Mineshaft Imaging Using 2d Electrical Resistivity Tomography in a Kaolin Mining Site at Kankara in North Central Nigeria

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. Mineshaft Imaging Using 2D Electrical Resistivity Tomography in a Kaolin Mining Site at Kankara in North Central Nigeria