Spokane Valley-based Revett Minerals Inc., which in December suspended mining at its Troy Mine in Montana due to safety concerns, says it won't resume operations there until late next year as it constructs a new underground route to copper and silver deposits.

Revett CEO John Shanahan says the company was scheduled to start the tunnel's construction at the end of October, and that the project is estimated to cost about $12 million. The tunnel will be about 2 1/2 miles long and will connect to existing underground infrastructure, he says.

The company halted operations 10 months ago because of unstable conditions and a rockfall along the mine's main hauling route, but Revett had planned to start production in the fourth quarter of this year by using a secondary route. However, neither of the current routes to lower deposits proved to be viable after inspections, Shanahan says.

"This whole new route is the best approach," he says. "There is no new access from the surface; it's from within our current underground infrastructure."

Shanahan says construction for the new route will go through barren rock, starting at about 4,000 feet from the mine's entrance, and leading downward through an undeveloped area.

Meanwhile, he says about 65 employees are working at the mine, down from 200 workers when Troy was in full production before the shutdown. Mine facilities such as an underground crusher, conveyor system, and surface mill will remain in use on a maintenance basis.

The company has adequate funds to start the tunnel project, a press release says.

With the new route, the company estimates it will gain access for resumed production late next year to mineralized zones of copper and silver in a mine area it calls the North C bed.

Revett says it plans to access deeper copper and silver deposits six months after reaching the North C bed.

"We remain confident the Troy Mine can safely resume operations," Shanahan says. "We have at least 10 years of mine life at Troy."

The company also is continuing its process to gain state and federal permits to develop another large Montana mine, named the Rock Creek Project, near Noxon, Mont.