The Kootenai National Forest has hired a geotechnical consultant to review a mine operator’s plans to extract silver and copper from underneath a Montana wilderness.
Forest Supervisor Bob Castenada ordered the review after an elliptical-shaped sinkhole, about 100 feet long, developed last month above the workings at the Troy Mine. The mine is operated by Revett Minerals, the same firm that wants to develop the Rock Creek Mine by tunneling underneath the Cabinet Mountains Wilderness Area.
Tetra Tech, a Helena firm, has received a $63,000 contract to review the geological data used to issue a permit for the Rock Creek Mine. Results should be available in late April.
The sinkhole is the second at the Troy Mine. Another, smaller sinkhole was reported last year.
The Sandpoint-based Rock Creek Alliance and six other environmental groups urged Castenada in a letter last week to revoke the mine’s permit until the sinkholes are fully investigated.
“How are we to trust this company to build a mine beneath the Cabinet Mountains Wilderness without harming the wilderness?” Tracy Stone Manning, executive director of the Clark Fork Coalition, said in a statement. “The Forest Service should pull its decision and take a long, hard look while giving the public the opportunity for review.”
The potential for the Rock Creek Mine to drain alpine lakes in the wilderness is a concern for environmentalists, said Jim Costello, Montana field coordinator for the Rock Creek Alliance, a longtime mine opponent. The Forest Service used the Troy Mine to determine that there was a low chance of these types of sinkholes occurring, Costello noted, even calling it a “perfect analog” for predicting such events.
Castenada did not return phone calls last week.
However, Revett officials said that stricter protections outlined in Rock Creek’s permit should reduce the chances of sinkholes occurring in the wilderness.
The permit requires a 450-foot buffer of earth between the surface and the excavation beneath the wilderness area. In addition, the company cannot drill within a 1,000-foot radius of alpine lakes, said Carson Rife, Revett’s vice president of operations.
Revett Minerals, which is based in Spokane Valley, reopened the Troy Mine in late 2004, after purchasing the property from Asarco Inc.
The cave-ins at the Troy Mine occurred in areas where the spaces had been opened up 350 and 260 feet below the earth’s surface, Rife said. Recent analysis suggests that both sinkholes could be linked to a fault zone in the area, he said. Asarco mined right up to and through faults – fractures in rock formations caused by shifting in the earth’s crust.
Revett’s Rock Creek permit doesn’t allow mining in the fault zones, because it increases ground instability, Rife said.
Revett Minerals estimates that the Rock Creek deposit contains 228 million ounces of silver and 2 billion pounds of copper, enough to run a mine for 30 years. But the Rock Creek Mine has been controversial since Asarco first proposed it in 1987.
The plan to site an industrial operation at the edge of the wilderness has been through numerous rounds of litigation. One of the latest battles involves is impacts on endangered grizzlies.
Last spring, a federal judge stopped exploration drilling at the Rock Creek deposit, ruling that the U.S. Fish and Wildlife Service had erred in allowing the mine to receive permits in 2003.
An estimated 15 grizzlies still roam the Cabinets. The federal agency, in its “biological opinion,” estimated that the mine could displace one or two grizzlies. With fewer than five female bears in the population, even the loss of two animals could be devastating to recovery efforts, wrote U.S. District Judge Donald Malloy.
Both Revett and environmental groups are awaiting the results of a revised biological opinion. The U.S. Fish and Wildlife Service hoped to issue the new opinion last fall but still has not released it.