Resolution Copper says, after completing the two-year-long rehabilitation phase of the underground mine, in Arizona, it is ready to move to the deepening phase of what could end up being one of the biggest copper mines in the world

Resolution, owned 55:45 by Rio Tinto and BHP, is the owner of the massive Resolution copper project.

In a project update, the company said the proposed mine continued to make progress on all fronts.

“Resolution Copper recently reached a key milestone in its development, with other critical work on track for completion in the near future,” the company said.

Work is progressing on schedule to deepen the historic No 9 shaft, originally constructed in 1971, according to the company. The project scope consists of rehabilitating the shaft, sinking it to approximately 2,086 m and linking it with the newer No 10 shaft completed in 2014.

The rehabilitation phase was completed in December 2018 after approximately two years, and the deepening phase will require another two years, commencing in the June quarter of 2019, according to Resolution. This would see the deepening phase completed in early 2021.

“Connecting the shafts will enhance safety and establish the basis for developing towards the copper deposit,” Resolution said. “The shaft connection will provide a second egress route between the two shafts and improve ventilation.”

The No 9 shaft deepening project has made significant achievements over the last three months, according to the company.

“Following successful cleanup of the existing shaft bottom in December 2018, the shaft crew proceeded to outfit the 4,000-ft (1,219-m) level with a bulk air cooler that will chill the intake air for the No 9 shaft sinking,” Resolution said.

“The crews sinking the shaft use a Galloway work stage (pictured), which allows the miners to do their work with a high degree of automation, withdraw during the blast, and then quickly return to the bottom and repeat the cycle.”

The five-deck work stage has four jumbo drills, two shaft mucking machines, a concrete pouring system, and all the tools needed to advance the utilities (pipelines, electricity, etc). The Galloway used to complete the shaft rehabilitation was also removed from the shaft to make room for the sinking Galloway, which is specially designed to support the deepening work, according to Resolution.

“Removal and installation of these Galloways involved technically complex lifts with multiple steps that were well planned for safe and efficient execution,” the company said.

Another significant achievement was the successful phase-1 commissioning and testing of the emergency generator system, Resolution said.

“In the event of a site power outage, the addition of these generators provides the ability to operate the auxiliary hoists for both No. 10 and No. 9 shafts and to restart the necessary refrigeration, ventilation and pumping to maintain the infrastructure at Temporary Pump Level 2,” Resolution said.

Looking forward, the project will focus on surface setup and shaft services work to support the sinking, completing the infrastructure installation on the 4,000 level, which is underway, and finishing the Oak Flat substation transformer upgrade, Resolution said.

The proposed underground block cave mine at Resolution is expected to become the largest copper mine in North America, capable of producing nearly 25% of US copper demand each year. As at Codelco El Teniente, the mining method will be panel caving, which allows for the mining of very large relatively low-grade underground orebodies by dividing the deposit into smaller strips, or panels, so that the ore can be removed in a safe and efficient manner.

Ore production from the underground operations will be a nominal 120,000 t/d after an extensive construction and ramp-up period. The maximum throughput will be approximately 150,000 t/d. Ore will be crushed underground and then transported by conveyor to two production shafts and hoisted to an underground midway offloading station within the two production shafts.

Resolution Copper will use a standard-gauge rail system that will allow bottom-dump railcars to be gravity-loaded with ore delivered from overhead chutes, according to the company. These railcars will be routed to the dump station above the underground crushing facilities. Resolution Copper will use electric semi-autonomous locomotives to pull the railcars. The rail system will be a looped configuration, with two parallel drifts spaced on approximately 18 m centres in the production areas.

In total, approximately 594 pieces of mobile equipment are expected to be employed, which includes the large LHD fleet for the extraction level, moving ore from the drawpoints to the ore passes.

The mine is expected to reach depths of up to 2,100 m and temperatures in excess of 70°C. Last year, Rob Atkinson, former Head of Productivity & Technical Support for Rio’s G&I team, said operating at such a depth meant it really had to be “a fully autonomous mine”.