BHP Billiton has sold a copper mine in the US for $US650 million ($A634.86 million) as the resources giant continues to off-load assets.

It has sold its Pinto Valley mining project and the associated San Manuel Arizona Railroad Company, including a 47km railway, to Canada's Capstone Mining Corp.

BHP had now sold $US5 billion ($A4.88 billion) in assets in the last 12 months, the company's president of copper, Peter Beaven, said in a statement on Monday.

It has at least another 10 assets it regards as non-core or underperforming for sale.

While such auctions are part of severe cost-cutting programs or paying down debt, shareholders hope they mean more cash for them - as demonstrated by Woodside increasing its dividends after it shelved the planned $US45 billion Browse Basin LNG facility.

Smaller resources companies can use the larger companies' urgency to sell to pick up assets for a cheap price.

Workers at the Pinto Valley project would become Capstone employees, Mr Beaven said.

The deal is subject to regulatory approval.

The mine was idled in 2008 during the global financial crisis but was re-started about 12 months ago.

BHP shares were 27 cents weaker at $32.30 in opening trade on Monday, following falls in commodity prices on Friday.