Key Highlights

  • The joint venture approved a further US$144 million for studies, engineering, water treatment and underground work.
  • Rio holds 55 per cent of Resolution Copper Mining LLC, so its share of the new spending is US$79 million.
  • The new funding adds to roughly US$500 million of preliminary expenditure announced in March 2026.
  • The approval does not amount to a final Investment decision to build the mine.

Rio Tinto (ASX:RIO) said on 5 November, US time, that the Resolution Copper joint venture in Arizona had approved a further US$144 million of investment to advance the project towards its next investment decision. Rio holds 55 per cent of Resolution Copper Mining LLC and BHP holds the remaining 45 per cent, putting Rio's share of the new spending at US$79 million.

The funding adds to roughly US$500 million of preliminary expenditure announced in March 2026. It does not amount to a final investment decision to build the mine. Commentary has characterised the move as the two majors stopping short of committing to construction, and Rio's own release described it as positioning the project for the next decision point.

Where the money goes

According to Rio Tinto, the US$144 million will fund feasibility studies and final design engineering for material handling systems in both of the project's shafts, as well as new water treatment facilities. It will also pay for exploration drilling, underground development, production equipment and long-lead electrical equipment, items that often need to be ordered well ahead of construction.

Rio Tinto Copper chief executive Katie Jackson said the funds "will accelerate underground development, create additional skilled roles". The company expects about 50 additional roles to be created as the work proceeds, adding to the existing workforce at the site.

A deep and long-dated project

Resolution Copper sits near the town of Superior, east of Phoenix. The orebody lies roughly 1,500 to 2,100 metres, or about 5,000 to 7,000 feet, below surface, a depth that makes it a technically demanding underground development. A land exchange with the US federal government was completed in March 2026, removing one long-standing step in the project's path. The exchange gave the joint venture title to the land above the deposit, which is a prerequisite for the type of large-scale underground mining being studied.

Rio says Resolution could Supply up to 25 per cent of United States copper Demand for decades and estimates the project's economic contribution to Arizona at about US$1 billion a year. Those are company projections that depend on the mine being approved, built and operated at the scale envisaged; they are not outcomes that have been achieved.

Staged spending of this kind is a common way for large miners to reduce technical risk before a full commitment. Shaft engineering, water treatment and underground development address some of the key uncertainties at a deposit this deep, including rock conditions, heat and water management. Ordering long-lead equipment early can also shorten the schedule if a construction decision follows, although it commits Capital to items that may be needed only if the project proceeds.

For Rio Tinto and BHP, the move maintains momentum on a large undeveloped copper deposit at a time when both have highlighted copper as a growth priority. The relatively modest size of the tranche, compared with the likely capital cost of a full development, signals that the partners are proceeding step by step rather than committing to construction now.

Risks and what comes next

Significant uncertainties do, however, remain. No final investment decision, construction budget or production timetable has been announced. The project has historically faced opposition and legal challenges, and further permitting, community and environmental issues could affect timing. Copper prices, construction cost Inflation and the outcome of the feasibility work will also bear on any eventual decision, as will the partners' assessment of competing uses for their capital.

The immediate work programme covers the studies, engineering and underground activities funded by this approval. Its results, including the feasibility studies and shaft engineering, will inform the joint venture's next investment decision, the timing of which Rio has not specified in its release.