The companies took on a 30-year lease for the mine in 2008, which has an estimated reserve of 11.08 million tonnes of copper.

The company was exploring the possibility of expanding production to as much as 30 million tonnes a year.

Shanghai's stainless steel contract, closely watched by Chinese nickel players, hit its own life-of-contract high last month.

Copper’s surge to record levels this year is spurring buyers in a key consumer market to mull cheaper alternatives.

Coal mining is more commonly criticised by environmentalists for polluting air and water, degrading landscapes and fuelling climate change than for creating new wildlife habitats.

The plant in Pomalaa, in Southeast Sulawesi province, is expected to produce 40,000 tonnes of mixed sulphide precipitate.

Refined tin exports stood at 7,497.19 tonnes in August, up from 6,158.67 tonnes last year and 14.27% higher than July.