Idaho’s Stibnite gold mine cleared another major federal permit hurdle Monday. The mine would be the only source of antimony in the country and is a site of environmental controversy.

In 2016, Perpetua Resources began the process to reopen the mine. Eighteen planned years of open pit mining would extract millions of pounds of gold, silver and antimony.

Federal regulators issued the project’s permit under the Clean Water Act on Monday – its last remaining permit needed. The Biden Administration and U.S. Forest Service gave final approval to the mine’s Environmental Impact Statement earlier this year.

In March, President Donald Trump issued an executive order to “increase American Mineral Production.” A month later, Stibnite was recognized by the Trump administration as a critical mining project for its antimony, which is used in ammunition, semiconductors and solar panels. It hasn’t been mined in the United States since 2001.

Sydney Anderson is Idaho Rivers United’s Mining and Policy Manager. The organization is one of several environmental groups opposed to the project.

Anderson says Perpetua’s current water treatment plan does not account for how climate change and air pollution could cause lasting harm to state water quality.

“Twenty, 25 years in the future, there’s just no good way of telling what the impacts will be, except that what they’re modeling now is probably a very, very conservative estimate.”

The mine also sits on ancestral land of the Nez Perce tribe, which stopped its salmon restoration work in the area when mining permits were approved.

Anderson says Perpetua’s plans to dredge up and reroute major sections of the East Fork South Fork Salmon River undermine the tribe’s decades of work restoring salmon habitats and spawning grounds.

“That can really cause issues with water temperature and water quality in oversimplification because it’s not connected to natural hydrology. So the natural water flow isn’t in that area anymore when you change the route of a river,” Anderson said.

Perpetua estimates antimony will make up only four percent of profits from minerals mined. The rest will come from gold and silver.

The company says there’s enough antimony in the mine to meet around one-third of the country’s demand for six years. Anderson said that isn’t enough to justify more mining.

Perpetua says it is taking steps to protect water quality and salmon habitats. In its 2023 environmental report, the company said it aims to eliminate legacy pollution from the mining area that could leak into rivers, and restore salmon routes disturbed by previous mining activities.

Perpetua has been removing legacy pollution alongside the EPA and U.S. Forest Service since 2021, with cleanup expected to conclude this year. The Environmental Protection Agency tried to designate the area as a hazardous Superfund site after finding high concentrations of heavy metals like arsenic in the water. Idaho has yet to accept the designation.

The federal permitting council expects to completely approve the Stibnite Gold Project by the end of July.