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, may remain closed for a year after inspectors determined that sand and concrete material that had leaked from a pipe into a mine shaft 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.

More than 200 people will lose high-paying jobs in the depressed Silver Valley region, and many will likely seek work elsewhere, said Phil Baker, chairman and chief executive of Hecla Mining Co.

"We are confident the employees will ultimately come back to work for us at the Lucky Friday," Baker said at a news conference at company headquarters.

The closure prompted Hecla to reduce its estimated silver production for 2012 from more than 9 million ounces to about 7 million ounces, all from its remaining Green's Creek mine in Alaska.

The Mine Safety and Health Administration's closure order was initially issued Jan. 5, but company officials said Wednesday they had been negotiating for several days with federal regulators before resigning themselves late Tuesday to the lengthy shutdown.

The news caused the stock price of Hecla Mining to tumble 21 percent on the New York Stock Exchange on Wednesday, down $1.23 to $4.61 per share.

About 275 people work at the mine, and about 185 of those employees will be laid off because of the closure, Baker said. The closure will also put another 50 to 100 contract workers out of a job, Baker said.

Miners average about $100,000 per year in pay and benefits in a region where there are few other job options.

Production is expected to resume in early 2013.

The mine has been shuttered since mid-December, when a rock burst injured seven miners.

Federal regulators since then have been conducting a close inspection of the mine because of the series of 2011 accidents. They decided they wanted the sand and concrete material removed because it can break off and fall down the shaft, injuring people or damaging the elevators.

The material federal regulators want removed isn't related to the December rock burst or any of the other accidents at the mine, 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 company might appeal the order, but no decision has been made, he said.

There are two entrances to the Lucky Friday, but both must be functioning in order for the mine to produce ore, Baker said.

Last month's rock burst was the latest in a string of incidents at the mine, which is 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.

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