The Olympic Dam is a huge mining centre located in South Australia, 560 km north-west of Adelaide. Home to a major oxide copper gold deposit producing copper, uranium, gold and silver, the site hosts an underground mine and an integrated metallurgical processing plant.
The project was opened in 1988 by WMC Resources, after discovering the large deposit in 1975. It was later expanded under a A$1.9 million programme, raising its capacity to 200,000tpa of copper and 4,300tpa of uranium, plus gold and silver.
In mid-2005, BHP Billiton gained control of WMC Resources in an A$9.2bn takeover. The company has a licence to mine the Olympic Dam until 2036 and it is extendable for 50 more years thereafter.
The deposit occurs in the basement rocks of the Stuart Shelf geological province in the north of South Australia, west of Lake Torrens.
Mineralisation consists of medium-grained chalcopyrite, bornite and chalcocite, fine-grained disseminated pitchblende, gold, silver and rare earth minerals that occur in a magnetic hydrothermal breccia complex beneath 350m of overburden. The ore occurs in distinct zones that determine the mine access and layout.
Proven reserves at the Olympic Dam mine as of June 2011 stand at 146Mt graded at 1.98% Cu, 0.58kg/t U3O8, 0.69g/t Au and 4.01g/t Ag. Probable reserves are estimated to be 406Mt graded at 1.79% Cu, 0.57kg/t U3O8, 0.78g/t Au and 3.19g/t Ag.
Measured resources at the mine as of June 2011 are estimated at 1,408Mt graded at 1.08% Cu, 0.32kg/t U3O8, 0.34g/t Au and 2.07g/t Ag. Indicated resources stand at 4,571Mt graded at 0.88% Cu, 0.28kg/t U~3~O~8~, 0.34g/t Au and 1.56g/t Ag.
Three vertical shafts and a decline access the orebody, which is worked using a variation of sublevel open stoping. Each stope may contain 300,000t of ore. Drill drives are driven on the stope centre line and blastholes drilled in vertical rings. These are charged with ANFO and detonated with shock tube detonators.
The drilling fleet comprises Atlas Copco and Tamrock production rigs, with development being carried out using two Tamrock (now Sandvik) jumbos. Atlas Copco has supplied two modified Simba H4356S production drilling rigs.
Stopes are backfilled with cemented aggregate of crushed ‘mullock’ (waste rock), deslimed mill tailings, cement and pulverised fuel ash (PFA). Automation has done much to reduce production costs at Olympic Dam. Innovations include the automated underground haulage system and the ‘smart’ loader, a robotics-driven, decision-making underground ore carrier.
Processing facilities consist of a copper concentrator, hydrometallurgical plant, copper smelter, sulphuric acid plant, copper and gold/silver refineries. Recent expansions included a Svedala autogenous mill, additions to the flotation sections, two counter-current decantation thickeners, an electric slag-cleaning furnace, a new anode furnace gas-cleaning plant and additional electro-refining cells.
Copper is recovered primarily by copper sulphide flotation from slurry before the copper concentrate is smelted and electro-refined to high-purity copper.
Wastes generated during electro-refining are treated to recover gold and silver. After treatment by flotation, the finely-crushed ore is leached with sulphuric acid to dissolve uranium and any remaining copper. The leach liquor is processed in the solvent extraction plant to separate the residual copper and uranium streams. Copper is recovered by electrowinning and uranium converted to yellowcake and calcined uranium oxide.
Installation of two pulsed columns increased uranium recovery from solution from 90% to about 97%. These columns use an air pulse to mix the acidic and organic solutions, providing better contact for the chemical reaction involved in transferring the uranium from one to the other.
Copper cathode sheets are transported by truck within Australia and to Port Adelaide for export. All uranium oxide produced at Olympic Dam is exported. The gold plant became fully operational in 2000. The Olympic Dam mine produced 194,100t of copper, 4,045t of uranium oxide, 111,368oz of refined gold and 982,000oz of refined silver in 2011.