Kloof 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 method Scattered stoping, mini-longwall stoping with closely spaced dip pillars (110 x 40m and 100 x 35m regional pillars) and surface rock-dump mining.

The Kloof is principally an underground mine with nominal surface reserves represented by SRDs and TSFs accumulated during the operating history of the mine.

The Kloof Operation is a complex of intermediate to ultra-deep level mines, predominantly mining the Ventersdorp Contact Reef, at depths of between 1,300m and 3,350m below surface. Kloof’s existing scope of operation is the result of the consolidation of the Kloof, Libanon, Leeudoorn and Venterspost mines in 2000.

Gold mining began in the area now covered by these operations in 1934.

Kloof’s operations comprise five producing shaft systems.

Kloof’s operations comprise two metallurgical gold plants. The Kloof 1 Plant (KP1) was commissioned in 1968 and originally designed to process underground ore. It was converted to process surface reclamation dumps in 2001. KP1 comprises three-stage crushing, open-circuit rod mills for primary grinding and closed circuit pebble mills for secondary milling. This is followed by cyanide leaching, filtration, zinc precipitation and smelting.

The Kloof 2 Plant (KP2) was commissioned in November 1990 and currently treats all of Kloof’s underground ore. Reef is trucked and conveyed to a central stacker pad, which feeds two SAG mills equipped with variable-speed ring motor drives. Milling is followed by cyanide leaching, CIP and treatment at an independent elution and smelting facility. The elution facility was upgraded in June 2001 and again in October 2003 to process loaded carbon from KP1 and the former KP3 (Libanon) plant. The upgrade included the installation of continuous electro-winning sludge reactors.

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