BHP Billiton Ltd. (BHP.AU) said Wednesday a mechanical failure has shut down the main haulage shaft used to extract ore from its underground Olympic Dam mine in South Australia state.

Analysts said the outage was unlikely to have a significant impact on BHP's earnings but could potentially have an affect on sentiment in a copper market that is already supply constrained.

BHP said a mechanical failure late Tuesday damaged the Clark shaft, which is the main shaft hauling ore from the underground copper, gold and uranium mine to the surface for processing.

A secondary haulage system, which has less capacity than the main system, continues to operate and a spokeswoman said it is too early to say what impact the incident may have on production.

No one was injured in the incident and BHP said it is investigating the cause of the failure and the extent of the damage.

"The safety of our workforce will take priority in determining any restart of haulage operations," the miner said in a statement.

ABN Amro analyst Warren Edney said the outage was unlikely to hurt BHP's earnings to any significant degree but that it could potentially affect sentiment in commodity markets, even though the mine is not a major producer of copper.

Olympic Dam produced 194,100 metric tons of copper in the financial year ended June 30, representing only about 1.1% of global production.

It is a more globally significant producer of uranium, with its output of 4,007 tons of yellowcake in fiscal 2009 representing more than 7% of global mine production.

BHP is planning to transform Olympic Dam into the world's biggest open pit mine, upping annual copper output to 730,000 tons and uranium to 19,000 tons, in a major expansion tipped by analysts to cost about US$15 billion.

-By Alex Wilson, Dow Jones Newswires; 61-3-9292-2094; alex.wilson@dowjones.com