Goose Mill Design Pairs a Ball Mill With a Stirred Mill to 45 µm Ahead of Pre-Aeration, Leach and a CIP Carousel

B2Gold's technical report on the Goose Project and Back River District in Nunavut, effective December 31, 2024, sets out a 4,000 t/d gravity, leach and carbon-in-pulp plant designed for 92.5% overall gold recovery.

The NI 43-101 Technical Report for the Goose Project and Back River District, Nunavut, Canada, was prepared for B2Gold Corp. with an effective date of December 31, 2024. It describes the process plant for gold ore from the Goose open pit and underground operations. The flowsheet combines three-stage crushing, ball milling and stirred-media fine grinding, gravity concentration with intensive leaching, pre-aeration and cyanide leaching, a carousel carbon-in-pulp (CIP) circuit, SO2/air cyanide destruction, and carbon elution, regeneration and refining. Tailings are thickened and sent to a tailings storage facility (TSF).

Critical Data

Overview

Ore from the open pit and underground mines will be hauled in 70 t trucks to a run-of-mine stockpile and fed by front-end loader to a static grizzly over the ROM bin, with a mobile rock breaker for oversize. The crushing circuit runs at 70% availability, and the dome-covered fine ore stockpile decouples it from the mill, which runs at 92% availability.

Grinding is in two stages: a ball mill to about 175 µm, then a 3 MW stirred media mill to a final P80 of 45 µm. Two gravity circuits, one on ball mill discharge and one on secondary cyclone underflow, target 40% of the gold, which is recovered by intensive leaching. The rest of the gold is leached after thickening and pre-aeration and adsorbed in an eight-tank CIP carousel. The design overall gold recovery is 92.5%.

Key Process Stages

Primary crushing. A vibrating grizzly feeder with 100 mm spacing draws from the ROM bin. Oversize feeds the primary jaw crusher, which produces about 170 mm, and undersize bypasses onto the crusher discharge conveyor.

Screening, secondary and tertiary crushing. A double-deck banana screen with 32 mm and 10 mm decks produces the final product at P80 about 7.4 mm. Top-deck oversize goes to a secondary crusher with a 25 mm closed side setting (product P80 about 22 mm). Bottom-deck oversize goes to a short-head tertiary crusher with a 12 mm closed side setting (P80 about 13 mm). Both discharge back to the screen. Bypass chutes let either crusher be shut down for maintenance at reduced throughput.

Fine ore stockpile. The dome-covered stockpile holds 9,440 t in total, about 2.5 days, and 2,000 t live, enough for 12 hours of milling without the crushers. Two belt feeders in a reclaim tunnel can each supply the full plant feed. Quicklime is added on the ball mill feed conveyor for pH control.

Grinding. The 4.6 m by 9 m ball mill with a 3.3 MW motor runs in closed circuit with a cyclone bank designed for 300% circulating load, discharging through a trommel to a trash bin. Cyclone overflow at about 175 µm goes to a secondary cyclone cluster (five operating, four standby) in closed circuit with the 3 MW stirred media mill, giving the final 45 µm grind.

Gravity concentration. A scalping screen protects the centrifugal concentrators, which are periodically switched to flushing mode to collect concentrate. The concentrate is treated in an Acacia intensive leach reactor, and its pregnant solution is electrowon in the refinery. Reactor tails and decanted fines return to the primary grinding circuit.

Thickening. Secondary cyclone overflow passes a 10.1 m² trash screen with 800 µm by 11 mm slots, then an 18 m pre-leach thickener that raises the slurry to 52% solids. Thickener overflow becomes process water.

Pre-aeration and leaching. Thickened slurry is pre-aerated to passivate sulphides, which reduces cyanide consumption and improves recovery, with lead nitrate added and dissolved oxygen held at 20 to 25 ppm. It is then leached for 32 hours at 250 ppm sodium cyanide in insulated tanks outside the main process building.

CIP carousel. The eight-tank CIP circuit inside the process building does not pump carbon counter-current. A distribution launder feeds the slurry to whichever tank is currently at the head of the series. When the head tank's carbon reaches about 5,300 g/t Au and 2,700 g/t Ag, its carbon is pumped to elution and replaced with regenerated carbon, and that tank becomes the last in the series. The average carbon concentration is expected to be 67 g/L.

Acid wash, elution and regeneration. Loaded carbon is washed with 3% hydrochloric acid. It is then stripped in one of two 4 t elution columns with about 1.5% sodium hydroxide and 0.2% sodium cyanide at 145°C, with a heat recovery exchanger on the outgoing solution. At 4,000 t/d one elution a day is expected. A horizontal rotary kiln treats 4 to 8 t/d of carbon. Virgin carbon is pre-attritioned before use.

Electrowinning and refining. Strip and intensive leach solutions are electrowon. The sludge is filtered, dried, fluxed and smelted in an induction furnace to doré, with 99% electrowinning recovery in the design criteria.

Cyanide destruction and tailings. Two agitated tanks of 1.35 hours each treat the CIP tails by the SO2/air process at 6.5:1 SO2:CNWAD, using sodium metabisulphite, copper sulphate at 24 ppm and lime to hold pH 8.0 to 8.5. Treated slurry is thickened and pumped to the TSF.

Additional Interesting Data and Summary

At design throughput the plant uses 504.5 m³/h of process water: 291.0 m³/h of pre-leach thickener overflow, 176.1 m³/h of tailings thickener overflow, 4.4 m³/h of gland water and 33 m³/h of reclaim water. Reclaim water from the TSF, 120.3 m³/h, serves areas that need cleaner water, and 38.2 m³/h of fresh water is pumped from Goose Lake. Consumables include 1.2 kg/t of grinding balls, 0.3 kg/t of ceramic media, 0.53 kg/t of sodium cyanide, 3.2 kg/t of quicklime, 1.24 kg/t of sodium metabisulphite, 0.12 kg/t of copper sulphate and 40 g/t of flocculant.

Some figures differ within Section 17 of the report. The text says three pre-aeration tanks in one place and two in another. The design criteria table gives a CIP carousel residence time of 2.1 hours, while the text describes a total CIP slurry retention of 16 hours in eight tanks. This article reports each figure as the report states it.

In summary, the Goose plant is a conventional gravity and leach-CIP gold design for 4,000 t/d. Its notable features are a fine 45 µm grind from a stirred mill, oxygen pre-aeration with lead nitrate ahead of the leach, and a carousel CIP circuit that moves the feed point instead of the carbon.

Key Processes

• Jaw crushing with secondary and tertiary cone crushing to P80 7.4 mm
• Ball milling and stirred-media fine grinding to P80 45 µm
• Gravity concentration with Acacia intensive leaching
• Pre-leach thickening to 52% solids
• Oxygen pre-aeration with lead nitrate
• Cyanide leaching
• Carousel carbon-in-pulp
• Acid wash, pressure elution and rotary kiln regeneration
• Electrowinning and induction furnace smelting to doré
• SO2/air cyanide destruction and tailings thickening

Source: Goose Project and Back River District, Nunavut, NI 43-101 Technical Report, prepared for B2Gold Corp., effective date December 31, 2024.