Rio Tinto has announced the progress of its Resolution Copper project in Arizona, US, following the publication of a draft environmental impact statement (DEIS) by the US Forest Service.

The review was conducted by the US Forest Service for a period of six years and included public engagement.

The permitting process for Resolution began in 2013.

The DEIS publication triggers a public consultation process of 90 days to issue the final environmental impact statement (EIS), and next steps in the permitting process for the project.

Rio Tinto Copper & Diamonds chief executive Arnaud Soirat said: “This is an important milestone for Resolution, with the future development of the project being shaped by years of engagement with the local community and extensive independent study by the US Forest Service.

“Achieving this significant milestone in the rigorous US permitting process allows us to continue progressing one of the world’s most significant untapped copper deposits towards development.

“Resolution has the potential to supply up to 25% of the US’ copper demand and complements Rio Tinto’s other copper projects.”

According to the company, the partners would spend more than $2bn by next year on the development and permitting process of the Resolution Copper project.

In April, Rio Tinto announced plans to invest another $302m to advance the Resolution Copper project, as the company looks to progress it to the final stage of its permitting phase.

Investments were made in sinking a new shaft to mining depth, rehabilitating an existing shaft, extensive drilling and ore body testing, in addition to the permitting and public engagement process. It also included reclamation of the historic Magma Copper Mine site.

Resolution is 55% owned by Rio Tinto subsidiary Resolution Copper Company and 45% by BHP Copper.