Detection of unconsolidated zones in coal mining site using resistivity data at Odagbo area, Kogi State, Nigeria

Abstract

A coal mining site at Odagbo area located in Kogi State, Nigeria, was investigated using resistivity data to detect unconsolidated zones, majorly caused by the mining of coal seam deposit. The resistivity measurement was carried out with the aid of ABEM Terrameter SAS 4000 and electrode selector equipment (ES 464). The resistivity data was acquired along three (3) profile lines at an equal interval of 50 m apart. The electrode array that was used for data acquisition was dipole-dipole array at electrode spacing of 5 m. The data acquired along the three (3) profiles were inverted with RES2DINV software. The inverted models were able to map-out air-filled/water-filled voids and showed the boundary between the unsaturated and water-saturated zone. The air-filled/water-filled voids have high (553 - 4000 Ωm) and low (3 - 70 Ωm) resistivity values with an average thickness of 11 m respectively. The unsaturated zone is 7 m thick and mostly consists of materials with resistivity values ranging from 195 to 4018 Ωm. The weathered zone is 17 m thick and is majorly dominated by water-saturated materials. The study shows that the unconsolidated zones in the subsurface of the study area lies within the weathered layer. These zones are the cause of environmental hazard and might even affect the probable potential coal resources of the study area.