Unlike other metals, gold usually occurs in its metallic form and needs no smelting, although to free it from other metals, and to increase its purity, it must go through complex refining processes.
Gold also occurs as a constituent in alloys, with other metals such as silver, copper and platinum. In the earth, metallic gold is released as dust or nuggets by mechanical forces like crushing and grinding, eventually appearing in surface soils, which may be reburied over time, or washing into streams.
The traditional form of extraction in Africa was by panning from such streams. Since the late 19th century, mines have been dug, the deepest going down 4000 metres (13,200 ft). In 1977, nearly 75% of the world’s supply of gold was produced in Africa, most prolifically in South Africa (95%) also Zimbabwe (2.26%), Ghana (2.24%) and 12 other African countries.