South Africa is famous for its rich deposits of gold, the vast majority of which come from the Witwatersrand Basin, an underground geological formation believed to have once been the floor of a prehistoric sea where rivers deposited their sediments, forming gold and other minerals.
The basin holds the richest reserve of gold ever discovered the world. Over 2 billion ounces of gold have been mined from its goldfields since their discovery in the late 19th century. It’s estimated that 40 to 50 percent of the all the world’s gold ever mined has come from Witwatersrand.
The basin stretches in an arc across 250 miles, from Johannesburg to Welkom, containing gold-bearing reefs along the northern and western margins.
According to atlasobscura