BILLINGS, Mont. (AP) -- A proposed silver and copper mine beneath northwestern Montana's Cabinet Mountains Wilderness cleared a significant hurdle Tuesday with the completion of an environmental study in the works for the past decade.

A final decision on the Montanore mine near the Idaho border could come by late January, said Craig Jones with the Montana Department of Environmental Quality.

Mines Management Inc. of Spokane, Washington, is proposing to remove up to 120 million tons of ore from the underground mine, which would disturb more than 1,500 acres of land just outside the wilderness area. Included is a 14-mile transmission line to carry power to the site near Libby, Montana.

State regulators and U.S. Forest Service officials must approve the project.

"It's been a long, 11-year journey permitting this project," said Mine Management Chairman Glenn Dobbs. "We look forward to being able to provide a lot of jobs in an area of the country that really needs them."

Environmental groups are strongly opposed. They sued the federal government in June over concerns that mining would harm federally protected grizzly bears and bull trout.

The Cabinet-Yaak ecosystem on the Montana-Idaho border is one of six areas in the continental United States where biologists are seeking to restore grizzly bear populations.

The U.S. Fish and Wildlife Service said last year that the mine could lead to the loss of one federally protected grizzly bear. But it said required mitigation — including the purchase of 5,000 acres of grizzly habitat at risk for development — will make up for the loss.

The agency said bull trout populations also could suffer losses in certain streams close to the mine site but not enough to threaten the species' overall survival.

An attorney for the plaintiffs in the lawsuit — Save Our Cabinets, Earthworks and Defenders of Wildlife— said federal officials offered too little evidence to support their claims.

"We believe the project will jeopardize those species," said Katherine O'Brien with the law firm Earthjustice. O'Brien said the plaintiffs would seek to halt the mine if it's approved, until their claims are resolved.

Once a decision is made, Dobbs said his company would spend up to two years and $30 million further evaluating Montanore's mineral reserves. It would take up to three years to construct the mine for about $500 million.

The mine would employ about 500 people during the construction phase and about 350 during mining.

Work on the mine site began around 1990 under different ownership but was suspended in 1991 due to low metal prices. Mines Management later took over and applied to the state for a mining permit in 2004.

Earlier this year, a group of investors led by former Montana Gov. Brian Schweitzer sought $10 million from Mines Management in a federal court proceeding. Schweitzer's group, known as Optima Inc., said it held mining rights in the area and deserved compensation.

U.S. District Judge Dana Christensen rejected Optima's arguments, saying its mining claims had no value. An appeal is pending.