Mapping a hazardous abandoned gypsum mine using self-potential, electrical resistivity tomography, and Frequency Domain Electromagnetic methods

Abstract

This paper is the first phase of an integrated geophysical investigation of an abandoned gypsum mine in Blackhawk, South Dakota, USA. Recent ground collapses have occurred over these tunnels, the extent of which was heretofore unknown. Summarized herein are survey results from the northern and northeastern parts of the study area. We used Electrical Resistivity Tomography (ERT) as the main method of exploration due to its high resolution, accuracy, and high data coverage. We measured nine resistivity lines using Wenner and Dipole-Dipole arrays. We also applied the Self-Potential (SP) and Frequency Domain Electromagnetic (EM31) methods in the northeastern part of the study area. Our results reveal: (1) many low-resistivity tunnel-shaped anomalies in the eastern zone, which is flooded; and (2) high-resistivity tunnel-shaped anomalies in the western zone, which is dry. The flooded and dry zones are clearly differentiated by the resistivity method. A negative SP anomaly—created by the downward seepage of CaSO4-water in the tunnels—is a key to outlining abandoned mine tunnels.