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The Witwatersrand plateau consists of a 5 000-to-7 000-metre-thick (3.1–4.3 mi) layer of mainly sedimentary rocks laid down over a period of about 260 million years, starting approximately 2.97 billion years ago. [9]
Individual mountains within the same mountain range do not necessarily have the same geology; for example, in the [dubious – discuss] Witwatersrand there is Pilanesberg, a mountain having a different orogeny from the main range and its subranges. [1]
Table Mountain. The geology of South Africa is highly varied including cratons, greenstone belts, large impact craters as well as orogenic belts.The geology of the country is the base for a large mining sector that extracts gold, diamonds, iron and coal from world-class deposits.
Like much of the African continent south of the Sahara, South Africa's landscape is dominated by a high Central Plateau surrounded by coastal lowlands. This plateau is rimmed by the Great Escarpment which extends northwards to about 10° south of the Equator (i.e. into Angola in the west, and the Muchinga Escarpment in Zambia in the east. [1])
Johannesburg is located in the eastern plateau area of South Africa known as the Highveld, at an elevation of 1,753 metres (5,751 ft). The former Central Business District is located on the southern side of the prominent ridge called the Witwatersrand (English: White Water's Ridge) and the terrain falls to the north and south.
The Witwatersrand rocks are followed, in succession, by the Ventersdorp lavas at a distance of about 35 km (22 mi) from the centre, and the Transvaal Supergroup, consisting of a narrow band of the Ghaap Dolomite rocks and the Pretoria Subgroup of rocks, which together form a 25-to-30-kilometre-wide (16 to 19 mi) band beyond that. [14]
The Confidence Reef is notable as the first site of a payable gold discovery on the Witwatersrand, an event that contributed to the establishment of Johannesburg, the "City of Gold.'' The discovery spurred the development of other major gold mines, including the Main Reef in 1886, one of the richest gold-bearing areas in history.
In the southern half of Gauteng, the Witwatersrand area is an older term describing a 120 km wide oblong-shaped conurbation from Randfontein in the West to Nigel in the East, named after the Witwatersrand, a geologically and economically important series of low ridges and their associated plateau that greater Johannesburg developed on.