Hecla Mining Company 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."
A 10-member rescue team was part of the rescue operation under way at the site in Mullan, Idaho, an historic mining town of 840 people. Baker said additional equipment was being flown in to allow crews to use a front-end loader remotely to dig away the material.
"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 tunnel. Officials say it's unclear if the entire 75 feet 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 locations of the mine when the collapse occurred, said Hennessey.
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.
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 called a stove 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 historic Lucky Friday Mine in the Silver Valley, spending $200 million to increase silver production by about 60 percent and extend the mine life beyond 2030.
In 2009 the company agreed to pay $177,500 in fines for violating federal clean water laws at its Lucky Friday Mine. EPA investigators say 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.