surface. Prepared by Lorax Environmental Services Ltd. for Pretium Resources Ltd. November 9, 2016.
Lorax Environmental Services Ltd. (Lorax), 2017. Assessment of an Increased Volume of Exposed PAG Waste Rock on the Subaerial Platform at the Brucejack Gold Mine. Prepared by Lorax Environmental Services Ltd. for Pretium Resources Ltd. July 21, 2017.
Pretium Resources Inc. (Pretivm), 2015. Applications for Mines Act and Environmental Management Act Permits. Submitted May 2015.
Pretium Resources Inc. (Pretivm), 2016a. 2015 Annual Report for Mines Act Permit M-243, Effluent Permit 107835, Air Permit 107025. Submitted March 2016.
Pretium Resources Inc. (Pretivm), 2017. 2016 Annual Report for Mines Act Permit M-243, Effluent Permit 107835, Air Permit 107025. Submitted March 2017.
Pretium Resources Inc. (Pretivm), 2018a. 2017 Annual Report for Mines Act Permit M-243, Effluent Permit 107835, Air Permit 107025. Submitted March 2018.
Pretium Resources Inc. (Pretivm), 2019. 2018 Annual Report for Mines Act Permit M-243, Effluent Permit 107835, Air Permit 107025. Submitted March 2019.
Pretivm Resources Inc. (Pretivm), 2018b. 3800 tpd Amendment Application for Permits M-243 and PE-107835. April 2018.
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27.10 | Hydrogeology |
BGC Engineering Inc., 2013. Brucejack Project Environmental Assessment – Numerical Hydrogeologic Model. June 18, 2013.
BGC Engineering Inc., 2014a. Brucejack Project Environmental Assessment – Numerical Hydrogeologic Model. June 6, 2014.
BGC Engineering Inc., 2015. Brucejack Project MA/EMA Permitting Phase – Numerical Hydrogeologic Model Update Report. April 27, 2015.
BGC Engineering Inc., 2018. Brucejack Gold Mine – 2017 Annual Groundwater Monitoring Report. March 19, 2018.
Environmental Simulations Inc. 2011. Groundwater Vistas – Version 6. http://www.groundwatermodels.com/Groundwater_Vistas.php.
Harbaugh, A.W., E.R. Banta, M.C. Hill & M.G. McDonald., 2000. Modflow 2000. The U.S. Geological Survey Modular Ground-water Model – User Guide to the Modularization Concepts and Ground-water Flow Process. U.S. Geological Survey Open File Report 00-92, 130 pp.
HydroGeoLogic Inc., 2012. Modflow-Surfact – A Code for Analyzing Subsurface Systems. http://www.hglsoftware.com/Modflow.cfm.
27.11 | Adjacent Properties |
American Creek Resources Ltd. websitehttp://www.americancreek.com.
BC MEMPR MINFILE No. 104B 105http://minfile.gov.bc.ca/Summary.aspx?minfilno=104B%20%20105.
Brucejack Project Overview http://www.pretivm.com/projects/snowfield/overview/default.aspx (March 29, 2019).
Nelson, J., and Kyba, J., 2014. Structural and stratigraphic control of porphyry and related mineralization in the Treaty Glacier – KSM – Brucejack – Stewart trend of western Stikinia. In: Geological Fieldwork 2013, British Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper 2014-1, pp. 111-140.
Pardoe, J., 2016. NI43-101 Technical Report on the Treaty Creek Property, Skeena Mining Division British Columbia, Canada. Report prepared for Tudor Gold Corp. May 21, 2016.
Puritch, E., Brown, F.H., and Armstrong, T., 2011. Technical Report and Updated Resource Estimate on the Snowfield Property. February 18, 2100.
Seabridge Gold Inc. website http://www.seabridgegold.net/resources.php.
Teuton Resources Corporation websitehttp://www.teuton.com.
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TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Alison Shaw, Ph.D., P.Geo.
I, Alison Shaw, Ph.D., P.Geo. of Vancouver, British Columbia, do hereby certify:
■ | I am a Senior Geochemist with Lorax Environmental Services Ltd. with a business address at 2289 Burrard Street, Vancouver, British Columbia, V6J 3H9. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of McGill University (B.Sc. Environmental Geosciences, 1996) and the University of California San Diego (Ph.D. Geochemistry, 2003). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (# 47412). My relevant experience includes management, analysis and interpretation of geochemical data sets from mine sites, development of site-specific water quality models and analysis of water quality data in mine-impacted receiving environments. I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was from July 17th to July 24th, 2014. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | Since my last site inspection, I have acted as the independent Technical Lead and Qualified Professional for geochemistry and water quality, responsible for directing the implementation of geochemistry and water quality monitoring programs; interpretation and assessment of site monitoring data, including for permit applications and annual reports; and development and maintenance of the site-specific water quality model. |
■ | I am responsible for Sections 20.3.2, 20.3.5, 25.5.1, 25.5.4, 26.6.1, 26.6.4, 27.8, and 27.9 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Vancouver, British Columbia.
“original document signed and sealed” | |
Alison Shaw, Ph.D., P.Geo. | |
Senior Geochemist | |
Lorax Environmental Services Ltd. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Catherine Schmid, M.Sc., P.Eng.
I, Catherine Schmid, M.Sc., P.Eng. of Kamloops, British Columbia, do hereby certify:
■ | I am a Senior Geotechnical Engineer with BGC Engineering Inc. with a business address at 234 St. Paul Street, Kamloops, British Columbia, V2C 6G4. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of Queen’s University (M.Sc. Engineering, 2005). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (#33195). My relevant experience is 16 years of mining rock mechanics projects, including consulting and operations experience. I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was December 1 and 2, 2018, inclusive. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property that is the subject of this Technical Report includes: rock mechanics site investigations, rock mechanics assessments, and associated reporting for the Preliminary Economic Assessment (PEA), Feasibility Study (FS), and Underground Crusher Chamber (UCC); update of the Ground Control Management Plan (GCMP); audit of the GCMP; annual underground ground control inspections; and as-needed operational support to the underground rock mechanics at Brucejack Property. |
■ | I am responsible for Sections 16.5, 25.3.1, 26.4.1, and 27.4 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Catherine Schmid, M.Sc., P.Eng. | |
Senior Geotechnical Engineer | |
BGC Engineering Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Ed Carey, P.Eng.
I, Ed Carey, P.Eng. of Vancouver, British Columbia, do hereby certify:
■ | I am a Principal Geotechnical Engineer with BGC Engineering Inc. with a business address at Suite 500-980 Howe Street, Vancouver, British Columbia, V6Z OC8. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of Dalhousie University (B.Sc. Civil Geotechnical, 1980). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (106852). My relevant experience includes heavy civil foundation design dam siting, earthfill embankment design for water retention and mine mill tailings, slope stability and remediation, seepage analysis, earthworks design, instrumentation planning and technical specification preparations. He has frequently been a member of multi-disciplinary study teams, which included engineers of various discipline, hydrogeologists, hydrologists, terrestrial and aquatic biologists, specialists in public consultation, acid mine drainage, air quality, seismicity and risk assessment. |
■ | I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | I have not visited the Property that is the subject of this Technical Report. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property that is the subject of this Technical Report includes Project Manager and Senior Technical Reviewer for following assignments: |
– | geotechnical site investigations and design recommendations from 2014 to 2016; |
– | quality assurance monitoring during Brucejack plant site construction 2016 to 2018; and |
– | design and IFC construction packages for various projects at Brucejack including the West Expansion Retaining wall, Contact Water Pond and ancillary components, West and East Contact water dam collection and conveyance. |
■ | I am responsible for Section 18.4 of this Technical Report. |
■ | I have read the Instrument and the section of the Technical Report that I am responsible for has been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Ed Carey, P.Eng. | |
Principal Geotechnical Engineer | |
BGC Engineering Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Hamish Weatherly, M.Sc., P.Geo.
I, Hamish Weatherly, M.Sc., P.Geo., of Vancouver, British Columbia, do hereby certify:
■ | I am a Principal Hydrologist with BGC Engineering Inc. with a business address at Suite 500-980 Howe Street, Vancouver, British Columbia, V6Z 0C8. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the University of British Columbia, (M.Sc., 1995). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (License #25567). My relevant experience is 22 years as a consultant specializing in water resources management. I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was on August 28, 2018. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property that is the subject of this Technical Report includes: ongoing calibration and validation of a site-wide water balance model; development of an Operation, Management, and Surveillance (OMS) Manual for all water management facilities; and development of a water management plan (WMP) for the Mine Site. |
■ | I am responsible for Sections 20.3.4. 25.5.3, 26.6.3, and 27.7 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Hamish Weatherly, M.Sc., P.Geo. | |
Principal Hydrologist | |
BGC Engineering Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Hassan Ghaffari, P.Eng.
I, Hassan Ghaffari, P.Eng., of Vancouver, British Columbia, do hereby certify:
■ | I am a Director of Metallurgy with Tetra Tech Canada Inc. with a business address at Suite 1000 10th Floor, 885 Dunsmuir Street, Vancouver, British Columbia, V6C 1N5. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the University of Tehran (M.A.Sc. Mining Engineering, 1990) and the University of British Columbia (M.A.Sc., Mineral Process Engineering, 2004). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (#30408). My relevant experience with respect to mineral engineering includes 27 years of experience in mining and plant operation, project studies, management, and engineering. As the lead metallurgist for the Pebble Copper-Gold Moly Project in Alaska, I was coordinating all metallurgical test work and preparing and peer reviewing the technical report and the operating and capital costs of the plant and infrastructure for both the scoping and prefeasibility studies. For the Ajax Copper-Gold Project in British Columbia, I was the project manager responsible for process, infrastructure, and overall management of the 60,000 t/d mill. As well, I was the project manager responsible for ongoing metallurgical test work and technical assistance for the La Joya Copper-Silver-Gold Project in Durango, Mexico. |
■ | I am a “Qualified Person” for the purposes of National Instrument 43-101 (the “Instrument”). |
■ | I visited the Property that is the subject of the Technical Report on March 13, 2019. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous experience with the Property that is the subject of this Technical Report includes Preliminary Economic Assessments in 2010 (Effective Date: September 10, 2010). |
■ | I am responsible for Sections 1.8, 18.1, 18.2 (except 18.2.2.1), 18.3, and 18.5 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Vancouver, British Columbia.
“original document signed and sealed” | |
Hassan Ghaffari, P.Eng. | |
Director of Metallurgy | |
Tetra Tech Canada Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo)
I, Ivor W.O. Jones, M.Sc., P.Geo., FAusIMM, CP(Geo) of Robina, Queensland, Australia, do hereby certify:
■ | I am a Principal Consultant with Ivor Jones Pty Ltd with a business address at 16 Ringwood Court, Robina, 4226, Queensland, Australia. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of Macquarie University (B.Sc. Geology, 1984, (Honours), 1986) and the University of Queensland (M.Sc. Resource Estimation, 2001). I am licensed as a Professional Geoscientist with Engineers and Geoscientists British Columbia (Licence No. 197172), and I am a Fellow and Chartered Professional (Geology) of the Australasian Institute of Mining and Metallurgy (AusIMM) (Member No. 111429). I have worked as a geologist continuously for a total of 35 years since graduation. I have been involved in resource evaluation for 28 years and consulting for 20 years, including resource estimation of hydrothermal gold deposits for at least 15 years. I have been involved in gold exploration and mining operations for at least 20 years. I am a “Qualified Person” for the purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was from August 20 to 24, 2018. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | I have had on-going, but periodic involvement with the Property that is the subject of this Technical Report since 2010. This includes preparation and sign-off on all Mineral Resources reported by the company since January 2012. |
■ | I am responsible for Sections 1.2, 1.3, 1.4, 3.2, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 14.0, 23.0, 25.1, 25.2, 26.2, 26.3, 27.1, and 27.11 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Ivor W.O. Jones, M.Sc., CP, FAusIMM | |
Principal Consultant | |
Ivor Jones Pty Ltd. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Jianhui (John) Huang, Ph.D., P.Eng.
I, Jianhui (John) Huang, Ph.D., P.Eng., of Coquitlam, British Columbia, do hereby certify:
■ | I am a Senior Metallurgist with Tetra Tech Canada Inc. with a business address at Suite 1000 – 10th Floor, 885 Dunsmuir Street, Vancouver, British Columbia, V6C 1N5. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of North-East University (B.Eng., 1982), Beijing General Research Institute for Non-ferrous Metals (M.Eng., 1988), and Birmingham University (Ph.D., 2000). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (License #30898). My relevant experience with respect to mineral engineering includes more than 30 years of involvement in mineral process for base metal ores, gold and silver ores, and rare metal ores. I am a “Qualified Person” for the purposes of National Instrument 43-101 (the “Instrument”). |
■ | I visited the Property that is the subject of the Technical Report on March 6 and 7, 2018 and on June 5 and 6, 2018. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous experience with the Property that is the subject of this Technical Report includes Preliminary Economic Assessment in 2010 (Effective Date: September 10, 2010), Feasibility Study in 2013 (Effective Date: June 21, 2013). Feasibility Study Update (Effective Date: June 19, 2014). Mill upgrading evaluations and technical supporting in 2017 and 2018. |
■ | I am responsible for Sections 1.1, 1.7, 1.10, 1.12, 2.0, 3.1, 13.0, 17.0, 19.0, 21.0 (except 21.1.3.1 and 21.2.2), 24.0, 25.4, 25.6, 26.1, 26.5, and 27.2 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of April 2019, in Vancouver, British Columbia.
“original document signed and sealed” | |
Jianhui (John) Huang, Ph.D., P.Eng. | |
Senior Metallurgist | |
Tetra Tech Canada Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Maritz Rykaart, Ph.D., P.Eng.
I, Maritz Rykaart, Ph.D., P.Eng. of Vancouver, British Columbia, do hereby certify:
■ | I am a Principal Consultant-Mining with SRK Consulting (Canada) Inc. with a business address at 2200-1066 West Hastings Street, Vancouver, British Columbia, V6E 3X2. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the Rand Afrikaans University (B.Eng. Civil Engineering, 1991; M.Eng. Civil Engineering, 1993) and the University of Saskatchewan (Ph.D. Geotechnical Engineering, 2001). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (#28531). My relevant experience includes continuously working on mine waste management projects since graduation. This includes all aspects of site selection, design, construction, operation and closure of tailings and mine waste rock piles. I have applied my expertise internationally covering 5 continents, including cold mountainous regions. I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was from September 19th to 20th, 2018. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property includes design of the waste rock pile dating back to 2014, as well as evaluation of subaqueous tailings deposition strategies at the same time. |
■ | I am responsible for Sections 18.2.2.1, 25.3.3, 26.4.3, and 27.5 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Maritz Rykaart, Ph.D., P.Eng. | |
Principal Consultant | |
SRK Consulting (Canada) Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Mark Horan, P.Eng.
I, Mark Horan, P.Eng., of Oliver, British Columbia, do hereby certify:
■ | I am a Senior Mining Engineer with Tetra Tech Canada Inc. with a business address at Suite 1000 – 10th Floor, 885 Dunsmuir Street, Vancouver, British Columbia, V6C 1N5. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the University of Witwatersrand, South Africa (B.Sc. Mining, 1997) and Rhodes University, South Africa (M.Sc., 2002). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (#170768). I have 18 years of experience, including working in precious metal operations and base metal mining operations in both open pit and underground. I am a “Qualified Person” for the purposes of National Instrument 43-101 (the “Instrument”). |
■ | I visited the Property that is the subject of the Technical Report from April 4th to 6th, 2019. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | I have no prior experience with the Property that is the subject of this Technical Report. |
■ | I am responsible for Sections 1.5, 1.6, 1.11, 3.3, 15.0, 16.0 (except 16.5), 21.1.3.1, 21.2.2, 22.0, 25.3.2, 25.7, 25.8, 26.4.2, and 27.3 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Mark Horan, P.Eng. | |
Senior Mining Engineer | |
Tetra Tech Canada Inc. |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Rolf Schmitt, M.Sc., P.Geo.
I, Rolf Schmitt, M.Sc., P.Geo. of Vancouver, British Columbia, do hereby certify:
■ | I am a Technical Director with Environmental Resources Management (ERM) with a business address at 15th Floor – 1111 West Hastings Street, Vancouver, British Columbia, V6E 2J3. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the University of British Columbia (B.Sc. Hons Geology, 1977) and the University of Ottawa (M.Sc. Geology, 1993). I am a member in good standing of the Association of Professional Engineers and Geoscientists of the Province of British Columbia (19824). My relevant experience includes practicing my profession from 1977 to present as a geologist (Texasgulf Inc. and Kidd Creek Mines), government research geochemistry (Geological Survey of Canada), government policy and regulatory scientist (BC MEMPR Senior BC Land Use Geologist), and consultant, Technical Director and manager of permitting with Rescan Environmental Consultants and ERM Consultants Canada Ltd. I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was from April 1st to 3rd, 2019. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property that is the subject of this Technical Report includes: senior technical review and QA of applications for major permits to construct and operate the Brucejack Mine and ancillary facilities including;Mines Act Permit,Environmental Management Act permits, Licences of Occupation, Water Licence, reclamation and closure plan and cost estimate. |
■ | I am responsible for Sections 1.9, 20.1, 20.2, 20.3.1, 20.3.6, 20.3.7, 20.3.8, and 27.6 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Vancouver, British Columbia.
“original document signed and sealed” | |
Rolf Schmitt, M.Sc., P.Geo. | |
Technical Director | |
ERM |
TECHNICAL REPORT ON THE BRUCEJACK GOLD MINE, NORTHWEST BRITISH COLUMBIA |
704-ENG.VMIN03070-01 | APRIL 2019 | ISSUED FOR USE |
Trevor Crozier, M.Eng., P.Eng.
I, Trevor Crozier, M.Eng., P.Eng. of Vancouver, British Columbia, do hereby certify:
■ | I am a Principal Hydrogeological Engineer with BGC Engineering Inc. with a business address at Suite 500-980 Howe Street, Vancouver, British Columbia, V6Z 0C8. |
■ | This certificate applies to the technical report entitled “Technical Report on the Brucejack Gold Mine, Northwest British Columbia” with effective date of April 4, 2019 (the “Technical Report”). |
■ | I am a graduate of the University of British Columbia (B.A.Sc., 1992; M.Eng. Geological Engineering, 2003). I am a member in good standing of the Association of Professional Engineers and Geoscientists of British Columbia (#22194). My experience with respect to hydrogeology includes 27 years as a geotechnical engineering consultant specialized in groundwater hydrology. Select relevant experience includes the KSM Project (BC), Gibraltar Mine (BC), Red Chris Mine (BC), the Ajax Project (BC), the Donlin Gold Project (AK), the Eagle Gold Mine (YT), Red Lake Gold Mines (ON) and La Coipa Mine (Chile). I am a “Qualified Person” for purposes of National Instrument 43-101 (the “Instrument”). |
■ | My most recent personal inspection of the Property that is the subject of the Technical Report was from September 18 to 20, 2017 inclusive. |
■ | I am independent of Pretium Resources Inc. as defined by Section 1.5 of the Instrument. |
■ | My previous involvement with the Property that is the subject of this Technical Report includes: hydrogeological and geotechnical site investigations, numerical groundwater flow modeling evaluations to support Preliminary Economic Assessment (PEA), Feasibility Study (FS), Environmental Assessment and Permitting applications; technical review for the Brucejack Project MA/EMA Permitting Phase Numerical Hydrogeologic Model Update Report, the 2015, 2016, 2017 and 2018 Annual Groundwater Monitoring Reports and the 2018 Groundwater Monitoring Well Installation and Site Investigation Report; and, as needed operational support related to hydrogeology and groundwater monitoring at Brucejack Mine. |
■ | I am responsible for Sections 20.3.3, 25.5.2, 26.6.2. and 27.10 of this Technical Report. |
■ | I have read the Instrument and the sections of the Technical Report that I am responsible for have been prepared in compliance with the Instrument. |
■ | As of the effective date of this Technical Report, to the best of my knowledge, information and belief, the sections of the Technical Report that I am responsible for contain all scientific and technical information that is required to be disclosed to make the Technical Report not misleading. |
Signed and dated this 14th day of May 2019, in Burnaby, British Columbia.
“original document signed and sealed” | |
Trevor Crozier, M.Eng., P.Eng. | |
Principal Hydrogeological Engineer | |
BGC Engineering Inc. |