Geology and Petrography of Migmatites Around Tillie and Environs Part of Sheet 148 Toro Se, Toro L.G.A Bauchi State

Abstract

This study investigates the geology, petrography, geochemistry, structural characteristics, and economic mineralization potential of the crystalline basement rocks of Tillie and environs, Toro Local Government Area, Bauchi State, Northeastern Nigeria. The study area forms part of the Nigerian Basement Complex within the Pan-African Mobile Belt that reflect multiple tectono metamorphic events related to the Pan-African orogeny. Field mapping, petrographic studies, structural analysis, and geochemical investigations were integrated to characterize the lithological units and evaluate their petrogenesis and mineralization potential. Geological mapping involved reconnaissance surveys, traverse mapping, outcrop description, structural measurements, GPS logging, and systematic sample collection. Thirty-seven representative rock samples and stream sediment samples were collected from various locations across the study area where 22 were analyzed. Structural data including foliations, fractures, joints, veins, and lineaments were measured using a compass clinometer to determine the tectonic framework which conformed to the NW- SE trend. Petrographic analysis was carried out using thin section microscopy under plane-polarized and cross-polarized light. The petrographic results revealed that the dominant lithologies include Banded orthogneiss, stromatic migmatites, alkali feldspar granites, syenogranites and associated pegmatite and trachyte. Mineral assemblages identified include quartz, plagioclase, K-feldspar, biotite, muscovite, garnet, orthopyroxene, mymerkite, and opaque minerals. Geochemical analyses using Energy Dispersive X-Ray Fluorescence (EDXRF) revealed compositional variations among the rock units and provided insight into their petrogenesis. The rocks generally display felsic compositions with enrichment in silica, alkalis, and light rare earth elements, consistent with crustal-derived melts, calc-alkaline, metaluminous to slightly peralkaline affinities. Geochemical signatures suggest that the granitic and migmatitic rocks were generated largely through partial melting and reworking of pre-existing continental crust during the Pan-African tectono-thermal event. Trace element distributions and rare earth element concentration indicate possible concentration for rare earth element-bearing accessory minerals, zircon concentration and highly anomalous concentration of Antimony (21.6 wt.%).