Geology and Geophysical Investigation using Electrical Resistivity Method in Parts of Minna, Sheet 164SW, North-Central Nigeria

Abstract

Geology and geophysical investigation using electrical resistivity method was carried out in parts of Minna, Sheet 164 SW, North-Central Nigeria to establish groundwater potential of the area. Geological mapping was done by both traverse and exposure mapping techniques and five representative samples were subjected to petrographic studies. Horizontal Electrical Profiling (HEP) employing Wenner array to probe 20 m, 40 m and 60 m depths were done on five stations along each of three profile lines oriented west to the east. This is in order to determine the lateral variations in apparent resistivity at various depths. Eighty Vertical Electrical Soundings (VES) were done using the Schlumberger array to a total depth (AB/2) separation of 110 m so as to study the variation of resistivity of the ground at variable depths. Geologic mapping and Petrographic studies results revealed granite as the major lithology with schist occurring in the east. Principal joint directions trend in the NE - SW direction indicating weathering and probable high groundwater potentials along this direction.. The HEP result showed lower resistivity to the middle portion of the study area indicating favourable areas for detailed VES. VES results revealed three geoelectric layers: the soil/lateritic (upper), the weathered and the fresh/fractured layers. Six different geo-electric curves were generated from the analysis namely: HA, AA, HK, AK, KH and QH portraying various aquifers within the region. The area is slightly weathered and the fractures were convergent to the middle portion of the study area indicating more groundwater accumulation towards that direction.