α-spectrometric investigations of radioactive disequilibrium in early Precambrian quarz pebble conglomerates

Samples of fresh and weathered quarz pebble conglomerates of the West Rand Group of the 2.5-2.8 Ga Witwatersrand gold-uranium deposit (South Africa) were investigated. Uranium and thorium element and isotope analyses were carried out by alpha spectrometry. Two different kinds of sample treatment were presented: bulk rock analysis and leaching process, and a detailed description of data evaluation from the alpha spectrometric measurements were given. Radioactive disequilibrium found in bulk rocks and leached solutions of all weathered samples indicate U redistribution processes, mainly U loss in the weathered zone of conglomerates. It could be shown that the use of alpha spectrometry and in addition the use of the two kinds of sample treatment is a good method for studying the behaviour of uranium during weathering processes. (author)