BHP Billiton is cutting 140 jobs, with the majority of those roles coming from its Adelaide office.

A company spokesperson said redeployment opportunities may be taken up by some employees, which will reduce the total impact.

"Our goal is to become a safe, high-performance organisation with a culture of respect, simplicity and collaboration," the spokesperson said.

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"All areas of the operation, including labour productivity, are being examined and we expect there will be some workforce reductions.

"When these are known, we will communicate with our employees who are affected quickly and respectfully."

BHP had planned a major expansion of the Olympic Dam mine in outback SA after taking over the site from WMC Resources in 2005.

Those plans were shelved in 2012 due to falling commodity prices and slow global economic growth.

The spokesperson said the affected employees were being consulted about proposed redundancies.

The job losses are in addition to the 90 positions cut by BHP Billiton in February.

Opposition Leader Steven Marshall said the announcement was a body blow for the state's economy.

"It comes at the worst possible time," he said.

"Of course, 8,700 full-time jobs lost in South Australia last month. It's in a difficult sector.

"We know that we've lost almost 5,000 mining jobs in this state in the last six months."

SA Treasurer Tom Koutsantonis said economic difficulties in the resources sector would get worse before they improved.

"We've seen the iron ore price nearly halve over the past few months but there are signs of the economy improving," he said.

"But let's be clear about this - this will get worse before it gets better in the resources sector.

"A lot of resources companies nationally and internationally are doing it very very hard."

Prior to these changes, the total workforce of Olympic Dam was about 4,000, including employees and contractors.

'Grandiose plans' not attractive to shareholders, analyst says

Both state and federal politicians are hoping the mine expansion will still go ahead, but independent market analyst Peter Strachan said it would probably not be in the near future.

"I think it's a while off, and I think that the shareholders of BHP have said to the company that they would rather see dividends and share buybacks than sort of grandiose plans," he said.

Mr Strachan expects copper prices will start to recover in the next 12 to 18 months.

He said Olympic Dam was still profitable.

"The mine is getting a bit long in the tooth. There will be things that need to be repaired and replaced, and they'll be focusing on getting that operation running and humming as smoothly as possible," Mr Strachan said.

"What they won't be wanting is project engineers looking at new and expansion opportunities, and perhaps some of their geological department might be surplus to requirements and be redeployed into other areas.

"So it's a change of mindset at Olympic Dam from, you know, making this mega-mine.

"I mean, it is a huge ore body and you know they'll be mining there 60, 80 years from today at the current rates of production."