Assessment of Subsurface Lithology Using Induced Polarisation Survey in Abeokuta, South West Nigeria

Abeokuta, the capital of Ogun State in South West Nigeria, is underlain by Precambrian basement rocks of diverse lithological character, including migmatitic gneisses, schists, and amphibolites, whose distribution has important implications for construction foundation design and mineral exploration. This study employs induced polarisation profiling and sounding to characterise subsurface lithology and identify zones of economic mineral potential in the Oke-Ogun corridor of Abeokuta. Frequency-domain induced polarisation measurements were acquired at 18 sounding stations along two profiles using the Schlumberger electrode configuration, yielding chargeability and resistivity data for joint interpretation. Chargeability anomalies exceeding 20 milliseconds are recorded at two stations and are attributed to disseminated sulphide mineralisation consistent with pyrite-bearing schist horizons. The resistivity-chargeability cross-plots are interpreted using established lithological discrimination criteria to map the spatial distribution of basement rock units beneath the weathered overburden. A three-layer earth model derived from joint inversion indicates a thin lateritic topsoil overlying fractured basement at depths of 12 to 35 metres. Areas of low chargeability and moderate resistivity correspond to clay-rich weathered profiles, presenting foundation engineering challenges. The results provide a lithological map of immediate practical value for infrastructure planning and mineral resource assessment in this fast-growing urban area. Keywords: induced polarisation, subsurface lithology, Abeokuta, basement characterisation, sulphide mineralisation