Abstract:

Accurate assessment of mine waste rock dumps (WRDs) requires detailed characterisation of properties such as waste rock mineralogy, neutralisation capacity, and distribution of pore space. However, these data are of limited use without information on bulk characteristics of WRDs, such as basement topography, internal structure, preferential flow paths, and distribution of lithologies.

Geophysical methods provide a means to rapidly collect information on WRD characteristics such as basement topography, volume, internal structure and distribution of sulfidic materials. This insight allows for efficient planning of costly, detailed, and time-consuming geochemical studies of WRDs for acid generation properties or potential reprocessing opportunities. This is especially relevant for legacy mine sites, where information on WRD construction may not exist.

This study applies 2D electrical resistivity imaging and induced polarisation geophysical methods to explore characteristics of a valley-infill WRD at a former tin mine in north-west Tasmania. Electrical resistivity imaging and induced polarisation successfully map the distribution of sulfidic materials and WRD structures, including basement topography, the location of subsurface drainages, and the division between high-capacity potential acid forming and non-acid forming cells. Additionally, zones of compaction within cells and potential seepage of contaminated high-capacity potential acid-forming leachates into underlying non-acid forming materials are identified.

Strong agreement of interpreted geophysical results with pre-WRD topography and WRD design plans confirm the validity of these methods. These findings demonstrate how electrical geophysical methods offer a rapid, cost-effective, and non-invasive overview of WRD physical characteristics, which can be used to improve overall WRD assessments through targeting of detailed geochemical studies.

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Dr. Matthew J. Cracknell