Olympic Dam uranium processing facility. Source: Australian Nuclear Science and Technology OrganisationOlympic Dam, a copper-uranium mine located approximately 570 km north of Adelaide, South Australia, contains the world's largest uranium resource, the fourth-largest copper resource, and sizeable quantities of gold and silver. Minerals at the site include medium-grained chalcopyrite, bornite and chalcocite, fine-grained disseminated pitchblende, and other rare earth minerals in a hematite breccia complex.

The deposits were discovered in 1975 by Western Mining Corporation Ltd, but the mine was not opened until 1988; it is now wholly-owned and operated by WMC (Olympic Dam Operations) Pty Ltd., a subsidiary of BHP Billiton Limited. In 1999, the mine underwent a $1.94 billion expansion, increasing the capacity to 200,000 tons/year of copper and 4,600 tons/year of uranium.

After fires in the solvent extraction plant, production recovered in 2004 and 2005 (at 4,370 & 4,335 tonnes oxide (U₃O₈) respectively). Uranium recovery has been about 72%, due to about half of the uranium being in the form of refractory brannerite, but an improved leach process has lifted recovery to 82%.

Olympic Dam has enormous reserves of ore, with over 390,000 tonnes of contained uranium oxide, so that even with the increased rate of production, reserves will be sufficient for over 70 years. The overall resource contains some 1.5 million tonnes of uranium. While the grade of the uranium ore is lower than that from many mines or potential mines which have the benefit of open cut operation, the fact that copper (Cu) is a co-product with uranium from that same ore (at 2.1% Cu in the proved and 1.5% Cu in the probable reserves) means that such grades are viable.

Before the mid-2005 takeover by BHP Billiton, WMC Resources committed 90 million Australian dollars (A$) (approximately 68 million US$) over two years to assess the potential for doubling the size of Olympic Dam, and in particular to take the resource categorization of the southern orebody through to proven reserves and thus demonstrate the viability of a much-expanded operation - up to 15,000 t/yr U₃O₈ (with 500,000 t/yr copper). The capital cost involved would be A$5 billion. The pre-feasibility study to decide among the development options, with the environmental impact study, will be completed by the end of 2007. A feasibility study to define the options will be complete in early 2009, and construction of the expanded operations is envisaged for 2009-13.

The mine is designed with many environmental protection systems including storage facilities for waste products and the ability to return any spillage of ore, concentrate, or process slurries to the process circuit. It also includes comprehensive air pollution and radiation control equipment, that monitor air emissions, noise, and personnel and environmental radiation exposure.

In 1994, a leak of contaminated water was detected under the Tailings Retention System (TRS). Although there were concerns about the highly acidic liquid seeping into the aquifer, any radioactive pollutants in the seepage were filtered out by clay liner at the base of the TRS and the acidity of the water was removed when it reacted with limestone beneath the TRS. The remaining water was of similar quality to the local groundwater, hence no environmental harm nor health impacts on the population of the adjacent mining town of Roxby Downs resulted.

BHP Billiton Olympic Dam submits an Environmental Management and Monitoring report annually to the Department of Primary Industries and Resources South Australia (PIRSA) and the Environment Protection Authority (EPA). This comprehensive report covers all areas of potential environmental impact, including air emissions, site groundwater management, water supply and management of the Great Artesian Basin, flora and fauna monitoring, and annual radiation dose to members of the public. Reporting on progress with action items identified in the Environmental Management Program is provided, as well as involvement with community activities.

Olympic Dam has a Rehabilitation and Closure Plan covering cost estimate basis, summary of closure requirements (for the metallurgical facilities, pilot plant, mine, tailings dams, wellfields, exploration areas, town facilities, power line corridor and miscellaneous facilities), community consultation requirements, closure strategy (including post operational land use objective and completion criteria) and closure plan review requirements. The plan provides a breakdown for each area to be decommissioned, including engineering works required (i.e., demolition and cleaning), environmental works (removal of contaminated material and rehabilitation), specific closure obligations for each area of plant, final land use objectives, closure assumptions, closure material sources, waste disposal sites, cost saving opportunities and liabilities/risks/hazards.

Demolition costs are budgeted based on quotations from a specialist demolition contractor and rehabilitation costs are estimated based on a quotation from a mining contractor with extensive rehabilitation experience. Progressive closure costs have been estimated for each year until actual closure of the site. The financial provision - A$244 million at mid-2006 - is calculated in line with BHP Billiton Accounting Standards.

Sources

• Kubiszewski, Ida (Lead Author); Ian Hore-Lacy (Contributing Author); World Nuclear Association (Content Partner); Cutler J. Cleveland (Topic Editor). 2008. "Olympic Dam, South Australia." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth September 2, 2006; Last revised February 12, 2008; Retrieved November 11, 2008]. <http://www.eoearth.org/article/Olympic_Dam,_South_Australia>