Geological and Electrical Resistivity Sounding of Olokonla Area in North-Central Nigeria

Geological mapping and Electrical resistivity sounding were carried out in Olokonla area in Moro Local Government of Kwara State in order to determine the apparent resistivities of the subsurface lithologies and correlate them with the exposed rocks observed during the geological mapping. The studies also delineate the pattern of fractures in the area which form prefential pathways for ground water. Three vertical electrical soundings (VES) were performed radially adopting the Schlumberger electrode configuration, with half-current electrode separation (AB/2) varying from 1m to 100m. Anisotropy polygon was also constructed based on the radial electrical sounding. The geoelectric parameters revealed five subsurface layers which were interpreted as topsoil, lateritic soil, dry sand soil, weathered granite and granite respectively. The geological mapping showed that the area is underlain by crystalline rocks comprising biotite granite, granite-gneiss and migmatite. The anisotropy polygon showed that a major fracture direction along 600 (northeast to southwest) and the coefficient of anisotropy is 0.79. Based on the apparent resistivities and the structural disposition, a potential aquifer was inferred at a depth of 45m. The fracture pattern in the area was constrained to northeast to southwest direction. The data obtained would be useful in borehole drilling for water within the study area.KEYWORDS: Vertical electrical sounding, aquifer, electrical resistivity, anisotropy polygon, geological mapping, fracture patter