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Coeur d'Alene Press, Jerome A. Pollos, Associated Press
In this file photo from Thursday, April 28, 2011, Sol Sandberg, a miner at the Lucky Friday Mine, holds his son Jimmy, 19 months, as they leave the memorial service for Larry Marek at Kellogg High School in Kellogg, Idaho. The Lucky Friday Mine in Idaho's Silver Valley will be closed for a year after federal safety inspectors determined that material must be removed from the main silver shaft. The news caused the stock price of Hecla Mining Co. to tumble on the New York Stock Exchange on Wednesday, losing a quarter of its value to fall to around $4.40 a share. The federal Mine Safety and Health Administration is investigating the mine after a series of accidents killed two miners past year. In mid-December, seven miners were injured in a rock burst at the mine.

COEUR D'ALENE, Idaho — Federal safety inspectors have ordered one of the nation's deepest underground mines closed in northern Idaho following an investigation prompted by a series of accidents that killed two miners over the last year.

The Lucky Friday Mine, one of the nation's top silver producers, will remain closed for a year after inspectors determined that sand and concrete material that had piled up over the years needed to be removed. The material is in the mile-deep Silver Shaft, the mine's main access shaft, and workers will spend the next year essentially power washing the material from the walls of the shaft.

The Mine Safety and Health Administration order was initially issued Jan. 5, but company officials said Wednesday they had been negotiating for several days with federal regulators before resigning themselves to the lengthy shutdown. The news caused the stock price of parent company Hecla Mining Co. to lose a quarter of its value on the New York Stock Exchange on Wednesday, tumbling to around $4.40 a share.

About 275 people work at the mine, and about 185 of those employees would lose their jobs because of the closure, Hecla CEO Phil Baker said. But the company hopes it can hire most or all of them back when mining operations resume in 2013.

The closure will also put another 50 to 100 contract workers out of a job, Baker said.

The mine has been shuttered since mid-December when rock burst injured seven miners. But the debris federal regulators want removed isn't related to the December accident or any of the other accidents that beset the mine in 2011, Baker said.

"While we are disappointed with this order and are considering what action we might take, work has already begun to resume production as quickly as possible," he said.

The closure forced the company to downgrade its production estimates for 2012, from a projected 9 million ounces to 7 million ounces. Hecla also operates a silver mine in Alaska.

Last month's rock burst was the latest in a string of incidents at the mine in Idaho's Silver Valley, about 50 miles east of Coeur d'Alene, where the company is based.

Miner Brandon Lloyd Gray, 26, was buried in rubble while trying to dislodge jammed rock on Nov. 17, and died two days later. On April 15, miner Larry "Pete" Marek was crushed when his work area collapsed. Federal inspectors found company safety failures led to his death.

Prior to last year, the mine had gone 25 years without a fatality.