Geochemistry of a lateritic mantle developed on basalt in the Cameroon Western Highlands (Cameroon Volcanic Line)

Abstract

Although lateritic mantles have been strongly documented, there is need to continuously characterise and update information at site-scale so as to optimize exploration and exploitation operations in various industrial domains. In this paper, four soil profiles developed on basalt are described in detail to appreciate their morphology, mineralogy, geochemistry, pedogenesis and ore potential. The basalt is composed of olivine, plagioclase feldspars and pyroxenes and accessory magnetite, sphene and apatite. The basalt shows high levels of Ba, Cr, V, Sr, Ni, Zn and Zr; meanwhile total REEs range from 185.03 to 199.45 mg kg−1. The weathering indices reveal an extreme weathering intensity of the parent rock. Newly formed minerals are kaolinite (15–48%), haematite (13–40%), Goethite (10.5–19%) and gibbsite (10–12%), magnetite (4–9.56%), feldspars (4.67–6.10), apatite (2.8–3.9) and sphene (1.77–2.46%). The weathered materials show high levels of Cr (40–850 mg kg−1), V (145–582 mg kg−1), Zr (300–583 mg kg−1) and Ce (24.2–510 mg kg−1). The total REEs of the weathered materials range from 126.52 to 1267.69 mg kg−1, with the predominance of LREE. The REE basalt-normalized patterns revealed slight LREE depletion, more pronounced for the B horizons relative to the underlying C horizons as well as HREE enrichment that increase with depth and altitude. In these soils, mass balance calculations reveal depletion of Si, Ca, Mg, Ba, K, Na, Mn, P, Rb, Sr, La and Lu, enrichment of Al, Fe, Ti, Ga, U, Zr, Dy, Hf, U, Tm and Yb meanwhile Cr, Cs, Sn, Ta, Th, Tl, V, W, Y, Nb, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Ho are either depleted or enriched from one profile to the other. Apart from Cr, V, Zr and Ce whose concentrations respectively attain 850 mg kg−1, 582 mg kg−1, 487 and 510 mg kg−1, the mining potential of the studied lateritic mantle is low.