GEOCHEMICAL AND MINERALOGICAL BEHAVIOR OF REE, TH AND U IN THE AKONGO LATERITIC PROFILE (SW CAMEROON)

The REE-U-Th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite (Akongo, SW Cameroon). Mass balance calculations have been done (1) in the syenite to determine the most important REE-U-Th bearing minerals and (2) in the soil profile to understand the movement of these elements. Thorium has been used as an immobile element for these calculations. The weathering of accessory minerals rich in REE and Th of the syenite (allanite, apatite, titanite and epidote) has been especially studied in the saprolite. Several REE-Th secondary minerals (florencite, rhabdophane, cerianite and thorianite), important to explain the fractionation of REE in supergene environments, have been found.