BILLINGS — U.S. officials on Tuesday announced approval of the first phase of a silver and copper mine beneath a northwestern Montana wilderness area, yet it’s uncertain when work could begin because of a legal dispute over pollution at other sites.

Kootenai National Forest officials announced their approval of plans by Hecla Mining Co. to begin exploration work for the Rock Creek Mine near Noxon.

The Idaho-based company would initially mine on 20 acres to determine the feasibility of a full-scale mine that would cover almost 500 acres and employ about 300 people.

Hecla Vice President Luke Russell said the exploration work won’t begin until the company resolves pending litigation with the Montana Department of Environmental Quality. Regulators from the agency in June sued to block Hecla CEO Phillips Baker Jr. from exploring or opening any new mines in the state.

The state alleged he was in violation of the state’s “bad actor” law because of ongoing pollution caused by Pegasus Gold Co., a mining company where Baker once worked. Since Pegasus went bankrupt, the state has paid more than $35 million for cleanup work at the company’s mines.

Baker denies responsibility and Hecla has asked a judge to reject the state’s claims.

If the company prevails, it would still need an operating plan approved by the federal government before starting on the planned exploratory work, said Kootenai Forest spokesman Willie Sykes.

Hecla is proposing a second mine in the area near the town of Libby.

Both of the projects would tunnel beneath the Cabinet Mountains Wilderness, an area rich with wildlife including grizzly bears and wolverines.

Sporadic mining has occurred in the area since the early 1800s, according to the U.S. Forest Service. But there are worries the large-scale projects proposed by Hecla could drain groundwater supplies, damaging the habitat of federally-protected bull trout.