Crystal chemistry, alpha decay damage, and geochemical alteration of brannerite and davidite

Abstract

To investigate the long-term stability of the uranium minerals brannerite and davidite, we have undertaken an electron microscopy study of samples from a range of geological environments worldwide. Our results indicate that both minerals are transformed to an amorphous phase after a dose of approximately 10 16 α mg-1, similar to other rare element oxide minerals. Both minerals are susceptible to alteration via interaction with hydrothermal fluids, although by different mechanisms. The U-Th-Pb chemical ages of brannerite are generally consistent with the known ages and geological histories of the host rocks. These ages are affected by U loss from altered areas and Pb loss from unaltered brannerite.