The developer of the proposed $2 billion Stibnite Gold Project in Idaho is moving to intervene in a lawsuit that could derail its future, telling a federal court that it has invested $400 million over 14 years and cannot afford more delays.

Perpetua Resources Corp. insists its massive mining project—set in the Boise and Payette national forests—would not only deliver gold, silver and antimony but also advance U.S. national security interests. The Nez Perce Tribe, however, argues the project will devastate treaty-protected land, fish, and waterways at the headwaters of the South Fork Salmon River.

Perpetua: A Stake Too Large to Lose

In a motion filed Thursday, Perpetua said blocking or even stalling the mine would sabotage its property rights, mineral development, and long-term investments. The company stressed that its work also aligns with Department of Defense funding, which has already poured nearly $75 million into the project to secure domestic antimony supplies for ammunition and other military uses.

“Such outcomes, including even a short delay, will interfere with Perpetua’s ability to help address the Department of Defense’s urgent national security concerns,” the company said.

The tribe has not opposed Perpetua’s formal intervention in the lawsuit.

The Nez Perce Challenge

Filed last month, the Nez Perce Tribe’s suit targets the U.S. Forest Service (USFS) and the Department of Agriculture, challenging their approval of the Stibnite mine. The tribe says the decision allows Perpetua to gouge open pits, erect a 475-foot tailings dam, and bury more than 400 acres of Meadow Creek Valley beneath 120 million tons of mine waste.

The tribe argues the project will obliterate fish spawning grounds, raze wetlands, and pollute both groundwater and surface water far beyond the mine’s lifespan. Tribal leaders say the plan will even divert the East Fork South Fork Salmon River into a tunnel for more than a decade, barring access to traditional fishing and hunting grounds.

“The Forest Service dismissed our requests to consider alternatives and instead adopted Perpetua’s goals,” said Chairman Shannon F. Wheeler. “We are filing suit to defend our treaty rights, our fisheries, and our future.”

Legacy Wounds and Restoration Promises

Perpetua counters that the Stibnite district has been environmentally scarred for a century. Past miners, it argues, left behind poisoned soils, eroded topsoil, and blocked fish passages dating back to 1938. The company says its project is designed not just to extract minerals but to fund restoration efforts, stabilizing sediment, improving water quality, and reopening habitats.

The USFS’ approval included plans to manage toxic legacy materials during construction and operations. Perpetua says the mine’s revenues will bankroll reclamation that previous miners abandoned.

Conservationists Join the Fight

The Nez Perce case is the second major lawsuit to challenge the mine. Earlier this year, the Idaho Conservation League, Center for Biological Diversity, and American Rivers sued in Idaho federal court, accusing the USFS of rubber-stamping the project without weighing its true environmental toll.

Those groups argue the mine would expand disturbance across 3,600 acres and double its footprint. They contend that the agency’s own documents admitted the “no-action alternative” was the only environmentally superior option.

What Comes Next

With billions of dollars, national security stakes, and tribal sovereignty on the line, the Perpetua Idaho Gold Mine suit may set precedent for how far corporations can push projects onto treaty-protected lands under the banner of economic development and defense.

The Nez Perce Tribe is represented in-house by Michael A. Lopez and Joseph J. Bushyhead. Perpetua Resources Idaho Inc. is represented by Laura K. Granie, Amelia Yowell, Murray Feldman, and Austin W. Jensen of Holland & Hart LLP.

Counsel for the U.S. Forest Service was not immediately available Monday.