The shaft, originally built in 1971, is now sinking to 7,000ft (2,134m). In 2021, the No. 9 shaft will be connected with the No. 10 shaft, which was completed in 2014.
The company previously said the cots for rehab plus the sinking and linking could reach US$200 million.
The underground operation, located east of Phoenix, has proposed using block caving. It will begin at a rate of 120,000t per day and ramp up to a throughput of 150,000t per day at prime levels.
Once in operation, it will be North America's largest copper operation.
Rio Tinto is majority owner of Resolution at 55%, while BHP holds the remaining 45%.
