Geological, Multispectral and Aeromagnetic Expressions of Pegmatite Hosted Mineralization of Keffi Sheet 208 NE, North-Central Nigeria

Abstract

An integrated spectral and structural interpretation of pegmatite hosted mineralization was carried out in sheet 208 NE in order to characterise specific spectral and geophysical features in an attempt to narrow down areas for further mineral exploration. The area is characterized by over eighty pegmatites exposures hosted by the gneiss, schist and igneous rock units. Landsat 8 Operational Land Imager (OLI), Shuttle Radar Topographic Mission Digital Elevation Model (SRTM DEM) and aeromagnetic datasets with acquired field geological information were used in this study. Data obtained from field structural mapping was used to produce a rose diagram to illustrate principal joint directions. Landsat 8 image was processed using band ratios for RGB colour composites for lineament extraction and target selection. SRTM DEM and aeromagnetic data were also processed to obtain derivative maps from which lineaments were also extracted. Lineaments from different datasets were integrated to form a composite lineament map of the area. Pegmatite bodies are more prominent in the schist. Geological boundaries and contact zones and a few shear zones have metal bearing pegmatites. Foliation planes (schist and gneiss) and fractures of granites are all rich with pegmatite veins and dykes. Rare-metal pegmatites are close to major and subsidiary fault structures. Structural analyses revealed a major NE-SW for the magnetic lineaments and NW-SE trend for the surface lineaments. Alteration zones marked by the presence of iron oxides, hydroxyl- bearing minerals and hydrothermal clays were delineated from a composite of different band ratios. The result of this study positively supports a more detailed exploration from selected alteration zones.