Despite the recent recommissioning of the copper smelter at WMC Resources’ Olympic Dam mine in South Australia, the company is still trying to finalise repairs to its copper solvent extraction plant, severely damaged in a fire involving kerosene in October 2001.
The best estimate is that the copper SX plant repairs will be completed by the end of this year, with commissioning in early part of 2004, at a revised cost estimated at $375m.
At that time it is expected that Olympic Dam, for the first time in its history, will hit its nameplate capacity of 235,000t of copper a year and 4000tpa of uranium oxide.
Olympic Dam has been bedevilled by operational problems at its processing plants, with the most recent being the spill of uranium-contaminated water from the plant last month. However, bunding secured the spill and the contaminated water was quickly pumped back into the mill circuit.
Meanwhile, the scheduled maintenance and construction work on the copper smelter at a cost of $127m is now finalised and production has resumed, after a close down on 20 August.
This has been a major project at Olympic Dam, involving relining of the flash anode and slag furnaces, refurbishment and repairs to the boiler, improvements to the gas handling system and the slag furnace, replacement of the electrostatic precipitator and additional repairs to the brickwork in the smelter hearth.
Although it is not uncommon to see wear around the edges of the hearth, particularly below tap holes as a result of normal operations, WMC says the degradation of the brickwork was more extensive than anticipated.
In fact, 30% of the hearth had to be demolished and replaced, affecting the scheduled October ramp up back to full operations.
Copper smelter campaign
WMC is putting a positive spin on this extra work saying it will add to the integrity of the next copper smelter campaign at a fraction of the cost of fixing the problem if it had happened during a campaign.
Nevertheless, it has had an impact on operations with the planned 185,000t of copper cathode production originally targeted for this year likely to be reduced to a lower figure of 178,000-180,000t.
The most recent quarterly report from WMC also says that uranium production improved by 19% during that period reflecting the contribution of the rebuilt uranium solvent extraction plant and that this is expected to increase further in the subsequent quarter, with full acid supply restored following completion of the smelter shutdown.
While WMC seems to be getting on top of its processing problems, the mine itself has emerged as the major constraint of further production improvements.
Olympic Dam, as the eighth largest copper orebody in the world and the largest uranium oxide deposit, has a life of at least 50 years at current production rates.
Copper production started in 1988 at 45,000tpa, rose to 66,000tpa in 1991, to 84,000tpa in 1995, 200,000tpa in 1999 and is now being optimised to 235,000tpa.
The question is to whether keep expanding production, each time incurring further capital costs that will further put off the day when the project actually covers the investment.
An expansion study project is currently underway, with 45 holes having been drilled to further delineate the existing resource and identify additional resources. The results will be modelled late this year to judge whether further expansion is possible.
Fine tuning
Meanwhile, fine tuning of the mine operations continues to meet the target of an annual 12Mt of ore being hoisted, for an annual smelter throughput of 500,000t and a refined copper production of 225,000t plus.
Among issues addressed at the mine have been such operational matters as moving to one firing a day, to minimise downtime, and the use of hot seat changeovers in equipment.
Other changes include the use of percussive cone fragmentation (PCF) technology for secondary breakage, and use of new autonomous Caterpillar Elphinstone loaders controlled from the surface.
WMC has also been involved in trials with ore pass radar and stope backfill radar.
It is also attempting to improve the reliability of the rail haulage system underground, by reducing the electrical, control and communications faults. Gearbox improvements are also in the firing line.
WMC is also running a backfill improvement project to reduce likely future costs. This has involved alternative binders and fill types, increased use of tailings from the processing plants and optimisation of the backfill system for the deeper slopes.
Another project concerns the generation of oversize ore. By increasing the geotechnical input into stope design and optimisation of drill and blast design, it is hoped to reduce oversize rock production.
Finally, there is an overall project to review mine design and generation of alternative long term scheduling.
To attain some of these aims, WMC has set up two new discrete business units at Olympic Dam: an engineering unit and one that goes under the lengthy title of technical/strategic/planning/business effectiveness.