Detrital gold, uranium, and pyrite concentrations related to sedimentology in the precambrian Vaal Reef placer, Witwatersrand, South Africa

This study integrates stratigraphical, structural, petrological, and mineralogical data with a comprehensive set of sedimentological data to synthesize a model that describes the genesis of the Vaal Reef placer. Results show that the Vaal Reef placer was a shoreline feature of the Upper Witwatersrand Basin and that its deposition was controlled, firstly, by the major structure of the basin and, secondly, by a minor transverse synclinal structure that induced an entry point. New geological aspects that have emerged are, firstly, that the tectonic framework during Vaal Reef Stage deposition was very much simpler than previously envisaged. There is no evidence of subsidiary incipient basining. Secondly, modifications of previous conceptual models are made which emphasize the importance that detailed dispersal patterns and subtle paleosurface forms had on heavy mineral distribution in the distal fluviodeltaic environment of carbon-seam placers. Thirdly, sedimentary responses involving unconformities, disconformities, and accumulation are evidently related to particular entry points and may not be specifically correlated beyond their local tectonic framework. Fourthly, tectonic instability and basining is dated between Lower and Upper Ventersdorp System time and certainly before deposition of the Transvaal System