Prediction of Metal Mobility from Sulfidic Waste Rocks Using Micro-Analytical Tools, Spray, Tasmania

The Zeehan Pb-Zn field in western Tasmania (Australia) contains over one hundred abandoned and historical mine sites. Combined with a temperate rainforest climate and abundant waste rock material, many sites are affected by acid rock drainage (ARD). The Spray mine, located southwest of the town of Zeehan, was one of the field’s largest historical producers of Pb and Ag. Abandoned in the early 1900s, the site contains numerous adits and waste rock piles which contribute to ARD in the region. The aim of this study was to predict the likely ARD surface water quality, using the major and trace element chemistry of sulfide minerals present within waste materials on site. Major ore sulfides are galena and sphalerite with associated Sb-rich sulfosalt minerals including boulangerite and geocrocite. These minerals contain minor concentrations of Ag, Bi, Cd , In and Sn. Minor arsenopyrite and abundant pyrite (average 7500 ppm As) represent the main repository for As. Siderite is a major gangue mineral, containing slightly elevated In, Pb, Sb and Zn (250–50 ppm). Metals and metalloids (Ag, As, Bi, Cd, Cu, In, Pb, Zn) contained within sulfides and siderite may be mobilized upon mineral dissolution into ARD waters. Consequently, micro-analytical analyses of sulfides and associated gangue minerals can assist in the prediction of aqueous metal and metalloid mobility from sulfidic waste rock piles.