Cooke is a deep level underground gold mine located along the northern and southwestern margins of the Witwatersrand Basin in South Africa. This mine is typical of the many Witwatersrand Basin operations, which have been the primary contributors to South Africa’s production of a significant portion of the world’s recorded gold output since 1886.

The Witwatersrand Basin comprises a 6,000-meter vertical thickness of sedimentary rocks, extending laterally for some 350 kilometres northeast to southwest by some 120 kilometres northwest to southeast, generally dipping at shallow angles toward the centre of the Witwatersrand Basin. The Witwatersrand Basin outcrops at its northern extent near Johannesburg, but to the west, south and east it is overlaid by up to 4,000 meters of volcanic and sedimentary rocks. The Witwatersrand Basin is Archaean in age, meaning the sedimentary rocks are of the order of 2.8 billion years old.

Gold mineralisation occurs within laterally extensive quartz pebble conglomerate beds called reefs, which are developed above unconformable surfaces near the basin margin. As a result of faulting and primary controls on mineralisation processes, the goldfields are not continuous and are characterised by the presence or dominance of different reef units. The reefs are generally less than two meters in thickness and are widely considered to represent laterally extensive braided fluvial deposits or unconfined flow deposits, which formed along the flanks of alluvial fan systems around the edge of an inland sea. Dykes and sills of diabase or dolerite composition are developed within the Witwatersrand Basin and are associated with several intrusive and extrusive events.

Gold generally occurs in native form, often associated with pyrite, carbon and uranium. Pyrite and gold within the reefs display a variety of forms, some obviously indicative of detrital transport within the depositional system and others suggesting crystallisation within the reef itself.

As early as 1923, the presence of uranium was noted in the Witwatersrand reefs. It was found that on average the reefs contain about 0.03% uranium and as a by-product of gold relatively low uranium grades can be recovered. Notwithstanding different opinions as to the origin of the uranium in the reefs, most theories accept localisation of both gold and uranium a function of sedimentary textures. Metal concentrations are directly related to the reefs. Exploration programmes and eventual evaluation of gold and uranium according to a placer philosophy, prove to be highly successful.

The most fundamental controls of gold and uranium distribution are the primary sedimentary features such as facies variation and channel directions. Consequently, the modeling of sedimentary features within the reefs and the correlation of payable grades within certain facies is key to in situ reserve estimation, as well as effective operational mine planning and grade control.

Mining methods:
• Cooke 1,2,3: conventional breast mining, scattered mining and pillar mining
• RSO: hydraulic reclamation (water jets), gravity feed to sump pump station and pumped via pipeline to processing plant

The current mine infrastructure consists of three producing shaft complexes that mine open ground and pillars (white areas). Cooke 4, previously operated at 1,634m below surface (58 Level at Cooke 4 SV Shaft), was declared non economical for exploitation from August 2016 and into the future. The decision was made to close the UG workings. The principal mining takes place on the Upper Elsburg Reef, which constitutes 75% of the underground Mineral Reserve ounces. The remainder of the mining takes place on the secondary reefs, namely the Kimberly formations (10%) and the VCR (10%). The remaining 5% is mined from historical surface TSF. The production from the previously four, now three, Cooke shafts is hoisted to surface separately.

U3O8 exclusions, as a result of logistics and the closure of Cooke 4 UG.

The Cooke Operations consist of three metallurgical plants.

The Cooke Plant was constructed in 1978 and has a nameplate capacity of 280,000tpm.

In 2005, it was converted from a reef treatment plant to treat sand from the nearby high-grade Dump 20 tailings storage facility (TSF). High grade ore from the Cooke 1, 2 and 3 shafts was diverted for toll treatment at Harmony’s Doornkop Plant. Doornkop ia a carbon-in-pulp plant.

Sibanye owns and manages significant extraction and processing facilities at its operations, where gold-bearing ore is treated and processed to produce gold doré.