Geology and Petrography of the Basement Complex Rocks of Tsauni and Environs, North Central Nigeria

Abstract

Detailed geological mapping and petrographic study of the rocks in Tsauni area and environs situated within Gwagwalada in Abuja Federal Capital Territory have been carried out to establish the geology relative to the rock types, texture, mineralogy, and mineralization. The area is part of the Basement Complex of North Central Nigeria and a newly discovered skarn environment with preserved basement metagranitoids of the migmatite-gneiss complex and lower grade metasedimentary schist belts. Major rock types identified include migmatite and various types of gneisses. Subordinate rocks include calc-silicate (skarn) rocks, ultramafic relicts and fine to medium grained granite all crosscut by younger Pan African granite, diorite, pegmatites, and quartzo-feldspathic veins. Two types of skarn; A and B were distinguished petrographically being the first mention of skarn occurrence in Nigeria. Petrographic study of selected rocks under plane and crossed polarized light alongside Back Scattered Electron (BSE) images from microprobe analysis showed the mineral suites to include quartz, feldspar (mostly plagioclase and subordinate alkali feldspar), biotite, minor amphibole, pyroxene, calcite and muscovite with accessory epidote, allanite, zircon, titanite, apatite and opaque minerals which selectively occur in both metagranitoids and skarn. Opaque minerals include magnetite, ilmenite± rutile, galena, pyrite sphalerite, and chalcopyrite. Structural features include foliation, joints, xenoliths and pendant (flame) textures, veins, and veinlets which are all aligned in the NE-SW, NW-SE, and minor N-S and E-W directions suggesting control from some deep-seated sources.