The operations are expected to add 30,000t of copper production at Kennecott operations, from early 2023 to 2027, alongside the open pit operations.
Last year, the open pit operations at the site reported the production of 59,400t of copper.
The underground mining will initially focus on the Lower Commercial Skarn (LCS), which has an estimated measured resource of 200,000t at 2.52% copper, 1.27g gold per tonne, 10.56g silver per tonne and 0.056% molybdenum.
Production from the operations is anticipated in early 2023, with full production expected to reach in the second half of the year.
The underground ore is planned to be processed through the existing facilities at the Kennecott site.
As part of underground development work, Rio Tinto is trialling the performance and suitability of the Sandvik Mining and Rock Solutions-supplied battery electric haul truck and loader at the Kennecott site.
The underground battery electric vehicles are expected to increase productivity and reduce carbon emissions.
Rio Tinto copper CEO Bold Baatar said: “We are progressing a range of options for a significant resource that is yet to be developed at Kennecott, which could extend our supply of copper and other critical materials needed for electric vehicles and renewable power technologies.
“Trialling underground battery electric vehicles is an exciting step in our work to create a safer workplace for our employees, increase the productivity of the mine and reduce emissions from our operations. We look forward to seeing their potential for deployment.”
Rio Tinto said that feasibility studies are being carried out to extend Kennecott open-pit mining beyond 2032.
The firm also intends to complete a feasibility study on the next phase of underground production next year.