Rio Tinto has agreed to sell its Eagle project in the US to Lundin Mining Corporation for an estimated $US35 million ($A37.26 million) in cash.

The transaction, which is subject to regulatory approval, is expected to close in the third quarter of 2013, Rio says.

Construction on the project, which includes a high-grade underground nickel-copper mine in the Upper Peninsula of Michigan, is around 55 per cent complete after beginning in 2010, it says.

Rio chief financial officer Chris Lynch says the sale reflects the company’s renewed discipline in allocating capital, and its focus on core assets.

“We are making good progress on a number of other potential divestments as part of our goal to achieve substantial proceeds from divesting non-core assets,” he said in a statement on Thursday.