OSBURN - Hecla Mining Co. has agreed to acquire Revett Mining Co., of Spokane Valley, in a merger announced Friday, and to eventually develop Revett's Rock Creek Mine.

The companies said the stock transaction is valued at $20 million, and is scheduled to be completed in the second quarter. The transaction is subject to approval by Revett shareholders.

Located in northwest Montana, approximately 50 miles north of Lucky Friday Mine, Rock Creek has one of the largest undeveloped silver and copper deposits in North America, the companies stated. Hecla announced it will continue with the permitting process to eventually develop the mine, which would bore under the Cabinet Mountains Wilderness.

The mine project has been opposed by environmental groups, which warn if the mine opens, its operations will threaten grizzly bear and bull trout habitat.

"We are acquiring Revett with an eye to the future, as Rock Creek is a world-class silver-copper deposit that we see becoming another Greens Creek," said Phillips S. Baker Jr., Hecla's president and CEO. Greens Creek is a silver mine Hecla owns in Alaska.

Rock Creek Mine contains an estimated 229 million ounces of silver and 2 billion pounds of copper.

Hecla said a supplemental Environmental Impact Statement is being produced and the U.S. Forest Service schedule indicates it will be issued later this year for public comment.

Revett has done a lot of work to mitigate and improve habitat, Baker said in an interview. He said Hecla doesn't plan to do anything different than what Revett planned for the mine's development.

"We're quite pleased with what Revett has done and the plans that they have," Baker said. "Obviously as we take things forward and learn more, we'll make changes and improvements."

Mary Costello, executive director of the Rock Creek Alliance based in Sandpoint, said Friday she has worked in opposition to the mine since 1995. She added the Rock Creek project ore body lies beneath the Cabinet Wilderness area near a direct tributary to the Clark Fork River, which supplies 90 percent of recharge to Lake Pend Oreille.

"We're still looking at the same bad mine proposal with a different company," she said.

Costello said Hecla would be the fourth mining company to try and develop the mine since she began working with the Rock Creek Alliance.

Baker said Hecla's experience of Greens Creek operating in a national monument in Alaska since 1997 will be invaluable as the company takes a "patient and persistent approach to permitting and then responsibly operating the Rock Creek Mine."

"I'm not impressed with their track record," Costello said. "The Greens Creek Mine has developed acid drainage that was not predicted and now requires water treatment for at least 100 years and probably in perpetuity."

Baker said Hecla's environmental record at Greens Creek has been exceptional.

"Hecla has been around for 125 years and we have been with Greens Creek in a national monument for 27 years ... and it's been a very successful operation, very successful, and it's grown over time," Baker said. "We think we can do the same thing with Rock Creek."

Revett president and CEO John Shanahan said Revett and Hecla have the same core values. Hecla, he said, has the financial and technical capabilities to develop Rock Creek deposits in an efficient and responsible manner.

"We believe our shareholders, along with the communities of northwest Montana who have been so supportive in our endeavors, will benefit greatly from this merger," Shanahan said.

Hecla reportedly expects to close the Troy Mine, which is also owned by Revett. The Troy Mine has been in care and maintenance status since January.

- Staff writer David Cole of the Coeur d'Alene Press contributed to this report.