Greenstone Gold Mine: Optimizing Gravity-Cyanidation Recovery

Source: Equinox Gold Corp (2026)
Website: https://www.equinoxgold.com/our-mines/greenstone-gold-mine/

Critical Data

Overview

Equinox Gold Corp. operates the Greenstone gold mine in Ontario, Canada, using a conventional gravity-cyanidation flowsheet with a nameplate capacity of 27,000 tonnes per day (t/d). Construction began in Q4 2021, with commissioning in Q1 2024. First gold was poured on May 22, 2024, and commercial production was reached on November 6, 2024. The plant processes run-of-mine ore through primary and secondary crushing, followed by a high-pressure grinding roll (HPGR) and ball mill comminution circuit. A gravity circuit captures coarse gold, while gravity tailings undergo leaching and carbon-in-pulp (CIP) adsorption. Loaded carbon is stripped via a Pressure Zadra system, and gold is recovered through electrowinning and smelting into doré bars. Cyanide destruction using the SO₂/O₂ process treats CIP tailings before storage in the tailings management facility. In 2025, the plant processed 7,777 kt of ore at an average head grade of 1.08 g/t Au, achieving an 84% gold recovery rate and producing 224,000 ounces of gold. The plant’s performance reflects a successful ramp-up towards nameplate capacity, with a peak daily throughput of 24 kt/d in 2025.

Key Process Stages

• Stage 1: Primary and Secondary Crushing – Run-of-mine ore is fed into a 1.3 m x 1.8 m gyratory crusher (450 kW) to achieve a P80 of 120–160 mm. Oversize screened material is further crushed by an MP1250 cone crusher to a P80 of 50–70 mm. Screen undersize at P80 35 mm is conveyed to a 57 kt crushed ore stockpile providing 16 hours of live storage.
• Stage 2: HPGR and Grinding with Gravity Recovery – Reclaimed ore passes through a 2.2 m x 2.0 m HPGR (2 × 2,580 kW) to produce a P80 of 25 mm. Screen undersize feeds two parallel ball mills (each 6.7 m diameter, 12.2 m EGL, 10,500 kW) in closed circuit with cyclones for a target grind of P80 90 µm. A gravity concentrator per line recovers coarse gold, feeding a single intensive leach reactor; gravity leach tailings return to the mill.
• Stage 3: Pre-Leach Thickening and Cyanidation – Cyclone overflow (P80 90 µm) flows to a 50 m diameter pre-leach thickener where flocculant increases slurry density to 55% solids. The thickened underflow enters a leach circuit comprising one pre-aeration tank and seven agitated leach tanks (each 18.6 m diameter × 23.5 m high, total residence time 30 h). Sodium cyanide and oxygen are added to dissolve gold, with lime maintaining pH 10–11.
• Stage 4: Carbon-in-Pulp – Leached slurry passes through seven CIP tanks (7 m diameter × 12 m high) in a carousel arrangement, each containing 18 tonnes of activated carbon at 50 g/L concentration. Gold cyanide complexes adsorb onto carbon over the counter-current flow. Once daily, loaded carbon (1 batch per tank) is pumped to the strip circuit via a loaded carbon screen; slurry returns to the CIP circuit.
• Stage 5: Carbon Elution, Regeneration, and Cyanide Destruction – Loaded carbon undergoes acid wash (HCl) to remove foulants, then elution in a 12-tonne Pressure Zadra system at 130°C and 450 kPa using a barren solution of 2% NaOH and 0.2% NaCN. Stripped carbon is regenerated in a 750 kg/h natural gas kiln. CIP tailings are treated in two 1,600 m³ agitated tanks via the SO₂/O₂ process (2 h retention, pH 8.5, copper sulphate catalyst) reducing CNWAD to 30 mg/L before pumping to the TMF.

Additional Interesting Data and Summary

The Greenstone process plant employs a comprehensive suite of reagents including sodium cyanide (briquette form, 18-tonne ISO containers), sodium hydroxide (50% liquid, 20-tonne tankers), quicklime (bulk silo, slaked to 23% slurry), flocculant (dry polymer), hydrochloric acid (33% solution, 22-tonne tankers), copper sulphate pentahydrate (1,250 kg bags), and liquid sulphur dioxide (two 80-tonne pressure vessels). Oxygen for leaching and cyanide destruction is supplied by an on-site vacuum-pressure swing-adsorption plant, backed by two liquid oxygen tanks. Power is generated by on-site natural gas turbines. Water supply includes process water (thickener overflow and TMF reclaim), treated water (from effluent treatment plant for strip circuit, ILR, gland seals, and reagent dilution), and potable water for safety showers and admin areas. The cyanide destruction process (SO₂/O₂) ensures environmental compliance by reducing weak acid dissociable cyanide to 30 mg/L. Economically, the mine produced 224,000 oz of gold in 2025, a significant increase from 112,000 oz in 2024, reflecting the ramp-up to nameplate throughput. Sustainability initiatives include reclaim water from the TMF, use of a carbon regeneration kiln to reduce fresh carbon consumption, and a carbon safety screen to capture fine carbon and recover residual gold. Future outlook involves continued optimization to reach consistent 27 kt/d throughput and further improve gold recovery beyond 84%. The facility is a modern, large-scale gold operation with a proven gravity-cyanidation flowsheet, representing a key asset for Equinox Gold Corp. in Ontario’s mining landscape.

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

Target Commodities: Gold, Copper