Delineation of Geological Boundary in Idi-Emi and Environs, Southwestern Nigeria Using Electrical Resistivity Method

Old geological maps in areas with complex rock formations often lack accuracy, risking misinformation, especially where lithological boundaries are subtle. This study integrates Vertical Electrical Sounding (VES) and 2D electrical imaging to improve subsurface mapping in the Idi-Emi area, southwestern Nigeria. The approach successfully identified three terrain types—sedimentary, transition, and basement complex—each with distinct resistivity and layer thickness ranges. The topmost geoelectric layers showed resistivities of 42–634 Ωm and thicknesses of 0.6–1.9 m across these terrains. New geological boundaries were delineated, refining the existing map and aligning with the Dahomey Basin framework. The enhanced geological model provides critical insights for groundwater aquifer delineation, hydrogeological exploration, and controlling illegal mining activities in the region. This integrated geophysical method demonstrates a valuable approach for accurate subsurface characterisation in geologically complex terrains.