Kopanang is situated in a structurally complex area of the Witwatersrand Basin, which has been subjected to numerous tectonic events. The VR is the principal economic horizon at Kopanang and the CR the secondary economic horizon. Both reefs are part of the Witwatersrand Supergroup and are stratigraphically located near the middle of the Central Rand Group. The CR forms the top of the Johannesburg Subgroup, while the VR lies approximately 255m below the CR. The two narrow tabular orebodies are both gold and uranium bearing and currently only the VR is mined, with limited CR mining planned during the LoM. The CR is accessible through the VR infrastructure. These conglomerate units dip at an average of 21° towards the south and occur in a 2,100m thick sedimentary sequence comprising the Central Rand Group.

Mining is complicated by the presence of an assortment of steep (85°–50°) north-dipping and younger low-angle (50°–15°) southdipping faults. The interplay of these main fault regimes, along with abundant pre and post dating dykes, makes for a complex and geologically challenging deposit.

The VR package varies from about 10cm or less in thickness to over 2.5m. It consists of a thin basal conglomerate (the C-Facies) and a thicker sequence of upper conglomerates (the A-Facies). These two sedimentary facies are separated by the B-Facies, which is barren interbedded orthoquartzite. The A-Facies is further subdivided into three sub-facies, known as the Bottom, Middle and Top sub-facies or the tripartite. The C-Facies is well developed at Kopanang and is the principal economic horizon of the VR. The C-Facies consists of a thin, basal pebble lag overlain by pebbly quartzites rather than clast-supported conglomerates. The overlying pebbly quartzites generally have a low gold content. Elevated gold grades have been known to be associated with well developed and well packed conglomerates; although at times these conglomerates may be thin in nature.

The CR is poorly developed with relatively small areas of economic interest. As with the VR, high uranium values are also often associated with high gold values and the presence of a 5mm to 2cm thick carbon seam is found at the base of the conglomerate.

Two gold-bearing VR and C-Reef horizons are accessed via a single-shaft system which descends to a maximum depth of 2,334m, while the main working levels are situated between 1,300m and 2,064m below surface. A sequential grid mining layout is used from which scattered mining takes place.

Stoping ore and development rock is hoisted and processed as one product. Moab Khotsong and Kopanang mines share the Great Noligwa gold plant, and this plant’s design capacity exceeds the maximum planned production from the two mines. Gold and uranium is recovered through gold cyanide and acid uranium leaching. The reef is milled at the Great Noligwa gold plant and processed at the South Uranium plant for uranium oxide extraction prior to gold extraction at the Great Noligwa gold plant.

Broken rock handling is track-bound, transferred to a number of inter-level sub-vertical transfer systems that gravity feeds to the main silos on 75 level. The rock is hoisted to surface through the main shaft. From the shaft the rock is transported to the processing plant by train. From December 2015 the decision was taken to process both stoping ore and development rock as one product. This allows for the independent re processing of the Kopanang low grade stockpile. Moab Khotsong and Kopanang mines share the Great Noligwa gold plant, and this plant’s design capacity exceeds the maximum planned production from the two mines. Gold and uranium is recovered through gold cyanide and acid uranium leaching.

The dissolved gold in the leached slurry is recovered onto activated carbon in the CIP (carbon in pulp) section consisting of eight mechanically agitated adsorption tanks. The gold loaded carbon is screened out of the slurry before being washed and transferred to the elution circuit.

In the elution circuit the carbon is washed with a hot caustic solution to strip the gold back into solution following which the gold bearing solution passes through the electrowinning section where the gold is plated onto stainless steel cathodes and smelted to produce gold bullion for refining.

The slurry exiting the adsorption section is pumped to the floatation plant where the material is acidified and conditioned prior to floatation for pyrite recovery. Backfill material for use as underground support is produced from the neutralised floatation residue material. The initial acidification and subsequent floatation process effectively destroys the residual cyanide in the material used to produce the backfill. The neutralised floatation residue material (Monitored for WAD Cyanide, Free Cyanide with a WAD Cyanide analyser) not taken for backfill production is pumped to the final residue stream exiting the plant to the Mispah TSF.

Low grade waste rock is also treated in the Noligwa gold plant through the low grade Mispah milling and recovery circuit. Following run-of mine milling, the slurry is subjected to a cyanide leach followed by gold adsorption in a carousel operated CIP plant. Cyanide dosing control to the Mispah leach circuit is achieved by means of an on-line cyanide titrator integrated into a control loop linked to the dry tonnage feed.