Deposits Formed by Sedimentary and Surficial Processes - Metals and Society: An Introduction to Economic Geology - page 117

Fig. 5.1 Sketch map of the Witwatersrand basin, showing the central disposition of the sands and
conglomerates of the Central Rand and West Rand groups, the flood basalts of overlying
Venterdorp Supergroup and the surrounding granites and greenstones, which were the probable
source of the gold (Modified from Schmitz et al. ( 2004 ) and Frimmel et al. ( 2005 ))
only a few years, and subsequent mining in each of these places became focused on
“lode gold”; i.e. gold in veins in solid rock deposited from hydrothermal fluids, as
described in Chap. 4. At present, gold production from placers is largely artisanal
and makes up only a minor fraction of total gold production. On the other hand,
production continues in the Witwatersrand ore bodies of South Africa (Fig. 5.1 ), a
(hydrothermally reworked) conglomeratic paleoplacer deposit that is the largest
gold deposit that we know of. The Witwatersrand ore bodies have produced nearly
half the gold that has ever been mined. In 1970 they still accounted for half of global
production but by 2007 the figure had fallen to 11% due to the exhaustion of
shallow and rich ore bodies in the Witwatersrand and the development of other
gold mines in many parts of the world. China is now the biggest producer.