MINERALOGICAL AND GEOCHEMICAL STUDIES OF SANDSTONE IN IMOBI STUDY AREA AND ITS ENVIRONS, SOUTHWESTERN NIGERIA.

Abstract

The combination of mineralogical and geochemical data of sedimentary rock can reveal the nature of source rocks, the tectonic settings of the sedimentary basins and the Paleoclimatic conditions. The aim of this research is to determine the geochemistry and mineralogy of the Imobi sandstones and to infer the provenance and possible depositional environment for these sand stones.

Eight rock samples were collected from the study area, some portion were used for geochemical analysis to determine the chemical composition using X-ray fluorescence and the remaining portion were also used for mineralogical analysis to determine the mineralogical compositions and to estimate the modal percentages of minerals in the Imobi sandstone samples with the aid of the Petrological microscope.

From the geochemical analysis, sixteen (16) elements and oxides were revealed and they includes SiO₂, Al₂O_3, Fe₂O_3, CaO, V₂O₅, ZrO₂, SO₃, K₂O, Br, P₂O₅, CuO, TiO₂, MnO, Rb₂O, As₂O₃, Cr₂O₃, while the mineralogical study show the presence of three minerals along with accessory minerals, they include quartz, iron oxide, microcline and accessory minerals.

The presence of element and oxides like Br, V₂O₅, ZrO₂, CuO, Rb₂O, As₂O₃ and MnO (especially Br which occurred in a recognizable quantity of about 12%-27%) suggests the depositional environment of the Imobi sandstone to be a shallow marine or near marine environments.  However the abundance

Of Fe₂O₃ infers the derivation of the sediments from a metamorphic source. The Petrography study reveals the presence of microcline, a feldspathic mineral commonly found in metamorphic rocks, and is consistent with the inference made from the geochemical composition that the provenance of these sandstones is from a metamorphic origin

Key words: Geochemical, Sandstone, Aluminum, Bromine, Marine, Quartz, Provenance.