The Witwatersrand Basin, or the "Golden Arc", is a massive gold field near Johannesburg, South Africa.The Witwatersrand Gold Rush, which occurred in 1886, led to the establishment of the city. Scientific studies have pointed to the fact that the "Golden Arc" which stretches from Johannesburg to Welkom was once a massive inland lake, and that silt and gold deposits from alluvial gold settled in the area to form the gold-rich deposits that South Africa is famous for. It holds the world's largest known gold reserves and has produced over 1.5 billion ounces (over 40,000 metric tons), which represents about 50% of all the gold ever mined on earth. (wikipedia.org)