US minerals exploration company Ivanhoe Electric plans to acquire a purpose-built, Crossover XRE tunnel boring machine (TBM) and materials handling system for decline development at the Santa Cruz copper project, in Arizona, at cost of about $64.7-million.

The equipment is being sourced from US-based TBM and technology supplier The Robbins Company, which recently bought the TBM back from diversified miner Anglo American, which originally bought the machine for use at its Grosvenor coal mine, in Queensland, Australia. The TBM successfully completed two declines totalling 1.8 km in 1 000 hours of use underground at Grosvenor.

"This specific crossover TBM is perfectly suited for accessing our high-grade orebodies at Santa Cruz and continues the derisking of our mine development with the best tunnelling technology America has to offer. Santa Cruz continues its journey to become the next large-scale 99.99%-pure copper cathode producer in the US, delivering the copper that America needs to support industry, technology and national defence.

"In addition, owning the TBM gives our engineers the ability to pursue a future phased expansion of the project, including the high-grade Texaco deposit, a mere 2 km away,” comments Ivanhoe Electric chairperson Robert Friedland.

Ivanhoe Electric points out that the Robbins TBM can move through hard rock, wet and mixed-face ground within a single drive, eliminating cost, schedule, and safety risks associated with machine swaps or re-mobilisation.

Testwork indicates that these mixed ground conditions are present throughout the decline development phase at Santa Cruz.

Further, the Robbins TBM’s earth pressure balance capability pressurises the cutterhead chamber against prevailing groundwater, directly controlling face stability and mitigating inflow through water-bearing zones and aquifer intersections. A bidirectional cutterhead is used for excavation in soft soils, mixed-face and hard rock geology, while a high-torque/high-speed cutterhead drive system delivers the needed power to pass through challenging geology and structures.

During decline development, the TBM system installs a continuous, fully supported and sealed segmental steel-reinforced concrete lining, preserving geotechnical integrity, enhancing long-term safety, and producing a permanent, flat-bottomed decline structure suitable for life-of-mine design. The integrated process also includes the construction of a permanent conveyor system for materials handling during development and ore handling during production.

As part of the purchase agreement with Ivanhoe Electric, Robbins will perform a substantial overhaul of the machine, which includes a fully refurbished 9.3-m-diameter cutterhead manufactured in Ohio. During refurbishment, Robbins will also upgrade the machine with current technology, including customised features designed for the geological conditions at the Santa Cruz project.

Arrival and assembly of the TBM is expected to begin on-site in Arizona in the first quarter of 2027. This will be followed by the start of decline development in the third quarter of 2027.

The TBM is designed to excavate a 4-km-long single decline in about 12 months.

Ivanhoe Electric expects underground mine development at Santa Cruz to start in the third quarter of 2028, with first oxide copper ore to be placed on the heap leach pads in the fourth quarter of 2028.

First copper cathode production is now expected to start in the second quarter of 2029.