keywords: Vertical electrical sounding (VES), Geoelectric, Groundwater, Aquifer, Borehole
Twenty four Vertical Electrical Soundings (VES) were conducted along predetermined profiles situated on latitude 11 o 7.6 / N to 11 o 7.7 / N and longitude 7 o 6.2 / E to 7 o 6.3 / E at Malumfashi, Nigeria. The survey was carried out to investigate the fractured zones of the area and to map out the subsurface layers along the profiles. Terrameter SAS 300 system was used for the data acquisition at station intervals of 100m using Schlumberger array. Maximum current electrode separation (AB) of 200m was used. Interpretation was performed using computer software (IPI2win and Sufer11.0). The interpreted result was used to produce geoelectric and geologic sections and specialized maps (Iso-resistivity map, Aquifer thickness map, Depth to the basement map) were also drawn from which conclusion was drawn. The result of the study indicates that the area is underlain by three to four subsurface layers. The resistivity of the first layer ranges from 14 ohm-m to 273 ohm-m with an average thickness of 2.0m. This layer is the superficial cover composed of sand, clay and silt. The second layer has resistivity value between 15 ohm-m to 567 ohm-m which is the weathered basement and lateritic sand in some places. The third layer has 109 ohm-m to 799 ohm-m. This layer is the fractured basement with varying thickness of 4.0m to 38.9m. The fourth layer is the crystalline basement rock with resistivity values greater than 1000 ohm-m and infinite thickness. The investigations show that the aquifer in the area which is confined occurs in the weathered and fractured basement. From the maps analyzed and other information in the survey area, the fractured regions around VES 04,11,12,16 and 17 are the most promising for groundwater exploration.