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Location: 11 km E from Randfontein, South Africa
Valkfontein 238-IqSowetoSouth Africa1829
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Doornkop is situated on the northwestern margin of the Witwatersrand Basin of South Africa, one of the most prominent gold provinces in the world. While there are several gold-bearing conglomerate reefs present within the mining right area, only the Kimberley Reef and South Reef are considered to have prospects for economic extraction at this stage.In the West Rand Goldfield, the Kimberley Reefs include a number of different gold-bearing conglomerate horizons. At Doornkop, it is the Kimberley K9 Reef horizon which comprises the Mineral Resources along with the South Reef. The K9 Reef rests on an unconformity and is a multi-pulse conglomerate which is divided into four cycles, each consisting of an upper conglomerate and a lower quartzite.The South Reef comprises a basal conglomerate unit and a cycle of trough cross-bedded sediments. The South Reef is dominated by silicate phases such as quartz, carbon (seam and specks), as well as sulphide phases such as pyrite, pyrrhotite and chalcopyrite. While the upper cycles may carry some gold values, up to 95% of the gold present is located in the lower cycle. Both the Kimberley Reef and the South Reef have been subjected to faulting and are intruded by a series of dykes and sills of various ages that cut across the reefs. The gold mineralisation is interpreted to have succeeded a period of deep burial, fracturing, and alteration. The gold and other elements are believed to have precipitated through the reaction of hydrothermal fluids at high temperatures along the reef horizons.The Doornkop shaft lease area lies to the south-east of the major north-easterly striking Roodepoort fault, which dips to the south and constitutes the southern edge of the Witpoortjie horst block or gap. This horst block comprises the stratigraphically older sediments of the West Rand Group, with the overlying Central Rand Group sediments having been removed by erosion. Doornkop is bounded by the Roodepoort fault and a number of other faults, including the Saxon fault, which constitute conspicuous structural breaks. Another major fault, the Doornkop fault, which trends in an east-west direction, occurs toward the southern portion of the lease area. This fault dips to the south and has an up-throw to the north.As nearly the entire upper Witwatersrand section lies within the lease area, all major zones are present. However, given the distance of the area from the primary source of gold, the number of economic bands and their payability is limited. Eight of the well-known reefs are present in the area but only the South Reef and potentially the Kimberley Reef are considered viable at this stage.The South Reef is between 7.5m and 60m above the Main Reef horizon. The hanging wall of the South Reef consists of siliceous quartzite with non-persistent bands of “blue shot” grit and thin argillite partings. The South Reef footwall is a light-coloured and fairly siliceous quartzite. Secondary conglomerate bands and stringers in the hanging wall and footwall of the South Reef may contain sporadic gold values. The general strike of the reef is east-west with a flat dip from 5 to 15 degrees.
