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Summary
The majority of discharged mine waste from the Mt Lyell copper mine was deposited as deltaic sediments at the mouth of the King River, Macquarie Harbour, Tasmania. These waste materials are composed of sulphide bearing tailings and are a significant environmental hazard due to their potential to generate highly acidic waters and mobilise heavy metals. This project aims to understand the internal structure of tailings deposited in the King River Delta (KRD) using coincident near surface geophysical methods, such as EM38, DC Resistivity, seismic refraction and shear-wave velocity analysis. This information is required to generate robust estimates of the volume of mine waste in the KRD, which will be used in a larger project that is assessing the environmental and economic feasibility of future tailings processing.
Inverted geophysical models are able to resolve four near surface layers within the KRD to a depth of ~20 m: (1) dry unconsolidated tailings to 2 m depth, (2) saturated unconsolidated tailings to 4-5 m depth; (3) salt water within unconsolidated sediments at depths >4-5 m; and (4) the transition to bedrock and/or consolidated sediments from >12 m depth. Unfortunately, the significant attenuation of seismic energy in the near surface and a decrease in seismic velocity with depth coupled with very low apparent resistivities of salt water prevent confident identification of the interface between mine tailings and the inferred underlying Quaternary fluvial sediments.