And it expects production to remain at the reduced level for up to three months.

However, the company has not yet said what impact this will have on its and contractor’s workforce at the mine.

In its production report for the September quarter, released yesterday, BHP Billiton only briefly mentioned the mechanical failure which closed the Clark shaft which contains the mine’s main automated hoisting system bringing ore to the surface.

The report stated: “On 6 October 2009, one of the two haulage systems at Olympic Dam (Australia) was damaged.

“We anticipate that ore hoisting will be at approximately 25 per cent of capacity until full production resumes in the third quarter of the 2010 financial year.”

The production report indicated that the company’s investigation into what went wrong and to determine the extent of the damage was still continuing.

BHP Billiton’s media relations spokeperson, Samantha Evans, confirmed the impact of the reduced production on underground crews had not been determined.

“I can’t tell you at this stage,” Ms Evans said when asked if the number of workers at the mine would be cut back until full production was resumed.