PERTH (miningweekly.com) – Diversified miner Rio Tinto has approved a $55-million investment to start underground mining at the Kennecott copper operations, in Utah.

The miner said on Tuesday that underground mining will initially focus on an area known as the Lower Commercial Skarn (LCS), which will deliver a total of around 30 000 t of additional high quality mined copper through to 2027 alongside opencut operations.

The first ore is expected to be produced in early 2023, with full production in the second half of the year.

The underground ore will be processed through the existing facilities at Kennecott, one of only two operating copper smelters in the US.

“This investment will allow us to quickly bring additional volumes of high-quality copper to the market and build our knowledge and capabilities as we evaluate larger scale underground mining at Kennecott,” said Rio copper CEO Bold Baatar.

“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.”

The LCS is the first step towards this, with a mineral resource of 7.5-million tonnes at 1.9% copper, 0.84 g/t gold, 11.26 g/t silver and 0.015% molybdenum identified based on drilling and a probable ore reserve of 1.7-million tonnes at 1.9% copper, 0.71 g/t gold, 10.07 g/t silver and 0.044% molybdenum.

Underground battery electric vehicles are currently being trialled at Kennecott to improve employee health and safety, increase productivity and reduce carbon emissions from future underground mining fleets.

A battery electric haul truck and loader supplied by Sandvik Mining and Rock Solutions are being used to evaluate performance and suitability as part of underground development work.

“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,” Baatar said.

Meanwhile, existing underground infrastructure is currently being extended to enable early access to the next underground resource and undertake characterisation studies. A feasibility study to inform decisions on the next phase of underground production is expected to be completed in 2023. This will be one of several potential stages currently being investigated.

Feasibility studies are also being progressed to extend openpit mining at Kennecott beyond 2032.