Geochemical and Mineralogical Studies of Kaolinitic Clays in Parts of Ilorin, Southwestern Basement Rock Area, Nigeria

Abstract

This study is focused on the clay deposits at Akerebiata area in Ilorin (north-central Nigeria), southwestern basement complex, Nigeria. The chemical and mineralogical compositions of the clays were investigated with the aim of determining their provenance, weathering history and most suitable use. X-Ray Diffraction (XRD) method was employed for the mineralogical analysis while X-Ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrophotometer (ICPMS) methods were used to for the determination of the bulk elemental composition. XRD analysis revealed kaolinite as the predominant clay mineral (54.2 to 90.9 wt. %) indicating intensive chemical weathering of aluminium-rich source rocks and exhaustive leaching under a warm, humid condition. Other non-clay minerals in the assemblages are quartz, rutile, anatase, microcline and plagioclase. Results of geochemical analysis show predominance of SiO₂ (47.14 to 64. 92 wt. %) and Al₂O₃ (19.47 to 29.39 wt. %) which support the kaolinitic nature of the clay and classify the clay as aluminosilicates. The relatively high mean values of the Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) (87.15 and 90.09) also suggest an intensive chemical weathering in the source area. Other relevant geochemical indices; plot of TiO₂, ratios of Th/Co, Th/Cr, Cr/Th and relative proportion of Ni and Cr reveal felsic igneous parent rock. The clays are characterized by light colour, fineness, low-moderate LOI, mineral assemblage and chemical composition that make them favorably compared with standards for refactory, ceramics, pottery and paints.