On the possibility of determining rates of removal of uranium from crystalline igneous rocks using U-series disequilibria—2: applicability of a U-leach model to mineral separates

Abstract

Preliminary U-series data are presented on the disequilibria of mineral separates of surface samples from the Eye-Dashwa lakes granite (Canada). Most analyses of the ferromagnesian, quartz-plus-feldspar, and zircon-plus-sphene grains, show that leaching of U has taken place such that 234U/ 239U≤ 1 and 230Th/ 234U 1. The simple leach model presented in a companion paper was used to explain these characteristic ratios. It is suggested that the leach model may be used on zircon and sphere grains to estimate U-leach rates, and this is relevant to the suggestion of using sphene-like hosts as the primary barrier in the safe disposal of nuclear waste. A full analysis of U mobility within a given rock volume was not possible due to our limited data base and to our inability to monitor labile U directly.