Rio Tinto said Aug. 9 that it hit a key permitting milestone at its Resolution copper joint venture in Arizona with BHP Group after the U.S. Forest Service released a draft environmental impact statement following a six-year review that started in 2013.

Resolution is 55%-owned by Rio Tinto, while BHP holds the remaining 45% stake. A 90-day public consultation will start for a final EIS. Resolution is said to have the potential to supply 25% of U.S. copper demand.

By 2020, the consortium will have spent over US$2 billion, with Rio Tinto footing US$1.1 billion. The figure includes US$302 million Rio Tinto invested in April to bring Resolution to the final stage of the permitting phase.

On top of the permitting process, work being undertaken at Resolution includes the reclamation of the historical Magma copper mine site, sinking a second shaft to mining depth and the rehabilitation of an existing shaft as well as extensive drilling and ore body testing.

In July, Rio Tinto Chief Executive Copper and Diamonds Arnaud Soirat said the miner may bring its Winu copper discovery in Western Australia's Paterson province into production ahead of Resolution.