Petrogenetic Studies of the Basement Rocks in Jimgbe and Environs, Northcentral Nigeria

Abstract

Geochemical and petrographic studies of Basement rock outcropped at southeastern Jimgbe have been carried out with the aim of characterizing and delineating the petrogenesis of the basement rocks. Field results with Facies analyses of the basement rocks in the study area revealed four (4) dominant rock units: Porphyritic granite, Migmatitic gneiss, Granite gneiss and Biotite gneiss. The minor rocks include quartzofeldspartic intrusion and quartz vein. The area has different structures such as fold, fracture and foliation which trends NW-SE and NE-SW direction, this is allotted to the Pan-African Orogeny imprints. Fourteen (14) analyzed for petrographic method and twenty-four (24) samples were analyzed for major elements using XRF geochemical method. The petrographic analysis result showed that the four rock types are granitic in origin due to their high quartz and feldspar contents. The major mineral compositions are quartz, plagioclase, microcline and biotite. Results of geochemical studies shows that the average oxide percentages are; SiO₂ (69.25%), Al₂O₃ (12.41%), CaO (5.72%), Na₂O (3.25%), K₂O (3.76%), MgO (2.76%), Fe₂O₃ (1.79%), TiO₂ (0.28%), MnO (0.33%) and P₂O₅ (0.47%). These results showed that the rocks are calcic, and are also of high K-Calc alkaline in nature, the rocks majorly plot in the eugeosynclinal field except for sample T4 which plots in the sedimentary field. They are mostly S-type peraluminous rocks except for T11 which is an I-type peraluminous rock and all plot in the Granodioritic field.