However, the company left its full-year production forecast unchanged.

Even in an optimistic low emission scenario for 2050, more than half the world’s copper mines will be in areas exposed to drought risk that’s deemed significant.

The bid may also be a tacit admission on BHP's part that buying copper assets is far easier than trying to find them and develop new mines.

Assays from the Satellite West target outlined the new area 500 metres west of the main deposit that hasn’t been drilled since 1997.

BHP's $39 billion bid will be the elephant in the room at Anglo American's Tuesday annual general meeting.

Freeport Indonesia's chief executive has previously said that it may have to slash copper ore output by 40% this year.

Its Tenke Fungurume site added new mining capacity in March, lifting annual capacity to 450,000 tons of copper and 37,000 tons of cobalt.

BHP is considering making an improved offer, Reuters sources said during the weekend.