A Beaverhead County District Court judge has temporarily halted all mining activity at the Calvert Tungsten Mine in the Big Hole River watershed, roughly 40 miles southwest of Butte, following a legal challenge from a Bozeman-based conservation organization.

Judge Luke Berger issued the temporary restraining order after Upper Missouri Waterkeeper filed a motion for an injunction in mid-June, targeting the Montana Department of Environmental Quality’s approval of a Small Miner Exclusion Statement for the project. That designation allows certain small-scale hard rock miners to proceed without obtaining standard operating permits.

Upper Missouri Waterkeeper said in a press release that the group moved quickly because Mithril Mining Corporation was prepared to begin work as soon as the Monday following the injunction filing, with what the group described as “minimal public notice.” The complaint names the Montana Department of Environmental Quality as the respondent.

A hearing is scheduled for June 30 in Beaverhead County District Court to determine whether the temporary restraining order should be extended or made permanent. The outcome could have broader implications for how the state’s small miner exclusion process is applied to projects in sensitive watersheds like the Big Hole, which supports blue-ribbon trout fisheries and is a focus of ongoing water access and conservation discussions statewide.

Mithril Mining Corporation has not publicly responded to the injunction filing, and the Montana Department of Environmental Quality has not announced any changes to its approval of the project’s exclusion statement pending the court’s decision.