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.
2D electrical resistivity tomography was observed at Ile-Ife seismographic station, Osun state Nigeria with the aim of investigating the geological structures beneath the station in order to identify areas of anomalous resistivity that might be related to fractures or fault lines and also determine the lithology of the subsurface. This is to ensure that data observed by the seismic station are gotten with less noise. The data was carried out with Terrameter SAS 1000 and ES 464 electrode selector equipment. Dipole-dipole configuration at electrode spacing of 2 m was used to acquire the data. The result showed that the station is underlain by three layers; overburden composed of lateritic clay, clayey sand, the weathered and fresh basement. Fault lines and fractured zones were not observed in all profiles.
A Kaolin mining site at Dajin Gwanma in north central Nigeria was investigated to detect subsurface voids created due to mining of kaolin deposit and to perhaps suggest areas prone to subsidence. This study was undertaken on conceptual resistivity model that subsurface voids characterized by higher or lower resistivity than the host, depending on weather the void is in-filled water or not. The data collection was carried out with Terrameter SAS 4000 and ES 464 electrode selector equipment. Dipole-dipole configuration at electrode spacing of 5 m was used to acquire the data along parallel profiles laid at equal interval in the study area. The acquired data along each profile were inverted with 2D algorithm. The results show that the voids are characterized by high resistivity (950 Ωm-2500 Ωm) at depth of between 0-4 m and low resistivity (10 Ωm-100 Ωm) at a depth of 5-30 m indicating both air-filled and water-filled voids respectively. The study shows that the voids increase in dimension with depth in NW-SE direction, suggesting that the voids are trending most probably along vertical bedrock joints. It also suggests that voids may overtime grow large enough that the overlying top soil can no longer bridge it, leading to its collapse.
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