UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

 

 

Form 6-K

 

 

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of March 2020

Commission File Number: 1-9059

 

 

Barrick Gold Corporation

(Registrant’s name)

 

 

Brookfield Place, TD Canada Trust Tower, Suite 3700

161 Bay Street, P.O. Box 212

Toronto, Ontario M5J 2S1 Canada

(Address of principal executive offices)

 

 

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  ☐            Form 40-F  ☒

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ☐

 

 

 


SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

 

Date: March 26, 2020     BARRICK GOLD CORPORATION
    By:  

/s/ Richie Haddock

    Name:   Richie Haddock
    Title:   General Counsel


EXHIBIT INDEX

 

Exhibit

  

Description

99.1    Technical Report on the Turquoise Ridge Complex, State of Nevada, USA
EX-99.1

Exhibit 99.1

 

    

PREPARED FOR BARRICK GOLD

CORPORATION AND NEWMONT

CORPORATION BY NEVADA GOLD

MINES LLC

TECHNICAL REPORT ON THE

TURQUOISE RIDGE COMPLEX,

STATE OF NEVADA, USA

NI 43-101 Report

Qualified Persons:

Charles Lynn Bolin, MBA, SME (RM)

Craig Fiddes, SME (RM)

Jay Olcott, SME (RM)

Steven W. Yopps, MMSA QP

 

 

March 25, 2020

Effective Date: December 31, 2019

1655 Mountain City Hwy. - Elko, Nevada 89801


 

 

FORWARD-LOOKING INFORMATION

This Technical Report contains forward-looking statements. All statements, other than statements of historical fact, are forward-looking statements. The words “believe”, “expect”, “anticipate”, “contemplate”, “target”, “plan”, “intend”, “project”, “continue”, “budget”, “estimate”, “potential”, “may”, “will”, “can”, “could” and similar expressions identify forward-looking statements. In particular, this Technical Report contains forward-looking statements with respect to cash flow forecasts, projected capital, operating and exploration expenditure, targeted cost reductions, mine life and production rates, potential mineralization and metal or mineral recoveries, and information pertaining to potential improvements to financial and operating performance and mine life at the Turquoise Ridge and Turquoise Ridge Surface mines that may result from the shaft-sinking project. All forward-looking statements in this Technical Report are necessarily based on opinions and estimates made as of the date such statements are made and are subject to important risk factors and uncertainties, many of which cannot be controlled or predicted. Material assumptions regarding forward-looking statements are discussed in this Technical Report, where applicable. In addition to such assumptions, the forward-looking statements are inherently subject to significant business, economic and competitive uncertainties, and contingencies. Known and unknown factors could cause actual results to differ materially from those projected in the forward-looking statements. Such factors include, but are not limited to: fluctuations in the spot and forward price of commodities (including gold, diesel fuel, natural gas and electricity); the speculative nature of mineral exploration and development; changes in mineral production performance, exploitation and exploration successes; diminishing quantities or grades of reserves; increased costs, delays, suspensions, and technical challenges associated with the construction of capital projects; operating or technical difficulties in connection with mining or development activities, including disruptions in the maintenance or provision of required infrastructure and information technology systems; damage to Nevada Gold Mines LLC’s, Barrick Gold Corporation’s, or Newmont Corporation’s reputation due to the actual or perceived occurrence of any number of events, including negative publicity with respect to the handling of environmental matters or dealings with community groups, whether true or not; risk of loss due to acts of war, terrorism, sabotage, civil disturbances and pandemics; uncertainty whether the Turquoise Ridge Underground, Turquoise Ridge Surface and Vista Underground mines will meet Nevada Gold Mines LLC’s capital allocation objectives; the impact of global liquidity and credit availability on the timing of cash flows and the values of assets and liabilities based on projected future cash flows; the impact of inflation; fluctuations in the currency markets; changes in interest rates; changes in national and local government legislation, taxation, controls or regulations and/or changes in the administration of laws, policies and practices, expropriation or nationalization of property and political or economic developments in USA; failure to comply with environmental and health and safety laws and regulations; timing of receipt of, or failure to comply with, necessary permits and approvals; litigation; contests over title to properties or over access to water, power and other required infrastructure; increased costs and physical risks including extreme weather events and resource shortages, related to climate change; and availability and increased costs associated with mining inputs and labour. In addition, there are risks and hazards associated with the business of mineral exploration, development, and mining, including environmental hazards, industrial accidents, unusual or unexpected formations, ground conditions, pressures, cave-ins, flooding and gold ore losses (and the risk of inadequate insurance, or inability to obtain insurance, to cover these risks).

 

   
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Many of these uncertainties and contingencies can affect Nevada Gold Mines LLC’s actual results and could cause actual results to differ materially from those expressed or implied in any forward-looking statements made by, or on behalf of, Nevada Gold Mines LLC. All of the forward-looking statements made in this Technical Report are qualified by these cautionary statements. None of Nevada Gold Mines LLC, Barrick Gold Corporation, Newmont Corporation, and the Qualified Persons who authored this Technical Report undertake no obligation to update publicly or otherwise revise any forward-looking statements whether as a result of new information or future events or otherwise, except as may be required by law.

 

   
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TABLE OF CONTENTS

PAGE

 

1.         SUMMARY

     1-1  

1.1.

 

Executive Summary

     1-1  

1.2.

 

Economic Analysis

     1-6  

1.3.

 

Technical Summary

     1-6  

1.4.

 

Conclusions and Recommendations

     1-22  

2.         INTRODUCTION

     2-1  

2.1.

 

Sources of Information

     2-2  

2.2.

 

List of Abbreviations

     2-3  

3.         RELIANCE ON OTHER EXPERTS

     3-1  

4.         PROPERTY DESCRIPTION AND LOCATION

     4-1  

4.1.

 

Land Tenure

     4-1  

4.2.

 

Royalties

     4-2  

4.3.

 

Economy, Taxation, Permits, and Environmental

     4-3  

5.         ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY

     5-1  

5.1.

 

Accessibility

     5-1  

5.2.

 

Climate

     5-1  

5.3.

 

Local Resources and Infrastructure

     5-1  

5.4.

 

Physiography

     5-2  

6.         HISTORY

     6-1  

6.1.

 

Turquoise Ridge Underground

     6-1  

6.2.

 

Turquoise Ridge Surface and Vista Underground

     6-4  

6.3.

 

Production History

     6-6  

7.         GEOLOGICAL SETTING AND MINERALIZATION

     7-1  

7.1.

 

Regional Geology

     7-1  

7.2.

 

Local and Property Geology

     7-4  

7.3.

 

Alteration

     7-15  

7.4.

 

Structure

     7-16  

7.5.

 

Mineralization

     7-21  

8.         DEPOSIT TYPES

     8-1  

9.         EXPLORATION

     9-1  

9.1.

 

Turquoise Ridge Underground

     9-1  

9.2.

 

Turquoise Ridge Surface and Vista Underground

     9-3  

10.       DRILLING

     10-1  

10.1.

 

Turquoise Ridge Underground

     10-1  

10.2.

 

Turquoise Ridge Surface and Vista Underground

     10-3  

10.3.

 

Turquoise Ridge Complex Combined Core Recovery

     10-5  

 

   
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10.4.

 

Drilling Used to Support Mineral Resource Estimation

     10-6  

11.        SAMPLE PREPARATION, ANALYSES AND SECURITY

     11-1  

11.1.

 

Turquoise Ridge Underground

     11-1  

11.2.

 

Turquoise Ridge Surface and Vista Underground

     11-3  

11.3.

 

Independent Laboratory

     11-9  

11.4.

 

Security

     11-10  

12.        DATA VERIFICATION

     12-1  

12.1.

 

Turquoise Ridge Underground

     12-1  

12.2.

 

Turquoise Ridge Surface and Vista Underground

     12-2  

13.        MINERAL PROCESSING AND METALLURGICAL TESTING

     13-1  

13.1.

 

Turquoise Ridge Underground

     13-1  

13.2.

 

Turquoise Ridge Surface and Vista Underground

     13-2  

14.        MINERAL RESOURCES ESTIMATE

     14-1  

14.1.

 

Summary

     14-1  

14.2.

 

Turquoise Ridge Underground

     14-3  

14.3.

 

Turquoise Ridge Surface and Vista Underground

     14-16  

15.        MINERAL RESERVES ESTIMATE

     15-1  

15.1.

 

Summary

     15-1  

15.2.

 

Underground Mineral Reserves

     15-3  

15.3.

 

Surface Mineral Reserves

     15-11  

16.        MINING METHODS

     16-1  

16.1.

 

Turquoise Ridge Underground

     16-1  

16.2.

 

Vista Underground

     16-7  

16.3.

 

Turquoise Ridge Surface

     16-8  

17.        RECOVERY METHODS

     17-1  

17.1.

 

Overall Process Summary

     17-1  

17.2.

 

Sage Mill Process Description

     17-3  

17.3.

 

Juniper Mill Description

     17-4  

17.4.

 

Leach Description

     17-4  

17.5.

 

Process Recovery Assumptions

     17-4  

17.6.

 

Stockpile and Sampling

     17-7  

17.7.

 

Turquoise Ridge Surface Cut-Off Grade Assumptions

     17-9  

17.8.

 

Gold Production

     17-11  

17.9.

 

Conclusions

     17-11  

18.        PROJECT INFRASTRUCTURE

     18-1  

18.1.

 

Infrastructure and Services

     18-1  

18.2.

 

Power Supply

     18-3  

18.3.

 

Haul Road Widening Project

     18-3  

19.        MARKET STUDIES AND CONTRACTS

     19-1  

20.        ENVIRONMENTAL STUDIES, PERMITTING, AND SOCIAL OR COMMUNITY IMPACT

     20-1  

20.1.

 

Environmental Studies

     20-1  

20.2.

 

Environmental Management System

     20-1  

 

   
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20.3.

 

Plan of Operation

     20-2  

20.4.

 

Environmental Targets and Strategies

     20-2  

20.5.

 

Permits

     20-2  

20.6.

 

Permitting Process and Schedule for Turquoise Ridge Surface

     20-3  

20.7.

 

Project Closure and Reclamation

     20-4  

21.        CAPITAL AND OPERATING COSTS

     21-1  

21.1.

 

Capital Cost Estimates

     21-1  

21.2.

 

Operating Cost Estimates

     21-2  

21.3.

 

Comments on Capital and Operating Costs

     21-4  

22.        ECONOMIC ANALYSIS

     22-1  

23.        ADJACENT PROPERTIES

     23-1  

24.        OTHER RELEVANT DATA AND INFORMATION

     24-1  

25.        INTERPRETATION AND CONCLUSIONS

     25-1  

25.1.

 

Accessibility, Climate, Infrastructure, and Physiography

     25-1  

25.2.

 

Geology and Mineral Resources

     25-1  

25.3.

 

Mining and Mineral Reserves

     25-2  

25.4.

 

Processing

     25-2  

26.        RECOMMENDATIONS

     26-1  

26.1.

 

Geology and Mineral Resources

     26-1  

26.2.

 

Mining and Mineral Reserves

     26-1  

26.3.

 

Processing

     26-1  

27.        REFERENCES

     27-1  

28.        DATE AND SIGNATURE PAGE

     28-1  

29.        CERTIFICATE OF QUALIFIED PERSON

     29-1  

LIST OF TABLES

PAGE

 

Table 1-1 Mineral Resources Estimate – December 31, 2019

     1-4  

Table 1-2 Mineral Reserves Estimate – December 31, 2019

     1-5  

Table 6-1 Summary of Gold Production

     6-7  

Table 10-1 Summary of Turquoise Ridge Underground Drilling

     10-2  

Table 10-2 Summary of Turquoise Ridge Surface and Vista Underground Drilling

     10-4  

Table 10-3 Summary of Turquoise Ridge Complex Core Recovery Summary

     10-5  

Table 10-4 Turquoise Ridge Underground Drilling

     10-6  

Table 10-5 Turquoise Ridge Surface Drilling

     10-7  

Table 10-6 Vista Underground Drilling

     10-8  

Table 11-1 Turquoise Ridge Surface Specified Gravity Results

     11-4  

Table 12-1 2019 Resource Extraction New Holes

     12-4  

Table 12-2 Vulcan ISIS Database Tables and Fields Checked

     12-5  

Table 12-3 Downhole Survey Validation Check Comments

     12-5  

Table 12-4 Historical Collar Validation Check

     12-6  

 

   
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Table 12-5 Turquoise Ridge Surface Model Coordinates

     12-7  

Table 13-1 Turquoise Ridge Surface Ore Control Matrix

     13-3  

Table 13-2 Number of Tests Conducted per Metallurgical Type

     13-4  

Table 13-3 Summary of Comminution Test Results

     13-5  

Table 13-4 Vista Pit Heap Leach Recovery Step Function

     13-8  

Table 13-5 Sage Mill Blending Criteria

     13-10  

Table 13-6 Turquoise Ridge Surface Refractory Ore Classification

     13-12  

Table 13-7 Refractory Material Guide and Destinations

     13-15  

Table 13-8 Oxide Material Guide and Routing Oxide

     13-16  

Table 13-9 Typical Sage Mill Constraints

     13-16  

Table 14-1 Mineral Resource Estimate – December 31, 2019

     14-2  

Table 14-2 Turquoise Ridge Underground Mineral Resource Estimate – December 31, 2019

     14-4  

Table 14-3 Turquoise Ridge Underground Block Model Lithologies and Codes

     14-7  

Table 14-4 Turquoise Ridge Underground Raw Assay and Composite Databases

     14-11  

Table 14-5 Turquoise Ridge Underground Block Model Setup

     14-11  

Table 14-6 Turquoise Ridge Underground Block Model Variables

     14-12  

Table 14-7 Turquoise Ridge Underground Grade Estimation Min/Max Samples

     14-13  

Table 14-8 Turquoise Ridge Underground Mineral Resource Cut-off Grade Parameters

     14-15  

Table 14-9 Turquoise Ridge Surface Mineral Resource Estimate – December 31, 2019

     14-17  

Table 14-10 Vista Underground Mineral Resource Estimate – December 31, 2019

     14-19  

Table 14-11 Turquoise Ridge Surface Database Extraction Model Boundaries

     14-20  

Table 14-12 Turquoise Ridge Surface Drill Holes in Model Boxes

     14-20  

Table 14-13 Turquoise Ridge Surface Drilling Summary of New Drill Holes

     14-24  

Table 14-14 Turquoise Ridge Surface Statistics by Domain

     14-26  

Table 14-15 Turquoise Ridge Surface 2019 Mega Pit Geologic Model Extents

     14-27  

Table 14-16 Turquoise Ridge Surface 2019 Model Tonnage Factors

     14-30  

Table 14-17 Turquoise Ridge Surface Model Definition Parameters

     14-31  

Table 14-18 Turquoise Ridge Surface Model Mineral Reserves Classification Distances

     14-35  

Table 14-19 Turquoise Ridge Surface Resource Cut-Off Grade Parameters

     14-37  

Table 14-20 Mineral Reserves Subject to Royalty Payment

     14-38  

Table 14-21 Mineral Resources Subject to Royalty Payment

     14-38  

Table 15-1 Mineral Reserves Estimate – December 31, 2019

     15-2  

Table 15-2 Turquoise Ridge Underground Mineral Reserves Estimate – December 31, 2019

     15-4  

Table 15-3 Turquoise Ridge Underground Reserves Cut-Off Grade Calculation

     15-6  

Table 15-4 Mineral Reserves Price Sensitivity (100% Basis)

     15-8  

Table 15-5 Vista Underground Mineral Reserves Estimate - December 31, 2019

     15-8  

Table 15-6 Vista Underground Operating and Capital Cost Assumptions

     15-11  

Table 15-7 Vista Underground Mineral Reserves Price Sensitivity

     15-11  

Table 15-8 Turquoise Ridge Surface Mineral Reserves Estimate - December 31, 2019

     15-12  

Table 15-9 Mega Pit Geotechnical Design Recommendations

     15-13  

Table 15-10 Vista Pit Geotechnical Recommendations

     15-14  

Table 15-11 Turquoise Ridge Surface Mining Costs

     15-15  

Table 15-12 Turquoise Ridge Surface Process Costs

     15-15  

Table 15-13 Mineral Reserves Price Sensitivity

     15-16  

Table 15-14 Ore Stockpiles in Proven Mineral Reserves End of Year 2019

     15-17  

Table 16-1 Mine Equipment

     16-6  

Table 16-2 Open Pit Mine Design Parameters

     16-11  

Table 16-3 Open Pit Mine Equipment Fleet 2020 Business Plan

     16-29  

 

   
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Table 16-4 Open Pit Equipment Productivity - 2019

     16-29  

Table 17-1 Calculated Cut-Off Grades – Sulphide Mill Ore

     17-9  

Table 17-2 Sulphide Mill Ore Cut-Off Grades by Layback

     17-10  

Table 17-3 Oxide Cut-Off Grades

     17-10  

Table 17-4 Summary of Turquoise Ridge Complex Processing Production in 2019

     17-11  

Table 21-1 Turquoise Ridge Complex LOM Capital Cost Estimate

     21-2  

Table 21-2 LOM Mining Costs per Tonne Mined

     21-3  

Table 21-3 LOM Processing Costs per Tonne Processed by Facility

     21-3  

LIST OF FIGURES

PAGE

 

Figure 4-1 Turquoise Ridge Location Map

     4-5  

Figure 4-2 Turquoise Ridge Property Map

     4-6  

Figure 4-3 Site Plan – Mega and Vista Pits

     4-7  

Figure 7-1 Regional Geology

     7-3  

Figure 7-2 Local Geology

     7-7  

Figure 7-3 Vertical Section Showing Generalized Turquoise Ridge Underground Stratigraphy

     7-8  

Figure 7-4 Modelled 3D Geology with Location of Cut 40 Design

     7-11  

Figure 7-5 General Geology of Cut 40 North Dig Face with Mine Design

     7-12  

Figure 7-6 Turquoise Ridge Surface Stratigraphy, with Cut 40 Interval

     7-13  

Figure 7-7 Spatial Relationship Between Gold Mineralization, Faults, and Folding

     7-18  

Figure 7-8 Relay Ramp Fault Interpretation of North-Striking Faults at Turquoise Ridge Surface

     7-19  

Figure 7-9 CP Fault in the Mega Pit Cut 23 South Highwall

     7-20  

Figure 7-10 Comus Oc3 Unit Above Upper Sill, July 2017 Block Model

     7-24  

Figure 7-11 Cut 40 Drill Hole TWD-02489 Core

     7-25  

Figure 7-12 Cut 40 Drill Hole TWD-02489 Core with Lower Grade at Basalt and Micrite Contact

     7-26  

Figure 9-1 Exploration Targets

     9-2  

Figure 10-1 Drill Collar and Resource Location Turquoise Ridge Underground

     10-9  

Figure 10-2 Drill Collar and Resource Location Turquoise Ridge Surface (Mega and Vista)

     10-10  

Figure 10-3 Drill Collar and Resource Location Turquoise Ridge Surface Vista Open Pit and Underground

     10-11  

Figure 11-1 Check Specific Gravity Results Turquoise Ridge Surface

     11-4  

Figure 11-2 Turquoise Ridge Surface Standards Box and Wisker Results for 25 Standards

     11-6  

Figure 11-3 Results of Nevada Gold Mines In-house Gravel Blank

     11-7  

Figure 11-4 Field Duplicate QA/QC Results

     11-8  

Figure 11-5 Pulp Duplicate QA/QC Results

     11-8  

Figure 11-6 Prep Duplicate QA/QC Results

     11-9  

Figure 13-1 Recovery as a Function of OC and Gold Head Grade

     13-2  

Figure 13-2 Cut 40 Recovery Curve (% Recovery vs. TOC/oz/ton Au)

     13-7  

Figure 13-3 Heap Leach Recovery Time Curve

     13-9  

Figure 13-4 Vista Pit Oxide Leach Recovery Comparisons

     13-10  

Figure 13-5 Sage Mill Actual Recovery

     13-11  

Figure 13-6 Stockpile Locations at Turquoise Ridge Surface

     13-13  

 

   
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Figure 13-7 Stockpiles and Process Facilities at Turquoise Ridge Surface

     13-14  

Figure 14-1 Mineralized Domains – Plan View

     14-9  

Figure 14-2 Mega and Vista Pits Model Boundaries

     14-21  

Figure 14-3 2019 Mega Pit Model New Holes

     14-23  

Figure 14-4 2019 Vista Pits with January 2020 Topographic Surface and New Drill Holes

     14-25  

Figure 14-5 Mega Pit Block Model Section 50,150N in Cut 25 and Composites

     14-33  

Figure 14-6 Mega Pit Block Model Section 51,400N in Cut 40 and Composites

     14-34  

Figure 15-1 Turquoise Ridge Underground Mineral Reserves – Breakdown by Mining Region

     15-5  

Figure 15-2 Vista Underground Mineral Reserves and Mineral Resources

     15-10  

Figure 16-1 Third Shaft Execution Strategy

     16-7  

Figure 16-2 Turquoise Ridge Surface Infrastructure

     16-10  

Figure 16-3 End of Year 2019 Ultimate Mega Pit Design

     16-12  

Figure 16-4 End of Year 2019 Ultimate Vista Pit Design

     16-13  

Figure 16-5 Cut 40 Infrastructure Relocation

     16-16  

Figure 16-6 Cut 25 Reserve Design in Plan View

     16-19  

Figure 16-7 Cut 40 Reserve Design in Plan View

     16-21  

Figure 16-8 Mega Pit Cut 55 Triangulation

     16-23  

Figure 16-9 Phase 8 Reserve Design in Plan View

     16-25  

Figure 16-10 Vista 9 Triangulation

     16-27  

Figure 17-1 Turquoise Ridge Complex Process Flow Sheet

     17-2  

Figure 17-2 Sage Mill Recovery Curve

     17-5  

 

   
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1. SUMMARY

 

  1.1.

EXECUTIVE SUMMARY

Nevada Gold Mines LLC (Nevada Gold Mines) operates the Turquoise Ridge Complex, located in Humboldt County, Nevada, USA. Nevada Gold Mines is a joint venture between Barrick Gold Corporation (Barrick) and Newmont Corporation (Newmont), Barrick is the operator of the joint venture and owns 61.5%, with Newmont owning the remaining 38.5%. Under the joint venture, Barrick’s Turquoise Ridge Mine and Newmont’s Twin Creeks Complex were combined as a single operation, now known as Turquoise Ridge. The combined mining operation is comprised of the Turquoise Ridge Underground, Vista Underground, and Turquoise Ridge Surface (the Mega and Vista open pits).

Certain of the disclosure contained in this report will reference Barrick’s former practices for the Turquoise Ridge Underground mine (which it previously owned) and Newmont’s former practices for Turquoise Ridge Surface and Vista Underground mines (which it previously owned), rather than the consolidated practices of Nevada Gold Mines for the Turquoise Ridge Complex, either for historical purposes or because the applicable mines currently have noteworthy differences in practices. Information in this report for the period prior to July 1, 2019 in respect of any property discussed was collected or produced by the prior operator of the property (i.e., Barrick or Newmont). Nevada Gold Mines considers data from operations conducted by Barrick and Newmont to be reliable. Certain references to Nevada Gold Mines in this Technical Report also include Nevada Gold Mines’ owners and their respective predecessors, as applicable.

The purpose of this Technical Report is to support the disclosure of the Mineral Resource and Mineral Reserve estimates for the Turquoise Ridge Complex as of December 31, 2019. This Technical Report conforms to National Instrument 43-101 Standards of Disclosure for Mineral Projects (NI 43-101). Unless otherwise stated, all data included in this Technical Report is disclosed on a 100% basis.

Barrick is a Canadian publicly traded mining company with a portfolio of operating mines and projects based in Toronto, Ontario, Canada. Newmont is a publicly traded gold producer with a portfolio of operations and exploration projects, based in Denver, Colorado, USA. On March 10, 2019, Barrick entered into an implementation agreement with Newmont to create a joint venture combining the

 

   
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companies’ respective mining operations, assets, reserves and talent in Nevada, USA. This includes Barrick’s Cortez, Goldstrike, Turquoise Ridge and Goldrush properties and Newmont’s Carlin, Twin Creeks, Phoenix, Long Canyon and Lone Tree properties. On July 1, 2019, the transaction closed, establishing Nevada Gold Mines LLC and Barrick began consolidating the operating results, cash flows and net assets of Nevada Gold Mines from that date forward.

The Turquoise Ridge Complex is located in the Potosi Mining District, approximately 64 km northeast of Winnemucca, Nevada. Refractory ore is processed at the Sage autoclave, while non-refractory ore is processed at the Juniper oxide mill or stacked on heap leach pads. All processing facilities are located at Turquoise Ridge Surface on what was formerly Newmont’s Twin Creeks property.

Turquoise Ridge Underground produces high-grade refractory (carbonaceous/sulphide) gold ore from a long-life (currently 19 years) underground operation, accessed via two shafts and a system of internal ramps, and utilizes underhand drift and fill mining methods with cemented rock fill. Turquoise Ridge Underground is currently hoisting 2,700 tonnes of ore per day, which is expected to increase following the completion of a Third Shaft that is currently under construction. The Vista Underground is a portal and ramp accessed vein-style stoping mine with an approximately two years of mine life remaining that produces approximately 1,000 tonnes per day of ore. Turquoise Ridge Surface has been in operation for over 30 years, and the current reserve mine life is expected to extend until 2030 at approximately 71,000 tonnes moved per day. Vista Underground produces sulphide ore, while Turquoise Ridge Surface produces oxide heap leach, oxide mill, and sulphide ore.

The Barrick Mineral Resources as of December 31, 2018 at the Turquoise Ridge Underground were reported exclusive of Mineral Reserves and exclude all areas that form Mineral Reserves. Mineral Resources in this Technical Report are reported on an inclusive basis and include all areas that form Mineral Reserves, reported at a Mineral Resources cut-off grade and associated commodity price. As a result, the 2018 Mineral Resources for the Turquoise Ridge Complex are not directly comparable to the Mineral Resources set out herein.

The total Measured and Indicated Mineral Resources for the Turquoise Ridge Complex, inclusive of Mineral Reserves, is 130 million tonnes (Mt) grading 4.30 g/t Au and contain approximately 18 million ounces (Moz) of gold as of December 31, 2019. In addition, Inferred Mineral Resources

 

   
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total 21 million tonnes (Mt) grading 2.7 g/t Au and contain approximately 1.8 million ounces (Moz) of gold (Table 1-1). These Mineral Resources are reported at 100% basis.

The total Proven and Probable Mineral Reserves for the Turquoise Ridge Complex are estimated to be 83 million tonnes (Mt) at 5.02 g/t Au, containing approximately 13 million ounces (Moz) of gold as of December 31, 2019 (Table 1-2). These Mineral Reserves are reported at 100% basis.

The Qualified Persons (QPs) are not aware of any environmental, permitting, legal, title, socioeconomic, marketing, fiscal, metallurgical, or other relevant factors which could materially affect the Mineral Resource estimates.

 

   
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Table 1-1 Mineral Resources Estimate – December 31, 2019

 

100% Basis   Measured   Indicated   Measured + Indicated   Inferred
 

    Tonnes        

(Mt)    

 

    Grade        

(g/t Au)    

 

    Contained    

Metal

(Moz Au)

 

    Tonnes    

(Mt)

 

    Grade      

(g/t Au)

 

    Contained    

Metal

(Moz Au)

 

    Tonnes    

(Mt)

 

    Grade    

(g/t Au)

 

    Contained    

Metal

(Moz Au)

 

    Tonnes    

(Mt)

 

    Grade    

(g/t Au)

 

    Contained    

Metal

(Moz Au)

Surface Operations

                                               

Stockpile

                                               

Turquoise Ridge Surface

  36   2.00   2.3               36   2.00   2.3            

Stockpile Total

  36   2.00   2.3               36   2.00   2.3            
                                                 

Open Pit

                                               

Mega

  2.9   2.76   0.26   36   2.26   2.6   39   2.30   2.9   16   1.7   0.85

Vista

              15   1.25   0.61   15   1.25   0.61   2.0   1.2   0.080

Open Pit Total

  2.9   2.76   0.26   52   1.96   3.2   55   2.00   3.5   18   1.6   0.93
                                                 

Surface Operations Total

  39   2.06   2.6   52   1.96   3.2   90   2.00   5.8   18   1.6   0.93
                                                 

Underground Operations

                                               

Vista Underground

  0.013   4.97   0.0020   0.83   6.29   0.17   0.85   6.27   0.17   0.16   7.1   0.036

Turquoise Ridge Underground

  22   10.00   7.2   16   9.23   4.8   38   9.68   12   2.8   9.2   0.82

Total

  22   10.00   7.2   17   9.09   4.9   39   9.61   12   2.9   9.1   0.86
                                                 

Underground Operations Total    

  22   10.00   7.2   17   9.09   4.9   39   9.61   12   2.9   9.1   0.86
                                                 

Turquoise Ridge Complex

Total

  61   4.95   9.7   68   3.72   8.2   130   4.30   18   21   2.7   1.8

Notes:

  1.

Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Definition Standards for Mineral Resources and Mineral Reserves dated May 10, 2014 (CIM (2014) definitions) were followed for Mineral Resources.

  2.

Mineral Resources are estimated using a long-term gold price of US$1,500/oz.

  3.

Underground Mineral Resources were estimated using cut-off grades (COGs) of 5.04 g/t Au (Turquoise Ridge Underground) and 2.74 g/t Au (Vista Underground). Open Pit Mineral Resources COGs are 0.19 g/t Au for oxide, and 1.09 g/t Au to 2.12 g/t Au for sulphide based on gold grade, chemistry, and recovery by ore type.

  4.

Open Pit Mineral Resources include stockpiled material.

  5.

Mineral Resources are reported inclusive of Mineral Reserves.

  6.

Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability.

  7.

Numbers may not add due to rounding.

  8.

Mineral Resources are reported on a 100% basis. Barrick’s and Newmont’s attributable shares of the Mineral Resource are 61.5% and 38.5%, respectively.

 

   
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Table 1-2 Mineral Reserves Estimate – December 31, 2019

 

100% Basis    Proven    Probable    Total
  

    Tonnes      

(Mt)    

  

    Grade      

(g/t Au)    

  

    Contained    

Metal

(Moz Au)

  

    Tonnes    

(Mt)

  

    Grade      

(g/t Au)    

  

    Contained    

Metal

(Moz Au)

  

    Tonnes    

(Mt)

  

    Grade      

(g/t Au)

  

    Contained    

Metal

(Moz Au)

Surface Operations

                                            

Stockpile

                                            

Turquoise Ridge Surface

   27    1.98    1.8                   27    1.98    1.8

Stockpile Total

   27    1.98    1.8                   27    1.98    1.8
                                              

Open Pit

                                            

Turquoise Ridge Surface

   1.80    2.59    0.15    25    1.86    1.5    27    1.91    1.7

Open Pit Total

   1.80    2.59    0.15    25    1.86    1.5    27    1.91    1.7
                                              

Surface Operations Total

   29    2.02    1.9    25    1.86    1.5    55    1.95    3.4
                                              

Underground Operations

                                            

Turquoise Ridge Underground

   16    11.56    5.9    12    10.28    3.9    28    11.01    9.8

Vista Underground

   0.0100    6.22    0.0020    0.73    6.86    0.16    0.74    6.86    0.16

Total

   16    11.55    5.9    13    10.08    4.1    29    10.90    10
                                              

Underground Operations Total            

   16    11.55    5.9    13    10.08    4.1    29    10.90    10
                                              

Turquoise Ridge Complex Total

   45    5.38    7.8    38    4.59    5.6    83    5.02    13

Notes:

  1.

CIM (2014) definitions were followed for Mineral Reserves.

  2.

Mineral Reserves are estimated using a long-term gold price of US$1,200/oz.

  3.

Underground Mineral Reserves were estimated using COGs of 7.15 g/t Au except Getchell Mine Area where a COG of 7.41 g/t Au has been used (poorer ground condition) and 3.42 g/t Au (Vista Underground). Open Pit Mineral Reserves COGs are 0.25 g/t Au for oxide, and 1.25 g/t Au to 2.28 g/t Au for sulphide, based on gold grade, chemistry, and recovery by ore type.

  4.

Numbers may not add due to rounding.

  5.

Mineral Reserves are reported on a 100% basis. Barrick’s and Newmont’s attributable shares of the Mineral Resource are 61.5% and 38.5%, respectively.

 

   
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  1.2.

ECONOMIC ANALYSIS

An economic analysis has not been included in this Technical Report as Barrick is a producing issuer, the properties are currently in production, and there is no material expansion of current production.

 

  1.3.

TECHNICAL SUMMARY

PROPERTY DESCRIPTION AND LOCATION

The Turquoise Ridge Complex is located in Humboldt County approximately 40 km northeast of the village of Golconda, Nevada, and approximately 64 km northeast of Winnemucca, Nevada. The Turquoise Ridge Complex is located at approximately 1,615 metres above sea level (MASL) and centred near latitude 41° 12’ 58’’ S and longitude 117° 14’ 39’’ W.

LAND TENURE

TURQUOISE RIDGE UNDERGROUND

Turquoise Ridge Underground covers an aggregate area of 2,402 ha (24.02 km2), which consists of 1,145 ha (11.45 km2) of unpatented mining and mill site claims and 1,257ha (12.57 km2) of patented/fee land. The surface rights secured for Turquoise Ridge Underground are sufficient to provide the necessary space required for all expected mining and quarrying activities.

As of the end of December 2019 all material permits were in compliance or were in the process of renewal.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

Turquoise Ridge Surface covers a total area of 7,925 ha (79.25 km2), of which 4,118 ha (41.18 km2) are unpatented mining claims and 3,808 ha (38.08 km2) are patented/fee lands. At Turquoise Ridge Surface, the eastern half of Section 13 (T39N, R42E, MDM) and FRM claims (Fraction claims), are subject to a 2% gross proceeds royalty, payable to Royal Gold Inc. This royalty applies to a small portion of the Mega Pit. The Fiberline project area is excluded from the Nevada Gold Mines’ joint venture area (332 ha). The Fiberline project, which is owned by Newmont, is located on the east side of the Mega Pit and currently does not encroach on the Mineral Reserve or Mineral Resource pit designs.

 

   
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As of the end of December 2019 all permits were in compliance or were in the process of renewal.

All Vista Underground mining activities are contained within the Turquoise Ridge Surface mining footprint and claim areas.

HISTORY

TURQUOISE RIDGE UNDERGROUND

Mining for copper, lead, and silver first began on the Turquoise Ridge Underground property in 1883. Tungsten was discovered in 1916 and mined sporadically until 1957. Gold was discovered at the present day Getchell mine site in 1933, with Getchell Mine Inc. operating the property from 1934 to 1945, producing a total of 788,875 ounces of gold. From 1960 to 2009, there was sporadic production at the Getchell mine including underground mining, open pit mining, and heap leaching of the dumps.

A deep drilling program began in 1993 in the Turquoise Ridge area. Planning and engineering for a new underground mine was completed in 1995. By mid 1998, a production shaft was completed at a depth of 555 m below the surface. In February 2000, mining was suspended at the Getchell Main underground mine. Drilling continued on the Turquoise Ridge and North Zone deposits, but due to depressed gold prices, the entire property was shut down in February 2002. Production resumed in February 2003.

As a result of operational and safety issues, Getchell Underground was placed on care and maintenance in April 2008. Full closure of the Getchell Underground mine occurred in the summer of 2009.

Barrick completed a merger with Randgold Resources on January 1, 2019. Shortly after, in March 2019, Barrick announced intent to enter into a joint venture with Newmont whereby the Nevada assets of both corporations, including Barrick’s Turquoise Ridge and Newmont’s Twin Creeks operations, would be combined in a joint venture, with Barrick serving as the mine operator. On July 1, 2019 Nevada Gold Mines was formed. Barrick is the operator of the joint venture and owns 61.5%, with Newmont owning the remaining 38.5%. Under the joint venture, Barrick’s Turquoise Ridge Mine and Newmont’s Twin Creeks Complex were combined as a single operation, now known as Turquoise Ridge. The combined mining operation is comprised

 

   
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of the Turquoise Ridge Underground, Vista Underground, and Turquoise Ridge Surface (the Mega and Vista open pits).

Since the inception of mining on the Getchell/Turquoise Ridge Underground property to the end of 2019, Turquoise Ridge Underground has produced approximately 6.8 million ounces of gold on a 100% basis.

TURQUOISE RIDGE SURFACE

In 1985, Gold Fields Mining Corporation (Gold Fields) discovered the Chimney Creek orebody. Nearby, Santa Fe Pacific Gold Corporation (SFPG) geologists were evaluating railroad grant sections in the Rabbit Creek area. By 1987, a strong trend was identified and drilled between the two deposits. In 1989 initial gold production commenced. Turquoise Ridge Surface (Newmont’s former Twin Creeks property) was created in 1993 by the consolidation of the Rabbit Creek Mine (Rabbit Creek) and the Chimney Creek Mine (Chimney Creek) by SFPG, following the asset exchange of Chimney Creek from Gold Fields. In May 1997, Newmont acquired the SFPG properties which remained wholly-owned by Newmont until the formation of Nevada Gold Mines in 2019. The former Rabbit Creek is located in the south end of the property, including what is now known as Mega Pit. The former Chimney Creek included the northern portion of the Mega Pit, the Vista Pit, and Vista Underground, which is located in the north end of the property near the Sage autoclave and Juniper oxide mill. On July 1, 2019, Nevada Gold Mines was formed, which now holds the Turquoise Ridge Complex.

GEOLOGY AND MINERALIZATION

TURQUOISE RIDGE UNDERGROUND

Turquoise Ridge Underground is situated within the Basin and Range province, near the northeast end of the Osgood Mountains.

The Getchell Fault, one of the most prominent structural features of the region, generally strikes north-south to north-northwest, and dips approximately 50° to the northeast in the vicinity of the mine site. The Turquoise Ridge North Zone mineralization largely mimics the orientation of the Getchell Fault, with complications from northeast and north-south structures.

The Turquoise Ridge deposit is a typical Carlin-type deposit and is characterized by structurally and stratigraphically controlled, sediment-hosted, replacement deposits containing disseminated micron sized gold. The gold occurs in arsenic-rich rims forming on pyrite, chiefly

 

   
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within decalcified, carbonaceous rocks. All gold bearing zones at Turquoise Ridge are located in proximity to granodiorite dikes that splay from the Osgood stock.

Lithology and structure strongly influence the geometry of the mineralization. To the north, Strataform mineralized domains exhibit strike lengths exceeding 304 m with typical thicknesses in the 61 m to 152 m range. Down dip lengths of over 304 m are common. Being dominantly stratigraphically controlled, the mineralized domains and bedding have a general north-northwest trending strike, and dip to the east (between 25° and 45°).

To the south, Strataform domains tend to strike north and dip to the east at approximately 30° to 60°. This generalized orientation is slightly different from mineralization occurring in the northern part of the deposit.

The two zones are separated by the northeast trending Turquoise Ridge shear zone, which could have contributed to the difference in alignment of the two zones.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

The Turquoise Ridge Surface property lies in an alluviated valley southeast of the Dry Hills, a northeastern outlier of the Osgood Range in northern Humboldt County, Nevada. The Dry Hills is an area of gently north-dipping Upper Paleozoic carbonate sediments, stratigraphically higher than rocks in the rest of the Osgood Range, which consists mainly of Lower Paleozoic elastic sediments intruded by a large Cretaceous pluton, which forms the backbone of the Osgood Range.

A broad zone of low-angle, west-dipping and northerly striking faults characterize a major Paleozoic thrust in the northern part of the Mega Pit. This fault contact between the Valmy and Comus Formations is correlated with the Roberts Mountains thrust. Intense shearing with attendant compressional features adjacent to the fault contact affects at least 18 m of the Comus Formation in the Mega North Pit.

The principal structural element in the Mega North Pit is the Conelea Anticline. It runs the length of the pit in a north-northwest orientation and is the most important ore-controlling structure in the Comus Formation. The fold probably developed during the Antler Orogeny when rocks of the Valmy Formation were placed above Comus rocks along the Roberts

 

   
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Mountains thrust. The Conelea Anticline does not affect rocks of the overlying Valmy and Etchart Formations.

Gold occurs in arsenic-rich rims or bands on pyrite grains associated with orpiment, realgar, stibnite, cinnabar and quartz. Adularia intergrown with gold-bearing arsenian pyrite in Comus mafic sills yields 40Ar/39Ar ages of 41.90 ± 0.25 and 42.11 ± 0.43 Ma (Groff et al., 1997), and 41.37 ± 0.23 and 42.13 ± 0.12 Ma (Hall et al., 2000). Four discrete pulses of alteration and related mineralization are recognized at Turquoise Ridge Surface.

Higher gold grades in the Mega North Pit occur in Comus carbonate sediments at the transition from Oc3 to Oc2 above the Upper Sill. Carbonate dominant stratigraphy transitions upward into a more tuffaceous and siliclastic sequence.

Mineralization is localized in decalcified carbonates but can occur less frequently in argillized and sulphidized basalt. Silicification is common in Comus sediments immediately adjacent to basaltic contacts with generally lower gold grades.

In the Vista Pit, stratabound high-grade oxide ore occurs primarily within pervasively decalcified sandy carbonate rocks of the lowermost Etchart near the unconformity between the Etchart and the Valmy formations. The unconformity is disrupted by northeast striking faults, forming a horst block in the central part of the pit. These and other structures contain high-grade gold in narrow zones in the Valmy formation and likely serves as feeders to the much larger stratabound orebody in the basal Etchart.

Vista Underground mineralization is largely confined to the Trench Fault shear zone. It has a mineable strike length of approximately 1,400 m and a dip length of 300 m. The ore consists of disseminated gold in arsenian pyrite and marcasite. The structure itself is a brecciated quartz-base “vein”, historically known as the Galena Vein. The mineralogy of the vein consists of milky vein quartz, fractured pyrite, massive fractured sphalerite with chalcopyrite, subhedral-euhedral pyrite, massive fracture galena, tennantite-tetrahedrite, microcrystalline quartz, sericite, and specular hematite. There is no recognized “ore horizon” within the deposit. The only constraint on the extent of gold mineralization is the surface and the 20K fault that truncates the Trench fault to the northeast.

 

   
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EXPLORATION STATUS

TURQUOISE RIDGE UNDERGROUND

Since acquisition of Turquoise Ridge Underground in 2006, Barrick has completed over 6,100 drill holes. The drilling programs from 2010 to 2019 were largely comprised of definition drilling to upgrade Mineral Resources adjacent to and within gaps into the Proven and Probable Mineral Reserve mining shapes.

Nevada Gold Mines maintains an aggressive exploration program principally comprising diamond drilling. Exploration is being carried out over several underground exploration targets at Turquoise Ridge Underground, including the Turquoise Ridge Corridor Fault Zone, Upper Footwall Pond, the down-dip and northeast extension of the Footwall Pond, the North Zone and South Zone Getchell Extensions, and the Powder Hill Extension. Near mining exploration targets are also being tested in 2020 on the southern extension of the Vista Underground. The Mega and Vista pits have a number of extension targets and will be reviewed for future step out drilling. An exploration team is on site at the Turquoise Ridge Complex to start drilling between the Turquoise Ridge Underground, Turquoise Ridge Surface, and Vista Underground mining areas.

TURQUOISE RIDGE SURFACE

Gold exploration activities began in the 1930s by two local Winnemucca prospectors, who first discovered Getchell. Getchell was operated intermittently between 1938 and 1984, when FRM and First Mississippi purchased the property. Exploration drilling in 1992 and 1993, was centered on the area around the original Getchell Main pit to delineate high-grade gold mineralization that had been discovered in the footwall of the Getchell Fault. Deep drilling began in 1993 in the Turquoise Ridge Underground area. A high-grade mineralized zone was discovered at a depth of 420 m to 600 m below the surface.

In 1984, Gold Fields discovered Carlin-type mineralization in Etchart Formation limestone in the hanging wall of the Discovery fault that later became part of the Vista Pit. Stripping of the initial Vista Pit began in April 1987 and first gold was poured in November 1987. Continued exploration to the south by Gold Fields led to the discovery of mineralization in the Mega North Pit area

Exploration drilling in the area spans over 32 years. Drilling methods included mud rotary, reverse circulation (RC) and diamond core. Initial drilling by Gold Fields was a combination of

 

   
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shallow core and RC holes to define an oxide resource. Deeper drilling by each method followed to evaluate the refractory potential

Near-mine exploration and growth drilling has been ongoing since 1998, almost continuously since 2008. Grade control and infill drilling was restarted in that year as well. The Turquoise Ridge Complex utilizes third-party drilling contractors to conduct drilling operations for both grade-control and step-out exploration programs.

MINERAL RESOURCES

TURQUOISE RIDGE UNDERGROUND AND VISTA UNDERGROUND

The Turquoise Ridge Underground and Vista Underground Mineral Resource estimates as of December 31, 2019, are reported in Table 1-1 at COGs of 5.04 g/t Au and 2.74 g/t Au respectively, based on operating costs, gold recoveries, and a gold price of US$1,500/oz.

Measured and Indicated Mineral Resources, inclusive of Mineral Reserves, total 39 million tonnes grading 9.61 g/t Au and contain 12 million ounces of gold. In addition, Inferred Mineral Resources total 2.9 million tonnes grading 9.1 g/t Au and contain 0.86 million ounces of gold.

All computer block modeling Mineral Resource estimation routines were conducted in Imperial units and have not always been converted to metric for reporting purposes.

The Mineral Resources were estimated by conventional 3D computer block modelling based on surface and underground diamond drilling and core assaying. Geologic interpretation of the drilling data was carried out and wireframes were constructed for mineralized gold domains. Assays were composited to ten-foot (3.05 m) intervals within the domains and statistical analysis was carried out to determine grade capping levels for each domain. Variography was used to determine search parameters and inverse distance squared (ID2) was employed for grade interpolation in the block model. Alternative interpolations by nearest neighbour (NN) methods were compared using swath plots for model validation. Variogram grade continuity ranges and the average distance to drill hole composites were used to classify Mineral Resources into Measured, Indicated, and Inferred categories. Grade smoothing was examined, and reconciliation with 2018 production was carried out for further validation of the estimate.

 

   
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The QPs are not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant factors which could materially affect the Mineral Resource estimate.

TURQUOISE RIDGE SURFACE

The Turquoise Ridge Surface Mineral Resource estimate as of December 31, 2019, is reported in Table 1-1 at a COG of
0.19 g/t Au for oxide ore, and a range from 1.09 to 2.12 g/t Au for sulphide ore, based on operating costs, gold recoveries, chemistry, and a gold price of US$1,500/oz. The COGs vary by ore type and are listed in Section 15 of this Technical Report.

Measured and Indicated Mineral Resources, inclusive of Mineral Reserves, total 90 million tonnes grading 2.00 g/t Au and contain 5.8 million ounces of gold. In addition, Inferred Mineral Resources total 18 million tonnes grading 1.6 g/t Au and contain 0.93 million ounces of gold.

All computer block modeling Mineral Resource estimation routines were conducted in Imperial units and have not always been converted to metric for reporting purposes

The Mineral Resources were estimated by conventional 3D computer block modelling based on surface and underground diamond drilling and core assaying. Geologic interpretation of the drilling data was carried out and wireframes were constructed for mineralized gold domains. Assays were composited to 6.1 m intervals within the domains and statistical analysis was carried out to determine grade capping levels for each domain. Variography was used to determine search parameters and ordinary kriging (OK) and localized indicator kriging (LIK) was employed for grade interpolation in the block model. Alternative interpolations by NN methods were compared using swath plots for model validation. Variogram grade continuity ranges and the average distance to drill hole composites were used to classify Mineral Resources into Measured, Indicated, and Inferred categories. Grade smoothing was examined, and reconciliation with 2018 production was carried out for further validation of the estimate.

The QPs are not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant factors which could materially affect the Mineral Resource estimate.

 

   
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MINERAL RESERVES

TURQUOISE RIDGE UNDERGROUND

The Turquoise Ridge Underground Mineral Reserves are estimated using a variable COG of 7.2 g/t Au to 7.4 g/t Au, based on 2018 and 2019 operating costs and adjustments on processing costs related to the cessation of the TMA. The methodology is appropriate for a process-capped operation, however, now that there is potential for higher production rates, the COG used may be conservative. Mineral Reserve estimates are based on a gold price of US$1,200/oz.

The Turquoise Ridge Underground Proven and Probable Mineral Reserves total 28 million tonnes grading 11.01 g/t Au and containing 9.8 million ounces of gold, consisting of:

 

   

Proven Reserves of 16 million tonnes grading 11.56 g/t Au and containing 5.9 million ounces of gold.

 

   

Probable Reserves of 12 million tonnes, grading 10.28 g/t Au and containing 3.9 million ounces of gold.

Dilution in addition to that incorporated into the design shapes is estimated by a factor of 12% to account for backfill dilution. Mining extraction is estimated as 100%, as confirmed by reconciliation to production results.

The 2019 reconciliation results, through December, show production of higher tonnage (111%), lower grades, (92%) and higher ounces of gold (102%) than estimated for Mineral Reserves, largely through identification of additional mineralization immediately before, and during mining.

This is a long-standing pattern at Turquoise Ridge, and not, in the QP’s opinion, any cause for concern or change in estimation or operating practices. Turquoise Ridge’s practice of strategic planning based on cases including factored Inferred Resources therefore seems reasonable.

The QP is not aware of any mining, metallurgical, infrastructure, permitting, or other relevant factors that could materially affect the Mineral Reserve estimate.

VISTA UNDERGROUND

Vista Underground Proven and Probable Mineral Reserve estimate, as of December 31, 2019, totals 0.74 million tonnes grading 6.86 g/t Au and containing 0.16 million ounces of gold consisting of:

 

   
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Proven Mineral Reserves of 0.01 million tonnes grading 6.22 g/t Au and containing 0.0020 million ounces of gold.

 

   

Probable Mineral Reserves of 0.73 million tonnes, grading 6.86 g/t Au and containing 0.16 million ounces of gold.

TURQUOISE RIDGE SURFACE

The Turquoise Ridge Surface Mineral Reserve estimate, as of December 31, 2019, totals 55 million tonnes grading 1.95 g/t Au and containing 3.4 million ounces of gold, consisting of:

 

   

Proven Mineral Reserves of 29 million tonnes grading 2.02 g/t Au and containing 1.9 million ounces of gold.

 

   

Probable Mineral Reserves of 25 million tonnes, grading 1.86 g/t Au and containing 1.5 million ounces of gold.

The Mineral Reserve is based on a gold price of US$1,200/oz.

Mineral Reserves include 1.7 million ounces of gold contained in ore from the Mega and Vista Pits. Mineral Reserves also include 1.8 million ounces of gold contained in refractory and oxide stockpiled ore.

The QPs are not aware of any mining, metallurgical, infrastructure, permitting, or other relevant factors that could materially affect the Mineral Reserve estimate.

MINING METHODS

TURQUOISE RIDGE UNDERGROUND

Turquoise Ridge Underground is accessed via two shafts and a system of internal ramps and utilizes underhand drift and fill mining methods with cemented rockfill. Turquoise Ridge Underground also employs mechanical mining as well as sill benching as mining methods. Turquoise Ridge Underground currently has two roadheaders in operation. Ground conditions at Turquoise Ridge Underground are poor, and the Rock Mass Rating (RMR) may be less than 20, or very poor, in ore headings. The mine is currently producing 2,700 tonnes of ore per day.

Key challenges in attainment of production levels and costs are the development of sufficient stoping areas and the transition from top-cut development to undercut stoping. Completion of the infrastructure development in the North Zone is necessary to achieve and optimize higher production levels. The Third Shaft project is well underway and is expected to be commissioned in late 2022. The shaft will drastically decrease the haulage requirements in the North Zone.

 

   
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VISTA UNDERGROUND

Vista Underground consists of two portals and a system of underground ramps accessing a steeply dipping (60° to near vertical) mineralized zone where narrow-vein longitudinal stoping is used. Vista Underground has been developed to access the vein in multiple horizons with two main barrier pillars to be mined on retreat. Stope production began near the centre of the orebody and progressed upward and outward in a triangular retreat sequence utilizing cemented rock fill for void replacement. Vista Underground currently produces approximately 1,000 tpd of ore. Initially, the mine proposed using Avoca stoping methods however poor rock mass conditions were encountered in the hanging wall which limited the maximum allowable strike length of the stopes. To minimize overbreak and improve operating conditions and production, the mining method was changed to retreat long hole stoping and more active stoping faces were opened to meet the production requirements.

TURQUOISE RIDGE SURFACE

Turquoise Ridge Surface mine operates the Vista and Mega pits, as well as providing ore rehandle and surface project work at Turquoise Ridge Underground. Turquoise Ridge Surface uses conventional open pit mining methods including drilling, blasting, loading, and hauling.

Surface mining operations occur in two developed open pit areas: Vista Pit to the north and Mega Pit to the south. Vista Pit measures approximately 1.1 km north to south, 1 km east to west, and the current pit depth is over 213 m. Mining in 2019 occurred in the Vista 8 (V8) phase, which will continue to deepen the pit by another 91 m in the ultimate design. The Mega Pit measures 4 km overall north to south, and approximately 1.6 km east to west. The current pit depth is over 1,200 feet (365m) and will deepen by approximately 50 m in the ultimate design. Mining in 2019 at the Mega Pit occurred in Cut 25.

PRODUCTION SCHEDULE

Nevada Gold Mines has prepared a life of mine (LOM) production schedule based on current Mineral Reserves for the three mines (Turquoise Ridge Underground, Turquoise Ridge Surface, and Vista Underground) and the processing facility with production planned into 2039. The currently planned production rates for the underground properties at Turquoise Ridge are approximately 2,700 tonnes of ore per day at Turquoise Ridge Underground and 1,000 tonnes of ore per day at Vista Underground. The current planned mining rate for Turquoise Ridge Surface is 71,000 tpd.

 

   
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MINERAL PROCESSING

Historically, all of the ore mined at Turquoise Ridge Underground was processed at the Turquoise Ridge Surface Sage autoclave under a Toll Milling Agreement (TMA).

The TMA was terminated with the formation of the Nevada Gold Mines Joint Venture. Ore produced from Turquoise Ridge Underground is rehandled by Turquoise Ridge Surface and processed at the Sage autoclave. The Sage/Juniper capacity is 12,000 tpd, however, actual throughput can vary depending on ore type and constituents.

The mill includes semi-autogenous grinding (SAG) mill followed by a ball mill. The cyclone overflow reports to a thickener. Thickener underflow reports to an acidification circuit where sulphuric acid is added as necessary to ensure adequate autoclave free acid solution levels. The free acid concentration for Turquoise Ridge Underground ore needs to be maintained greater than 30 g/L. Thickener overflow solution is returned to the milling circuit. After acidification, ore slurry is added to two identical autoclaves that are operated in parallel. Two stages of flash heat recovery are utilized. Autoclave discharge is cooled before reporting to the lime neutralization circuit. Autoclave waste gas is cooled and scrubbed before discharging to the atmosphere.

Oxide ore and acidic oxidized sulphide ore slurry are combined in the neutralization circuit. After neutralization with the carbonate oxide ore and supplemental lime, the ore slurry reports to a carbon-in-leach (CIL) circuit where the ore is leached in cyanide solution to extract the gold. Final tailings slurry is pumped to the tailings containment area. Tailings settle and decant solution is reclaimed and reused in the grinding circuit.

Loaded carbon from the CIL circuit is transferred to the recovery plant. After acid washing to remove inorganic contaminants, the carbon is transferred to the pressure Zadra stripping circuit. Gold is stripped from the carbon using caustic and cyanide solution at elevated temperature and pressure. Pregnant solution from the stripping circuit is pumped to an electrowinning circuit where precious metal is removed from the solution as sludge. The sludge is filtered, dried in a mercury retort, mixed with fluxes, and refined into doré bars.

After carbon stripping, the barren carbon reports to the kiln regeneration circuit and returns to the CIL circuit.

 

   
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Run-of-mine (ROM) higher grade oxide ore from the Turquoise Ridge Surface ore sources are blended for gold grade, hardness, and carbonate content and fed to the Juniper Oxide Mill. The oxide mill consists of a variable speed SAG mill operating in closed circuit with a discharge screen. SAG mill product is fed to a ball mill operating in closed circuit with cyclones. Final product grind size is 90%—200 mesh. Cyclone overflow product is fed to the neutralization circuit. Here the carbonate in the oxide ore is used to neutralize the acidic autoclave discharge slurry. The combined oxide slurry and autoclave discharge slurry are further neutralized with lime before treatment in the CIL. The CIL circuit is used to concurrently leach gold from the ore and adsorb it onto activated carbon. The final tailings slurry is pumped to the tailings dam. The gold loaded carbon is stripped, acid washed, kiln reactivated, and recycled back to the CIL circuit. The gold stripped from the carbon is electrowon and refined into doré for shipment to an off site refinery.

ROM lower grade oxide ore from the Turquoise Ridge Surface sources are delivered to the Juniper heap leach pads. This ore is normally stacked in 6 m lifts. When a cell is full and ripped, drip irrigation lines are installed to apply barren cyanide solution to the top surface. The cyanide solution is used to leach gold from the ore as the solution percolates through the stacked ore and collected on an impermeable liner at the bottom of the heap. This pregnant solution is fed to a carbon-in-column (CIC) circuit to adsorb the gold onto carbon. The CIC barren solution is then recycled back to the top of the leach pad. The gold loaded carbon is stripped, acid washed, kiln reactivated, and recycled back to the CIC circuit. The gold stripped from the carbon is electrowon and refined into doré for shipment to an off-site refinery.

MINE INFRASTRUCTURE

TURQUOISE RIDGE UNDERGROUND

Existing infrastructure at Turquoise Ridge Underground comprises:

 

   

Two shafts (7.3 m and 6.1 m diameters, 552 m and 519 m depths to collar, respectively)

 

   

Mobile equipment mining fleet

 

   

Limestone backfill quarry and 225 tonnes per hour backfill crushing facility

 

   

Two Underground backfill plants (fed from surface silos)

 

   

Two Underground shotcrete plants (fed from surface silo)

 

   

Underground dewatering facility

 

   

Surface compressor house

 

   

Surface cement plant (positioned for use at Third Shaft for project support)

 

   

Multiple surface workshop facilities

 

   
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120 kV electrical power line connection to the grid

 

   

Office building

 

   

Warehouse

 

   

3,500 gpm water treatment plant with three sets of Rapid Infiltration Basins (RIBS)

 

   

Tailings facility

Third Shaft Project

The Third Shaft Project at Turquoise Ridge Underground consists of sinking and equipping a 7.3 m diameter, concrete-lined shaft to 990 m total depth. Shaft infrastructure will include two skipping levels, and a shaft bottom pump level. Shaft equipping will include a headframe and collar house; hoists and hoistroom; shaft steel; surface and underground material handling; and a shaft bottom pumping system.

The new shaft will serve as a second production shaft, and provide the following advantages:

 

   

Increased ventilation capacity

 

   

Increased hoisting capacity

 

   

Shorter hauls underground as mining at Turquoise Ridge Underground is currently concentrated in the North Zone

 

   

Provide a secondary escapeway for the north end of the mine

Site preparation for the Third Shaft started in 2017, and shaft sinking began in 2019 with final commissioning expected in late 2022.

VISTA UNDERGROUND INFRASTRUCTURE AND SERVICES

Vista Underground uses the existing infrastructure of Turquoise Ridge Surface.

Existing infrastructure comprises:

 

   

Surface mobile equipment shop

 

   

Surface cement silos (Contractor owns and operates backfill plant)

 

   

Surface metal removal plant

 

   

Underground dewatering/pumping infrastructure

 

   

Surface administration buildings

 

   

Surface dry/change house

TURQUOISE RIDGE SURFACE INFRASTRUCTURE AND SERVICES

The main existing infrastructure comprises:

 

   
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Two open pits

 

   

Three active waste dumps

 

   

One in pit backfill waste dump

 

   

Two active tailings facilities

 

   

Numerous stockpiles of oxide and refractory ore, separated by chemistry and grade

 

   

One oxide mill (Juniper)

 

   

One refractory mill (Sage) with two autoclaves

 

   

One active leach pad (Izzenhood)

 

   

Refinery

 

   

Assay lab

 

   

Several administration buildings with locker rooms

 

   

Dewatering and utility shop

 

   

South mine maintenance shop area

 

   

Two warehouses (north and south)

 

   

Mine rescue building

 

   

Dewatering, piezometer, and potable water wells

 

   

Extensive dewatering and potable water pipelines

 

   

Electrical power throughout mine site

 

   

Fiber optic lines and network communication

 

   

Mine radio network

 

   

Caterpillar Minestar dispatch system

 

   

Powder magazine area

The addition of the Cut 40 layback to reserves will involve relocation of a section of power lines, dewatering pipelines, haul road, a waste rock facility, and an expansion of the heap leach pad. Tailings expansions are scheduled throughout the LOM.

ENVIRONMENTAL, PERMITTING AND SOCIAL CONSIDERATIONS

Over the years, many environmental studies have been completed, as required. Total permitted surface disturbance for the Turquoise Ridge Complex is approximately 10,327 hectare (ha) (103.27 km2), of which Turquoise Ridge Underground covers a total area of 2,402 ha (24.02 km2) and Turquoise Ridge Surface covers a total area of 7,925 ha (79.25 km2), respectively. The Vista Underground lies beneath and is contained within the footprint of the Turquoise Ridge Surface mining and claim areas.

 

   
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The Turquoise Ridge Complex maintains a number of permits for the operation, and permits are tracked carefully to ensure ongoing compliance. Nevada Gold Mines environmental staff carries out sampling, monitoring, and record keeping and are involved in permit applications and renewals as required.

There are no major challenges with respect to government relations, non-governmental organizations, social or legal issues, and community development. The Turquoise Ridge Complex has a community and social relations policy that is consistent with Barrick’s core values and governance.

There are both ongoing and active reclamation and closure activities as well as historic or legacy activities.

Ongoing reclamation activities include the Turquoise Ridge Underground and legacy Getchell mine facilities; water treatment plant and infiltration system; potable water system; wastewater treatment system; tailings impoundment; and access and haul roads. These components will be reclaimed and closed at the end of the mine life. Reclamation of the historic Getchell processing facilities and legacy areas has essentially been completed.

Ongoing reclamation activities at Turquoise Ridge Surface include sloping and regrading of waste rock facilities. Seeding of the waste dump for future plant growth and for erosion control is ongoing. Leach pads are rinsed once the gold has been recovered from the facility. A LOM reclamation schedule and cost estimate is updated annually for Turquoise Ridge Surface.

The Turquoise Ridge Complex closure costs are updated each year, with increases or decreases in disturbed areas noted and quantified; the current cost for rehabilitation and closure of the Turquoise Ridge Complex according to the calculation model is approximately $105 million for the entire site.

CAPITAL AND OPERATING COST ESTIMATES

Current LOM capital costs for the Turquoise Ridge Complex are estimated to be $1,047 million (on a 100% basis). Large capital items for the LOM include continued expenditure on the Third Shaft and associated infrastructure, Juniper and Sage Mill Tailings Expansions, Surface Mine Equipment and Replacements, and Process Upgrades and Equipment. These costs are in line with historical costs.

 

   
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The total operating cost has been estimated for the Turquoise Ridge Complex based on historical costs and assumptions over the LOM plan (2020 to 2039). The operating costs are considered to be appropriate for the mining and processing methods.

 

    1.4.

CONCLUSIONS AND RECOMMENDATIONS

CONCLUSIONS

In the opinion of the QPs there are no significant risks and uncertainties that could reasonably be expected to affect the reliability or confidence in the exploration information, Mineral Resource or Mineral Reserve estimates, or projected economic outcomes in this Technical Report.

ACCESSIBILITY, CLIMATE, INFRASTRUCTURE, AND PHYSIOGRAPHY

 

   

The existing and planned infrastructure, availability of staff, existing power, water, and communications facilities, and methods whereby goods can be transported to the mining operations are well-established and well-understood by Nevada Gold Mines given the decades of experience that Barrick and Newmont have from their previous mining operations on the Turquoise Ridge Complex.

 

   

Within Nevada Gold Mines’ ground holdings, there is sufficient area to allow for the operation of all required project infrastructure, and sufficient room remains if expansions to the existing infrastructure are required.

 

   

Mining operations can be conducted year-round.

GEOLOGY AND MINERAL RESOURCES

 

   

The understanding of the deposit settings, lithologies, and geologic, structural, and alteration controls on mineralization is sufficient to support estimation of Mineral Resources and Mineral Reserves.

 

   

The mineralization styles and settings are well understood and can support declaration of Mineral Resources and Mineral Reserves.

 

   

The geological knowledge of the area is adequate to reliably inform mine planning.

 

   

The drilling, sampling, and quality assurance/quality control (QA/QC) is appropriate for the style of mineralization.

 

   

Nevada Gold Mines is of the opinion that the Mineral Resource estimate has been completed to industry standard and is suitable to support the disclosure of Mineral Resources and Mineral Reserves.

 

   

Nevada Gold Mines is not aware of any environmental, permitting, legal, title, taxation, socio-economic, marketing, political, or other relevant factors which could materially affect the Mineral Resource estimate.

 

   
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Exploration potential remains considerable, and Nevada Gold Mines is pursuing the growth potential both near current operations and between the Turquoise Ridge Complex’s component properties.

MINING AND MINERAL RESERVES

 

   

In the opinion of the QPs, the mining methods used are appropriate to the geological, geotechnical, and hydrogeological characteristics of each deposit and employ conventional mining tools and mechanization. The LOM plan has been appropriately developed to maximize mining efficiencies, based on the current knowledge of geotechnical, hydrological, mining and processing information on the Turquoise Ridge Complex.

 

   

Nevada Gold Mines is of the opinion that the Mineral Reserve estimate has been completed to industry standard and is suitable for disclosure.

PROCESSING

 

   

The processing facilities that comprise the Turquoise Ridge Complex are adequate to meet or exceed the production forecasts from the mineralization contained within the Mineral Reserves and Mineral Resources. The ore blending strategies utilized at the Sage autoclave facility should facilitate a stable operation.

 

   

The recovery equations that are presented have been well calibrated against actual plant data when possible or based on representative test work for future ore domains.

 

   

The Turquoise Ridge Complex sampling and metallurgical accounting methods are reasonable and consistent with industry standards.

 

   

The Sage autoclave and Juniper oxide mill are existing processing plants and are well suited to process Cut 40 ores. No modifications to the existing flow sheets are expected to be necessary to process Cut 40 ores. A leach pad expansion engineered design will be completed in 2020 by an outside consultant

RECOMMENDATIONS

GEOLOGY AND MINERAL RESOURCES

 

   

Continue to work with regional exploration to capitalize on opportunities to establish continuity between ore bodies and improve the geologic model.

 

   

Evaluate methodology for Mineral Resource classification across the various deposits looking for opportunities to improve through sharing techniques and perhaps standardising the approach.

 

   

Continue to develop understanding of controls on geochemistry elements important for ore processing. Use this understanding to improve estimation of these elements, including domaining, estimation parameters, and validation of results.

MINING AND MINERAL RESERVES

 

   

With Turquoise Ridge Underground production less limited by processing constraints, continue to review potential for higher mine production.

 

   
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Continue to focus on reducing operating costs and optimization of Mineral Reserve and Mineral Resource pit designs at Turquoise Ridge Surface.

 

   

Continue optimization of mechanical mining methods to increase mine throughput.

 

   

Continue optimization scenarios at Turquoise Ridge Underground to fully capitalize upon synergies derived from termination of the TMA (reduced COG through milling cost reductions and improved throughput due to the removal of an artificial ore processing limit at the autoclave).

 

   

Continue Vista Underground optimization through mining efficiency improvements until the end of mine life.

PROCESSING

 

   

Future test work should be conducted at coarser grind sizes for the high grade, Turquoise Ridge Underground ore to better understand the impact on recovery when operating the Sage autoclave at increased throughput.

 

   
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2. INTRODUCTION

Nevada Gold Mines LLC (Nevada Gold Mines) operates the Turquoise Ridge Complex, located in Humboldt County, Nevada, USA. Nevada Gold Mines is a joint venture between Barrick Gold Corporation (Barrick) and Newmont Corporation (Newmont), Barrick is the operator of the joint venture and owns 61.5%, with Newmont owning the remaining 38.5%. Under the joint venture, Barrick’s Turquoise Ridge Mine and Newmont’s Twin Creeks Complex were combined as a single operation, now known as Turquoise Ridge. The combined mining operation is comprised of the Turquoise Ridge Underground, Vista Underground, and Turquoise Ridge Surface (the Mega and Vista open pits).

The purpose of this Technical Report is to support the disclosure of the Mineral Resource and Mineral Reserve estimates for the Turquoise Ridge Complex as of December 31, 2019. This Technical Report conforms to National Instrument 43-101 Standards of Disclosure for Mineral Projects (NI 43-101). Unless otherwise stated, all data included in this Technical Report is disclosed on a 100% basis.

Barrick is a Canadian publicly traded mining company with a portfolio of operating mines and projects. Newmont is a publicly traded gold producer with a portfolio of operations and exploration projects, based in Denver, Colorado, USA. On March 10, 2019, Barrick entered into an implementation agreement with Newmont to create a joint venture combining the companies’ respective mining operations, assets, reserves and talent in Nevada, USA. This includes Barrick’s Cortez, Goldstrike, Turquoise Ridge and Goldrush properties and Newmont’s Carlin, Twin Creeks, Phoenix, Long Canyon and Lone Tree properties. On July 1, 2019, the transaction closed, establishing Nevada Gold Mines LLC and Barrick began consolidating the operating results, cash flows and net assets of Nevada Gold Mines from that date forward.

The Turquoise Ridge Complex is located in the Potosi Mining District, approximately 64 km northeast of Winnemucca, Nevada. Refractory ore is processed at the Sage autoclave, while non-refractory ore is processed at the Juniper oxide mill or stacked on heap leach pads. All processing facilities are located at Turquoise Ridge Surface on what was formerly Newmont’s Twin Creeks property.

 

   
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    2.1.

SOURCES OF INFORMATION

This Technical Report was prepared by the following Nevada Gold Mines employees, each of whom is a Qualified Person (QP) under NI 43-101, and who have all visited the Turquoise Ridge Complex. :

 

   

Charles Lynn Bolin, MBA, SME (RM), Chief Surface Engineer

 

   

Craig Fiddes, SME (RM), Manager – Resource Modelling

 

   

Jay Olcott, SME (RM), Project Manager

 

   

Steven W. Yopps, MMSA QP, Manager - Growth Projects

Mr. Olcott is responsible for Sections 2 to 12, 19, 20, and 23 of the Technical Report. Mr. Bolin and Mr. Fiddes share responsibility for Sections 14 to 16, 18, 21, and 22 of the Technical Report. Mr. Yopps is responsible for Section 13 and 17 of the Technical Report. All QPs share responsibility for Sections 1 and 24 to 27.

Contributing Authors:

 

   

Tyson Gibbs, SME(RM), Mineral Resource Manager Turquoise Ridge Open Pit and Underground

 

   

Edward Tester, Turquoise Ridge Mineral Resource Growth Manager

 

   

Kathy Steele, SME(RM) Turquoise Ridge Chief Surface Engineer

 

   

Ben Gunn, Turquoise Ridge Chief Underground Engineer

 

   

Jon Carlson, C.P.G., Turquoise Ridge Senior Resource Geologist

 

   

David Thompson, PE, Turquoise Ridge Senior Underground Planning Engineer

 

   

Yaya Hamadou, Turquoise Ridge Chief Metallurgist

 

   

Dennis Hosack, Turquoise Ridge Environmental Manager

 

   

Orson Tingey, Nevada Gold Mines Land Department

The documentation reviewed, and other sources of information, are listed at the end of this Technical Report in Section 27 References.

 

   
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    2.2.

LIST OF ABBREVIATIONS

Units of measurement used in this Technical Report conform to the US standard system of weights and measures, except where metric units are noted. All currency in this Technical Report is US dollars (US$) unless otherwise noted.

 

µ    micron    kVA    kilovolt-amperes
µg    microgram    kW    kilowatt
a    annum    kWh    kilowatt-hour
A    ampere    L    litre
bbl    barrels    lb    pound
Btu    British thermal units    L/s    litres per second
°C    degree Celsius    m    metre
C$    Canadian dollars    M    mega (million); molar
cal    calorie    m2    square metre
cfm    cubic feet per minute    m3    cubic metre
cm    centimetre    MASL    metres above sea level
cm2    square centimetre    m3/h    cubic metres per hour
°d    day    mi    mile
dia    diameter    min    minute
dmt    dry metric tonne    µm    micrometre
dwt    dead-weight ton    mm    millimetre
°F    degree Fahrenheit    mph    miles per hour
ft    foot    MVA    megavolt-amperes
ft2    square foot    MW    megawatt
ft3    cubic foot    MWh    megawatt-hour
ft/s    foot per second    oz    Troy ounce (31.1035g)
g    gram    oz/ton    ounce per short ton
G    giga (billion)    ppb    part per billion
Gal    Imperial gallon    ppm    part per million
g/L    gram per litre    psia    pound per square inch absolute
Gpm    Imperial gallons per minute    psig    pound per square inch gauge
g/t    gram per tonne    RL    relative elevation
gr/ft3    grain per cubic foot    s    second
gr/m3    grain per cubic metre    st    short ton
ha    hectare    stpa    short ton per year
hp    horsepower    stpd    short ton per day
hr    hour    t    metric tonne
Hz    hertz    tpa    metric tonne per year
in.    inch    tpd    metric tonne per day
in2    square inch    US$    United States dollar
J    joule    USg    United States gallon
k    kilo (thousand)    USgpm    US gallon per minute
kcal    kilocalorie    V    volt
kg    kilogram    W    watt
km    kilometre    wmt    wet metric tonne
km2    square kilometre    wt%    weight percent
km/h    kilometre per hour    yd3    cubic yard
kPa    kilopascal    yr    year

 

   
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3. RELIANCE ON OTHER EXPERTS

This Technical Report has been prepared by Nevada Gold Mines. The information, conclusions, opinions, and estimates contained herein are based on:

 

   

Information available at the time of preparation of this Technical Report,

 

   

Assumptions, conditions, and qualifications as set forth in this Technical Report.

The properties and mineral rights are owned or controlled through various forms of ownership patents issued by the Government of the USA and by ownership of unpatented mining and mill site claims held subject to the paramount title of the USA.

Nevada Gold Mines has relied on Barrick for guidance on applicable taxes, royalties, and other government levies or interests, applicable to revenue or income from the Turquoise Ridge Complex as stated in Section 4 of this Technical Report.

Except for the purposes legislated under provincial securities laws, any use of this Technical Report by any third party is at that party’s sole risk.

 

   
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4. PROPERTY DESCRIPTION AND LOCATION

The Turquoise Ridge Complex includes Turquoise Underground, Turquoise Ridge Surface, and Vista Underground and is located in Humboldt County approximately 40 km northeast of the village of Golconda, Nevada, and approximately 64 km northeast of Winnemucca, Nevada (Figure 4-1). The Turquoise Ridge Complex covers a total area of 10,327 hectares (ha) (103.27 km2) (Figure 4-2). Individual claims are outlined within the boundary. Blank areas without claims are administered by the Bureau of Land Management (BLM). Project boundaries are established along the Public Land Survey by section and subsection per the official BLM master title plan for T39N, R42E, MDM and T38N, R42E, MDM.

The Turquoise Ridge Complex is located at approximately 1,615 metres above sea level (MASL) and centred near latitude 41° 12’ 58’’ S and longitude 117° 14’ 39’’ W. All Vista Underground mining activities are contained within the Turquoise Ridge Surface mining footprint and claim areas.

 

     4.1.

LAND TENURE

Mineral rights for the Turquoise Ridge Complex are managed by Nevada Gold Mines’ Land Department in Elko, Nevada. The Turquoise Ridge Complex controlling interests are held by lode and mill site unpatented mining claims, private surface and minerals, private surface only and leased minerals. All mining claims are located on public lands and administered by the BLM.

Turquoise Ridge Underground is located within the following Humboldt County Township/Range/Sections as described below:

 

   

Township 38 North, Range 42 East, MDM, Sections 2-5, 9-11, 13.

 

   

Township 39 North, Range 42 East, MDM, Sections 21-23, 26-29, 32-35.

 

   

Township 38 North, Range 43 East, MDM, Section 6.

Turquoise Ridge Underground covers a total area of 2,402 ha (24.02 km2), which consists of 1,145 ha (11.45 km2) of unpatented mining and mill site claims and 1,257 ha (12.57 km2) of patented/fee land. The surface projection of the Turquoise Ridge Underground workings is presented in Figure 4-2.

 

   
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Turquoise Ridge Surface is located within the following Humboldt County Township/Range/Sections as described below:

 

   

Township 38 North, Range 43 East, MDM., Sections 3-5, 9, 15, 17.

 

   

Township 39 North, Range 43 East, MDM., Sections 3-10, 15-22, 27-33.

 

   

Township 40 North, Range 43 East, MDM., Sections 31, 32.

 

   

Township 39 North, Range 42 East, MDM., Sections 12, 13, 24, 25, 36.

Turquoise Ridge Surface covers a total area of 7,925 ha (79.25 km2), of which 4,118 ha (41.18 km2) are unpatented mining claims and 3,808 ha (38.08 km2) are patented/fee lands. The surface projection of the Turquoise Ridge Surface workings is presented in Figure 4-3. The Fiberline project area, which is owned by Newmont, is excluded from the Nevada Gold Mines’ joint venture area (332 ha). The Fiberline project is located on the east side of the Mega Pit and currently does not encroach on the Mineral Reserve or Mineral Resource pit designs.

The Turquoise Ridge Surface property controls 613 unpatented mining and mill-site claims. The Turquoise Ridge Underground property controls 246 unpatented mining and mill-site claims. The claims are located on public lands and are held subject to the paramount title of the USA. The claims are maintained on an annual basis, and do not expire as long as the maintenance fee payments are timely filed with the BLM. Details of the claims are a matter of public record, available at the BLM Land & Mineral Legacy Rehost System (LR2000 website). All mining leases and subleases are managed and reviewed on a monthly basis by the Nevada Gold Mines Land Department and all payments and commitments are paid as required by the specific agreements. Patented and fee lands require annual payment of tax assessments to Humboldt County.

All pertinent permits have been received for the operation. An Exploration Plan of Operations is in place which allows for the continued exploration of the property.

Details on permits may be found in Section 20 of this Technical Report.

 

     4.2.

ROYALTIES

In connection with the formation of Nevada Gold Mines, both Barrick and Newmont were granted a 1.5% net smelter returns royalty over the respective properties they contributed (including Barrick’s 75% interest in Turquoise Ridge Underground and Newmont’s 25%

 

   
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interest in the Turquoise Ridge Underground and its 100% interest in Turquoise Ridge Surface and Vista Underground). Each of these “retained royalties” is only payable once the aggregate production from the properties subject to the royalty exceeds the publicly reported reserves and resources as of December 31, 2018.

Turquoise Ridge Surface is subject to the following royalties:

 

   

T39N, R42E, Section 12: E2, No royalty except for a “sliver” south of Chim 136 and within the Shar 1R claim, 2% gross proceeds to Royal Gold Inc (Royal Gold). Area is less than 1 acre within Section 12.

 

   

T39N, R42E, Section 13: E2, 2% gross proceeds to Royal Gold after 50,000 ounces of gold has been sold from this area (which threshold has been met).

 

   

T39N, R42E, Section 24: All, No royalty except that portion within the FRM 269 claim, 2% gross proceeds to Royal Gold. Sliver north of Chim 170, less than 1 acre.

Vista Underground

Mineral Resources and Mineral Reserves are not subject to any royalties.

Turquoise Ridge Underground

Mineral Resources and Mineral Reserves are not subject to any royalties.

The State of Nevada imposes a 5% net proceeds tax on the value of all minerals severed in the State. This tax is calculated and paid based on a prescribed net income formula which is different from book income.

 

     4.3.

ECONOMY, TAXATION, PERMITS, AND ENVIRONMENTAL

The State of Nevada is, in general, a mining friendly jurisdiction, with strong local support for mining and the associated businesses mining supports. However, the permitting environment has changed significantly, gradually increasing the necessary time to permit an operation. The QPs are of the opinion that the Cut 40 permitting will be aided by a long record of experience gained at Turquoise Ridge Surface and the success of the Mega and Vista pits. All Nevada and Federal taxes are applicable.

The QPs are not aware of any material environmental liabilities on the property. Both properties have all required permits to conduct the proposed work on them. The QPs are not aware of

 

   
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any other significant factors and risks that may affect access, title, or the right or ability to perform the proposed work program on the property.

 

   
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5. ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY

 

     5.1.

ACCESSIBILITY

The Turquoise Ridge Complex is located in Humboldt County, Nevada, approximately 64 km northeast of Winnemucca, Nevada. The site is accessible from Interstate 80 approximately 24 km east of Winnemucca at the small town of Golconda. From Golconda, there is a paved road for 24 km followed by an improved gravel road to the mine gates (16 km to west mine gate, 24 km to the east mine gate).

The nearest airfield is the Winnemucca Airport, located 83 km southwest of the mine site by road. The nearest regional airfield is the Elko Airport, located 216 km east of the mine site by road.

 

     5.2.

CLIMATE

The climate is a semi-arid, steppe climate characterized by dry, hot summers and cold winters. Average monthly temperatures range from a low of -5ºC in December to a high of 29ºC in July. The Turquoise Ridge Complex receives an annual average of 7.6 cm of precipitation, which falls primarily as snow in the winter months, though light seasonal rains commonly occur in April and September. The Turquoise Ridge Complex operates on a year-round basis and is not regularly affected by climatic conditions. Certain types of construction activities may possibly be impacted by severe winter conditions

 

     5.3.

LOCAL RESOURCES AND INFRASTRUCTURE

Northern Nevada is an active mining area, with many large underground and open pit operations. Personnel and supplies for mining operations are relatively easily sourced from the local market, though some personnel, particularly professionals, are sourced from both out of state and foreign labour markets.

 

   
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The surface rights secured for the Turquoise Ridge Complex are sufficient to provide the necessary space required for all mining and quarrying activities. Sufficient land area exists on the property to accommodate all foreseeable processing plants, tailings and waste storage areas, and waste disposal areas.

The following infrastructure is available at the Turquoise Ridge Complex:

 

   

Road Access

 

   

Electrical Power

 

   

Propane supply

 

   

Natural gas (North area only)

 

   

Process water

 

   

Telephone (Land line & Cell)

 

   

Internet/Intranet

Water volumes necessary for mining operations are available both through reclamation of groundwater inflows into the mine as well as water pumped to surface from several water wells which have been drilled across the property. Electrical power is supplied by one 120 kV electrical transmission line which enters the property from the southeast.

 

     5.4.

PHYSIOGRAPHY

The Turquoise Ridge Complex lies in proximity to the base of the Osgood Mountains, one of many typically north-south trending mountain ranges in the area, at approximately 1,615 MASL. These ranges vary in height, from valley floors at approximately 1,341 MASL to peaks at elevations between 1,798 MASL and 2,590 MASL.

The Turquoise Ridge Complex is located within a region classified by the United States Geological Survey (USGS) as having a moderate earthquake hazard. There is a 2.0% chance that an earthquake with a peak ground acceleration of 14% to 30% of gravity would occur within a 50 year period.

Vegetation in the vicinity of the Turquoise Ridge Complex is dominated by low dense shrubs and sage bush mixed with sparse native grasses and low flowering plants.

 

   
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6. HISTORY

 

     6.1.

TURQUOISE RIDGE UNDERGROUND

Mining for copper, lead, and silver first began on the Turquoise Ridge Underground property in 1883. Tungsten was discovered in 1916 and mined sporadically until 1957.

In in the fall of 1934, Edward Knight and Emmett Chase, two Winnemucca prospectors, found gold at the present day Getchell mine site. Later that year Noble H. Getchell purchased Knight’s interest in the property and in 1935, approached George Wingfield to invest, whereby Wingfield purchased Chase’s shares. From this partnership Getchell Mine Inc. (Getchell) was formed in 1935. Development of the Getchell open pit mine began and a full-scale operation was planned, including construction of a mill. Mill construction required additional financial support, so Mr. Bernard Baruch agreed to invest in the mine. In 1936, Newmont also agreed to help finance the construction of the Getchell mine as the third partner. Production began in early 1938 with first gold poured some time later and the company paying its first dividend in September of the same year.

Getchell operated the mine from 1934 to 1945, producing and selling 788,875 ounces of gold. From 1939 to 1944, the Getchell mine paid out more than $3 million in dividends. In 1941 a Cottrell electric precipitating unit was installed to collect the arsenic liberated by roasting the sulphide ore. Despite wartime restrictions on gold producers from 1943 to 1945 the Getchell mine was permitted to continue operations as it was a producer of strategic arsenic. In 1945, however, mining of gold ore was suspended due to labour and material shortages, and activities limited to underground development, reconstruction and expansion of the plant, and metallurgical research. Processing of stockpiled ore continued into 1946. The discovery of additional sources of oxidized ore enabled gold production to be resumed in 1948 and continued through to 1950.

In 1951, however, the Getchell mine ceased producing gold entirely and converted its plant to treat tungsten ore. Under authorization from the Defense Production Act of 1950, the Defense Minerals Administration and the Defense Production Administration instituted measures providing for the purchase of a standard-grade (60% tungsten trioxide) concentrate at a ceiling price of $76 per ton unit. The Getchell mine was one of the major tungsten producers in the

 

   
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USA. Tungsten production ceased in 1957 following the termination of the purchase program in 1956.

Following the cessation of tungsten production, Getchell began formulating plans for resuming gold operations. These plans, however, were dependent on developing solutions to several metallurgical problems pertaining to the separation of gold from the sulphide ores.

Getchell was purchased by Goldfield Consolidated Mines (Goldfield) in 1960. Goldfield modified the mill and a Dorr-Oliver fluidized solids reactor was installed to roast sulphide ores.

The mine was closed in 1967 and the mill dismantled, because the tungsten deposit was mined out.

In the mid to late 1970s the Getchell mine was purchased by Conoco Inc. (Conoco) as the price of gold was on the rise. While extensive development drilling was completed, production never began. E. I. du Pont de Nemours and Company (DuPont) purchased Conoco in 1983 and instructed Conoco to sell all mineral interests. The Getchell mine was subsequently sold via closed bids.

FRM Minerals Inc., a subsidiary of First Mississippi Corporation (First Mississippi), purchased the property from Conoco in 1984 for $5 million. Heap leaching of the dumps and a drilling program to verify gold deposits in the pit walls and below the pit floor began in 1986. A feasibility study (FS) was completed and identified the property’s reserves. In 1987, First Miss Gold Inc. (First Miss), a Nevada corporation and subsidiary of First Mississippi, was created to conduct mineral exploration and related mining activities. In October 1987, development of the Getchell open pit mine and construction of the processing facility began. By February 1989, construction of the new mine and 3,000 short tons per day (stpd) cyanide plus pressure oxidation mill was completed, and production began shortly after.

Exploration drilling centred on the area around the original Getchell Main pit until 1992. In 1993, a multi-phase exploration project was commenced. The purpose of the project was to delineate high grade gold mineralization that had been discovered in the footwall of the Getchell Fault. At the conclusion of the exploration program, an economic evaluation was undertaken to determine the feasibility of an underground mine. Planning and engineering

 

   
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were completed, and initial underground production began in July 1995 from the Getchell Main Underground mine (Getchell Underground).

In June 1993, the Turquoise Ridge Underground deposit was discovered at 1,800 ft (549 m) NE of the Getchell Main pit. A high grade mineralized zone was discovered at a depth of 1,400 ft to 2,000 ft (425 m to 610 m) below the surface. Based on the results of the drilling program, a FS was initiated for a second underground mine at Turquoise Ridge Underground.

In June 1996, First Miss, changed its name from First Miss Gold Inc. to Getchell Gold Corporation (Getchell Gold), also changing its state of incorporation from Nevada to Delaware. In 1996 Getchell Gold began construction of Turquoise Ridge Underground. By mid 1998, a production shaft was completed at a depth of 1,820 ft (555 m) below the surface.

Placer Dome Inc. (Placer) and Getchell Gold announced their intent to merge on December 13, 1998, and on May 27, 1999 the merger was completed. Following an initial evaluation Placer suspended production and milling operations at Turquoise Ridge Underground in July 1999, amid a rapid drop in gold prices, in order to focus on exploration and development. Underground operations at the Getchell Underground continued through to February 2000, when it was determined that additional development was required, and mining was also suspended. Placer’s development efforts focused on continued drilling of the Turquoise Ridge Underground and North Zone deposits. Due to depressed gold prices, the entire property was shut down in February 2002.

In June 2002, Placer staff defined a vision for the property, based on the concept of operating a low-tonnage, high-grade underground mine, in a safe and efficient manner. In August 2002, a start-up study was initiated to develop the defined vision into a mining plan and to assess economic impacts.

As gold prices rose in late 2002, the decision was made to restart Getchell Underground using contract mining, production began in February 2003. On April 15, 2003, Placer announced commencement of construction and the subsequent start-up of Turquoise Ridge Underground. Effective December 23, 2003, Placer and Newmont formed the Turquoise Ridge Joint Venture (TRJV) with Placer owning a 75% interest and Newmont the remaining 25% interest in the Turquoise Ridge property, which included the Turquoise Ridge and Getchell deposits. Under the ore sale agreement, Newmont contributed pre-existing royalties and would purchase up to

 

   
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approximately 2,000 stpd of TRJV ore and process it cost at its nearby Twin Creeks Sage autoclave. In January 2006, Barrick acquired Placer’s 75% interest in the property as part of its acquisition of Placer.

As a result of operational and safety issues, Getchell Underground was placed on care and maintenance in April 2008. Full closure of Getchell Underground occurred in the summer of 2009.

Barrick completed a merger with Randgold Resources on January 1, 2019. Shortly after, in March 2019, Barrick announced intent to enter into a joint venture with Newmont whereby the Nevada assets of both corporations, including Barrick’s Turquoise Ridge and Newmont’s Twin Creeks operations, would be combined in a joint venture, with Barrick serving as the mine operator. On July 1, 2019 Nevada Gold Mines was formed. Barrick is the operator of the joint venture and owns 61.5%, with Newmont owning the remaining 38.5%. Under the joint venture, Barrick’s Turquoise Ridge Mine and Newmont’s Twin Creeks Complex were combined as a single operation, now known as Turquoise Ridge. The combined mining operation is comprised of the Turquoise Ridge Underground, Vista Underground, and Turquoise Ridge Surface (the Mega and Vista open pits).

Since the inception of mining on the Getchell/Turquoise Ridge Underground property to the end of 2019, the project produced approximately 6.8 million ounces of gold (Table 6-1).

 

     6.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

In 1985, Gold Fields Mining Corporation (Gold Fields) discovered the Chimney Creek orebody. Nearby, Santa Fe Pacific Gold Corporation (SFPG) geologists were evaluating railroad grant sections in the Rabbit Creek area. By 1987, a strong trend was identified and drilled between the two deposits. In 1989 initial gold production commenced. Turquoise Ridge Surface (Newmont’s former Twin Creeks property) was created in 1993 by the consolidation of the Rabbit Creek Mine (Rabbit Creek) and the Chimney Creek Mine (Chimney Creek) by SFPG, following the asset exchange of Chimney Creek from Gold Fields. In May 1997 Newmont Gold Company acquired the SFPG properties which remained wholly-owned by Newmont until the formation of Nevada Gold Mines in 2019. The former Rabbit Creek is located in the south end of the property, including what is now known as Mega Pit. The former Chimney Creek included

 

   
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the northern portion of the Mega Pit, and the Vista Pit which is located in the north end of the property near the Sage autoclave and Juniper oxide mill. In April 2019, Newmont and Goldcorp merged, followed by the Nevada Gold Mines joint venture with Barrick in July 2019, as discussed in Section 6.1.

Exploration drilling in the Mega North Pit by Gold Fields dates to 1986. This drilling defined an initial reserve in the Chimney Creek deposit that has since been mined by Gold Fields, SFPG and Newmont. Gold mineralization, primarily refractory, is in the Cambrian-Ordovician sedimentary and intrusive rocks of the Comus Formation, in structural and geologic domains defined by the Conelea Anticline and fault blocks.

Since 2005, Turquoise Ridge Surface long range planning has considered Cut 40 as a potential layback at higher gold prices. Researching engineering files and reports, the layback may have first been included with non-reserve mineralization at the EOY 2009 and included as part of the Mega North Pit area in end of year reporting. The Cut 40 layback was specifically listed as non-reserve mineralization in 2014, with 15 million tons ore at an average gold grade of 0.057 ounces per ton for 845,000 contained ounces of gold.

In February 2015, a proposal for an extensive Cut 40 study was developed, which set up the framework for alternative analysis and options to improve the economics of the deposit. In October 2016, a Turquoise Ridge Surface Growth Team was established to work on Cut 40 and Deposit 55, both areas in the Mega Pit. An approval for expenditure (AFE) for $2.8 million dollars was approved in August 2017 and Cut 40 was placed into Newmont’s Investment System as a Stage 2A project. The Cut 40 Stage 2A Bridge AFE covered metallurgical and geotechnical drilling, environmental humidity cell testing, metallurgical column testing, ore grinding, and salary costs for the Growth Team. The work and information associated with the AFE will be complete by the second quarter of 2019.

An exploration opportunity fund AFE was approved in April 2017, in the amount of $1.1 million dollars. This money was used to drill 46 holes covering over 32,500 ft (9,906 m), to provide drill spacing confidence for reserve declaration. Due to this effort, a Cut 40 ramp retreat design added 149,000 contained ounces of gold to the 2017 reserves. The conversion cost for this drill program was $7.38/oz Au.

 

   
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A second exploration opportunity fund AFE was approved in July 2018, requesting $2.05 million of budgeted drilling funds. The request was to fund the drilling of 36 holes for a total of 11,950 ft (3,642 m) of reverse circulation (RC) and 12,450 ft (3,795 m) of core. The program utilized available drill platforms. The estimated conversion cost for this drill program is $3.00/oz Au.

A surface drilling program targeting the Vista Underground was initiated in 2009 to 2010 to confirm the economics of the project. The intent of the program was to increase the geologic confidence in the mineralization prior to committing the funds necessary to drive an exploration drift.

The success of the surface drilling program led to the development of the North Portal and underground drifting in 2011. The drifting was used to support underground exploration drilling in the northern portion of the orebody. From January 2011 to May 2013 the South Portal and additional underground drifting were developed to support definition drilling. The project was placed on care and maintenance in May of 2013 due to economic constraints. Commercial production began in 2018.

 

     6.3.

PRODUCTION HISTORY

The history of gold production at the Turquoise Ridge Complex (100% basis) is summarized in Table 6-1.

 

   
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Table 6-1 Summary of Gold Production

 

Years  

Turquoise Ridge

Underground

Gold Produced

(oz)

   

Turquoise Ridge

Surface and

Vista Underground

Gold Produced

(oz)

   

Turquoise Ridge

Complex

Gold Produced

(oz)

 

1938-1945

    330,002               0               330,002          

1948-1950

    46,804               0               46,804          

1962-1967

    340,406               0               340,406          

1986-1999

    2,029,103               5,930,417               7,959,520          

2000-2009

    1,364,226               9,238,182               10,602,408          

2010

    160,913               409,172               570,085          

2011

    169,880               407,761               577,641          

2012

    191,322               492,299               683,621          

2013

    186,332               463,688               650,020          

2014

    259,345               365,204               624,549          

2015

    289,421               414,675               704,096          

2016

    327,743               379,526               707,269          

2017

    339,581               332,295               671,876          

2018

    350,085               333,141               683,226          

2019

    370,392               283,039               653,431          

Total

    6,755,555               19,049,399               25,804,954          

 

   
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7. GEOLOGICAL SETTING AND MINERALIZATION

 

     7.1.

REGIONAL GEOLOGY

The Turquoise Ridge Surface, Underground, and Vista Underground are situated within the Basin and Range province, near the northeast end of the Osgood Mountains. The Osgood Range is underlain by Cambrian Osgood Mountain Quartzite, Cambrian Preble Formation, Ordovician “Comus” Formation and the “upper plate” Valmy Formation. These units are unconformably overlain by the Permian Etchart Formation (Antler Peak Equivalent) of the Roberts Mountains overlap assemblage, and by the Triassic Golconda allochthon. These uppermost units form a belt of outcrops flanking the western and northern sides of the Osgood Range. All of these units are intruded by two generations of felsic intrusive rocks – a set of 114 Ma dacite dikes and sills at Turquoise Ridge Underground and Turquoise Ridge Surface and the 92 Ma Osgood Stock and temporally related dikes and sills (Figure 7-1). To date, no Eocene intrusive rocks have been identified at the Getchell, Turquoise Ridge Surface, or Pinson camps.

The Cambrian-Ordovician rocks were deposited on the platform and slope of the western margin of the North American Craton during the breakup of the Rodinia super-continent. The basal Osgood Quartzite and Preble Formation are generally regarded to represent sourcing from a continental land mass and consist of quartz arenite (Osgood), siltstone, and shale with subordinate carbonate lenses (Preble). Carbonates of the Preble were deposited in an open shelf or upper slope marine environment and have undergone minor re-working (winnowed oolitic and algal pellet limestones, fragmented trilobites). Carbonates in the upper part of the Preble formation are time equivalent to rocks described as “Comus Formation” at Pinson and Turquoise Ridge Surface. The Ordovician Comus Formation, as it is described in the deposits of the Getchell Trend represents a significant departure from the continental derived clastic and argillaceous sediments of the Osgood and Preble formations. The Comus Formation in the footwall of the Getchell Fault is characterized as thin- to medium-bedded carbonate turbidites, slumps, and debris flows with interlayered siliciclastic turbidites and argillaceous mudstone. The carbonate beds are interpreted to be derived from a carbonate sea-mount (Cook, internal reports and field notes) somewhere east of the Osgood Range. Algal pellets,

 

   
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fragmented coral, and crinoids have been observed as clasts in the carbonate debris flow conglomerates.

Turquoise Ridge Underground occupies the hanging wall of the Getchell Fault, which is a major, moderately east-dipping range front structure bounding the east side of the Osgood Mountains. At Turquoise Ridge Underground, the hanging wall of the Getchell Fault consists of Ordovician seafloor basalt and mafic sills interlayered with the carbonates and siliciclastic/argillaceous sediments.

The Getchell Fault is one of the most prominent structural features of the region and plays a significant role in controlling mineralization and the distribution of rock types. The Getchell Fault generally strikes north-south to north-northwest, and dips approximately 50° to the northeast in the vicinity of Turquoise Ridge Underground. Geophysical interpretations (mostly gravity and magnetic data), coupled with limited outcrop data, suggest that several footwall splays are present north of the Getchell Underground workings, and that the fault continues to the north along several strands to the northern end of the Osgood Mountains.

The Turquoise Ridge Underground North Zone mineralization largely mimics the orientation of the Getchell Fault, with complications from northeast and north-south structures. The North Zone consists of several discrete bodies which generally strike north-northwest and dip moderately to the northeast.

 

   
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     7.2.

LOCAL AND PROPERTY GEOLOGY

TURQUOISE RIDGE UNDERGROUND

The stratigraphy at Turquoise Ridge Underground consists of carbonaceous mudstones and limestones, tuffaceous mudstones and limestones, polylithic megaclastic debris flows, fine-grained debris flows, and basalts, all part of the Ordovician Comus Formation. This formation is divided into several stratigraphic units in the vicinity of Turquoise Ridge Underground. The sedimentary members are commonly characterized by extensive soft-sediment deformation. The units are described from bottom to top as follows:

Distal Slope Unit: This unit is characterized by planar beds, fairly undisturbed intercalated carbonaceous mudstones and limestones, with occasional graded calcarenite beds characteristic of mid to lower shelf facies. The thickness is estimated at 120 m to more than 240 m.

Proximal Slope Unit: This is a polylithic unit consisting of blocks and lenses of both carbonaceous and tuffaceous mudstones and limestones, characterized by pervasive soft sediment deformation, slumping, and debris flows. Internal contacts between the carbonaceous and tuffaceous rocks are sharp, however, lithologies cannot be correlated laterally with confidence. Carbonaceous rocks, though deformed, appear similar to those of the Distal Slope unit, whereas the tuffaceous rocks are similar those of the overlying the Powder Hill unit. Minor amounts of fragmental rocks are similar to the overlying Black Fragmental unit. Additionally, limestones reminiscent of the overlying Black Powder Hill (BPH) Limestone unit are also present. The black carbonaceous rocks are dominant within this unit except in the south, where grey and brown tuffaceous rocks are more common. The thickness of the Proximal Slope unit varies from 45 m to more than 500 m.

Black Fragmental Unit: This unit is identified by abundant pebble-sized, tabular to subangular, monolithologic micrite clasts in a carbonaceous mudstone matrix. It can also contain lenses of Proximal Slope rocks and BPH Limestones. The upper and lower contacts that bound this unit are based on the predominance of fragmental rock within the section rather than precise lithologic breaks. The thickness ranges up to approximately 90 m.

BPH Limestones: This limestone consists of thinly bedded to laminated, intercalated mudstones and micritic limestones with subordinate amounts of tuffaceous mudstone, and

 

   
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local black fragmental rocks. Soft-sediment deformation is pervasive. The thickness ranges up to approximately 100 m.

Powder Hill Unit: This unit is composed of a mix of grey to brown mudstones, intercalated mudstones and limestones, and fragmental rocks. The fragmental rocks have a tuffaceous mud matrix supporting micritic limestone clasts. Soft-sediment deformation is pervasive. Clasts within fragmental portions of this unit exhibit soft-sediment deformation; they do not appear to have been brittle at the time of deformation. The upper contact is bounded by basalts. The thickness of the Powder Hill unit is estimated at up to 105 m.

Basalt Unit: The upper Basalt unit consists of massive basalt with minor intercalated sedimentary layers, with a total thickness of up to 180 m.

Cretaceous Granodiorite Dikes: Fine-grained to porphyritic leucocratic granodiorite dikes crosscut all units. The largest and most continuous dike is subparallel to the Getchell Fault. The thickness of the dikes ranges up to 15 m.

These units are overlain by more basalts, mudstones, and cherts that may be part of the Ordovician-aged Valmy formation or a continuation of the Comus Formation. The thickness of this package ranges from approximately 365 m to 460 m.

Stratigraphy varies significantly from south to north. In the south, the Powder Hill unit directly overlies Proximal Slope rocks and is overlain by thin, discontinuous basalts that are part of the uppermost sequence of Comus rocks. Further north, Black Fragmental rocks appear between the Powder Hill unit and the Proximal Slope rocks. Yet further north, the BPH Limestones appear above the Black Fragmental unit and are bounded above by the Powder Hill unit.

Farthest north, the basalt, occurring above the base of the Powder Hill unit, thickens and crosscuts stratigraphy, in places down to the top contact of the Black Fragmental unit. Stratigraphy at Turquoise Ridge Underground is interpreted as having been formed in a passive continental mid-shelf setting with a carbonate source likely to the southeast. North-dipping monoclinal folding at the north end of Turquoise Ridge Underground may be related to deep-seated normal faulting associated with basin margin rifting. The monocline affects all the units except the basalt and the overlying Comus strata. Development of this monocline possibly caused the formation of the Black Fragmental unit as a basal breccia derived from

 

   
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sliding of an overlying block of carbonaceous limestones, the remains of which form the BPH Limestone unit. Thick basalts in the north appear to occupy a post-monoclinal submarine canyon that cut through existing stratigraphy prior to basaltic volcanism.

The local geology is illustrated in Figure 7-2 and the generalized mine stratigraphy is illustrated in Figure 7-3.

 

   
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TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

Turquoise Ridge Surface lies in an alluviated valley southeast of the Dry Hills, a northeastern outlier of the Osgood Range in northern Humboldt County, Nevada. The Dry Hills is an area of gently north-dipping Upper Paleozoic carbonate sediments, stratigraphically higher than rocks in the rest of the Osgood Range, which consists mainly of Lower Paleozoic elastic sediments intruded by a large Cretaceous pluton, which forms the backbone of the Osgood Range.

Silty limestone, dolomitic siltstone, and minor tuff of the latest Cambrian-earliest Ordovician Comus Formation rest unconformably on the Preble Formation. The Comus Formation has a thickness of 460 m to 550 m and is subdivided into four informal units with gradational contacts. The lowermost Comus unit, C4, contains black, thin-bedded silty limestone and laminated silty mudstone with lesser but prominent light gray calcareous quartz sandstone interbeds and medium beds of light gray micritic limestone. Two widespread sills are recognized in C4, a coarse-grained ultramafic body up to 36 m thick consisting mainly of olivine and pyroxene with lesser amounts of phlogopite and magnetite known as the Ear peridotite, and very fine-grained, non-porphyritic basalt called the HGO sill.

Overlying C4, the C3 unit is characterized by black, thin to locally thick bedded, silty limestone, micrite, calcarenite, calcareous siltstone, and fine to coarse lapilli tuff and debris flows. One coarse lapilli tuff debris flow in C3, the Upper Tuff, is found throughout the Mega Pit and is the most important marker horizon. In addition, numerous basaltic sills intrude C3, including four that are mineralogically distinct. These intrusions include from lowest to highest stratigraphic position: a plagioclase-phyric basalt containing abundant amygdules, Main Sill, a thick sill containing fine-grained pyroxene, the Upper Sill, a very fine grained, sparsely porphyritic basaltic sill containing conspicuous euhedral plagioclase, the Upper Porphyry, and an uppermost pyroxene-bearing basalt, F2 Sill. The C3 unit is the best gold host in the Comus, in part because of its greater thickness, an abundance of relatively reactive thin-bedded silty limestone, and the presence of abundant sills, which undoubtedly localized flow of gold-bearing hydrothermal fluids. Figure 7-4 is a cross section looking north through Cut 40 at the Mega Pit depicting 3D modelled geologic formations and structures. The Main and Upper Sills were modelled to emphasize the shape of the east-verging, overturned Conelea Anticline (fold hinge dashed). In most instances these mafic sills are not continuous yet have been stretched into a series of lenticular boudins.

 

   
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The contact between the C3 and C2 units marks the transition from dominantly thin to lesser medium-bedded lower carbonate-rich rocks to the more siliciclastic and tuff-rich rocks higher in the Comus. The contact is also marked by the occurrence of a fine-grained lapilli tuff about 4.5 m thick. The C2 unit consists of planar laminated, dolomitic siltstone, mudstone, and tuffaceous sandstone, with lesser amounts of thin-bedded silty limestone. Tuffaceous interbedded rocks are light gray in contrast to the dark gray to black carbonaceous siltstone and mudstone interbeds.

C2 contains several basaltic sills, which are difficult to correlate because all but one are fine grained and non-porphyritic. The distinct sill in C2, the plagioclase-pyroxene porphyry, is a coarsely and abundantly (15%) porphyritic basalt with euhedral plagioclase and pyroxene phenocrysts, commonly found near the base of the C2 unit.

The uppermost unit, C1, contains abundant tuff, including two thick, coarse lapilli tuffs, each of which grades upward into a sequence of thin-bedded and laminated, fine-grained lapilli tuff. Interbedded with tuff are laminated dolomitic siltstone, silty limestone, and mudstone. A medium-grained intrusion, the Sage basalt, containing abundant glomeroporphyritic plagioclase in addition to groundmass phlogopite, is present at or near the base of C1.

The mafic and ultramafic sills and flows that comprise a large part of the Comus Formation at Turquoise Ridge Surface are alkalic and contain visible groundmass phlogopite in coarser grained units and elevated concentrations of K, Ti, and rare-earth elements. These alkalic rocks are similar to ocean island basalts (OIB) or intraplate basalts and differ greatly from the depleted character of more common mid-ocean ridge basalt (MORB).

 

   
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Cut 40 represents a high grade refractory ore deposit located along the northern perimeter of the Mega Pit. This phase of mining would deepen Cut 24 and extend mining several hundred metres around the current pit limit. General geology of Cut 40 looking north is shown in Figure 7-5.

 

Figure 7-5 General Geology of Cut 40 North Dig Face with Mine Design

The summary that follows draws heavily from the work of Breit et al (2005) and the references therein with additions from more recent mapping and modeling (Figure 7-6).

Cut 40 mineralization is hosted in complexly deformed Comus Formation carbonate and tuffaceous sediments, and locally mafic units, with some leach grade occurrences in the overlying Valmy Formation. The higher grade mineralization is hosted in the upper portion of the Comus package, mostly unit Oc3 and above.

 

   
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The overlying Ordovician Valmy Formation is separated from the Comus by the Roberts Mountains Thrust fault. The Valmy Formation is approximately 1,000 m thick and composed predominantly of pillow basalt, massive flow basalt, hyaloclastites, siliceous mudstones, and debris flow breccias. At Turquoise Ridge Surface, the Valmy Formation has been divided into two units: the Lower and the Upper. The Vista Pit and Vista Underground are hosted in the upper unit of the Valmy Formation. Gold mineralization in these basalts tends to be concentrated in veins that form a sooty-sulphide stockwork system. The basalts of the Valmy likely formed along a volcanic rift that cut across a passive abyssal plain, thus explaining the presence of minor interbedded abyssal sediments.

The Battle Formation consists of gray, quartzite cobble conglomerate, with a gray sandy matrix, derived from the Osgood Mountains formation and is up to 9 m thick. It locally unconformably overlies the Comus in the Mega Pit area and was mineralized to a similar extent as the underlying Comus rocks. The presence of Battle Formation rocks lying unconformably on the Comus indicates that an erosional window had formed through the Valmy Formation, suggesting pre-late Paleozoic uplift and/or arching.

The rocks of the Pennsylvanian-Permian Etchart Formation unconformably overlie the Valmy Formation in most of the district. The Etchart Formation, from 930 m to 1,100 m thick, is divided into three subunits that consist of: 1) a lowermost calcareous sandstone to sandy limestone, with local quartzite pebble conglomerate at the base; 2) middle peloidal limestone, cross-bedded calcareous quartz-arenite, and quartzite/chert pebble conglomerate; and 3) upper calcareous siltstone and silty limestone. These rock types suggest deposition by settling, grain flow, and debris flow in a high-energy shelf and slope environment, subunits 1 and 2, within a deeping marine basin, subunit 3. Rocks of the lower Etchart were by far the major host for gold mineralization in the Vista deposit.

The Mississippian-Permian Havallah Sequence was emplaced above the Pennsylvanian-Permian Etchart Formation along the Golconda thrust, which is exposed in the hanging wall of the 20K fault in the northeast portion of the Vista Pit and just north of the pit in the Dry Hills. In the Vista Pit, the Havallah Formation is generally thin-bedded, light brown calcareous sandstone and lesser interbedded gray, thin-bedded chert. The Havallah elsewhere consists of mudstone, siltstone, calcareous sandstone, limestone, chert, and altered basalt.

 

   
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Several Cretaceous-aged dikes and sills, approximately 114Ma, play a significant role as secondary controls on gold mineralization in both the Vista Pit and in the Vista Underground. The porphyritic dacite dikes are characterized by pervasive phyllic alteration and locally are mineralized.

 

     7.3.

ALTERATION

TURQUOISE RIDGE UNDERGROUND

Thermal metamorphism associated with intrusion of the Cretaceous Osgood Stock at 92 Ma is present in the Turquoise Ridge Underground area and is characterized by ubiquitous development of biotite hornfels within the tuffaceous mudstones throughout Turquoise Ridge Underground, and formation of calc-silicate alteration within carbonates only in the southern areas where they are close to the Osgood Stock. Thermal metamorphism associated with basalts has not been recognized. Hydrothermal alteration consists of locally extensive, complete decalcification and argillization of all rock types, spotty silicification, and the addition of gold-bearing fine-grained iron sulphides, the main mineralization of the deposit and late arsenic sulphides. Hydrothermal alteration boundaries can be extremely sharp even where susceptible rocks are in direct, nonfault contact with altered rocks. To the east, mineralization is spatially related to north-south and northeast faults. All structures are considered potential conduits for gold mineralization. Calcareous rocks are the most important hosts for mineralization occurring as disseminated replacement ore bodies in the Comus and Etchart Formations. Valmy Formation basalts and related sediments host structurally controlled mineralization, such as the Vista shear zone.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

As in other Carlin-type deposits, alteration is manifested mainly through decalcification of carbonate-bearing sedimentary rocks, with lesser silicification and dolomitization. Less altered Paleozoic igneous rocks are propylitized, whereas overprinting clay alteration accompanies gold-related mineralization. Cretaceous sills and dikes are altered to quartz-sericite-(illite)-pyrite.

 

   
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     7.4.

STRUCTURE

TURQUOISE RIDGE UNDERGROUND

In the mine, no major faults appear to offset either stratigraphy or the Cretaceous dikes. Faults with presumably small offsets are commonly observed underground. Some of these are probably accommodation faults associated with compaction of ore zones due to volume loss from decalcification. GoCAD modeling of RQD values indicate the presence of a northeast trending fracture zone intersecting the northern part of Turquoise Ridge Underground. Additional GoCAD modeling of 0.3 g/t and 1.7 g/t mineralization is suggestive of subtle Getchell fault parallel structures, in the form of sympathetic, north-trending, east dipping fracture zones.

Synformal and antiformal geometries within the stratigraphy are indicative of modest east to west compression; probably prior to intrusion of the undeformed Cretaceous dikes. Disharmonic soft-sediment slump folding is common and is especially well developed in the BPH limestones and the limestones and mudstones of the Powder Hill unit.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

Mineralization at the Mega and Vista Pits are spatially related to north-south and northeast faults, their intersections and fault intersections with folded stratigraphy. All structures are considered potential conduits for gold mineralization. Fold hinges whether open or overturned (Conelea Anticline) are particularly favorable sites in the Mega North Pit. Calcareous rocks are the most important hosts for mineralization occurring as disseminated replacement ore bodies in the Comus and Etchart Formations. Vista Formation basalts and related sediments host structurally controlled mineralization.

ROBERTS MOUNTAINS THRUST:

A broad zone of low-angle, west-dipping and northerly striking faults characterize a major Paleozoic thrust in the northern part of the Mega Pit. This fault contact between the Valmy and Comus Formations is correlated with the Roberts Mountains thrust shown in Figure 7-6. Intense shearing with attendant compressional features adjacent to the fault contact affects at least 18 m of the Comus Formation in the Mega North Pit.

CONELEA ANTICLINE:

The principal structural element in the Mega North Pit is the Conelea Anticline, which runs the length of the pit in a north-northwest orientation and is the most important ore-controlling

 

   
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structure in the Comus Formation. The fold probably developed during the Antler Orogeny when rocks of the Valmy Formation were placed above Comus rocks along the Roberts Mountains thrust. The Conelea Anticline does not affect rocks of the overlying Valmy and Etchart Formations. The geometry of the anticline is complex and has been somewhat obscured by cross cutting faults, but generally it is asymmetrical, east verging and doubly plunging. The western limb dips shallowly (30º) to the west and northwest while the eastern limb is overturned and dips steeply (70º to 80º) to the west. The fold hinge opens up where it projects into the Mega North Pit highwall.

NORTHEAST FAULTS:

In the Mega North Pit northeast-striking, mostly northwest-dipping high angle faults with apparent dextral, down-to-the-north displacement cut the Conelea Anticline. These faults include the TC and DZ, shown in Figure 7-7. Observed dextral offset across northeast faults in the Mega Pit is as much as 396 m. Northeast faults in the Comus Formation may have developed as either tear faults contemporaneous with folding, which accommodated differential amounts of folding, or as transverse joints that were later reactivated. These faults can reach 10 m in thickness with local intense shearing and brecciation, as observed in the Mega Pit TC fault and the Trench fault at Vista Underground.

 

   
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NORTH-STRIKING FAULTS:

North-striking, moderate to steeply dipping faults are recognized to be both pre- and post-mineral, and some appear to have a long lived history of continuous movement, particularly the CP fault (Figure 7-8). The distribution of these faults suggests a possible right stepping nature.

 

Figure 7-8 Relay Ramp Fault Interpretation of North-Striking Faults at Turquoise Ridge Surface

The north-striking faults truncate and offset the northeast faults. They also cut Quaternary age alluvium. In Figure 7-9, the CP fault does not offset upper 15 m of alluvium. There is approximately 18 m of vertical displacement at the Valmy (Ov), alluvium (Qal) contact. The bench height is 12 m.

 

   
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Figure 7-9 CP Fault in the Mega Pit Cut 23 South Highwall

In the Vista Pit, north-south and northeast-striking faults cut through mostly Valmy and Etchart formations. The northwest striking, northeast dipping 20K fault truncates the Trench fault. The Trench fault is in fact a shear zone approximately 2 m to 3 m thick.

 

   
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     7.5.

MINERALIZATION

TURQUOISE RIDGE UNDERGROUND

Mineralization of the Turquoise Ridge Underground deposit generally consists of disseminated, micron-sized gold occurring in arsenic-rich rims forming on pyrite, chiefly within decalcified, carbonaceous rocks. All gold bearing zones at Turquoise Ridge Underground are located in proximity to granodiorite dykes that splay from the Osgood stock. Mining and exploration activities at Turquoise Ridge Underground are centered on limestone and mudstone horizons adjacent to these dykes.

The mineralization at Turquoise Ridge Underground is located in two main zones, North and South. In the North Zone, the strongest mineralization appears to be associated with BPH Limestone, Black Fragmental rocks, and carbonaceous rocks within the Proximal Slope unit. Stratigraphic contacts between these units and contacts with the Cretaceous dikes are important primary controls on mineralization. Powder Hill rocks, Distal Slope rocks, basalts, and dikes are insignificant hosts for mineralization in the north.

The North Zone of Turquoise Ridge Underground extends over an area of 800 m x 800 m and at present consists of over
33 mineralized domains. The domains are divided into the following groups based on mode/control of mineralization:

 

   

Stratigraphic/stratabound

 

   

Cross-stratigraphic, structurally controlled

 

   

East-west structural

 

   

Other

North Zone stratigraphic mineralized domains exhibit strike lengths in excess of 305 m with typical strike dimensions in the
61 m to 152 m range. Down dip lengths of over 305 m are common. Being stratigraphically controlled, the mineralized domains and bedding have a general north-northwest trending strike, of approximately 330° to 340°, and dip shallowly to the east (between 25° and 45°). Mineralization is typically in the order of six metres to nine metres thick, but in some instances, may pinch down to less than three metres or swell out to 30 m in thickness.

North Zone cross-stratigraphic domains have been modelled at near perpendicular angles to the bedded domains. This mineralization cuts across bedding and is grouped as structural, as

 

   
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mineralization may be driven by low angle shearing, faulting, or joint sets. General trends of these domains are a north-northwest strike (340° to 360°) and a west dip of 10° to 20°. Widths of these domains may be in excess of 30 m.

Most of the North Zone domains are grouped as east-west stratigraphic and are economically important or currently being mined. Two of the domains are large, steeply dipping, and sheet-like with strike lengths in the order of 152 m and 305 m. Dip dimensions are approximately 48 m and 110 m, respectively. Thickness is variable but averages six metres to 12 m.

The remaining five domains in the “Other” category are irregular sheet-like bodies with various orientations. Dimensions range from 152 m to 198 m in strike length, 100 m to 122 m in dip length, and thicknesses from three metres to over 30 m.

Mineralization in the South Zone is largely restricted to the Powder Hill unit, with only minor amounts present in the upper parts of the Proximal Slope unit. Fragmental rocks of the Powder Hill unit are the most important host for mineralization, followed by tuffaceous intercalated limestones and mudstones, then by carbonaceous intercalated mudstones and limestones of the Proximal Slope unit. Mineralizing fluids appear to have interacted with favourable host rocks via discrete fault and fracture zones, although specific pathways are usually not readily identifiable.

The South Zone extends over an area of 610 m by 305 m and at present consists of over 15 mineralized domains. The domains are divided into the following groups based on mode/control of mineralization:

 

   

Cross-stratigraphic, structurally controlled

 

   

Steeply-dipping Strataform

 

   

Moderately-dipping Strataform

The six cross-stratigraphic bodies strike north and are generally steeply dipping to the west or nearly vertical. Strike lengths vary from 30 m to 198 m with an average length of 122 m. Dip lengths vary from 61 m to 152 m with an average dip length of 99 m. Thicknesses average 20 m.

The South Zone Strataform domains tend to strike north and dip to the east at approximately 30° to 60°. This orientation is significantly different from the North Zone. The two zones are

 

   
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separated by the northeast trending Turquoise Ridge shear zone, which could have contributed to the difference in alignment of the two zones. The three steeper dipping bodies (-58°E to -80°E) have an average strike length of 70 m , average dip length of 49 m and average thickness of 12 m. The six moderately dipping (-30°E to -50°E) range from 90 m to 520 m. The average dip length is approximately 260 m and thicknesses average 30 m.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

Gold occurs in arsenic-rich rims or bands on pyrite grains associated with orpiment, realgar, stibnite, cinnabar and quartz. Adularia intergrown with gold-bearing arsenian pyrite in Comus mafic sills yields 40Ar/39Ar ages of 41.90 Ma ± 0.25 Ma and 42.11 Ma ± 0.43 Ma (Groff et al., 1997), and 41.37 Ma ± 0.23 Ma and 42.13 Ma ± 0.12 Ma (Hall et al., 2000). Four discrete pulses of alteration and related mineralization are recognized at Turquoise Ridge Surface.

Higher gold grades in the Mega North Pit occur in Comus carbonate sediments at the transition from Oc3 to Oc2 above the Upper Sill (Figure 7-10). Carbonate dominant stratigraphy transitions upward into a more tuffaceous and siliclastic sequence.

Mineralization is localized in decalcified carbonates but can occur less frequently in argillized and sulphidized basalt. Silicification is common in Comus sediments immediately adjacent to basaltic contacts with generally lower gold grades.

 

   
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A more recent Cut 40 drill hole TWD-02489 (Figure 7-11 and Figure 7-12) exhibits two styles of Comus Formation mineralization:

 

   

Gold in variably altered silty micrite, this is the most common occurrence.

 

   

Gold in argillized and sulphidized basalt appears to be related to faulted and fractured intervals. Lower grade in silicified micrite can be observed at the contact with basalt.

North and northeast striking faults with larger cumulative slip, such as the CP, TC, and DZ may have acted as feeders for mineralization, however, gold mineralization tends to be discontinuous and of lower grade along them, possibly as a result of post-mineral movement. Visible gold, however, was noted in oxidized quartz breccia material from the DZ fault zone.

North striking faults have focused gold with higher grades in and near the faults even where less favourable host rocks are present. Mega Pit Cut 23, which straddles the CP fault, is a good example.

 

Figure 7-11 Cut 40 Drill Hole TWD-02489 Core

 

   
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Figure 7-12 Cut 40 Drill Hole TWD-02489 Core with Lower Grade at Basalt and Micrite Contact

In the Vista Pit, stratabound high grade oxide ore occurs primarily within pervasively decalcified sandy carbonate rocks of the lowermost Etchart near the unconformity between the Etchart and the Valmy formations. The unconformity is disrupted by northeast striking faults, forming a horst block in the central part of the Vista Pit. These and other structures contain high grade gold in narrow zones in the Valmy formation and likely serve as feeders to the much larger stratabound orebody in the basal Etchart.

At Vista Underground, mineralization is largely confined to the Trench Fault shear zone. It has a mineable strike length of approximately 1,400 m and a dip length of 300 m. The ore consists of disseminated gold in arsenian pyrite and marcasite. The structure itself is a brecciated quartz-base vein, historically known as the Galena Vein. The mineralogy of the vein consists of milky vein quartz, fractured pyrite, massive fractured sphalerite with chalcopyrite, subhedral-euhedral pyrite, massive fracture galena, tennantite-tetrahedrite, microcrystalline quartz, sericite, and specular hematite. There is no recognized ore horizon within the deposit. The only constraint on the extent of gold mineralization is the surface and the 20K fault that truncates the Trench fault to the northeast.

 

   
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In the opinion of the QP:

 

   

The understanding of the deposit settings, lithologies, and geologic, structural, and alteration controls on mineralization is sufficient to support estimation of Mineral Resources and Mineral Reserves.

 

   

The mineralization styles and settings are well understood and can support declaration of Mineral Resources and Mineral Reserves.

 

   

The geological knowledge of the area is adequate to reliably inform mine planning.

 

   
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8. DEPOSIT TYPES

The Turquoise Ridge Underground deposit is a typical Carlin-type deposit and is characterized by structurally and stratigraphically controlled, sediment-hosted, replacement deposits containing micron-sized gold.

Along with the Turquoise Ridge Underground deposit, the Preble, Pinson, Getchell, and Turquoise Ridge Surface deposits collectively define the Getchell gold belt, which could be described as the northern extent of the Battle Mountain – Eureka gold belt as currently defined. It is recognized that both the Carlin and Battle Mountain – Eureka gold belts are alignments of sediment hosted gold deposits within structural windows, where autochthonous, lower-plate rocks of the Roberts Mountains thrust are exposed through allochthonous, upper-plate rocks. The origin of these structural openings is thought to be the product of multiple deformation events beginning with middle-late Devonian Antler Orogeny and continuing through at least Cretaceous time.

The Vista Underground is a high-grade refractory gold deposit located in the bottom of the Vista Phase 6 Pit. Mineralization occurs along the steeply dipping trench fault also known as the Vista Shear.

 

   
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9. EXPLORATION

 

  9.1.

TURQUOISE RIDGE UNDERGROUND

The Turquoise Ridge Underground deposit was discovered at a depth of 425 m to 610 m below the surface by a deep drilling program. While surface exploration has been completed on the property in the past, very little was directed at the Turquoise Ridge deposit, which was developed via drilling, deep penetration geophysical surveys, and structural mapping to extend the known dimensions of the mineralized zones.

Nevada Gold Mines has an extensive database of historic soil, rock chip geochemical sampling, and geophysical surveys (gravity, airborne electromagnetic, magnetic, controlled source audio magnetotellurics (CSAMT), magnetotellurics (MT), and seismic). Gold mineralization is not directly detectable by geophysical methods, however, surveys map subsurface properties that are useful in interpreting lithology, alteration, and structure as guides to gold mineralization.

Definition of sampling procedures, potential biases in sampling, information already collected and significant results and interpretations are located in Section 11.

EXPLORATION POTENTIAL

Nevada Gold Mines maintains an aggressive exploration program principally comprising diamond drilling. A brief description of the main targets follows (and shown in Figure 9-1).

 

   

BPE Extensions – Apparently continuous mineralization at the base of the North Pillow Basalt along both low-angle (separate-type) and high-angle (northeast striking, northwest dipping) faults.

 

   

Turquoise Ridge Corridor Mineralization – Apparently continuous mineralization along the known high grade Turquoise Ridge Corridor faults.

 

   

Getchell Fault – Possibly continuous mineralization along the Getchell Fault and associated intersecting structures (BBT, Turquoise Ridge Corridor).

 

   

Summer Camp – Poorly drilled mineralization south of Turquoise Ridge Underground in a former open pit. Possible analog to Getchell/Turquoise Ridge deposit, but at a smaller scale.

 

   

South Zone – Lower-grade mineralization concentrated on mostly BBT-type structures in the Second Shaft area.

 

   

Nevada Gold Mines is also pursuing the growth potential both near current operations and between the Turquoise Ridge Complex’s component properties.

 

   
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  9.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

In 1984, Gold Fields discovered Carlin-type mineralization in Etchart Formation limestone in the hanging wall of the Discovery fault that later became the Vista Pit. Stripping of the initial Vista Pit began in April 1987 and first gold was poured in November 1987. Continued exploration to the south in Section 18 by Gold Fields led to the discovery of mineralization in the Mega North Pit area. This blind discovery was attributed to a sagebrush biogeochemical anomaly (A. Leger, 2016).

While Gold Fields was developing the Section 18 Chimney Creek deposit, SFPG was mining the adjacent Section 19 Rabbit Creek deposit. SFPG consolidated the property in 1993 with Newmont acquiring SFPG in 1997.

Exploration drilling in the area spans over 32 years. Drilling methods included mud rotary, RC, and diamond core. Initial drilling by Gold Fields was a combination of shallow core and RC holes to define an oxide resource. Deeper drilling by each method followed to evaluate the refractory potential.

Definition of sampling procedures, potential biases in sampling, information already collected and significant results and interpretations are located in Section 11.

EXPLORATION POTENTIAL

Near mine exploration programs are principally completed with RC pre-collars and diamond core tails. Current targets include (Figure 9-1):

 

   

Cut 55 – Scattered, potentially continuous mineralization beneath the Mega Pit.

 

   

Vista Underground – Possible extension of mineralization along the Trench Fault, southwest of existing infrastructure, down-dip extents of mineralization on the Trench Fault below the water table.

 

   

Cut 40 – Continuous mineralization below the current Mega Pit.

 

   

Nevada Gold Mines is also pursuing the growth potential both near current operations and between the Turquoise Ridge Complex’s component properties.

 

   
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10.

DRILLING

Nevada Gold Mines maintains an aggressive exploration program principally comprising diamond drilling. Exploration is being carried out over several underground exploration targets at Turquoise Ridge Underground, including the Turquoise Ridge Corridor Fault Zone, Upper Footwall Pond, the down-dip and northeast extension of the Footwall Pond, the North Zone and South Zone Getchell Extensions, and the Powder Hill Extension. Near mining exploration targets are also being tested in 2020 on the southern extension of the Vista Underground. Turquoise Ridge Surface has a number of extension targets and will be reviewed for future step out drilling. Additionally, the Turquoise Ridge Complex has an exploration team on site and budget to start drilling between the Turquoise Ridge Underground and the Mega Pit, Vista Pit and Vista Underground mining areas.

 

  10.1.

TURQUOISE RIDGE UNDERGROUND

Gold exploration activities began in the 1930s by two local Winnemucca prospectors, who first discovered Getchell. Getchell was operated intermittently between 1938 and 1984, when FRM and First Mississippi purchased the property. Exploration drilling in 1992 and 1993, was centered on the area around the original Getchell Main pit to delineate high-grade gold mineralization that had been discovered in the footwall of the Getchell Fault. Deep drilling began in 1993 in the Turquoise Ridge Underground area. A high-grade mineralized zone was discovered at a depth of 420 m to 600 m below the surface.

Since acquisition of Turquoise Ridge Underground in 2006, Barrick has completed over 6,100 drill holes. The drilling programs from 2010 to 2019 were largely comprised of definition drilling to upgrade Mineral Resources adjacent to and within gaps into the Proven and Probable Mineral Reserve mining shapes.

Table 10-1 lists all the drilling completed at Turquoise Ridge Underground since 1992. Since 2009, Barrick has completed over 5,900 drill holes for a total of approximately 427 km.

 

   
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Table 10-1 Summary of Turquoise Ridge Underground Drilling

 

        Year            Number of Holes
1992-2008    913
2009    1,872
2010    336
2011    241
2012    432
2013    648
2014    864
2015    262
2016    294
2017    280
2018    267
2019    422
Total    6,831

The cut-off date for the drill data for the end of year (EOY) 2019 Mineral Resource and Mineral Reserve model was June 11, 2019. All 2019 drilling to June 11, 2019 was completed in the Turquoise Ridge Underground area.

The database for the geologic and Mineral Resource models resides in Elko, Nevada, and is maintained and administered by Barrick Exploration. Paper copies of the assay certificates are maintained on site at the Turquoise Ridge Complex.

The drilling programs from 2010 to 2019 consisted predominantly of definition drilling to upgrade Mineral Resources and Mineral Reserves adjacent to and within gaps in the Proven and Probable Mineral Reserve shapes. In addition to definition drilling there were approximately 30,480 m in 174 step out and advanced exploration holes.

LOGGING PROCEDURES

Logging is conducted by Nevada Gold Mines geology staff and contract geologists. Geological information is entered directly into the acQuire database by the geologists for production holes. On advanced exploration and step-out holes more detailed logs are collected on paper and then transferred to acQuire. Paper logs are digitized and archived.

CORE SAMPLING

Nevada Gold Mines follows conventional, industry standard practices for geologic and engineering data acquisition and sampling. Drill core is logged manually for geotechnical data

 

   
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and geology and photographed in a modern facility. Drill holes are logged by the Nevada Gold Mines geologist or contract logging geologist who describes the downhole lithology, structure, alteration, and mineralization. The entire length of the core is sampled. Core samples are nominally 1.5 m but can vary to a minimum of 0.3 m to respect lithological contacts, at the discretion of the geologist. All mineralized intervals selected for split core assaying are bracketed on either end with a minimum of 4.6 m of visibly unaltered core.

REVERSE CIRCULATION SAMPLING

RC drill holes are sampled on 1.5 m intervals, designated by measured intervals on the drill’s pull down apparatus (cables, chains). Drill cuttings are initially collected in a standard cyclone to reduce the sample’s velocity to a safe speed and dropped through a splitter. The splitter is actively managed to produce a sample of approximately five kilograms, but sample mass can vary from five kilograms to 15 kg. Standards, blanks, and duplicate samples are inserted/collected at the same prescribed rate as for diamond drill holes.

PRODUCTION SAMPLING

Production sampling underground consists of five kilogram samples of drill cuttings collected by the drill operators after drilling of the round, at a rate of three to five samples per round. The objective is to standardize sampling at one per 32 tonnes. Due to low Rock Mass Rating (RMR) in ore, drilling results in well fragmented muck and samples are 95% sand size.

Waste material is sampled before skipping to surface to confirm material routing. Waste round samples grading above 3.4 g/t Au are re-routed as ore.

 

  10.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

In 1984, Gold Fields discovered Carlin-type mineralization in Etchart Formation limestone in the hanging wall of the Discovery fault that later became the Vista Pit. Stripping of the initial Vista Pit began in April 1987 and first gold was poured in November 1987. Continued exploration to the south by Gold Fields led to the discovery of mineralization in the Mega North Pit area

 

   
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Exploration drilling in the area spans over 32 years. Drilling methods included mud rotary, RC, and diamond core. Initial drilling by Gold Fields was a combination of shallow core and RC holes to define an oxide resource. Deeper drilling by each method followed to evaluate the refractory potential

Near-mine exploration and growth drilling has been ongoing since 1998, almost continuously since 2008. Grade control and infill drilling was restarted in that year as well. The Turquoise Ridge Complex utilizes third-party drilling contractors to conduct drilling operations for both grade-control and step-out exploration programs.

Table 10-2 lists all the drilling completed at Turquoise Ridge Surface and Vista Underground since 2016.

Table 10-2 Summary of Turquoise Ridge Surface and Vista Underground Drilling

 

Year        Number of Holes   

Total Drilling

(m)

2016    105    22,085
2017    15    2,370
2018    38    12,289
2019    48    10,945
Total    206    47,689

LOGGING PROCEDURES

Turquoise Ridge Surface geologists used a digital logging program developed by Newmont called Visual Logger. This program captures both geologic and geotechnical data via a computer based program that is then easily downloaded to Nevada Gold Mines’ exploration database, GED. Historic logging information was collected on paper templates and manually loaded to earlier databases. Since the consolidation of operations into the Turquoise Ridge Complex, all logging is completed directly in Acquire.

CORE SAMPLING

Samples from diamond core drilling are taken from the core tube and placed into coated cardboard boxes containing a nominal capacity of 3.05 m. Intact core may be broken to make it fit into the box slots. Drilling fluids used during coring include water based ‘mud’ systems, typically with bentonite (clay) and inorganic polymer added. The core boxes are stacked sequentially onto pallets and transported to the Turquoise Ridge Surface core shed daily. Diamond cores are logged by Nevada Gold Mines geologists after completion of the drilling. Sample intervals are recorded and provided to Nevada Gold Mines geotechnicians who

 

   
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photograph and then sample the core. Core may be cut by a water cooled diamond saw into 12 or 14 segments depending on resource category, geologic constraints or for metallurgical testing. The samples are placed in bar-coded fabric bags, loaded in metal bins, and stored at the core shed until the core shed staff oversees loading of the bins onto a transport truck provided by the commercial lab. As with the RC drill holes a paper copy sample log with hole number, length, and sample numbers is checked by geologists and technicians for consistency. Technicians then enter the information into the computer system.

RC SAMPLING

RC samples are collected at 1.5 m intervals. The drill discharge is routed through a rotary splitter at a rate and volume capacity to maintain a sample weight between two kilograms and 10 kg. Representative chip samples for each interval are collected from the waste discharge tube of the splitter and placed in a plastic tray with each compartment representing 1.5 m each, or 30 m total for an entire chip tray. RC samples are collected at the drill rig in fabric bags and closed by a zip-tie. Bags are labeled with hole-ID and footage. Nevada Gold Mines supplied bar codes are affixed to each sample. Samples are placed in metal sample bins, which are taken to the core shed when the hole is complete. Nevada Gold Mines geotechnicians complete the sample submittals and oversee the loading of the bins onto transport trucks provided by the commercial laboratory.

 

  10.3.

TURQUOISE RIDGE COMPLEX COMBINED CORE RECOVERY

Table 10-3 displays core recovery by location for the Turquoise Ridge Complex.

Table 10-3 Summary of Turquoise Ridge Complex Core Recovery Summary

 

Location   

Number of  

Core Holes  

 

   Drilled Length   

  Length-Weighted  

  Average Recovery  

(%)

  

 

(ft)

 

  

 

(m)

 

Turquoise Ridge Surface

Mega Pit

   4,339    3,207,945     977,782     95

Vista Pit

   3,243    1,500,515     457,357     85
Underground Areas

Turquoise Ridge Underground

   3,966    3,008,691     917,049     95

Vista Underground

   605    377,369     115,022     92

 

   
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In the opinion of the QP:

 

   

Drilling and logging are adequate to the understanding and definition of the ore bodies and supports declarations of Mineral Resource and Mineral Reserves at the Turquoise Ridge Complex.

 

  10.4.

DRILLING USED TO SUPPORT MINERAL RESOURCE ESTIMATION

Drilling has historically been a mix of diamond drilling (DD) and RC across the operations, with occasional conventional and mud drilling at Mega and Vista pits. DD is the primary method currently in use at Turquoise Ridge Underground and Vista Underground. At Turquoise Surface, RC and DD are deployed for both near-mine exploration and grade control purposes.

The geometry of the mineralized bodies can be variable, largely controlled by structural and stratigraphic complexities. Uncertainty about the morphology and vertical or lateral extent is mitigated by drilling at various orientations to the mineralized body.

TURQUOISE RIDGE UNDERGROUND

Drill hole spacing at Turquoise Ridge Underground is approximately 15 to 25 meters. Variography of the local domains determines the required spacing for measured, indicated, and inferred classifications. DD accounts for just over half of the drilling used in the Mineral Resource database (Table 10-4), but now currently accounts for nearly 90% of drilling activities, with drill hole diameters ranging in size from PQ to NQ (3 3/8 inches to 1 3/8 inches). RC drilling using 4.5 inch diameter borehole has been limited in recent years, as geotechnical and sample quality have been better than DD.

Table 10-4 Turquoise Ridge Underground Drilling

 

Drill Type      Number of Core Holes    Drilled Length   

 

Percentage of Total Drilling

(%)

   (ft)    (m)

Core-(DD)

   3,070    533,908     162,735     53%

RC

   2,729    318,618     97,115     47%

Totals

   5,799    852,526     259,850     100%

Planned drill hole collar locations are marked up by drill services personnel using a Trimble total station to determine the location of every hole and to establish front- and back-sites for all angle holes. Drillers utilize a north-seeking azimuth aligner to ensure proper setup. After collaring the hole, drill services will pick up the collar coordinates using the Trimble. Figure

 

   
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10-1 illustrates the locations of core and RC collars at Turquoise Ridge Underground used in the Mineral Resource estimation.

Downhole surveys are performed on all holes. In the past, surveys were conducted using both magnetic and gyro instruments, but are now completed using a combination of north-seeking and conventional gyros. Surveys are conducted by the drillers during the drilling process either at final depth or when adverse ground conditions are encountered. International Directional Services LLC (IDS) conducts the surveys for holes collared from surface targeting mineralization at depth.

TURQUOISE RIDGE SURFACE

Drill spacing at Turquoise Ridge Surface is approximately 25 m to 35 m for the Mega Pit and approximately 20 m to 35 m for the Vista Pit (Figure 10-2). Table 10-5 summarizes the TR Surface drilling statistics.

Table 10-5 Turquoise Ridge Surface Drilling

 

Drill type      Number of Core Holes      Drilled Length   

 

Percentage of Total Drilling

(%)

   (ft)    (m)

Mud

   59    32,647      9,951      1%

Conv

   93    12,725      3,879      1%

Core

   2,863    1,378,434      420,147      31%

RC

   6,089    3,284,654      1,001,163      67%

Totals

   9,104    4,708,460      1,435,139      100%

Planned drill hole collar locations are marked up by geologists or drill services personnel using a Trimble global positioning system (GPS) to determine the location of each hole and to establish front- and back-sites. After drilling, survey will pick up the collar coordinates using a real-time kinematic GPS.

Downhole surveys are performed on all holes using a combination of north-seeking and conventional gyros. Surveys are conducted by IDS.

VISTA UNDERGROUND

Drill spacing at Vista Underground is approximately 10 m to 25 m (Figure 10-3). Table 10-6 summarizes the drilling statistics for Vista Underground.

 

   
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Table 10-6 Vista Underground Drilling

 

Drill type            Number of Core Holes      Drilled Length   

Percentage of Total Drilling

(%)

   (ft)    (m)

Core  

   605    377,369      420,147      100%

Totals  

   605    377,369      420,147      100%

Planned drill hole collar locations are laid out by survey or geologic personnel measuring off lasers/reference points. Once center of rotation is established a TN-14 azimuth aligner tool is used to place each hole. All collars are picked up by survey using a Trimble. Previously, there was a guideline that did not require holes less than 150 feet to have a survey. However, all current holes are surveyed with the IDS tool. In 2016 and 2017, IDS performed all downhole surveys with either a maxibore or a mims north-seeking gyro depending on tool availability. In 2018 and 2019, a north seeking gyro was used to perform surveys. An azimuth aligner tool has been used for all drilling since 2016, prior to that azimuth/incline was established with front and back sights.

 

   
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11. SAMPLE PREPARATION, ANALYSES AND SECURITY

 

  11.1.

TURQUOISE RIDGE UNDERGROUND

TURQUOISE RIDGE UNDERGROUND LABORATORY

All Turquoise Ridge Underground drill holes from 2009 to 2019, inclusive, used for Mineral Resource estimation were assayed at the Turquoise Ridge Underground laboratory. The mine laboratory which analyzes production samples is not certified. Exploration drill hole samples followed a separate protocol and were assayed off site by an accredited commercial laboratory. Starting in August 2019 all assaying of drill holes were completed at ALS Mineral laboratories located in Reno, Nevada and/or Vancouver, British Colombia, Canada.

SAMPLE PREPARATION AND ANALYSIS

The procedures followed by the Turquoise Ridge Underground laboratory are as follows. Samples are dried for a minimum of eight hours at 49°C and crushed to minus 9.5 mm. The crusher is cleaned with compressed air following each sample. A weekly sieve analysis is performed to confirm the material size and adjustments are made accordingly.

The entire crushed sample is split with a Jones riffler to achieve a 150 g sub-sample which is pulverized to 90% passing 150 mesh (89 µm) using a ring and puck pulveriser. Daily sieve analyses are conducted to ensure the particle size. Every twentieth sample is pulverized separately as a separate quality assurance/quality control (QA/QC) sample for analysis at an independent laboratory.

Samples are analyzed using fire assay (FA) with a gravity finish. Every batch of 20 samples contains a standard, blank, and duplicate sample for QA/QC. If any of the three QA/QC samples returns results outside the accepted range, the entire batch is re-run.

QUALITY ASSURANCE/QUALITY CONTROL

The QA/QC program for core and production samples processed at the Turquoise Ridge Underground laboratory consists of the insertion of certified reference material (CRM) or standard, blank , and pulp duplicates as internal laboratory checks in each batch of samples.

 

   
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The insertion rate used is approximately 1:20 for standards, blanks, and duplicates. Duplicate samples are also sent to ALS Minerals Reno (ALS Reno) in Reno, Nevada, or ALS Minerals Vancouver (ALS Vancouver) in Vancouver, Canada for analysis.

Nevada Gold Mines purchased standards from well-known Canadian distributors CDN Resources Labs (CDN) in Vancouver, British Columbia. CDN prepares its own standards in-house. All standards came in 100 g sealed envelopes. Standards prepared by CDN are widely employed in the industry. They represent a grade range from near-detection to nearly 34 g/t gold and include both oxide and sulphide compositions.

A Nevada Gold Mines in-house blank is a hard white pebble gravel obtained locally from Gentec and Ace Hardwares used to test for potential contamination.

CRM and blank samples are considered a failure if the assayed value is greater than two standard deviations from the expected value. When standards fall out of tolerance, the laboratory is contacted and asked to rerun five samples above and below the failed standard (or blank). Pulp duplicates are compared to the original results using the Sign Test which tests the number of positive and negative differences in sample pairs. The t-Test is used to compare the means. The results are also analyzed using regression analysis.

Ongoing monitoring of QA/QC results is completed as assay data are received from ALS Reno and ALS Vancouver laboratories before uploading into the Turquoise Ridge Complex master database. Monthly and quarterly review and comprehensive analysis of the QA/QC results are conducted. The QA/QC program is monitored closely, and all issues identified with assay results are resolved prior to data approval and its importation into the mine database.

The QP also notes that coarse crush duplicate samples (rejects) are not used by Turquoise Ridge Underground. Coarse crush duplicates would show contamination at the sample preparation stage that would not otherwise be evident. The QP recommends that coarse crush duplicates be analyzed on a regular basis.

The QP reviewed the results for mine geology samples analyzed at the Turquoise Ridge Underground laboratory between January 1 and September 30, 2017. A total of 3,097 in-house standards, 3,139 blanks, and 3,644 laboratory pulp duplicates were inserted into the sample

 

   
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stream during this period. There were 25 standard failures and two blank failures during this period. The pulp duplicates showed no systematic bias.

During the period from January 1, 2019 to December 17, 2019, 4,704 pulp duplicates were inserted. The Sign Test, t-Test, and regression analysis indicate that there is no systematic bias in the two sets of data. Additionally, 4,005 blanks with 5 failures, and 3,969 standards with 13 failures, were analyzed at ALS Reno.

These failure rates are acceptable and in the QP’s opinion the QA/QC results indicate that the data is acceptable for Mineral Resource estimation.

 

  11.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND LABORATORY

Legacy assay work was completed by Shasta Analytical, Barringer Labs, Legend, American Assay, Chemex and Bondar Clegg. ALS Reno and ALS Vancouver have assayed drill samples since 2002. LECO analysis is a method of estimating total organic carbon (TOC) using an instrument known as a LECO carbon analyzer by combusting the organic carbon and measuring the resulting carbon dioxide produced. Historic LECO analysis was mostly completed by the mine site lab but was moved to ALS Reno or ALS Vancouver in 2014.

DENSITY DETERMINATIONS

Twelve core samples (Table 11-1) with Nevada Gold Mines calculated specifc gravity determinations were sent to ALS Reno for check analysis. A best fit regression line (Figure 11-1) of the two data sets yields an acceptable 0.9984 correlation.

 

   
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Table 11-1 Turquoise Ridge Surface Specified Gravity Results

 

Hole ID   

Duplicate

Type

  

Original

Value

   Check Value    Original Date    Check Date
TWD-02435    SG Check    2.7512    2.7600    3/6/2017    4/25/2017
TWD-02436    SG Check    2.6851    2.7000    3/7/2017    4/25/2017
TWD-02449    SG Check    2.6196    2.6100    6/1/2017    8/1/2017
TWD-02452    SG Check    2.8550    2.8700    5/19/2017    6/2/2017
TWD-02454    SG Check    2.8862    2.8900    9/19/2017    11/1/2017
TWD-02456    SG Check    2.9566    2.9600    9/19/2017    11/1/2017
TWD-02462    SG Check    2.6976    2.7000    6/1/2017    8/1/2017
TWD-02463    SG Check    2.7954    2.8100    5/19/2017    6/2/2017
TWD-02464    SG Check    2.6518    2.6600    7/11/2017    8/1/2017
TWD-02466    SG Check    2.8072    2.8100    9/19/2017    11/1/2017
TWD-02471    SG Check    2.3421    2.3400    7/11/2017    8/1/2017
TWD-02487    SG Check    2.5940    2.6200    2/5/2018    2/16/2018

 

 

 

PARENT COLUMN

HEADER

   CATEGORY   

DUPLICATE

TYPE

   R_SQUARED

SG_UNK_GRAV_NGC

 

  

DENSITY

 

  

CHECK

 

  

0.9984

 

Figure 11-1 Check Specific Gravity Results Turquoise Ridge Surface

SAMPLE METHODS

Listed below are the analytical descriptions of the various assaying procedures employed by ALS Reno or ALS Vancouver.

ALS Au-AA23 testing: Fire gold AAS finish

 

   

FA Fusion with AAS finish for Au

 

   

30g nominal sample weight

 

   

0.005 ppm to 10 ppm lower/upper limit

 

   
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>100 ppm over limit testing by gravimetric

ALS Au-AA31 testing: Cyanide leach and preg rob capacity

 

   

Cyanide Leach with Au spike; AAS finish for Au

 

   

10g nominal sample weight

 

   

0.03 ppm to 500 ppm lower/upper limit

 

   

Au-AA31a testing:

 

   

Cyanide Leach without Au spike; AAS finish for Au

 

   

10g nominal sample weight

 

   

0.03 ppm to 500 ppm lower/upper limit

ALS ME-MS41 testing: multi-element trace elements

 

   

Aqua Regia Digestion with ICP-AES and ICP-MS

 

   

0.50 g nominal sample weight

 

   

51 element suite with automatic ore-grade testing on over limits

 

   

Over limits specific to each element

LECO testing: Carbon and sulphur speciation for autoclave blending

 

   

Total Sulphur and Carbon by LECO furnace analysis

 

   

HCI (25%) leach of carbonates with LECO furnace analysis for organic carbon (OC)

 

   

S (sulphate) by pyrolysis and LECO furnace analysis

 

   

0.1 g to 0.2 g nominal sample weight

 

   

0.01% to 50% lower/upper limit by weight

QUALITY ASSURANCE/QUALITY CONTROL

Nevada Gold Mines exploration drilling QA/QC information from 2002 forward was evaluated by the geology department using a variety of statistical procedures over different time periods resulting in multiple spreadsheets, reports, and memos. No critical issues were identified, but a significant number of pre-Nevada Gold Mines legacy issues concerning assay, collar and down hole survey were documented.

The QA/QC discussion that follows evaluates gold assays in the Cut 40 area from 2017 and 2018 using a Microsoft Excel (MS Excel) spreadsheet template developed by Newmont senior consulting geologist Richard Inglis. Sampling constants K=5 and a= 0.89 used in the analysis are from a Vista Pit blast hole heterogeneity study (Bucknam and Seidel, 1996). The

 

   
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spreadsheet exercise generates a summary table with related graphs and charts at selected threshold levels. ALS Reno is the primary assay lab. Check pulps were submitted to American Assay lab, also located in Reno, Nevada.

STANDARD REFERENCE MATERIAL

A total of 25 standards were utilized during the multi-year drill campaign. They represent a grade range from near-detection to nearly 34 g/t gold and include both oxide and sulphide compositions. The results indicate acceptable accuracy with a minimal negative bias (Figure 11-2).

 

Figure 11-2 Turquoise Ridge Surface Standards Box and Wisker Results for 25 Standards

BLANKS

A Nevada Gold Mines in-house blank sourced locally from Quaternary gravel was used to test for potential contamination. Results were acceptable with less than ten percent of assays greater than 10x detection limit (Figure 11-3).

 

   
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Figure 11-3 Results of Nevada Gold Mines In-house Gravel Blank

DUPLICATE SAMPLES

Results for field duplicates (Figure 11-4) and pulp/check duplicates (Figure 11-5 and Figure 11-6) show acceptable precision at 1s and 2s thresholds. Some noise exists above this level, mostly at the 0.00x gold grade range. Preparation duplicate precision is acceptable across all grade ranges.

 

   
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Figure 11-4 Field Duplicate QA/QC Results

 

Figure 11-5 Pulp Duplicate QA/QC Results

 

   
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Figure 11-6 Prep Duplicate QA/QC Results

 

  11.3.

INDEPENDENT LABORATORY

ALS USA Inc. ALS Reno or ALS Vancouver are the primary independent analytical facilities for analysis of Turquoise Ridge Complex pulp samples from core and RC drilling. ALS Reno and ALS Vancouver are independent, accredited testing laboratories and conform to the requirements set out by CAN-P-1579 and CAN-P-4E (ISO/IEC 17025:2005), the Requirements for the Accreditation of Mineral Analysis Testing Laboratories and General Requirements for the Competence of Testing and Calibration Laboratories, respectively. ALS Reno and ALS Vancouver are independent of Nevada Gold Mines.

Sampling is conducted by Nevada Gold Mines personnel as described previously.

ALS Reno and ALS Vancouver uses FA with an atomic absorption spectroscopic (AAS) finish for low grade samples and FA with a gravimetric finish for AAS assays ³10 g/t. A multi-element (51) analysis is performed on selected samples of interest for accessory metals and trace elements. The ALS codes are PREP-31Y for preparation, Au-AA23 and Au-GRA21 for gold, and ME-MS41 for multi-element analysis:

 

   

Au-AA23: FA fusion and AAS on a 30 g aliquot (0.005 g/t Au to 10 g/t Au)

 

   
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Au-GRA21: FA fusion and gravimetric finish on a 30 g aliquot (0.05 g/t Au to 1,000 g/t Au)

 

   

ME-MS41: Aqua regia (full to partial) digestion and inductively couple plasma mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES) analysis determination for 51 elements

 

  11.4.

SECURITY

Samples were transported from the drill rig to the core storage facilities at the Turquoise Ridge Complex by the drilling contractor, where the geological staff logged and sampled the core. Drill core in cardboard core boxes is currently stored on racks inside a recently built secure core storage facility until they ae transported directly to the ALS Minerals sample preparation laboratory in Reno, Nevada. Rejects and pulps are returned from the Reno laboratories to site. Pulps are stored indoors on the second floor of the re-purposed drill core laboratory and are secure.

The QP is of the opinion that the sample preparation, analysis, QA/QC, and security procedures are appropriate for use in Mineral Resource estimation.

It is the QP’s opinion that Turquoise Ridge Underground should proceed with the planned adoption of utilizing an external lab for assays used in Mineral Resource estimates.

 

   
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12. DATA VERIFICATION

 

  12.1.

TURQUOISE RIDGE UNDERGROUND

Nevada Gold Mines has checked previous Turquoise Ridge Underground estimates and external data reviews, in addition to conducting independent reviews in 2011, 2013, 2016, 2018, and again in the preparation of this Technical Report. Nevada Gold Mines completed a variety of validation queries and routines in Vulcan to identify any remaining data entry errors. A validity check for data errors such as out of range values, missing intervals, and overlapping intervals was conducted. The database was found to be acceptable and no significant problems were identified. Nevada Gold Mines did not collect independent samples as the historical production clearly demonstrates the presence of economic mineralization.

DATABASE

The Turquoise Ridge Underground technical database is being managed by the acQuire system implemented in 2004, which replaced the previous database system. Exploration data from a variety of sources is imported into acQuire using a variety of techniques and procedures to check the integrity of the data entered. Data that is logged on paper is subject to validation using built-in program triggers that automatically check manually entered data upon upload to the database. In May 2000, Second Door Industries performed a data verification project comparing pre-2000 certificates and assay data. A total of 327,222 assays of the 343,069 recorded passed the verification process. Analytical data is uploaded from digital sources. Survey data is uploaded by the project geologist from digital survey files. Verification is performed on all digitally collected data upon upload to the main database, and includes checks on surveys, collar co-ordinates, lithology data, and assay data.

Database security and integrity is accomplished by restricting access and user level permissions that are set by the Database Manager. Once data entry and validation are completed for a drill hole, access is locked. There are procedures for updates that retain all the original information and prioritize use of the updates.

Due to the historic nature of the assay data, several different assay laboratories have been used. Several negative values below 0.00 g/t gold were in the database. Generally, laboratories have reported assays with different detection limits. It is apparent that assays

 

   
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returning values below detection limits have been seeded with a negative value. As this value is arbitrarily selected through the years, this value may have changed depending on the people or company in charge. Turquoise Ridge Underground has set all historic negative assay values to a 0.000 value for standardization.

As such there are now only two negative values residing in the dataset. They are -99 and -66. A -99 value represents an interval that was purposely not sampled whereas a -66 value indicates an interval of lost core, a lost sample, non-recovered interval, or shotcrete or backfill.

Reports are available for QA/QC programs dating from 2002 to present, which suggests any drilling performed by Placer has been verified and validated. Drilling data prior to Placer are included in the datasets, and the validity is assumed to be good.

The data, which has now been used extensively for the last ten years, has been corrected for location and orientation. Suspect holes are flagged and will not export. A visual examination of the drill holes, in Vulcan, show spatially valid drill hole collar locations.

Based on past evaluations and current review, it is the QP’s opinion that the data is acceptable for the purposes of overall Mineral Resource and Mineral Reserve estimation and economic assessments. Some of the data may result in minor inaccuracies in local estimates.

 

  12.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

DATABASE

The Turquoise Ridge Surface and Vista Pit Underground drill database was created from the merger of Gold Field’s Chimney Creek and SFPG’s Rabbit Creek databases in 1993. In 1997, the drill database was transferred to Newmont’s database system and has been updated through the years as required. Since 1997, any errors found in the database require a data support request form for the database analysts to make corrections to the database, which allows for formal documentation of all database changes. Generally, the project geologist is responsible for submitting the data support request form. When the proper data support requests are received database analysts’ flag and remove questionable drill holes with collars, assays, or surveys from the approved database. After the change has been completed the

 

   
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project geologist reviews the amendments in the database to make sure corrections are complete.

The Newmont technical database has been managed by a team of database analysts since 2016 using an in-house developed database system known as GED (Global Exploration Database). Exploration data from a variety of sources were imported into GED using a variety of techniques and procedures to verify the integrity of the data entered. Data logged on paper is subject to validation using built-in program triggers that automatically check manually entered data loaded to the database. Nevada Gold Mines has completed the data transfer from Newmont and is now the control of the Turquoise Ridge Surface pits and Vista Underground database. Nevada Gold Mines transferred the database data from GED to acQuire.

On March 6, 2019, an approved resource data extraction was completed and received from the database analysts. The 2019 resource data extraction for Turquoise Ridge Surface and Vista Underground was compared against the equivalent 2018 resource data extraction. The database analysts, project geologist, and resource modeller perform independent data validations of the reserve extraction using the following software: Winmerge, Vulcan ISIS utility, and MS Excel and MS Access. There were seven holes removed from the 2019 resource extraction that were included in the 2018 approved resource extraction. Six of the holes were removed for bad downhole surveys (VUC-00092, VUC-00261, VUC-00262, VUC-00301, VUC-00321, VUC-00416) and one Halo exploration hole (tWE-00170) was removed because of no collar survey. There were 134 new approved holes in the 2019 resource extraction. A list of the new hole ID’s are shown in Table 12-1.

 

   
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Table 12-1 2019 Resource Extraction New Holes

 

             
HolelD   HolelD   HolelD   HolelD   HolelD   HolelD   HolelD
TWD-02540   TWD-02564   TWD-02586   VUC-00507   VUC-00529   VUC-00549   VUC-00569
TWD-02541   TWD-02565   TWD-02587   VUC-00509   VUC-00530   VUC-00550   VUC-00570
TWD-02542   TWD-02566   TWD-02588   VUC-00510   VUC-00531   VUC-00551   VUC-00593
TWD-02543   TWD-02567   TWD-02589   VUC-00511   VUC-00532   VUC-00552   VUC-00594
TWD-02545A   TWD-02568   TWD-02590   VUC-00512   VUC-00533   VUC-00553   VUC-00595
TWD-02546   TWD-02569   TWD-02591   VUC-00513   VUC-00534   VUC-00554   VUC-00597
TWD-02547   TWD-02570   TWD-02592   VUC-00514   VUC-00535   VUC-00555   VUC-00598
TWD-02551   TWD-02571   TWD-02593   VUC-00515   VUC-00536   VUC-00556   VUC-00599
TWD-02552   TWD-02572   TWE-00203   VUC-00516   VUC-00537   VUC-00557   VUC-00614
TWD-02553   TWD-02573   TWE-00204   VUC-00517   VUC-00538   VUC-00558   VUC-00615
TWD-02554   TWD-02574   TWE-00205   VUC-00518   VUC-00539   VUC-00559   VUC-00616
TWD-02555B   TWD-02575   TWE-00206   VUC-00519   VUC-00540   VUC-00560   VUC-00617
TWD-02556   TWD-02576   VUC-00499   VUC-00520   VUC-00541   VUC-00561   VUC-00618
TWD-02557   TWD-02579   VUC-00500   VUC-00521   VUC-00542   VUC-00562   VUC-00619
TWD-02558   TWD-02580   VUC-00501   VUC-00522   VUC-00543   VUC-00563    
TWD-02559   TWD-02581   VUC-00502   VUC-00523   VUC-00544   VUC-00564
TWD-02560   TWD-02582   VUC-00503   VUC-00524   VUC-00545   VUC-00565
TWD-02561   TWD-02583   VUC-00504   VUC-00525   VUC-00546   VUC-00566
TWD-02562   TWD-02584   VUC-00505   VUC-00526   VUC-00547   VUC-00567
TWD-02563   TWD-02585   VUC-00506   VUC-00527   VUC-00548   VUC-00568

The project geologist validated the data using the Vulcan ISIS database checking tool to assess the database for the tables and fields shown in Table 12-2. The output report file from the Vulcan ISIS checking tool was imported into MS Excel and used to summarize the Vulcan output using data filtering and VLOOKUP tables. An example of the comments from the validation review are shown in Table 12-3.

 

   
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Table 12-2 Vulcan ISIS Database Tables and Fields Checked

 

     
Vulcan ISIS Utility Check    Table    Field

Unique Location

   Collar    East, North, Elevation

Total Depth

   Collar    TD Null Value: 0.0
   Overwrite total depth: FALSE
   Bottom Depth table: ASSAY Field:
   TO Comparison: Equal

Overlapping Intervals

   Assay    Bottom Depth
   To

Increasing/Decreasing Value

   Survey    DEPTH Type: Increasing
   Allow Equals: False
   Null Value: 0

Maximum Consecutive Variation

   Survey    INCLINATION Tolerance: 10
   Null Value: 0
   AZIMUTH Tolerance: 20
   Null Value: 0

Unique Values

   Collar    HOLEID

Empty Table

   Collar    No empty table

Table 12-3 Downhole Survey Validation Check Comments

 

HolelD    Error Check    File    Field    From   

From

 

Record

   To   

To

 

Record

   Comment

TWE-00203

   Maximum Variation    SURVEY    AZIMUTH    258.24    Rec=1    295.31    Rec=2    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    126.09    Rec=1    210.54    Rec=2    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    221.36    Rec=3    245.67    Rec=4    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    245.67    Rec=4    216.40    Rec=5    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    192.36    Rec=8    310.78    Rec=9    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    310.78    Rec=9    16.03    Rec=10    Vertical hole, O.K.

TWE-00205

   Maximum Variation    SURVEY    AZIMUTH    16.03    Rec=10    64.14    Rec=11    Vertical hole, O.K.

TWE-00170A

   Maximum Variation    SURVEY    AZIMUTH    281.70    Rec=9    258.00    Rec=10    Near vertical part of hole

TWE-00170A

   Maximum Variation    SURVEY    AZIMUTH    258.00    Rec=10    236.40    Rec=11    Near vertical part of hole

The project geologist used an MS Excel spreadsheet using VLOOKUP functions to:

 

   

Find the HoleId in the current extraction in the prior ones.

 

   

If the hole exists, a pass or fail ranking is returned. If the hole not present a #N/A values is returned.

 

   

If the hole exists, in another column the prior validator’s comments are returned. This checks for the presence of un-approval comments, indicating if a previously un-approved hole was extracted.

An example of the historical collar spreadsheet used to check the new resource collars is shown in Table 12-4.

 

   
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Table 12-4 Historical Collar Validation Check

 

                 
HolelD    Error Check    HolelD2    Table    Easting      Northing      Elevation      Check    Comment

TWD-01645

TWD-01653

   Unique Location
Unique Location
   TWD-01653
TWD-01645
   COLLAR

COLLAR

    

16438.43

16438.43

 

 

    

52298.924

52298.924

 

 

    

4358.51

4358.51

 

 

   pass

pass

    

TWD-01651

TWD-01677

   Unique Location
Unique Location
   TWD-01677

TWD-01651

   COLLAR

COLLAR

    

15845.253

15845.253

 

 

    

51198.504

51198.504

 

 

    

4339.68

4339.68

 

 

   pass

pass

    

TWD-01656

TWD-01657

   Unique Location
Unique Location
   TWD-01657

TWD-01656

   COLLAR

COLLAR

    

18640.785

18640.785

 

 

    

41036.849

41036.849

 

 

    

3901.168

3901.168

 

 

   pass

pass

    

TWD-01658

TWD-01659

   Unique Location
Unique Location
   TWD-01659

TWD-01658

   COLLAR

COLLAR

    

18011.252

18011.252

 

 

    

41310.654

41310.654

 

 

    

3900.617

3900.617

 

 

   pass

pass

    

TWD-01896

TWD-01897

   Unique Location
Unique Location
   TWD-01897

TWD-01896

   COLLAR

COLLAR

    

18255.961

18255.961

 

 

    

62365.473

62365.473

 

 

    

5599.065

5599.065

 

 

   pass

pass

    

TWD-02499

TWD-02500

   Unique Location
Unique Location
   TWD-02500
TWD-02499
   COLLAR

COLLAR

    

14981.605

14981.605

 

 

    

52059.238

52059.238

 

 

    

5109.504

5109.504

 

 

   pass

pass

   Lost invividual collars due to over cementing Lost invividual collars due to over cementing

TWD-02489

TWD-02503

   Unique Location
Unique Location
   TWD-02503

TWD-02489

   COLLAR

COLLAR

    

17479.013

17479.013

 

 

    

51406.201

51406.201

 

 

    

3853.48

3853.48

 

 

   pass

pass

  

Same Pad as TWD-02503

Same Pad as TWD-02489

VUC-00048

VUC-00049

   Unique Location
Unique Location
   VUC-00049

VUC-00048

   COLLAR

COLLAR

    

19995.329

19995.329

 

 

    

62467.719

62467.719

 

 

    

4765.958

4765.958

 

 

   pass

pass

    

VUC-00110

VUC-00111

   Unique Location
Unique Location
   VUC-00111

VUC-00110

   COLLAR

COLLAR

    

19051.32

19051.32

 

 

    

61989.21

61989.21

 

 

    

4853.67

4853.67

 

 

   pass

pass

    

VUC-00268

VUC-00269

   Unique Location
Unique Location
   VUC-00269

VUC-00268

   COLLAR

COLLAR

    

20531.34

20531.34

 

 

    

62810.95

62810.95

 

 

    

4709.54

4709.54

 

 

   pass

pass

    

Z96-0080

Z96-0081

   Unique Location
Unique Location
   Z96-0081

Z96-0080

   COLLAR

COLLAR

    

17160

17160

 

 

    

47300

47300

 

 

    

4300

4300

 

 

   pass

pass

    

Z96-0084

Z96-0085

   Unique Location
Unique Location
   Z96-0085

Z96-0084

   COLLAR

COLLAR

    

17450

17450

 

 

    

47000

47000

 

 

    

4278

4278

 

 

   pass

pass

    

Z96-0107

Z96-0122

   Unique Location
Unique Location
   Z96-0122

Z96-0107

   COLLAR

COLLAR

    

17350

17350

 

 

    

51265

51265

 

 

    

4616

4616

 

 

   check

check

  

Remove from approved list

Remove from approved list

The quality of historical mud rotary gold assays used in the resource models was questioned at the geology model handoff meeting in 2018. As a result, 137 drill holes were removed from the approved reserve database extraction, additionally assays where mud rotary drilling was used were removed. The core drilling assays at the bottom of these holes remain in the approved extraction. There are eight remaining mud assays in the database extraction, and they occur where there were overlaps in the interval from the mud rotary versus core drilling.

John Ring, a Newmont Nevada Consulting Geologist II, audited the database in January 2018 and reported the results in the audit report: “Twin Creeks Cut40_55 Database audit_Final_1_30.pdf”. The database audit recommended removing the mud holes from the resource estimation approved database and noted that it was in process at the time of the audit.

The Turquoise Ridge Surface database extraction model coordinates are presented in Table 12-5 and includes project codes TW and VUC. The data extraction completed March 2019 contained 7,968 drill holes. The 2018 data extraction contained 7,775 drill holes.

 

   
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Table 12-5 Turquoise Ridge Surface Model Coordinates

 

Model Boundaries  

Easting

 

Min

 

Easting

 

Max

 

Northing

 

Min

 

Northing

 

Max

 

Elevation

 

Min

 

Elevation

 

Max

Turquoise Ridge Open Pits   9,300   32,300   26,000   68,400   2,000   5,800

Mega Pit

  13,650   23,040   37,760   55,940   2,000   5,800

Vista Pit

  16,500   22,500   56,300   63,500   3,800   5,680

Based on past evaluations and current review, it is the QP’s opinion the data extraction from March 6, 2019 is acceptable for the purposes of overall resource and reserve estimation and economic assessments. Some of the data may result in minor inaccuracies in local estimates.

The QP is of the opinion that the data verification programs undertaken on the data collected from the Turquoise Ridge Complex adequately support the geological interpretations, the analytical and database quality, and therefore support the use of the data in Mineral Resource and Mineral Reserve estimation.

 

   
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13. MINERAL PROCESSING AND METALLURGICAL TESTING

The following is a summary of the metallurgical test work which has been carried out on the Turquoise Ridge underground and surface operations.

 

  13.1.

TURQUOISE RIDGE UNDERGROUND

METALLURGICAL TESTING

In 2017, Hazen Research Inc. completed a series of six tests using a sample from Turquoise Ridge that had a head grade of 17.14 g/t Au and 0.6% OC and variable testing conditions. The results were consistent with the historical results; Turquoise Ridge Underground OC, though of similar concentrations, is less preg-robbing than the Mega Pit OC.

Based on the view that the underground ore domains will not change appreciably with respect to metallurgical characteristics, the QP considers historical plant data to be more representative of the recoveries that will be achieved going forward.

Figure 13-1 shows the average monthly recovery as a function of OC/Au head grade from January 2014 to December 2019. In general, the correlation of daily data on a monthly basis is much better than the correlation indicated in the figure due to the varied blend of ore types and process changes over five years. For budgeting and forecasting, the linear correlation is updated to account for the most recent plant performance.

 

   
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Figure 13-1 Recovery as a Function of OC and Gold Head Grade

Figure 13-1 shows that, based on the very low coefficient of correlation (i.e., R2), there does not appear to be a relationship between gold recovery and the OC concentration divided by the gold head grade in oz/ton Au, as assumed by the gold recovery equation.

 

  13.2.

TURQUOISE RIDGE SURFACE AND VISTA UNDERGROUND

METALLURGICAL TESTING

The Sage autoclave has 20 years of experience processing ores very similar to Cut 40 material. This includes ore from Cut 22 and Cut 24, which were located adjacent to Cut 40. The autoclave is positioned very well to accept Cut 40 materials without significant changes to operating strategies, practices, or procedures. Equipment and experienced labour are already in place. Processing of Cut 40 material should closely follow results from processing similar Cut 22 and Cut 24 materials.

Thirty-four variability composites were subjected to autoclave studies. These composites were collected from core and pulp rejects from previously drilled holes.

 

   
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Samples were selected by grade range, sulphide sulphur (SS2) range, carbonate (CO3) range, and OC range. The SS2, CO3, and OC ranges were determined using the current Turquoise Ridge Surface ore control matrix and ore types (Table 13-1). Classifying Cut 40 material this way allows for seamless integration of Cut 40 materials into current Sage autoclave operating, planning, and blending practices.

Table 13-1 Turquoise Ridge Surface Ore Control Matrix

 

Ore

    Type    

 

Sulphide

(%)

 

Carbonate

(%)

 

OC

(%)

   Comments
A   < 4   > 4 and < 8   < 0.6    Med-Low Carbonate / Low Sulphide
B   > 4   > 4 and < 12   < 0.6    Medium Carbonate / High Sulphide
C   > 4 and < 6   < 4   < 0.6    Low Carbonate / Medium Sulphide
D   < 4   < 4   < 0.6    Low Carbonate / Low Sulphide
E   any value   < 8   > 0.6 and < 1    Low Carbonate / Med-High Organic Carbon
F   any value   > 12 and < 18   < 0.6    High Carbonate
G