Investigation of Ewekoro Formation using 2D electrical resistivity tomography—a case study from Nigeria

Geophysical investigation of the Ewekoro Formation around Ibese mines, Ogun state, Nigeria, was carried out by deploying the 2D electrical resistivity tomography (ERT) method for characterizing the sub-surface stratigraphy sequence and cavitation zones. Eight 2D profiles were established, and electrical resistivity data were acquired using dipole–dipole and pole-dipole arrays. A maximum of four geoelectric layers/strata were mapped. The uppermost beds are composed mainly of clay and in some cases sand and shale at depths ranging from 0 to 7.5 m and resistivity values between 1.0 and 5550 Ωm. The second layer is composed of shale and, in some cases, limestone with a resistivity range of 1.0–13,000 Ωm and depth range of 1.0–36 m. The high resistivity (1000 to 13,000 Ωm) in this band was interpreted to be limestone. The third geoelectric component was predominantly made up of limestone at depths 3–39.4 m and resistivity of 80–13,000 Ωm. The fourth layer is composed of marl occurring from 17 to 57 m and resistivity of 10.7–400 Ωm. The overburden was evaluated to be between 2.0 and 14.5-m thick while the limestone thickness was found to be between 5.9 and 31.45 m. This research established the presence of cavity structures with a resistivity range of 1.0–50 Ωm which could help guide mining engineers in preventing geohazard and flooding during the mining operation.