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.

Kloof, a shallow to ultra-deep level gold operation, was formed when the Venterspost, Libanon, Leeudoorn and Kloof gold operations were amalgamated in 2000. The first shaft however, was already established in 1934 at Venterspost. The Kloof operation is situated in the West Wits Line of the Witwatersrand Basin, near the towns of Randfontein and Westonaria, approximately 60km west of Johannesburg, in the Gauteng province of South Africa.

Kloof has seven vertical shaft complexes (four with sub-shafts) and two mineral processing plants. Supporting infrastructure to service the operating shaft sections is also in place:
• Thuthukani (1 Shaft) – operational;
• Hlalanathi (3 Shaft) – operational;
• Ikamva (4 Shaft) – operational;
• Manyano (7 Shaft) – operational;
• Masimthembe (8 Shaft) – operational;
• 9 Shaft – care and maintenance;
• Celemanzi (10 Shaft) – pumping;
• Kloof 1 plant – operational, processing SRD material;
• Kloof 2 plant – operational, processing underground and SRD material.

Mining method

Underground:
• Scattered-conventional breast mining – 79%;
• Pillars extraction (white areas) – 21%.

Surface
• SRD mining (LHD and trucks).

Key developments and brownfield projects (on-mine)
The depth extension project at 4 Shaft, to access the area between 45 and 47 Levels, progressed to 46 Level during 2019 and development will continue to 47 Level. This project is aimed at LoM extention.

The Kloof 8 Shaft expansion project, designed to increase current production levels at 8 Shaft to 300ktpa, has commenced on 14, 15 and 16 Levels as planned.

The Kloof integration project, designed to optimise operating shafts and close redundant infrastructure, has commenced. The lower levels of 3 Shaft will be accessed via 4 Shaft infrastructure by Q4 2020 and the sub-vertical and tertiary shaft barrels will be decommissioned. 7 Shaft production has been rationalised and the shaft will serve as a shorter access route for the long-life 4 Shaft. Main Shaft opening-up and development towards 3 Shaft is progressing according to plan and will allow for the complete closure of 3 Shaft which represents a significant cost saving.

The Eastern boundary area remains a significant very high grade opportunity and is included in the Mineral Resource.

Kloof’s operations comprise two metallurgical gold plants:

• Kloof 1 CIL plant – operational, processing SRD material, Design capacity of 180 tpd;
• Kloof 2 CIP plant – operational, processing underground and SRD material, Design capacity of 120 tpd.