Regolith Geochemistry and Mineralogy of the Mbalam Itabirite-Hosted Iron Ore District, South Eastern Cameroon

摘要

Mbalam is a major emerging iron ore district in Cameroon. The regolith over the Mbalam itabirite, consists of relict, erosion and depositional units. Itabirite rock fabric is preserved in the relict regolith, the erosion unit is marked by erosion of the carapace cap regolith, with the depositional unit dominated by canga (loose fragments of hematite and/or itabirite cemented by goethite) or loose scree. Fe concentration increases from average of 46.18 wt% in the depositional soil material to as much as 79.08 wt% in the relict regolith regime with variation due to supergene weathering. Fe is the least mobile of the major elements, and the Fe oxides become significant phases and control the distributions of many elements. Absorption of P by iron oxides or oxyhydroxides appears to be the major mechanism of P retention in the different regolith environment. Au dispersion in the weathering profile occurs by two possible mechanisms (mechanical and hydromorphic) and it distribution is sporadic. Zr maintains a positive correlation with Al and Ti indicating extensive chemical weathering in the source area and resulting in a relative concentration of those residual elements. The weathered material show relatively high ΣREE; this is due to upward remobilisation from the lower primary itabirite, and the downward leaching of the upper mineralisation horizons by the descending epigenetic solutions.