Courageous Lake Gold Recovery: POX & Merrill-Crowe Process

Source: Unnamed_Company_16 (2026)
Website: https://www.newsfilecorp.com/release/301656/Valor-Gold-Announces-Exploration-Plans-for-the-Courageous-Lake-Project

Critical Data

Overview

Valor Gold Corp’s Courageous Lake Project employs a comprehensive gold recovery flowsheet designed to process refractory sulfide ore at a design throughput of 7,500 tonnes per day. The project, supported by a pre-feasibility study effective January 2024 and amended in March 2026, is situated in Canada and leverages a three-stage crushing circuit, primary ball mill grinding, sequential rougher and cleaner flotation, pressure oxidation (POX), cyanide leaching, and Merrill-Crowe precipitation to produce gold-silver doré bars. The flowsheet was selected based on extensive metallurgical testwork from programs conducted by SGS (2003, 2011), G&T (2007), and ALS (2023), addressing variable mineralogy, feed grades, and rock hardness. The process begins with run-of-mine material crushed to a P80 of 9 mm, followed by grinding to 106 µm with a 6.5 MW ball mill. Flotation concentrates gold-bearing sulfides, achieving 88% recovery to concentrate, which is then reground to 43 µm and acidulated before entering the POX autoclave (200°C, 2,150 kPa, 90-minute residence). Oxidized slurry is washed via three-stage counter-current decantation (CCD), neutralized, and leached with cyanide for 12 hours, achieving 97% gold extraction. The pregnant solution undergoes Merrill-Crowe zinc cementation (>99% efficiency), and the precipitate is smelted into doré bars. The facility includes robust reagent handling with on-site storage for 12 months, a cyanide destruction circuit using the SO2/air process to reduce WAD cyanide below 25 mg/L, and comprehensive environmental controls. This integrated gold recovery methods approach represents a technologically advanced solution for refractory gold deposits, with optimization opportunities identified for future implementation.

Key Process Stages

• Stage 1: Crushing and Stockpiling – Run-of-mine material feeds a primary jaw crusher (110 kW) via a vibrating grizzly, with oversize reduced to a P80 of 94 mm. Secondary and tertiary cone crushers (335 kW and 480 kW respectively) further reduce the material to a final product P80 of 9 mm. A fine ore stockpile with 12-hour live capacity ensures consistent feed to the grinding circuit. Belt magnets and metal detectors remove tramp metal throughout the crushing stages.
• Stage 2: Primary Grinding and Classification – Reclaimed material is fed to a 6.5 MW ball mill operating in closed circuit with a cyclone cluster. Process water maintains mill discharge at 70% solids, and the circuit is designed for 347 t/h throughput at 90% availability. Cyclone overflow at 35% w/w solids reports to flotation with a target P80 of 106 µm. Copper sulphate and promoter are added to the cyclone feed pumpbox to activate gold-bearing sulfides.
• Stage 3: Flotation (Rougher and Cleaner with Regrind) – Rougher flotation uses five 58 m³ cells with PAX collector, copper sulphate activator, and MIBC frother to produce a concentrate at 25% w/w solids. Rougher tailings combine with cleaner tailings for thickening. Cleaner flotation (four 12 m³ cells) upgrades the rougher concentrate, which is then reground in a 100 kW ball mill in closed circuit with cyclones to achieve a product P80 of 43 µm. Cleaner mass pull is limited to 4.2% of overall circuit feed.
• Stage 4: Pressure Oxidation and CCD – Reground concentrate slurry (50% w/w solids) is acidulated with sulfuric acid at 50°C in two agitated tanks (1-hour residence) to remove carbonates, reducing CO₂ generation in the autoclave. The acidulated slurry is fed to a horizontal autoclave with four compartments, operating at 200°C and 2,150 kPa (oxygen partial pressure 690 kPa) for 90 minutes. Oxidation autogenously maintains temperature. Oxidized slurry is flashed to atmospheric pressure and washed in a three-stage CCD circuit (3:1 wash ratio) to remove acid. A portion of the acidic overflow is recycled to pre-acidulation; the remainder is neutralized with lime and flotation tailings.
• Stage 5: Cyanide Leaching and Merrill-Crowe – Neutralized oxidized slurry (pH 10.5–11, 40% solids) undergoes cyanide leaching in three agitated tanks with oxygen sparging (20 ppm DO) for 12 hours, targeting 97% Au and 69% Ag extraction. The leached slurry is washed in a six-stage CCD circuit (5:1 wash ratio, >99% washing efficiency). Pregnant solution is clarified and deoxygenated, then mixed with zinc dust, lead nitrate, and cyanide in the Merrill-Crowe circuit (>99% precipitation efficiency). Precipitate is filtered and smelted in an induction furnace to produce gold-silver doré bars. Barren solution is recycled to CCD washing. Cyanide destruction using the SO₂/air process (1.5 hours residence) reduces WAD cyanide to <25 mg/L before tailings disposal.

Additional Interesting Data and Summary

The Courageous Lake Project’s gold recovery methods are underpinned by extensive design criteria summarized in Table 17-1. Key metallurgical parameters include head grades for gold (5.65 g/t), silver (0.8 g/t), sulfur (0.48%), arsenic (0.3%), and iron (2.3%). The flotation circuit achieves 85% silver recovery to concentrate, while the leach circuit extracts 97% gold and 69% silver. The POX autoclave operates at 90-minute residence time, 200°C, and 2,150 kPa, with oxygen partial pressure of 690 kPa. The three-stage CCD after POX uses a 3:1 wash ratio, and the six-stage CCD after leaching uses a 5:1 wash ratio to achieve >99% washing efficiency. The Merrill-Crowe circuit demonstrates >99% precipitation efficiency for both gold and silver. Cyanide destruction via the SO₂/air process treats leach residue in two parallel tanks (90 minutes residence) to reduce WAD cyanide below 25 mg/L. Reagent handling includes 12-month on-site storage for all consumables delivered via winter road. Key reagents include quicklime (slaked on site), copper sulphate (15% solution), PAX collector, Aero 208 promoter, MIBC frother, flocculant, and sodium cyanide. Environmental controls are integrated throughout: acidic solutions from POX are neutralized with lime and flotation tailings to pH 8.5 (solution) and pH 10.5–11 (solids) prior to leaching or disposal. The plant layout ensures dust collection, HCN gas detection, and secure gold room facilities. Economically, the pre-feasibility study and preliminary economic assessment (PEA) formed the basis for flowsheet selection, minimizing capital and operating costs without compromising functionality. The 2023 ALS testwork confirmed design parameters and identified optimization opportunities (see Section 25.3.2.3) for future implementation, such as potential improvements in reagent consumption or circuit configuration. The facility’s 12.6-year mine life at 2.74 Mt/a throughput underscores the project’s long-term significance in processing refractory gold ore. Forward-looking statements include continued refinement of the flowsheet to enhance gold recovery methods for this complex sulfide deposit.

Key Processes: Flotation, Cyanidation, Gravity Separation, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper, Zinc, Lead