NI 43-101 Resource Estimate for the Whistler Project, Alaska — 2022

Whistler Gold-Copper Project — 2026 Technical Report

Executive Summary

The Whistler Gold-Copper Project process plant is designed to treat 40,000 t/d of mineralized material from the Whistler gold-copper porphyry deposit. This plant recovers copper, gold and silver by froth flotation and leaching to produce copper concentrate and gold doré over a 14.6-year mine life.

The process flowsheet for the project is based on preliminary metallurgical laboratory testing, as discussed in Section 13, and preliminary economic modelling. The selected unit operations are conventional technologies commonly applied in copper and gold processing plants of similar throughput. The proposed flowsheet includes the following process areas and unit operations: Crushing, Grinding, Copper flotation, Copper concentrate handling, Gold leaching, Gold recovery and carbon regeneration, and Cyanide destruction and tailings management.

The life-of-mine (LOM) average feed grades and recoveries are summarized in Table 17-1. Copper feed grade is 0.16%, Gold feed grade is 0.44 g/t, and Silver feed grade is 1.83 g/t. Average overall recovery over LOM is 77.8% for Copper, 88.9% for Gold, and 55.6% for Silver.

Website: https://www.usgoldmining.us/project/whistler-gold-project/

Report Date: 2026

Region: N/A

Project Status:

Commodity: Copper, Gold, Silver

Throughput: 

Mine Life: 

Mine Type: 

Ore type:

Whistler Project — 2016 Technical Report

Executive Summary

This NI 43-101 Technical Report for the Whistler Project in Alaska, dated March 24, 2016, outlines the recovery methods and metallurgical design parameters for the proposed processing plant. The report focuses on Section 17, detailing the process design parameters based on metallurgical testwork, with a target plant throughput of 11 million tonnes per annum (Mtpa). The ore is described as metallurgically amenable, allowing for the production of saleable, high-quality copper concentrates with acceptable recoveries of both copper and gold.

The proposed process flowsheet utilizes a conventional SABC (SAG, Ball mill, and Pebble crushing) grinding circuit followed by rougher flotation, regrinding of rougher concentrate, and two stages of cleaning. Key design parameters include a revised Bond Work Index (BWI) of 19.9 for the ball mill and a Rock Work Index (RWI) of 23.9 for the SAG mill. The revision to the BWI parameters resulted in a reduction of ball mill power requirements by 6 MW, while allowing for a single mill configuration instead of the originally planned two, thereby reducing circuit complexity.

Crushing is designed around an 89” x 60” gyratory crusher, suitable for the hard competent ore indicated by the high BWI figures. Flotation parameters include a mass pull to roughers of 15% and specific residence times derived from lab tests. The report notes that recovery and upgrade levels for copper and gold are relatively insensitive to feed grade, which is a significant positive result for the project given the low head grades associated with the Whistler ore.

Processing Overview

• Crushing:: 89” x 60” Gyratory Crusher
• Grinding:: SAG Mill, Ball Mill, Pebble Crusher (SABC)
• Flotation:: Rougher, Regrind, 2 stages Cleaner
• Leaching:: None

Reports

• reports/2016_Whistler_Project_Alaska

Website: https://www.usgoldmining.us/project/whistler-gold-project/

Report Date: 2016-03-24

Region: Alaska

Project Status:

Commodity: Copper, Gold

Throughput: 

Mine Life: 

Mine Type: 

Ore type:

Whistler Gold-Copper Recovery: Flotation & Leaching Process

Source: U.S. GoldMining Inc (2026)
Website: https://www.usgoldmining.us/project/whistler-gold-project/

Critical Data

Overview

The Whistler Gold-Copper Project, owned and operated by GoldMining Inc. and U.S. GoldMining Inc., is a proposed open-pit mining operation located in Alaska, USA. The project’s NI 43-101 Preliminary Economic Assessment (PEA) with an effective date of March 2, 2026, outlines a processing plant designed to treat 40,000 tonnes per day of mineralized material from the Whistler gold-copper porphyry deposit. The recovery methods combine conventional froth flotation and cyanide leaching to produce a high-grade copper concentrate and gold doré over a 14.6-year mine life. The significance of this project lies in its ability to economically process a low-grade porphyry resource (0.16% Cu, 0.44 g/t Au) while achieving an overall gold recovery of 88.9% through an integrated flowsheet. The process begins with primary gyratory crushing, followed by high-pressure grinding roll (HPGR) milling and ball mill grinding to a target P80 of 120 µm. Copper flotation with a rougher and three-stage cleaner circuit produces a 25% copper concentrate, while flotation tailings undergo gold leaching via cyanidation and carbon-in-pulp (CIP) adsorption. Loaded carbon is stripped using the AngloAmerican Research Laboratories (AARL) system, followed by electrowinning and smelting to produce doré bars. Cyanide destruction via the INCO sulfur dioxide/air method ensures environmental compliance, and tailings are thickened for disposal in a centralized dry-stack facility (CDSF). The Whistler Gold-Copper recovery process is designed for high availability (92% for most areas) and incorporates proven technologies to maximize metal extraction while minimizing environmental impact.

Key Process Stages

• Stage 1: Crushing and Stockpiling – Run-of-mine ore (F80 635 mm) is dumped by 240 t haul trucks into a gyratory primary crusher (600 kW, open circuit, CSS 120 mm) producing a P80 of 136 mm. Crushed material is conveyed to a 21,750 t live-capacity stockpile (12-hour buffer). Secondary crushing uses three cone crushers (2 duty/1 standby, each 671 kW) in closed circuit with double-deck vibrating screens (top deck 90 mm, bottom deck 60 mm) to reduce the ore to a P80 of 41 mm.
• Stage 2: HPGR and Ball Mill Grinding – Secondary crushed material feeds a single HPGR unit (8,700 kW) in closed circuit with double-deck screens (top 15 mm, bottom 5 mm) to achieve a P80 of 3.25 mm. HPGR screen undersize reports to two parallel ball mills (each 18,100 kW, overflow discharge, 8.53 m dia. x 12.50 m EGL) operating at 350% circulating load. Cyclone overflow at P80 120 µm is the feed to copper flotation.
• Stage 3: Copper Flotation and Concentrate Handling – Slurry from grinding enters a rougher flotation bank (5 x 500 m³ forced-air cells) with collector and frother. Rougher concentrate is reground in two stirred mills (each 3,800 kW) to a P80 of 15 µm, then cleaned in three stages (Cleaner 1: 4 x 37 m³; Cleaner 2: 3 x 6 m³; Cleaner 3: 2 x 6 m³). Final concentrate grades 25% Cu. The concentrate is thickened (11 m dia. high-rate thickener) and filtered (60 m² pressure filter) to 8% moisture for off-site transport.
• Stage 4: Gold Leaching and Carbon-in-Pulp Adsorption – Rougher flotation tailings are pre-leach thickened (61 m dia. high-rate thickener) to 48% solids, then leached in two parallel trains of eight tanks each (8,600 m³ per tank, 48-hour residence). Sodium cyanide (0.5 kg/t) and lime (1.4 kg/t) are added. Leach discharge passes through two parallel CIP trains (six tanks each, 1,400 m³ per tank, 6-hour residence) where gold is adsorbed onto activated carbon.
• Stage 5: Gold Recovery, Carbon Regeneration, and Cyanide Destruction – Loaded carbon undergoes acid wash (3% HCl) and cold cyanide wash in a 15 t column, then elution at 90°C using the AARL system. Pregnant solution is electrowinned, filtered, and smelted to produce doré bars. Barren carbon is regenerated at 750°C in a rotary kiln. Tailings from CIP undergo cyanide destruction in two parallel tanks (3,310 m³ each, 120-min residence) using the INCO SO₂/air process (target CNWAD <5 mg/L) before final thickening (73 m dia. high-rate thickener) and disposal.

Additional Interesting Data and Summary

The Whistler Gold-Copper Project’s recovery methods are underpinned by extensive metallurgical testwork conducted by Base Metallurgical Laboratories Ltd. The flotation circuit design includes scale-up factors of 2.5 for rougher and cleaner residence times, resulting in plant design times of 30 minutes for rougher flotation, 12.5 minutes for cleaner 1, 7.5 minutes for cleaner 2, and 5 minutes for cleaner 3. The regrind circuit achieves a target P80 of 15 μm with a specific energy of 50 kWh/t. In the gold leaching circuit, leach extraction is 74.8% for gold and 20.5% for silver at design grade, with a 48-hour residence time. CIP adsorption residence is 6 hours, and soluble recovery to doré is 95% for both gold and silver. Cyanide destruction uses the INCO sulfur dioxide/air process with a 120-minute residence time, reducing weak acid dissociable cyanide (CNWAD) from 200 mg/L to below 5 mg/L (design target 1.0 mg/L), using sodium metabisulfite (SMBS) at 5 g SO₂/g CNWAD. Major equipment includes a Superior MK-III 62-75 gyratory crusher, HP900 cone crushers, an 8,700 kW HPGR, two 18,100 kW ball mills, two 3,800 kW stirred regrind mills, and sixteen 8,600 m³ leach tanks. The tailings thickener (73 m diameter) underflows at 60% solids for dry stacking. From an environmental perspective, the project emphasizes water recovery—thickener overflows report to the process water tank for reuse—and the cyanide destruction step ensures regulatory compliance. Economically, the 14.6-year mine life at 40,000 t/d produces a copper concentrate grading 25% Cu and doré bars, with life-of-mine recoveries of 77.8% for copper, 88.9% for gold, and 55.6% for silver. Reagent consumption includes 0.5 kg/t NaCN for leaching and 1.4 kg/t lime for pH control. The plant operates with high availability (92% for grinding and flotation) and includes an emergency HPGR stockpile of 7,245 t for operational flexibility. Future outlook for the Whistler Gold-Copper Project involves advancing from PEA to feasibility study, with potential for optimization in HPGR circuit design and flotation reagent schemes. The integration of flotation and leaching provides a robust approach for low-grade porphyry ores, positioning the project as a significant gold-copper development in Alaska.

Key Processes: Flotation, CIP/CIL, Cyanidation, Gravity Separation, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper

Whistler Gold-Copper Project: 40,000 t/d Flotation & Leaching Recovery

Source: GoldMining Inc (2026)
Website: https://www.usgoldmining.us/project/whistler-gold-project/

Critical Data

Overview

The Whistler Gold-Copper Project, operated by GoldMining Inc. and U.S. GoldMining Inc., is a large-scale mining development located in Alaska, USA. The project’s process plant is designed to treat 40,000 tonnes per day of mineralized material from the Whistler gold-copper porphyry deposit, employing a combination of froth flotation and gold leaching to produce high-grade copper concentrate and gold doré over a 14.6-year mine life. Based on preliminary metallurgical testing and economic modelling, the plant leverages conventional technologies widely used in similar operations. The significance of the Whistler Project lies in its robust overall gold recovery of 88.9% and copper recovery of 77.8%, achieved through an integrated flowsheet that includes primary and secondary crushing, high-pressure grinding rolls (HPGR), ball milling, copper flotation with regrind and three-stage cleaning, cyanide leaching with carbon-in-pulp (CIP) adsorption, and AngloAmerican Research Laboratories (AARL) carbon stripping for gold recovery. The process design emphasizes operational efficiency, environmental responsibility through cyanide destruction using the INCO sulfur dioxide/air process, and water recovery via tailings thickening. The effective date of the technical report is March 2, 2026, marking a key milestone for the project. This article details the recovery methods that make the Whistler Gold-Copper Project a technically sound and economically attractive venture.

Key Process Stages

• Stage 1: Crushing – Run-of-mine material (F80 635 mm) is fed into a primary gyratory crusher (600 kW) operating in open circuit, producing a P80 of 136 mm. Crushed material is conveyed to a 21,750 t stockpile providing 12 hours of live capacity. Reclaimed material undergoes secondary crushing via three cone crushers (2 duty, 1 standby, each 671 kW) in closed circuit with double-deck vibrating screens (top deck 90 mm, bottom deck 60 mm), generating a final crushed product P80 of 41 mm.
• Stage 2: Grinding – Crushed ore feeds an HPGR (8,700 kW) in closed circuit with vibrating screens (15 mm top, 5 mm bottom) to produce a P80 of 3.25 mm. HPGR product then enters two parallel ball mills (each 18,100 kW, 8.53 m dia. x 12.50 m EGL) in closed circuit with cyclone clusters at 350% circulating load. Cyclone overflow achieves a target P80 of 120 μm, with slurry density maintained at 60% solids using slaked lime and process water.
• Stage 3: Copper Flotation – Cyclone overflow feeds a rougher flotation bank of five forced-air mechanical cells (500 m³ each) with frother and collector addition. Rougher concentrate is reground in two parallel stirred mills (each 3,800 kW) to a P80 of 15 μm, then cleaned through three stages: Cleaner 1 (4 x 37 m³ cells), Cleaner 2 (3 x 6 m³ cells), and Cleaner 3 (2 x 6 m³ cells). Final concentrate grades 25% Cu with copper recovery of 78.1%.
• Stage 4: Gold Leaching – Rougher flotation tailings are thickened in a 61 m high-rate thickener to 48% solids, then leached with sodium cyanide and slaked lime in two parallel trains of eight tanks each (8,600 m³ per tank) for 48 hours residence time. Leach discharge proceeds to two parallel trains of six CIP adsorption tanks (1,400 m³ each, 6 hours residence time). Gold leach extraction is 74.9% with silver extraction at 20.5%.
• Stage 5: Gold Recovery and Cyanide Destruction – Loaded carbon from CIP undergoes acid washing (3% HCl) and cold cyanide wash (2% NaCN/2% NaOH) in an AARL column system (15 t capacity). Gold is stripped at 90°C, electrowon, filtered, and smelted into doré bars (95% gold recovery). Barren carbon is regenerated at 750°C in a rotary kiln. Tailings from CIP are treated in two parallel tanks (3,310 m³ each, 120 min) using the INCO SO₂/air method to reduce CNWAD from 200 mg/L to <5.0 mg/L, then thickened (73 m thickener) to 60% solids for disposal.

Additional Interesting Data and Summary

The Whistler Gold-Copper Project’s recovery methods are supported by comprehensive design criteria that drive efficiency and sustainability. The comminution circuit relies on a Bond ball mill work index of 22.2 kWh/t (75th percentile) and an abrasion index of 0.130 g, with HPGR achieving a 100% circulating load. The crushing circuit operates at 75% availability for primary crushing and 92% for secondary, grinding, and flotation, ensuring high utilization. Flotation residence times incorporate a 2.5x scale-up factor from laboratory tests: rougher at 30 minutes, Cleaner 1 at 12.5 minutes, Cleaner 2 at 7.5 minutes, and Cleaner 3 at 5 minutes. Copper concentrate handling includes a high-rate thickener (11 m diameter, 0.2 t/m²/h) and a pressure filter producing 8% moisture cake with 260 kg/m²/h filtration rate. The gold leaching circuit uses 0.5 kg/t NaCN and 1.4 kg/t lime, with 48-hour leach and 6-hour CIP adsorption. Cyanide destruction targets a CNWAD concentration of 1.0 mg/L using 5 g SO₂/g CNWAD, managed through two 3,310 m³ tanks with 120-minute residence. Tailings thickening uses a 73 m diameter thickener at 0.7 t/m²/h, recovering water for recycle. Environmental considerations are integrated: the INCO process effectively detoxifies tailings, and high-rate thickeners minimize water loss. The economic impact is substantial—production of a 25% Cu copper concentrate and gold doré over a 14.6-year mine life creates long-term value. Sustainability initiatives include HPGR energy efficiency (reducing overall comminution power), water recovery (thickener overflow recycled), and use of conventional reagents (lime, flocculant, cyanide) with strict containment. Future outlook indicates potential optimization through advanced process control and possible expansion, leveraging the established flowsheet. The Whistler Project stands as a technically robust example of modern gold-copper recovery, combining proven flotation and cyanidation technologies with high environmental standards.

Key Processes: Flotation, CIP/CIL, Cyanidation, Gravity Separation, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper