Colorado-based Newmont holds onto the top spot.

Representatives of the company are traveling to Singapore and Hong Kong to meet bondholders.

Vale is exploring a copper mine, comparable to massive Grasberg site.

"Chile's new mining royalty law will not materially weaken the competitiveness of the country's copper mining sector, but it will increase taxes, modestly pressuring miners' cash flows," Fitch said.

Glencore has said it plans to run down its mines by the mid-2040s.

The company recorded six fatalities in its financial year which ended on June 30.

The study estimates an after-tax net present value of $1.3 billion with an after-tax internal rate of return of 23%.

Since reaching a year-high peak in July, Fortescue’s shares have fallen more than 15% in Sydney.