Integration of surface and groundwater studies to support closure planning at the legacy Hercules Mine, Tasmania

MMG Limited owns and operates the Rosebery Mine in Rosebery, on the west coast of Tasmania. When the company purchased the mine in 2009, it also inherited the Hercules Mine legacy site located in the headwaters of Baker Creek on Mount Hamilton, approximately 8 km south of the Rosebery Mine. The Hercules site is remote and located in challenging mountainous terrain, with steep slopes, unstable ground, limited level areas and high rainfall. The mined area is drained by the steeply sloping Baker Creek, which receives inputs of highly acidic (pH 2–3) metalliferous drainage (AMD) from several adits draining poorly mapped mine workings, and runoff from disseminated surface deposits of sulfidic waste rock. It has thus been a major challenge to apportion the contribution from different contaminant sources to the acid and metal load reporting to Baker Creek. MMG is investing substantial effort to enhance its understanding of the primary sources of AMD, the relative contribution from each key source, and the key transport pathways in the system to better define rehabilitation and closure options and closure completion criteria for the site. Integrated studies of surface and groundwater quality and flows are currently underway to better understand the interaction between the various surface and underground sources, the behaviour of contaminants within them and the key drivers that need to be managed to reduce post-closure loads of contaminants to the downstream aquatic environment.