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