Practical Application of Geophysical Methods for Characterisation of Waste Rock Dumps

Traditional geochemical characterisation of waste rock dumps (WRDs) often faces challenges due to the complexity, heterogeneity, and spatial variability of the material, creating difficulties in optimising sampling locations and predicting environmental risks. Geophysical methods offer an approach to fill these knowledge gaps and provide a more comprehensive understanding of WRD properties. This study explores the use of electrical resistivity imaging, seismic refraction, ground magnetics, and electromagnetic ground conductivity methods to investigate basement topography, volume, internal structure, water table, and potential zones of acid and metalliferous drainage (AMD) within a WRD at a former tin mine in northwest Tasmania. Interpreted basement topography based on a combination of geophysical methods closely matches known pre-WRD topography, with a calculated WRD volume of 866,000 m3, ≈ 5% greater than the volume based on pre-WRD topography. Investigation of internal WRD structures defined the extent of potentially acid forming (PAF) and non-acid forming (NAF) cells, the boundary between these cells, installed WRD drainage features, and low resistivity zones within the PAF cell interpreted as perched water tables. Variations in water table levels and the infiltration of potential AMD leachates into the underlying NAF cell were also identified with ERI. Multidisciplinary geophysical methods can provide a valuable, cost-efficient, and non-invasive first-pass assessment of WRD characteristics and inform subsequent waste management strategies. Use of these results can ensure more efficient planning of targeted, time-consuming, and costly geochemical studies by locating the most appropriate sites for observations boreholes and sample locations.