Hecla Mining Co. President Phil Baker said the collapse at the Lucky Friday Mine occurred Friday afternoon close to where two employees were working. One worker escaped without injuries, but there's been no contact with the other, whose condition was unknown.
The missing miner's name was not released.
"We are doing every effort possible to expedite this in a safe manner," said Melanie Hennessey, a company spokeswoman. "It is a rescue mission."
The mine is tucked into the forested mountains of Mullan, a historic mining town of 840 people in Idaho's Panhandle. Baker said additional equipment was being flown in so crews could use a front-end loader remotely to dig away material clogging the tunnel.
"We're securing the ground as we go," Baker said. "We're doing everything we can to reach the employee. We're just very concerned for the miner and his family right now."
Mike Dexter, another Hecla spokesman, said the two employees had just finished watering down blasted-out rock and ore when the collapse occurred about 75 feet from the end of the 6,150-foot deep tunnel. Officials say it's unclear if the entire 75-foot section collapsed, or only a portion of it, possibly leaving the miner trapped on the other side.
"We don't know if the collapse went all the way to the end," Dexter said.
The mine employs roughly 275 workers, about 50 of whom were underground in various parts of the mine when the collapse occurred, Hennessey said.
On its website, Hecla describes itself as the oldest U.S.-based precious metals mining company in North America and the largest silver producer in the U.S. It is headquartered in Coeur d'Alene, Idaho.
Hecla currently produces silver from two mines, Greens Creek and Lucky Friday, a mine that has been operational since 1942 and is one of the nation's deepest underground mines.
Mine Safety and Health Administration officials were helping coordinate the rescue effort. So far, no cause for the collapse has been identified.
Baker said the collapse was in an area where mine material is watered down and cooled before being shipped to the next phase of processing.
"We're not yet focused on how and why it occurred," Baker said. "All of our efforts now are on rescuing the miner."
Hecla Mining has been expanding its Lucky Friday Mine in the Silver Valley, spending $200 million in recent years to increase silver production by about 60 percent and extend the mine's life beyond 2030.
The company appears to have a good record of health and safety at Lucky Friday. There have been no fatalities dating back to 2000, according to a Mine Safety and Health Administration database. The federal regulator has cited the mine for violations, but none in the last year specifically tied to the kind of accident that occurred Friday.
In 2009, the company agreed to pay $177,500 in fines for violating federal clean water laws at Lucky Friday. EPA investigators said the mine exceeded discharge levels for metals such as lead, zinc, cadmium and suspended solids between September 2008 and February 2009. Discharges flow into the South Fork Coeur d'Alene River above the town of Mullan.