The VR is the principal economic horizon at Moab Khotsong and the C Reef is the secondary economic horizon and contributes less than 5% of the mining. Both reefs are narrow tabular deposits forming part of the Witwatersrand Supergroup and are stratigraphically located near the middle of the Central Rand Group. The Vaal Reef lies approximately 255m below the C Reef.

The geology at Moab Khotsong is structurally complex with large fault-loss areas between the three predominant mining areas (Top mine, Middle mine and Zaaiplaats). The geological setting is one of crustal extension, dominated by major south-dipping fault systems with north-dipping Zuiping faults sandwiched between them. The De Hoek and Buffels East faults structurally bound the reef blocks of the Middle mine to the north west and south-east respectively and the northern boundary is a north-dipping Zuiping fault. Extensive drilling is taking place on the extremities of Middle mine targeting potential preserved blocks. Close infill drill spacing is required to delineate the structural definition between the major structures to optimise the mine design and extraction of the orebody.

The VR 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 a layer of barren orthoquartzite. The A Facies is the principal economic horizon at Moab Khotsong, but remnants of the C-Facies are sporadically preserved below the A-Facies. High gold values in the VR are often located at the base of this unit and are associated with high uranium values as well as with the presence of carbon. Uranium is an important by-product.

The C Reef is mined on a limited scale, in the central part of Top mine where a high-grade, north-south orientated sedimentary channel, containing two economic horizons, has been exposed. To the east and the west of this channel, the C Reef 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 at the base of the conglomerate. To the north of the mine, the C Reef sub-crops against the Gold Estates Conglomerate Formation and, in the extreme south of the mine, the C Reef has been eliminated by a deep Kimberley erosion channel and the Jersey fault.

The tabular nature, along with the depth and structural complexity of the orebody dictates the mining method utilised at Moab Khotsong mine. Mining at Moab Khotsong is based on a scattered mining method together with an integrated backfill support system that incorporates bracket pillars. The economic horizons are exploited between 1,791m and 3,052m below surface.

From December 2016 the decision was taken to hoist and process both stoping ore and development waste rock as one product. Moab Khotsong and Kopanang mines share the Great Noligwa gold plant. The design capacity of the Great Noligwa plant exceeds the maximum planned production volume from the two mines. The Great Noligwa plant employs the reverse gold leach method, whereby gold and uranium are recovered through gold cyanide and acid uranium leaching.

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.