The North Mara Mine is situated within the Mara Greenstone Belt. The underlying geology comprises felsic and mafic volcanics intercalated with sediments which are intruded by various granitoid and gabbroic plutonic rocks. Tertiary volcanic lava flows partially cover the underlying Archaean geology and the ore bodies are structurally controlled, shear-hosted lode gold deposits. There are several types of gold mineralisation including shear-zone-related quartz vein and disseminated gold.

The mine is a combined open pit and underground operation from two deposits, Gokona (underground) and Nyabirama (open pit).

At Gokona, Acacia utilizes an existing exploration decline for initial access to the planned underground mine. Two major declines are included in the mine plan. Mining will be by long hole open stoping with cemented aggregate fill.

Both oxide and sulphide reserves are mined and processed by conventional carbon-in-leach (CIL) technology.

The ore is hauled in 80 tonne dump trucks up to the Run of Mine (ROM) pad at Nyabirama. The ore is drawn out of the ROM bin and fed onto a vibrating grizzly screen by means of an apron feeder. The undersize material passes through the grizzly onto a conveyor belt while the oversize material passes through a jaw crusher which discharges onto the same conveyor belt. The ore is fed onto a banana screen via a two tier conveyor system. The undersize from the banana screen passes onto a conveyor belt which feeds the SAG mill feed stock pile while the oversize material is fed into a secondary cone crusher. The crushed ore from the secondary stockpile is tipped onto the SAG feed stockpile.

The ore is drawn from underneath the SAG mill feed stockpile onto the SAG mill feed conveyor belt by means of three vibrating feeders. It is fed into the SAG mill for primary grinding. The SAG mill discharge is pumped to a cluster of twelve cyclones for classification. The cyclone overflow is fed to two trash screens whilst the underflow reports to a scalping screen prior to gravity concentration. Screen overflow is recombined with gravity circuit tails and reports to 2 ball mills in closed circuit with the classification cyclones. The concentrate from the Knelson Concentrators is fed to the Acacia reactor in the gold room for gold recovery by intensive Cyanidation. Acacia tailings are returned to the ball mill circuit and pregnant solution is pumped to electrowinning cells.

The trash screen overflow falls into a bunker whilst the underflow is fed to two thickeners. Thickened slurry is pumped to the CIL circuit and water recovered from the thickeners is pumped back to the mill circuit as process water. The CIL circuit consists of three pre-leach tanks and nine adsorption tanks. Carbon is transferred counter current to slurry flow by means of air lifts and is pumped from Tank 4 over the loaded carbon screen before being transferred to the acid wash section.

Residue from the CIL section is pumped to a cyanide detoxification circuit where WAD cyanide concentrations are reduced to less than 50ppm before final plant tailings are routed to the tailings storage facility (TSF). Following deposition, solution from the TSF supernatant pond is pumped back to the plant as process water.

Loaded carbon from the CIL circuit is acid treated using HCl before loaded gold is stripped from the carbon using the AARL (Anglo American Research Laboratory) elution process. Cyanide is not used in the elution circuit. Eluted carbon is regenerated in a rotary kiln and returned to the CIL circuit.

Eluate solution is passed to two electrowinning cells for gold recovery. Gold electroplates onto cathodes which are periodically removed and washed with high pressure spray water to produce a gold slime which is dewatered in a plate and frame filter press. The gold sludge filter cake is dried in calcine ovens and smelted on site before being dispatched as dorê bars.

The process plant has the capacity to process an average of 8,000 tonnes of ore per day, (or c. 2.8 million tonnes per year) and produces doré.