Geology, Petrology and Geochemistry of the Basement Rocks around Ihima, Southwestern Basement Complex, Nigeria

ABSTRACT

The field geological mapping of the area around Ihima, in Adavi Local Government of Kogi State, Southwestern Nigeria Complex has been carried out. This area is underlain by metamorphic (gneissic) rocks. The gneisses around Ihima area consist of varieties such as porphyroblastic gneiss, biotite gneiss, banded gneiss and granite gneiss. Minerals such as quartz, biotite, microcline, plagioclase, hornblende, muscovite, epidote forms the major components in the gneisses while garnet, zircon and sphene are the accessories minerals. The minor rocks/intrusions include feldspathic intrusion and quartz vein. The area has different structures such as fracture and foliation which trends dominantly in NE-SW direction, this is allotted to the Pan-African Orogeny imprints. Foliation in the gneisses is defined by parallel alignment of mafic and felsic minerals (bands) having a major trend in NE-SW direction. Geochemical analysis result shows that the average oxide percentages for banded gneiss are; SiO₂ (56.66%), Al₂O₃ (21.95%), CaO (6.63%), Na₂O (2.26%), K₂O (4.74%), MgO (0.77%), Fe₂O₃ (6.07%), TiO₂ (0.01%), MnO (0.01%) and P₂O₅ (0.77%) while granite gneiss consists of; SiO₂ (62.61%), Al₂O₃ (20.88%), CaO (1.66%), Na₂O (1.65%), K₂O (9.31%), MgO (0.61%), Fe₂O₃ (2.67%), TiO₂ (0.01%), MnO (0.01%) and P₂O₅ (0.60%) respectively. These results show that the rocks are calcic, and is also of high K-Calc alkaline in nature, the rocks majorly plot in felsic field. The absence of minerals like sillimanite, kyanite, cordierite and staurolite which are typical of paragneiss confirmed an igneous protolith of the gneisses investigated. Due to their felsic nature, they are suitable for construction works, cut, and polished for ceramic or tile making.

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WSN 190(2) (2024) 70-100

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