Iron sulfide (pyrite and pyrrhotite) was mined by open pit methods at Brukunga, located 40 km east of Adelaide in the Mount Lofty Ranges of South Australia, between 1955 and 1972 to provide feedstock for sulphuric acid production in the South Australian fertiliser industry. The site has been managed by Primary Industries and Resources South Australia (PIRSA) since 1998. Eight million tonnes of waste rock (2 wt % S) were mined and stored in three waste rock dumps. 3.5 Mt of tailings (1.7 wt % S) were produced and stored in an above ground facility. The total area of disturbance at the Brukunga Mine site is 155 ha, comprising the tailings dam, waste rock storages, quarry and Brukunga township. Oxidation of the mine and processing waste, and exposed remnant sulfidic rock mass, has resulted in acid drainage (pH<3) with elevated sulfate and dissolved metals. A hydrated lime-based water treatment plant was commissioned at Brukunga in September 1980 to treat acid drainage. The plant initially treated acidic seepage from the tailings storage facility (estimated at mine closure to be 80,000 m3/year), but has subsequently been expanded to treat acidic drainage collected from the waste rock dumps and the mine workings. The plant was upgraded to a high-density sludge operation, which has improved reagent efficiency and water quality, and also reduced overall treatment costs. Dawesley Creek drains the mine site precinct and prior to June 2003 this acid drainage entered this Creek making the water unsuitable for livestock and irrigation use for up to 20 km downstream. A diversion drain was constructed in June 2003 to separate non-mine related flow in Dawesley Creek from acidic mine drainage, which is collected and treated in the water treatment plant, in an attempt to reduce the total volume of water requiring treatment. Water treatment timelines to reduce acid, metal loads are estimated to range from 300 to greater than 1000 years. PIRSA has implemented a process for determining the most effective long-term solution for the remediation of the Brukunga Mine site. The goal of the Brukunga Remediation Project is to develop a walk-away solution, which is remediation allowing return of the land to a landuse suitable for release of the land from Government ownership such that the site requires no further intervention by, ongoing responsibility for or cost to Government and/or community.
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