Morphological, mineral and geochemical characterization of soil profiles in Meïganga as tools for rock weathering intensity and trend evaluation and residual ore deposit prospection in the mineralized domain of central Cameroon

Abstract

AbstractThis paper focuses on the use of morphological, mineral and geochemical characterization of soil profiles to assess rocks weathering trends and intensity as tools for mineral prospection in Meïganga. To that effect, seven soil profiles developed on micaschist, orthogneiss, granite and quartzite vein were analysed. Macroscopic description of these soil profiles exhibited shallow weathered soils with thickness not exceeding 4 m. Minerals recorded in their weathering products were: quartz, 60.3–93.9%; kaolinite, 0.8–22.3%; phlogopite, 0.2–15.3%; goethite, 1.9–13.0%; hematite, 0.5–8.5%; halloysite, 0.2–4.6%; and smectite, 0.5–4.3%. Geochemically, SiO2 contents globally decreased upward, while Al2O3, Fe2O3 and TiO2 contents increased. Alkaline and alkaline earths contents were almost completely leached. The total reserve in bases and Parker's weathering index (TRB, 416–11 mg kg−1; WIP, 56–4%) decreased upward, except in the soil profile associated with the quartzite veins (TRB, 2–100 mg kg−1; WIP, 0–29%). The chemical index of alterations were 5–92% with the index of lateritization 8–39% and the silica exportation ratio was greatly above 1 (Ki 2–9). Trace elements in soil profiles were, in order of decreasing contents, S, Ba, Sr, Zr, Cr, V, Zn, Rb, Ni, Y, Sb, Cu, Pb, Li, Co, Ga, Nb, Th, Sc, Cs, Hf, Sn, U, Mo and W. Scandium, V, Cr, Sb, Cs and Pb were enriched, while S, Rb and Sr were depleted, and Ba, Zr, Zn, Ni, Y, Cu, Li, Co, Ga, Nb, Th, Hf, Sn, U, Mo and W showed complex behaviour. The most abundant rare earth elements (REEs) were, in order of decreasing contents, Ce (29–273 ppm), La (26–91 ppm), Nd (14–83 ppm) and Pr (4–22 ppm). Almost all the REEs were enriched in soil profiles with respect to parent material, and strongly fractionated, with fractionation intensity increasing from light to heavy REEs. The most significant useful elements identified were: refractory metals (Zr, Cr, V, Nb, Hf, Mo and W), semi-precious metal (Cu), non-precious unreactive metal (Sb) and actinide group element (U). Statistical analysis indicated that, in soil profiles, Nb, Mo, U, W and Hf had strong affinity with Al2O3; Mo, Cr, V, Zr, Hf and Sb had strong affinity with with Fe2O3; U, Hf and Sb had strong affinity with with P2O3; and Nb, Zr, V and Cr had strong affinity with with TiO2. Fe2O3, Al2O3 and TiO2 are respectively the greatest markers for Mo; Nb, Mo, W, Nb and U; and Nb, V and Cr prospection in soil profiles. The Clarke of concentrations of useful elements were: Sb, 60.00; Mo, 0.83–4.17; W, 1.60; Cr, 0.08–1.56; Nb, 0.60–1.55; U, 1.11–1.48; Hf, 1.33; V, 0.36–1.27; and Zr, 0.96. Exploitability concentrations for Cr and U in soil profiles varied respectively from 1.20 to 23.85% and from 0.15 to 0.20%.