Olympic Dam Copper-Uranium Mine, Adelaide, Australia

The Olympic Dam copper-uranium mine and plant is situated in South Australia, 580km north west of Adelaide. Opened in 1988, Olympic Dam is wholly owned and operated by WMC Resources, which discovered the deposit in 1975. An A$1,940m expansion programme was completed in 1999, raising its capacity to 200,000t/y of copper and 4,300t/y of uranium, plus gold and silver. In mid-2005, BHP Billiton gained control of WMC Resources in an A$9.2bn take-over.

In 2007 BHP Billiton announced that it would undertake an $A6–7bn expansion of the Olympic Dam mine. The company says that annual ore production will increase up to 70 million tonnes, a seven-fold increase if the expansion proceeds. Copper production will increase from approximately 180, 000t a year to approximately 730,000t.

This would include 500,000oz of gold, 500,000t of copper and 15,000t of yellowcake. Existing average gold production is 80,000oz pa. The additional proven reserves of uranium now make Olympic Dam one of the most promising uranium mines in the world.

Intierra's Minmet data base puts current Olympic Dam proven-probable reserves at 756 million tonnes grading 1.5% copper, 0.5kg/t U308, 0.5 g/t gold and 3.1g/t silver. The measured to inferred resources were 3.214 billion tonnes at 1.025% copper, 0.337kg/t U308, 0.442g/t gold and 2.144g/t silver. On these figures, without improved grades or increased tonnage, Olympic Dam has proven reserves of a contained 12.153Moz gold and contained resources of 45.62Moz.

The results of the study ended much speculation within the mining and investment communities, which were especially abuzz about the potential upgrade of gold reserves.

Once fully complete, the expansion would make Olympic Dam the biggest mine in the world. Concerns have naturally been voiced about how the necessary infrastructure will be funded and deployed. Finding skilled labour will be another challenge.

The proposed expansion is likely to see the current underground mining operation eventually converted to open pit.

GEOLOGY AND RESERVES

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.

As of December 2004, the total mineral resource at Olympic Dam stood at 3,810Mt grading 1.1% copper and 0.4kg/t U3O8. WMC Resources is currently carrying out 340km of exploration drilling as part of its expansion study, with recent results having increased the mineral resource on the property by over 30%. At the end of 2004, Olympic Dam had proved and probable ore reserves of 761Mt at 1.5% copper, 0.6kg/t U3O8 and 0.5g/t gold.

MINING

The current scope and logistical demands of the mine are about to be increased by a few orders of magnitude once the expansion gets into full swing. The mine will gradually be transformed from an underground operation to open pit.

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.

ORE PROCESSING

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 has 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. A fire in 2002 at the solvent extraction / electrowinning plant cost over A$300m to repair, while WMC also spent A$127m on renovating the copper smelter during 2003.

EXPANSION

In 1988, Olympic Dam produced 45,000t/y of copper plus associated products. In 1992 and 1995, expansions increased production to 85,000t/y of copper. The latest expansion, completed in 1999, has included a third haulage shaft, a new crusher station and a rail-based ore handling system underground, the new autogenous mill, expansion of the hydrometallurgical plant and copper refinery, and a new smelter complex.

Scheduled to produce 11Mt/y of ore by 2005 and 12Mt/y by 2007, Olympic Dam mined 8.22Mt of ore in the year ending June 2006, and milled 9.64Mt of material averaging 2.19% copper and 0.61kg/t uranium.

Electro-refined copper cathode output was 186,400t and electrowon cathode production was 17,900t. Refined gold and silver outputs were 102,236oz and 896,000oz respectively, while uranium oxide concentrate production was 4,341t.

The much-publicised expansion of Olympic Dam is expected to virtually quadruple total production of the mine, with gold seeing the biggest increase up from around 80,000oz pa to now over half a million.

ENVIRONMENT

Olympic Dam maintains storage facilities for all waste products. The plant has been designed so that any spillage of ore, concentrate or process slurries can readily be returned to the process circuit. The plant also includes comprehensive air pollution control equipment and both air emissions and noise are monitored. Extensive radiation monitoring of personnel and the environment is ongoing.

The Australian and South Australian governments jointly determined that the proposed Olympic Dam expansion must be formally assessed through an Environmental Impact Statement (EIS).