Mobility and fractionation of rare earth elements during weathering of a granodiorite

Abstract

The rare earth elements (REE) have been mobilised and fractionated during supracrustal alteration of the Torrongo granodiorite. Compared with the parent granodiorite, incipiently and moderately altered rocks are particularly enriched in the heavy REE, while the extremely altered residual products are especially depleted in the heavy REE. Mobilisation of the REE probably results from pH changes of soil and ground waters as they encounter different chemical environments while fractionation may largely result from mineralogical controls. Submarine and subaerial weathering processes may affect REE similarly, producing intensively weathered materials appreciably depleted in the REE. Spilitisation and hydrothermal alteration processes may affect basaltic rocks in much the same way as do weathering processes.