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

The REE-U-Th geochemistry and mineralogy have been studied in a lateri tic 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 und erstand the movement of these elements. Thorium has been used as an im mobile element for these calculations. The weathering of accessory min erals rich in REE and Th of the syenite (allanite, apatite, titanite a nd epidote) has been especially studied in the saprolite. Several REE- Th secondary minerals (florencite, rhabdophane, cerianite and thoriani te), important to explain the fractionation of REE in supergene enviro nments, have been found.