The Geology and Hydrogeology of Parts of Minna Sheet 164 NE

Abstract

A study of the geology and hydrogeology of a part of Minna was conducted with the aim of determining the geological conditions controlling groundwater flow and storage and safe abstraction methods. Many boreholes have failed in this area principally as a result of poor understanding of the groundwater conditions and relying solely on geophysical surveys using Electrical Resistivity. The area is basically underlain by rocks of the Nigerian Basement Complex system comprising chiefly of granite, gneiss, migrnatites and schist. Geologic mapping was conducted on a scale of 1 :25,000, surface fracture orientations where mapped to determine the principal joint directions. Hydrogeologic mapping was conducted on existing dug wells and boreholes using the gridding method. This information was used to plot the water level elevation map, water level change map and depth to water map. Groundwater in the parts of Minna studied occurs mostly within weathered to fractured portions of the underlying rock. The weathering profile is shallow and mostly between 3 - 10m. Water level contour map revealed that areas with greatest potential are located within the central and north-western portions of the area. No appreciable change was noticed in the water level change map. Sites that could be exploited for groundwater development showed target areas having the highest water level and the least depth to water levels. Groundwater potential was found to be higher in areas underlain by granite followed by gneiss with schist having the lowest potential for groundwater storage and transmission. The schist in the part of Minna studied was found to belong to the Birnin-Gwari Schist belt. This research has buttressed the need for Geological and Hydrogeological studies in choosing sites for the development of groundwater resources.