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Diversified major Rio Tinto has approved a $108-million investment in underground development at its Kennecott copper operations, in the US, to enable early orebody access and undertake orebody characterisation studies for underground mining.

The investment builds on $25-million approved in early-2020 to complete a prefeasibility study to determine the viability of underground mining operations at Kennecott.

Potential underground mining would occur concurrently with openpit operations and result in increased copper output, the miner said this week.

“Kennecott holds a range of options to extend our supply of copper and other critical materials, to meet the strong demand being driven by electric vehicles and renewable power technologies,” Rio copper CEO Bold Baatar said.

“The operation is uniquely positioned to supply these emerging markets, with one of only two operating smelters in the US that also processes concentrates from third parties, a long history delivering high quality products and significant resources that are yet to be developed.”

Kennecott holds the potential for a significant and attractive underground development, with declared mineral resources of 20-million tonnes at 3.65% copper and 1.62 g/t gold with further upside potential based on drilling.

The feasibility study work will focus on gathering critical geological, geotechnical and hydrogeological data to inform Rio’s assessment of underground development options and is expected to be completed in 2024.

Existing infrastructure from previous underground projects will be extended to access the North Rim Skarn orebody, allowing for the development of crosscuts and further drilling of the resource. The project includes approximately 15 000 feet of lateral development, 1 000 feet of vertical development and associated support infrastructure.

The project will also include the trial of underground battery electric vehicles to reduce carbon emissions at Kennecott and across Rio’s global operations, with Sandvik Mining and Rock Solutions supplying a battery electric haul truck and loader to evaluate performance and suitability for future underground mining fleets.

Prefeasibility studies are also being progressed to extend openpit mining at Kennecott beyond 2032, with a further push back of the North Wall to allow access to mineral resources. This follows a $1.5-billion investment in the second phase of the South Wall Pushback project, approved in 2019, to allow opencut mining to continue between 2026 and 2032.