Lead Isotope Evidence on the Detrital Origin of Witwatersrand Pyrites and its Bearing on the Provenance of the Witwatersrand Gold

Abstract

The lead isotopic composition of sulfides from primary gold deposits of the early Precambrian greenstone belts of the eastern Transvaal, South Africa, is compared with the lead isotopic composition of detrital and authigenic pyrites from the placer gold deposits of the Witwatersrand basin to test the hypothesis that the detrital sulfides and the gold of the Witwatersrand sediments were derived from greenstone belts of the Swaziland Sequence.The isotopic composition of the lead of some detrital pyrite samples from the placer deposits was found to be similar to that observed in sulfides from primary gold deposits. The lead of one of the detrital samples, originating from the Orange Free State Goldfield, is identical to the lead of galena from the Rosetta Mine, a primary gold deposit in the Barberton Mountain Land. The same lead forms also the first-stage lead of two other detrital pyrite samples obtained from the same locality in the Orange Free State Goldfield. These results, therefore, constitute strong evidence that the greenstone belts of the Swaziland Sequence and their numerous gold deposits contributed detritus to the Witwatersrand depository.