THE GEOLOGY AND PETROGRAPHY OF ROCKS IN ALIZAGA AND UMME, IN NASARAWA EGGON L.G.A, NASARAWA STATE, NIGERIA

This research focuses on the geology and petrography of rocks in Alizaga and Umme, within Nasarawa Eggon Local Government Area, Nasarawa State, Nigeria. Detailed geological field mapping on a scale of 1:25,000 was carried out to update existing geological knowledge of the area. Fieldwork involved the description of outcrops, identification of lithological units, and measurements of structural features including foliations, faults, veins, joints, and dykes. Representative rock samples were collected and subjected to thin-section petrographic analysis for mineralogical characterization. The study area is underlain by four main rock types: granite gneiss, rhyolite, quartz feldspar porphyry, and biotite granite. Petrographic analysis revealed that these rocks are dominated by quartz, plagioclase, orthoclase, and biotite, with minor muscovite, chlorite, and opaque minerals. Structural analysis shows that the rocks are affected by foliations, faults, joints, veins, and lineations, trending predominantly in the NW–SE, NNE–SSW, and NNW–SSE directions, with faulting and vein emplacement largely aligned NE–SW. These patterns are consistent with the tectonic imprint of the Pan-African Orogeny. Economically, the crystalline rocks of the area host industrial minerals such as quartz, feldspar, and kaolin, as well as metallic ores including cassiterite and columbite, with evidence of local artisanal mining. The updated geological map and petrographic data highlight the area’s mineral potential and provide a basis for further geological exploration and resource development in Nasarawa Eggon and adjoining regions.