The Tom's Gully mill is a carbon-in-leach mill with a capacity of 250,000 tonnes per year or 800 tonnes per day and was commissioned in 1995. It is designed to recover gold from arsenopyrite rich ore. The gold is typically 1-2 micron particles associated with the arsenopyrite, and requires fine grinding to liberate sufficiently to attain the target 85% gold recovery. It consists of:

Two stage crushing circuit
Closed circuit single stage primary ball mill grinding circuit
Sulphide flotation section
Ultra fine grinding circuit for flotation concentrates
Thickening circuit for float tails and reground concentrates
Five stage CIL circuit
Two tonne carbon AARL (Anglo American Research Laboratories) carbon stripping plant, carbon regeneration and gold room.

There are two permitted tailings dams constructed at Tom's Gully.

Crushing

Run of Mine ore is reclaimed from stockpiles by a wheel loader and tipped into a ROM bin protected by a 600 millimetre aperture grizzly.

A vibrating feeder transports ore from the ROM bin to a 24 inch by 36 inch Jaw Crusher. Jaw crusher product is transported to a 14 millimetre aperture single deck screen by conveyor belts. Tramp steel in the Tom's Gully ore is removed by a belt magnet to protect the secondary cone crusher and conveyor belts. Screen undersize (minus 14 millimetre) product is conveyed to a 800 tonne stockpile, while screen oversize (plus 14 millimetre product) is transported to a Sandvik H3800 secondary cone crusher. Secondary crusher product returns to the screen.

Primary Grinding

Stockpiled crushed ore is reclaimed using a wheel loader and tipped into a 30 tonne capacity Mill Feed bin. Ore is transported by conveyors from the bin to a 1 megawatt 5.7 metre by 3.4 metre Outokumpu Primary Ball Mill. The ball mill is in closed circuit with hydrocyclone classifiers, with primary grind product designed to be 80% passing 75 microns at 31 tonnes per hour.

Flotation

Primary grind product reports to an agitated flotation conditioning tank. Copper sulphate activator is added to improve the flotation response of the sulphide minerals in the ore, particularly the arsenopyrite, then sodium isobutyl xanthate is added as the flotation collector. Frother is added to the first flotation cell. Two rougher flotation cells of 20 cubic metre total capacity recover approximately 25% of the total feed mass into a flotation concentrate, which reports fine grinding. Flotation tailings report to the Carbon-in-Leach feed thickener.

Fine Grinding

Flotation concentrate at approximately 8 tonnes per hour reports to a 600 kilowatt 5 metre by 3 metre secondary ball mill in closed circuit with hydrocyclones, designed to further reduce product size to 80% passing 38 microns. Hydrocyclone overflow product of less than 38 micron size reports to a 250 kilowatt Vertical Tower Mill which is in closed circuit with hydrocyclones, designed to grind the flotation concentrate down to a final product size of 80% passing 12 microns. Fine grinding final product reports to the Carbon-in-Leach feed thickener.

Carbon-in-Leach

The CIL Feed is thickened to 50% solids by weight in a 14 metre diameter hydraulic drive thickener. Slaked lime for pH control is dosed into the thickened CIL feed slurry which then reports to a 3 metre by 1.2 metre 800 micron aperture Trash Screen to remove contaminant trash particles. Screened slurry product has cyanide solution added and reports to the first of six 115 cubic metre volume leach/adsorption tanks. Total residence time for leaching and adsorption is 14 hours. Activated carbon is maintained at a concentration of 30 grams per litre in the slurry, and carbon is moved counter-current to the slurry flow using batch movement. Carbon is retained within each tank by mechanically wiped 1 millimetre cylindrical screens. CIL tailing from the last tank is passed over a 800 micron carbon safety screen before being pumped to the tailings dam for final deposition.

Elution/Goldroom

Loaded activated carbon is recovered on a batch basis from the first CIL tank once a gold-on-carbon loading target of approximately 3000 g/t is achieved. The loaded carbon is screened and washed to remove slurry, and the carbon is placed in a 2 tonne capacity elution column. The carbon is acid washed to remove inorganic contaminants. Elution of the carbon is conducted using the AARL soak-wash method at 110°C. Pregnant eluate solution reports to an electrowinning cell where the gold is won to steel wool cathodes. The cathode gold is smelted to bullion in a gas-fired furnace.

Barren carbon is transferred from the elution column to a storage hopper, before being dewatered and dried and regenerated in a gas-fired vertical kiln. Regenerated carbon is passed over a fine carbon removal screen, then returned to the last CIL tank for gold adsorption.