The investment will be used to carry out additional drilling, ore-body studies, infrastructure improvements and permitting activities.
The move comes after Rio Tinto’s board approved $368m in late 2017 to improve infrastructure and facilitate permitting and mine planning at the Resolution Copper project as part of the pre-feasibility study.
Once fully operational, Resolution is expected to supply nearly 25% of the copper demand in the US.
Rio Tinto chief executive JS Jacques said: “Resolution is one of the most significant undeveloped copper deposits in the world and this additional funding demonstrates Rio Tinto’s commitment to bring the mine into production.
“The rise of electric vehicles, battery storage, new transmission technology and other green energy innovations are highly copper intensive.
“We need to prepare now to meet this future demand. Resolution will be well positioned to provide North American manufacturers the copper that is essential to their products.”
At present, the comprehensive permitting process for the Resolution Copper project is underway with the environmental impact study on track to be completed next year.
The environmental review and approval process is conducted by the US Forest Service under the National Environmental Policy Act.
With this latest investment, project partners will have invested more than $2bn in the development of Resolution since 2004.
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.
Resolution is 55% owned by Rio Tinto subsidiary Resolution Copper Company and 45% by BHP Copper.