BHP Billiton and Rio Tinto have announced plans to expand the Escondida mine in Chile in a bid to boost their copper output.
The two firms have approved plans to invest a combined $4.5bn (£3bn) in the mine, which is the world's biggest.
They want to boost their capacity so that they can meet the growing demands from China and other emerging nations.
BHP also announced plans to reopen its idled Pinto Valley mine in Arizona.
BHP said the expansion at the Escondida mine will "help ensure it remains the world's leading copper operation for decades to come".