Judge B. Lynn Winmill

Judge B. Lynn Winmill

BOISE — Exploration work by a Canadian company hoping to build an open-pit gold mine in Idaho west of Yellowstone National Park was halted following a federal judge’s ruling involving its impact on groundwater.

U.S. District Court Judge B. Lynn Winmill on Monday amended his previous decision that Otis Gold Corp. had interpreted as allowing exploration drilling.

The new ruling sought by the Idaho Conservation League and Greater Yellowstone Coalition vacates two 2018 U.S. Forest Service documents approving the drilling in the Centennial Mountains.

“This is what we wanted,” said Bryan Hurlbutt, an attorney at Advocates for the West that is representing the environmental groups. “Now, the project cannot proceed unless the Forest Service approves it again.”

Ontario-based Excellon Resources acquired British Columbia-based Otis Gold in February. Robert Maynard, an attorney representing the company, which intervened in the lawsuit, didn’t immediately return a call Tuesday seeking comment. The U.S. Department of Justice, which defends federal agencies in lawsuits, declined to comment.

The proposed Kilgore Project would cover about 19 square miles (50 square kilometers) on Forest Service land and land managed by the state of Idaho in Clark County, about 60 miles (100 kilometers) north of Idaho Falls. The company says the area contains about 825,000 ounces (23.4 million grams) of gold.

The conservation groups filed the lawsuit in late 2018 seeking to halt the exploratory drilling. In a December ruling, Winmill said the Forest Service hadn’t done an adequate analysis involving groundwater quality in the Dog Bone Ridge drainage area, home to Yellowstone cutthroat trout. The trout are considered a sensitive species facing threats to its population or habitat.

But Wimill let stand the Forest Service’s environmental assessment of the exploratory drilling and a decision called a “finding of no significant impact” based on the assessment.

Otis Gold then issued a news release saying the decision allowed it to continue its five-year exploratory drilling in areas outside Dog Bone Ridge. The company had already completed its first year of drilling.

The new ruling Monday shuts down drilling at least until the Forest Service completes its groundwater analysis at Dog Bone Ridge and issues new approval documents. That requires a public process with comment periods.

Winmill said Otis Gold’s plan to continue drilling outside Dog Bone Ridge essentially split the project in two, something not allowed under U.S. environmental laws.

“The area is an important site for grizzly bears and other wildlife, especially wildlife that needs to migrate from Yellowstone to other parts of the Rockies,” Hurlbutt said.