Mineralogy and geochemical dispersion in tropical residual soils overlying a talc deposit in southwestern Nigeria

Abstract

Soil profiles overlying a talc deposit and associated amphibolite country rock have been investigated in order to determine the mineralogy and nature of geochemical dispersion, as a potential tool of industrial mineral prospecting in tropical terraines. Results of mineralogical analysis show that in soils overlying the talc body, talc still persists as a major component of the soil, in association with quartz, chlorite, illite and goethite, whereas in the amphibolite soil, most primary minerals have decomposed to kaolinite, quartz and goethite. Chemical variations in the soils are characterized by general enrichment in Fe 2O 3 and Al 2O 3, and depletion in Na 2O, K 2O, CaO, MgO and FeO relative to the parent rocks. Trace-element abundances show inconsistent patterns. While Ni and Co are depleted relative to the parent rocks, Zn and Cu show considerable enhancement. In spite of the intense weathering characteristics of tropical environments, high MgO contents of the soils seem to be the only reliable geochemical indicator of the existence of talc deposits beneath the soil cover. This parameter in conjunction with X-ray diffraction analysis of the soils may constitute an invaluable exploration tool for detecting buried talc deposits.