The Geology, Geochemistry and Petrogenetic Studies of the Precambrian Basement Rocks around Iworoko, are and Afao Area, Southwestern Nigeria

Abstract

The geology, geochemistry and petrogenetic studies of the Precambrian basement rocks around Iworoko, Are and Afao Ekiti were carried out to determine their geochemical and petrogenetic characteristics. Three lithologies including migmatite-gneiss, granite gneiss and banded gneiss with a pegmatite dyke that occurred as an intrusion were recognized in the study area. A total of seventeen rock samples were collected from the study area which were described based on their field relationships. Ten fresh rock samples were later selected for geochemical analysis. The result of the geochemical analysis revealed that silica (SiO₂) is the most abundant major oxide when compared with other oxides present in all the rock samples analyzed with an average percentage composition of 66.31%. The average percentage composition of other oxides present in all the rock samples are as follows; (16.41%) Al₂O₃, (3.67%) Fe₂O₃, (0.25%) CaO, (4.28%) K₂O, (3.53%) Na₂O, (1.75%) MgO, (0.78%) P₂O₅, (0.54%) TiO₂ and (0.061%) MnO. The results of the trace and rare earth elements analyses revealed that Barium (Ba) is the most abundant with an average value of 328.7ppm compared to other trace and rare earth elements present in the rock samples. The high concentration of barium in the migmatite-gneisses of the study area revealed the radioactive nature of this lithology. Petrological and chemical data suggests a sedimentary protolith, probably greywacke for the migmatite gneiss, gneiss and banded gneiss in the study area which may have been derived from a continental environment.

Keywords: Are; Afao;  Iworoko; Lithologies; Geochemical plots; Statistics.