Paleo-lateritization and metalliferous ore formation over the metadioritic rock in the Poli group – Northern Cameroon

This study reports on the geochemical characterization of paleo-lateritic covers cropping out in the Poli area, Northern Cameroon. This study aimed at obtaining a better understanding of their formation processes in regard to climate changes and implication in the occurrence of metalliferous ores. Hence, an analytical approach was adopted and consisted of inductively coupled plasma (ICP) atomic emission for major element geochemistry and mass spectrometry for trace and REEs (ICP-AES and ICP-MS respectively). The Poli study area belongs to the geomorphic unit of the Benoue plain and displays two main geomorphic sub-units: the upper and lower landsurfaces. Macroscopically, paleo-lateritic surfaces in this area rest on a Neoproterozoic basement mostly composed of metavolcanic and metasedimentary rocks passing upwards to a soil which consists of three main horizons (bottom to top): saprolitic horizon, spotted clayey horizon and iron-rich duricrust. These horizons result to an intense chemical weathering and moderate lateritization of metadiorite (CIA: 96.6–99.1%; IOL: 41.2–61.7%), related to Cenozoic era known as age of paleo-lateritic surface formation in Africa and during which the Northern Cameroon was located in the humid tropical zone of the Earth's surface. The paleo-lateritization process in the Poli study area is characterized by a moderate loss of silica (RR: 3.2 to 1.7) and a near-complete leaching of alkali, alkaline earth elements (TRB: 742.3 to 7.1 mg kg−1; WIP: 44.1 to 0.9%). Fe2O3 (9.6–43.5 wt %) showed significant variation with increasing trend from the bedrock to the iron duricrust. Among trace elements, Ba, U, Pb, Zr, Hf, Cr, Co, Cu, Ni, Sc and V are significantly enriched in the iron rich duricrust and constitute the mineralization indices with maximum enrichment factor in the lower landsurface. However, only V with an average content of 740 mg kg−1 in the upland and 667 mg kg−1 in the lowland indicates an economic level. Therefore, according mostly to the Fe2O3 and V contents, the iron duricrust cover of Poli displays a considerable mining potential.