Witwatersrand basin

The Witwatersrand Basin is a geological region in South Africa that hosts the world's largest reserves of gold with production of over 1.5 billion ounces of gold. Situated in the heartland of the South African gold mining industry, the basin is a large area of gold-bearing reefs that stretches from forty miles east of Johannesburg to ninety miles west, then swings southwest into Free State province.

Nearly half of all the gold ever mined has come from the extensive Witwatersrand Basin that was first found near Johannesburg in 1886. The gold occurs in reefs, or thin bands, that are mined at depths of up to 10,000 ft (3,050 m). The Savuka mine is the world's deepest gold mine at 3,777m (12,391ft) [http://www.gold.org/value/markets/supply_demand/mine_production.html] . Although many of the older mines are now nearly exhausted, the Witwatersrand Basin still produces most of South Africa's gold and much of the total world output. Silver and iridium are recovered as gold-refining byproducts, and the basin also has coal mines, although they are bit players in the overall mining of the Basin.

Witwatersrand (meaning 'white water ridge' in Afrikaans) is often called simply "the Rand," and is located in the Gauteng province (formerly a part of Transvaal) of South Africa.