Courageous Lake Gold Recovery: POX, Flotation & Merrill-Crowe Process

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

Critical Data

Overview

The Courageous Lake Project, owned by Valor Gold Corp and located in Canada, employs a sophisticated, multi-stage gold recovery process designed to handle variable mineralogy and refractory ore. The flowsheet was selected based on extensive metallurgical testwork and economic modelling, combining standard technologies with a complex pressure oxidation (POX) circuit to achieve high gold and silver extraction. The process begins with three-stage crushing followed by ball mill grinding to a P80 of 106 µm. Rougher and cleaner flotation upgrade the gold-bearing sulphides, producing a concentrate that undergoes acidulation and POX at 200°C to liberate encapsulated gold. The oxidized slurry is washed in a three-stage CCD circuit and then leached with cyanide for 12 hours. Pregnant solution is processed via Merrill-Crowe precipitation, where zinc dust cements gold and silver, which are smelted into doré bars. Tailings are detoxified using the SO₂/air process before disposal. With a design throughput of 7,500 t/d and a gold head grade of 5.65 g/t, the recovery methods at Courageous Lake are optimized for both refractory and free-milling ore fractions, making it a significant gold project in Canada. The plant achieves 88% gold recovery to concentrate and 97% leach circuit extraction, underscoring the effectiveness of the integrated flowsheet. This comprehensive gold recovery process reflects the project’s commitment to technical robustness and environmental responsibility.

Key Process Stages

• Stage 1: Crushing and Grinding – Run-of-mine ore is reduced through a primary jaw crusher (110 kW), secondary cone crusher (335 kW), and tertiary cone crusher (480 kW) to a P80 of 9 mm. Crushed material is stockpiled and fed to a 6.5 MW ball mill operating in closed circuit with cyclones, producing a grinding circuit product P80 of 106 µm. Process water is added to maintain mill discharge at 70% solids.
• Stage 2: Rougher and Cleaner Flotation – Cyclone overflow at 35% solids reports to five rougher flotation cells (58 m³ each) using PAX, CuSO₄, and MIBC. Rougher concentrate (max 11% mass pull) is upgraded in four cleaner cells (12 m³ each) to a maximum of 4.2% mass pull, achieving 88% Au and 85% Ag recovery to concentrate. Cleaner concentrate is reground in a 100 kW ball mill to a P80 of 43 µm.
• Stage 3: Concentrate Acidulation and Pressure Oxidation – Reground concentrate at 50% solids is acidulated with sulfuric acid at 50°C for 1 hour to decompose carbonates, then fed to a horizontal autoclave operating at 200°C and 2,150 kPa with 90 minutes residence time. Oxygen sparging maintains 690 kPa partial pressure. Oxidized slurry is flashed to atmospheric pressure and washed in a three-stage CCD circuit.
• Stage 4: Cyanide Leaching and CCD – Neutralized solids (pH 10.5–11) are leached in three agitated tanks with cyanide and oxygen for 12 hours. Leach extraction is 97% Au and 69% Ag. A six-stage CCD circuit washes the leach residue with a 5:1 wash ratio, achieving >99% washing efficiency. Pregnant solution is clarified before Merrill-Crowe.
• Stage 5: Merrill-Crowe Precipitation and Refining – Clarified pregnant solution is de-aerated in a tower and mixed with zinc dust, lead nitrate, and cyanide to precipitate gold and silver. Precipitation efficiency exceeds 99%. The precipitate is filtered, dried, and smelted in an induction furnace to produce gold-silver doré bars. Barren solution is recycled to the CCD circuit.

Additional Interesting Data and Summary

The Courageous Lake Project recovery methods incorporate extensive technical data to ensure robust performance across variable ore types. Key design parameters include a Bond crusher work index of 24 kWh/t, a Bond rod mill work index of 18.1 kWh/t, and a Bond abrasion index of 0.19. The regrind mill specific energy is 9.2 kWh/t, and the oxidation circuit operates at 200°C with a design pressure of 2,580 kPag. The POX circuit has a residence time of 90 minutes, followed by a three-stage CCD with a 3:1 wash ratio. Cyanide leaching residence time is 12 hours, and the Merrill-Crowe circuit achieves >99% precipitation efficiency using zinc dust and lead nitrate. The cyanide destruction system, employing the SO₂/air process, reduces WAD cyanide to <25 mg/L in tailings before disposal to the Leach Residue Tailings Facility (LRTF). Reagent handling and storage are designed for 12-month supply via winter road deliveries, with lime, copper sulphate, PAX, MIBC, flocculant, and sodium cyanide stored on site. Annual reagent consumption is summarized in the report but not detailed here. Environmental considerations are integrated throughout: acidic solutions from POX are neutralized with lime and flotation tailings to pH 8.5–10.5, and the plant includes dust collection and HCN gas detection systems. Economically, the project is based on a 12.6-year mine life at 2.74 Mt/a throughput, with processing costs optimized through trade-off studies. Sustainability initiatives include high water recycling via CCD circuits and detoxification of tailings. Future outlook, as noted in Section 25.3.2.3, identifies opportunities for further optimization based on 2023 testwork, potentially improving recovery and reducing costs. The facility’s design emphasizes operational reliability with 90% availability for grinding and oxidation circuits, and a plant layout that minimizes footprint while enabling safe, efficient maintenance. This gold recovery process sets a benchmark for refractory ore treatment in northern Canada, balancing technical complexity with environmental stewardship and economic viability.

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

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