Uranium distribution and redistribution in a suite of fresh and weathered Pre-Witwatersrand and Witwatersrand conglomerates from South Africa

Uranium analyses of fresh and weathered Precambrian uraniferous conglomerate samples revealed that the weathered material suffered considerable uranium depletion. Alpha-spectrometric and gamma-spectrometric investigations as well as uranium leaching tests were carried out on the samples. They indicated that in weathered conglomerates only insignificant amounts of uranium are still available for supergene redistribution and that the bulk of the uranium was removed very early in the weathering history of the rocks. Consequently, gamma- and alpha-spectrometric measurements do not yield useful informations on the original uranium content of the weathered rocks. However, lead isotope analysis was found to give good estimates of the fresh-rock uranium tenor of weathered conglomerates. This method is not sensitive to recent uranium redistributions and in geologic terranes similar to the ones investigated it provides a helpful tool in the exploration for uranium deposits. (author). 5 refs, 9 figs, 1 tab