Detecting the occurrence of shallow mining cavities by electrical resistivity imaging method. A study case on the Victoria cave, Cartagena (SE Spain)

Former mining areas which have been under intensive mining activity raise some geotechnical concerns. These are due to the collapse of the mining cavities from natural alteration processes during the course of time. In these intensive mining areas, geophysical techniques can play a significant role in the detection of voids. The Sierra Minera La Union-Cartagena (SE, Spain) is a huge mining area covering a surface of 2000 Ha. For centuries several ores like sphalerite (ZnS), pyrite (FeS2), galena (SPb), and manganese-iron bearing ores were extracted from these mountains. Mining stopped in the eighties because of the depletion of the mineral resources. In order to check its reliability the electrical resistivity imaging (ERI) method was tried out on a selected area of La Sierra Minera, where the location and orientation of the main caves are well known. This technique was chosen because the climate of the study area is semi-arid and the cave space is occupied by air, so the electrical resistivity contrast between the cave itself and the host rock could be expected to be high. The geophysical results have shown a close correlation with the position of known caves but further have highlighted the position of new cavities previously unknown before employing the ERI method.