South Deep is located in the Far West Rand Goldfield on the north-western rim of the Witwatersrand Basin. This basin comprises a 6,000 metre-thick sequence of predominantly clastic sedimentary rocks, the upper part of which, the Central Rand Group, is characterised by the occurrence of auriferous and uraniferous quartzpebble conglomerates (reefs) that are sporadically interspersed between finer grained quartzitic units. All major reef units are developed above unconformity surfaces. The angle of unconformity is typically greatest near the basin margin and decreases toward more distal areas.

The reefs are considered to represent extensive fluvial deposits into a yoked basin, some 350 kilometres long in an east-north-easterly direction, and 200 kilometres wide in a northnorth-westerly direction. The reefs are continuous as a consequence of the regional nature of the erosional surfaces. Preferential reef development within channel systems and sedimentary features such as facies variations and channel frequency assist in mapping out local gold distributions.

The gold is deemed to be primarily of detrital origin, deposited syngenetically with the conglomerates. Although the gold generally occurs in native form and is usually associated with pyrite and carbon, most of it has been subsequently modified and locally remobilised during secondary hydrothermalism. The most fundamental control to the gold distribution remains the association with quartz-pebble conglomerates on intrabasinal unconformities. The Modified Palaeoplacer Model is the favoured mineralisation model that is currently in use.

South Deep is an underground mine, using an owner mining workforce. Operations are accessed through development and a 5.5m high destress cut to manage rock stress and seismic activity. A number of selective mining methods, including drifts and benches, are employed but long-hole stoping with paste fill is the primary bulk mining method. Significant focus has been on frontline coaching to improve compliance to stope design and productivity. Mining method and extraction sequence optimisation is ongoing.

The workings are accessed from the surface through two shaft systems, the Twin Shaft Complex (main and ventilation shafts), of which the main shaft a single-drop to 110A level, a depth of 2,998m, the vent shaft to 110 level (2,947m) and the South Shaft Complex, which is a sub-vertical system (three operating shafts) to 95 level at a depth of 2,786m.

The mine is divided into three main areas:

1. Current Mine (CM), characterised by selective mining methods scattered over a large area originally exploited by means of conventional tabular mining. CM is accessed from four active levels (90, 93 and 95) from both the South Shaft and Twin Shaft complexes.

2. The NoW area, directly south of CM, comprises six mining corridors separated by regional pillars that extend southwards to the Wrench fault. A bulk non-selective mining method is applied here resulting in a higher Resources to Reserves conversion ratio.

3. SoW East and West, situated south of NoW, which will be mined in the same manner as NoW.

The milling circuit includes a semi-autogenous grinding (SAG) mill for primary and secondary milling, which is conducted in two overflow ball mills. Classification is done using a cluster of cyclones. Four Knelson concentrators facilitate the recovery of free gold and the concentrate is tabled in the smelthouse using a Gemini Table. The cyclone overflow is thickened before the slurry reports to the leach circuit, which has 10 mechanically agitated tanks, each with a 3,000 cubic metres volume.

Cyanide is used for gold dissolution and lime is added to ensure protective alkalinity. An eight-stage, carousel-type carbon-in-pulp (CIP) circuit is used for gold adsorption. Each tank in the train is 200 cubic metres. Carbon stripping is achieved using the AARL elution system, while carbon regeneration is carried out in a rotary kiln at a rate of 500 kg/hr.

Gold is recovered from the solution by using electro-winning Sludge Reactors, and then dried. This is followed by sme ........