The field geological mapping of the area around South-Eastern part of Jimgbe, in Ajaokuta Local Government of Kogi State has been carried out. Four (3) dominant rock units were revealed which are: Porphyritic granite, Migmatitic gneiss, Granite gneiss and Biotite gneiss. The minor rocks include quartzo-feldspartic 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. The petrographic analysis result shows that the four rock types are granitic in origin due to their high quartz and feldspar contents. The major mineral composition are quartz, plagioclase, microcline and biotite. Geochemical analysis result 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 show that the rocks are calcic, and is 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. They all plot in the Granodioritic field.
Key words: Precambrian; Basement Rocks; Geochemistry; Pan-African Orogeny; Jimgbe; Ajaokuta
|
