The application of U-Th-Pb isotope systematics in the investigation of potential uranium source rocks in the Natal precambrian basement

U-Pb isotopic data indicate that the sporadic high concentrations of uranium (up to approximately 250ppm), found in pegmatites and granitoids in the Precambrian rocks which comprise part of the Natal basement, were introduced during very extensive metamorphic and igneous acitivity which occurred in southern Natal about 1 050 Ma ago. The uraniferous pegmatites and granites probably represent highly differentiated products that were initially derived from a source region characterized by a bulk-earth U/Pb ratio. Uranium lost recently from the pegmatites and granites has been reconcentrated along veins and in weathered basement rocks which are characteristically biotite-rich or carbonaceous. There is no indication of the presence of more extensive zones of U enrichment beneath the present erosional surface. Apart from the recent secondary redistribution, there is no evidence to suggest that the uranium in the pegmatites and granites has been mobilized since 1 050 Ma ago