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.

The Kloof operation is a mature, established mine with all the permanent infrastructure required to access and mine the underground ore.

Mining method:
• Underground: Scattered-conventional breast mining;
• Surface SRD’s: Load, Haul and Dump (LHD) trucks.

The Kloof Integration Project aims to optimise and rationalise the infrastructure between No. 3 and No. 4 Shafts, and between No. 1 and No. 3 Shafts, resulting in significant cost savings. Rationalisation of infrastructure between No. 3 and No. 4 Shaft has allowed for the phased closure of No. 3 Sub Vertical Shaft by Q1 2022. The final phase requires the closure of the main barrel in 2023. This phase entails the re-opening of old development between No. 1 and No. 3 Shafts which will allow the mining of the remaining VCR at No. 3 Shaft, as well as significant secondary reef potential on the LR and KR from No. 1 Shaft, well into the latter part of the Kloof LoM.

The Kloof Integration Project also involves the development of inclined access between 41 Level at No. 4 Shaft up to 40 Level at No. 7 Shaft. The development of this phase is complete and equipping is in progress. An additional phase of the same project entails a similar access to link 42 and 43 Levels. This project will allow access via No. 7 Shaft resulting in more face time for crews. The access development for this phase started in 2021.

The Kloof No. 4 Shaft Depth Extension Project, consists of a decline two levels below infrastructure. The decline between 45 and 46 Levels has been developed, and the remaining portion of the decline to 47 Level is in progress. The access ramp is being developed by means of mechanised mining equipment. Once the access has been completed, raisebore drill holes will be drilled and reamed back up to 45 Level for infrastructure and return ventilation purposes. The first raisebore hole will be completed early in 2022.

Kloof’s operations comprise two metallurgical gold plants:

• Kloof 1 CIL plant – operational, processing underground and SRD material, Design capacity of 180 ktpm;
• Kloof 2 CIP plant – operational, processing underground material, Design capacity of 165 ktpm.