Organic matter and trace elements in Precambrian rocks from South Africa

Precambrian cherts from the Fig Tree and Onverwacht groups of South Africa contain unusually high concentrations of chromium and nickel. The organic carbon content of these cherts (0.02–1.58%) shows a considerable variation with a maximum abundance in the Onverwacht group. Atomic H/C ratios (0.08–1.38) of the associated organic matter (kerogen) support the suggestion that the carbon isotopic values of kerogen have not been isotopically enriched by metamorphic processes. Chemically bound alipathic structures amount to about 10% by weight of the organic carbon content of a chert from the lowermost Theespruit succession.