Geoelectrical Survey for Mapping Basement Configuration in the Precambrian Terrain of Niger State

This study applies geoelectrical methods to map the configuration of the Precambrian basement and overburden conditions in parts of Niger State, North Central Nigeria. Niger State lies within Nigeria's basement complex terrain, where groundwater occurrence is controlled by the depth, thickness, and degree of weathering of the basement rock. Delineating zones of thick weathering and fractured basement is essential for productive borehole siting in an area experiencing increasing water demand from rapid urbanisation. This study acquires Schlumberger VES data at 42 stations distributed along six profiles in Paikoro, Gurara, and Lavun local government areas, with maximum half-current electrode spacing of 300 metres. Data are processed and interpreted using IPI2WIN and WINRESIST inversion software. Layer models are extracted and used to compute hydraulic parameters following Frohlich and Kelly's approach. A basement depth map and an overburden thickness map are constructed by kriging interpolation of the VES layer model results. Findings reveal a basement surface that undulates between 10 and 72 metres depth, with the deepest weathering pockets concentrated along northeast-trending lineaments visible in SRTM topographic data. Overburden resistivity values of 20 to 80 ohm-metres in target areas suggest lateritic and saprolite materials with moderate to good aquifer potential. Seventeen sites with overburden thickness exceeding 35 metres and intermediate resistivity values in the 25 to 60 ohm-metre range are identified as favourable borehole sites. The study concludes that VES-based basement mapping is an efficient first-pass groundwater exploration tool in Niger State's basement terrain.

Keywords: geoelectrical survey, basement mapping, weathered basement, Niger State, groundwater prospecting.