Geoenvironmental characterisation of the abandoned Scotia Mine, northeast Tasmania: implications for management practices

The Scotia mine site, northeast Tasmania was operated by Van Diemen Mines (VDM) Pty Ltd (2007 to 2009) and predominantly targeted tin and sapphire. Whilst production of these commodities was never formally reported, the footprint of the mine included the processing area, main pit, three tailings dams and a freshwater dam. Since 2010, the mine has been in the care of the Tasmanian Government with no rehabilitation works having been undertaken by VDM.

This study examining the mineralogy and geochemical properties of tailings (n = 85; depth of 1.5 m) and sediments from around the site (n = 68; depth of 1 m) to identify potential geoenvironmental risks. In addition a detailed pit-lake chemistry study was conducted, and kinetic cells (n = 12) were established to evaluate the benefits of introducing a lime-cover if dewatering of the tailings dams was to occur as part of a larger rehabilitation programme. The tailings mineralogy is dominated by silicates with only trace- content of sulphides and no primary neutralisers. Despite this, the sampled materials were geochemically classified as potentially acid forming. As these materials are under water covers sulphide oxidation is retarded, but mildly acidic pH values still prevailed in each dam, with the chemistry of the main-extraction pit lake indicating metal concentrations in excess of ANZECC (2000) guidelines. The use of commercial lime sufficiently raised leachate pH to an alkaline range in kinetic trials and largely prevented continuous elution of metals (including As, Cu, Cd, Pb and Zn) above ANZECC (2000) aquatic protection values (80 % trigger-level) with the exception of Al. Trials to attenuate metals in solution using red mud were effective for the majority of metals, however, caution was exercised to maintain the pH conditions at 6-8 to prevent Al from dissolving. These results have assisted in developing a rehabilitation plan for this site.