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The future of a US copper mine owned by Rio Tinto and BHP has been thrown into fresh doubt after US lawmakers passed a bill that seeks to stop its development.
The House of Representatives Natural Resources Committee on Thursday passed an amendment that added the Save Oak Flat Act and a number of other measures to Joe Biden $3.5tn domestic spending package, which has yet to be voted into law.
Oak Flat, 65 miles east of Phoenix, Arizona, is home to a giant underground ore body that holds enough copper to satisfy 25 per cent of US demand for 40 years.
Resolution Copper, a joint venture between Rio and BHP, wants to mine it but has faced opposition from the San Carlos Apache Tribe for whom the site has special religious significance.
Their efforts have been supported by Arizona congressman Raúl Manuel Grijalva, who has been trying to get the Save Oak Flat Act passed for several years.
The act seeks to repeal a 2014 land swap agreement that allowed for the transfer of 2,400 acres of national forestland, including Oak Flat, to Resolution Copper, in exchange for 5,400 acres of land owned by the two miners.
The Committee’s decision to adopt Grijalva’s amendment comes as Rio’s chief executive Jakob Stausholm prepares to visit Resolution Copper, one of the company’s most important projects.
Copper, used in electric vehicles and wind turbines, will play a leading role in the fight against climate change. However, high-grade deposits in politically stable jurisdictions are becoming increasingly difficult to find.
Rio’s other big underground copper project in Mongolia is running late and over-budget. Its development has also been marred by repeated disagreements with the government.
From the mid 1950s Oak Flat was protected from mining under federal law. That changed in 2014 when Arizona senators John McCain and Jeff Flake added an amendment to the National Defense Authorization Act to allow the land swap.
However, there was a caveat: the swap could not occur until the US Forest Service completed a Final Environmental Impact Study (FEIS), which would assess the potential effects of the mine development
In the last days of the Trump presidency, the 3,000-page document was finally released, setting in motion the land exchange. However, the Biden administration, which has pledged to respect tribal sovereignty, swiftly rescinded the FEIS, saying additional time was needed to “fully understand concerns raised by tribes and the public”
Rio said it was monitoring the process to finalise the $3.5tn US spending plan.
“We continue to consult with local communities and Native American Tribes to guide further shaping of the Resolution Copper project and the significant benefits it could deliver,” the company said in a statement.
The final shape of the spending package has yet to be determined and because it has no Republican support, Democrats have to pass it using a special budgetary procedure called “reconciliation”. This will allow it to be approved by a simple majority in the Senate.
Resolution Copper is 55 per cent owned by Rio and 45 per cent by BHP. The two miners have already spent $2bn on the project, including a 2km deep shaft.