Copper-Gold Recovery Methods at Centerra Gold’s Kemess Project

Source: Centerra Gold Inc (2026)
Website: https://www.centerragold.com/operations/kemess-project/default.aspx

Critical Data

Overview

Centerra Gold Inc. operates the Kemess Project, a major copper-gold mining operation located in north-central British Columbia, Canada. The original plant operated from 1999 to 2011 and has been on care and maintenance since; now it is being restarted with a 16-year mine life processing 50,000 tonnes per day. The recovery methods are designed to produce a gold-rich copper concentrate and gold doré, combining conventional flotation with a carbon-in-pulp (CIP) leach plant. The process begins with two-stage crushing: a gyratory crusher for open-pit ore from the Main Zone and a jaw crusher for underground material. After crushing to 150 mm, ore is conveyed to a coarse stockpile then fed to two parallel SAG and ball mill grinding circuits. The grinding target is a P80 of 42 µm for flotation feed. Rougher flotation using Wemco cells produces a concentrate that undergoes regrinding in a ball mill followed by high-intensity grinding in an HIGmill. Three stages of cleaning, including a Jameson Cell and flotation columns, upgrade the concentrate to approximately 23% copper. Cleaner-scavenger tails, containing 0.49–1.15 g/t gold, are processed in a conventional cyanide leach circuit with six leach tanks and a six-tank CIP circuit. Gold is stripped via high-temperature elution and electrowinning to produce doré bullion. Leach tailings undergo SO2/O2 cyanide destruction before deposition in the old Kemess South pit. This integrated flowsheet achieves design recoveries of 89.1% for copper and 61.0% for gold, with the flexibility to adjust concentrate grade based on market conditions.

Key Process Stages

• Stage 1: Crushing and Material Handling – Open-pit ore is crushed by a new gyratory crusher (50,000 tpd, 70% availability) to a P80 of 150 mm, while underground ore is crushed by a new jaw crusher (8,000 tpd). Both streams are conveyed via a multi-leg overland system with energy-recovery drives to a coarse stockpile with 74,200 t live capacity. Reclaim uses six apron feeders feeding two SAG mill conveyors.
• Stage 2: Grinding Circuit – Two parallel lines each consist of a 10.36 m diameter × 4.65 m SAG mill with twin 5,250 kW motors (variable speed) and a 6.7 m × 11.1 m ball mill with twin 5,250 kW motors. Line B is refurbished; Line A is new. SAG mill discharge is screened; oversize pebbles return without crushing. Ball mill circuit achieves a cyclone overflow P80 <42 µm at 36% w/w solids, with a ball mill circulating load of 380%.
• Stage 3: Rougher Flotation and Regrind – Grinding cyclone overflow feeds three parallel banks of Wemco rougher cells (eight 130 m³ per bank). Rougher concentrate (10% mass pull) is classified in a regrind cyclone cluster; underflow reports to a refurbished 16.5 ft × 36.5 ft regrind ball mill (1,100 kW) targeting P80 of 40 µm. A gravity concentrator treats a portion of the circulating load, sending gold directly to final concentrate. Cyclone overflow advances to first cleaner flotation.
• Stage 4: Cleaner Flotation with High-Intensity Grinding – First cleaner and cleaner-scavenger stages use eight 130 m³ tank cells (re-purposed fourth rougher line). First cleaner concentrate is reground in a new HIGmill (1,100 kW) with Cyclopac to P80 <20 µm. Product feeds a new Jameson Cell for secondary cleaning; concentrate advances to a refurbished third cleaner column and scavenger column. Column concentrate goes to dewatering; column tails recycle to first cleaner. Cleaner-scavenger tails report to the leach plant.
• Stage 5: CIP Leach and ADR Gold Recovery – Cleaner-scavenger tails are thickened (38 m diameter pre-leach thickener) to 50% w/w solids, then leached in six 13 m × 16 m agitated tanks with cyanide and oxygen (residence time ~12 h). Leach slurry enters a six-tank CIP circuit in carousel mode. Loaded carbon (4 t batches) is acid-washed, eluted at 135°C and >240 kPa, and gold is recovered by electrowinning and smelting into doré bullion. Stripped carbon is regenerated at 750°C. Cyanide destruction using SO2/air in two tanks (3 h retention) treats final tails before disposal.

Additional Interesting Data and Summary

The Kemess Project recovery methods incorporate extensive refurbishment of existing equipment combined with new installations to reinstate a 50,000 tpd throughput. Process design criteria include a Bond abrasion index of 0.06, SMC parameters (Mia 19.4 kWh/t, Mib 20.5 kWh/t, Mic 7.4 kWh/t), and a SAG mill circulating load of 29%. Flotation mass pull to final concentrate is 0.58%, with concentrate thickening designed at 0.1 t/m²/h and filtration at 610 kg/m²/h. Reagent consumption is managed through a comprehensive system: lime for pH control and pyrite depression, SEX as collector, CMC as depressant, R3477 activator, MIBC frother, and flocculant for thickeners. The leach circuit adds hydrochloric acid, sodium cyanide, activated carbon, sodium hydroxide, and liquid SO2 for cyanide destruction. Environmental considerations are integral: tailings are deposited into the old Kemess South pit for the life of mine, and cyanide destruction via SO2/air ensures detoxification before discharge. No separate leach tailings are generated as the CIP circuit processes only cleaner-scavenger tails. Economic impact is significant, producing a gold-rich copper concentrate (target 23% Cu) shipped via truck to Mackenzie, BC, then rail to North Vancouver for ocean transport. Gold recovery from the CIP/ADR circuit boosts global gold recovery by processing a pyrite-rich feed grading 0.49–1.15 g/t Au. Sustainability initiatives include energy-recovery drives on downhill conveyor segments, reuse of existing infrastructure, and refurbishment of major equipment to reduce capital and environmental footprint. The future outlook is robust with a 16-year mine life, processing material from the Main Zone and underground deposits. The design flexibility to adjust concentrate grade based on metal prices and smelter terms provides operational resilience. Overall, the Kemess Project represents a strategic restart of a brownfield site with established infrastructure, leveraging advanced flotation and cyanidation technologies to maximize copper and gold recovery while minimizing environmental impact.

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

Target Commodities: Gold, Copper