A major Archean, gold- and crust-forming event in the Kaapvaal craton, South Africa.
The 2.89- to 2.76-gigayear-old conglomerates of the Central Rand Group of South Africa host an immense concentration of gold. The gold and rounded pyrites from the conglomerates yield a rhenium-osmium isochron age of 3.03 +/- 0.02 gigayears and an initial 187Os/188Os ratio of 0.1079 +/- 0.0001. This age is older than that of the conglomerates. Thus, the gold is detrital and was not deposited by later hydrothermal fluids. This Middle Archean gold mineralization event corresponds to a period of rapid crustal growth in which much of the Kaapvaal craton was formed and is evidence for a significant noble metal flux from the mantle.
Kirk
Jason
J
Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA. jkirk@geo.arizona.edu
Ruiz
Joaquin
J
Chesley
John
J
Walshe
John
J
England
Gavin
G