The federal government on Thursday temporarily shut down a mile-deep silver mine in Idaho that has been the site of three serious accidents this year, including one this week that left seven miners injured.
Two miners died in separate accidents earlier this year at the Lucky Friday Mine. On Wednesday night, seven miners were injured during a rock burst while working 5,900 feet below the surface; all were safely rescued.
The incident prompted the U.S. Mine Safety and Health Administration to shut down the Lucky Friday while it investigates the cause.
"We've issued a closure order so the entire mine is shut down," said Amy Louviere, spokeswoman for the agency in Washington, D.C. "We will conduct a thorough investigation and we will not allow it to reopen until we are sure it is safe."
She could not say how long the mine would be closed.
The agency issued a scathing report after the April death of a miner at the Lucky Friday. A second miner died in a November accident.
"Certainly two fatalities and a serious accident are great cause for concern," Louviere said. "That's why we are going to take a real hard look at what happened."
Until this year, the mine had operated without a fatality for 25 years.
In the Wednesday night accident, none of the seven miners suffered life-threatening injuries. All were brought to the surface within an hour of the rock burst, said Melanie Hennessey, spokeswoman for owner Hecla Mining Co.
"There was a broken arm and some stitches, but overall they were quickly removed from the area and brought to local hospitals to be treated," Hennessey said.
The area where the miners were injured had suffered a rock burst _ defined as a spontaneous fracturing of rock _ about a month ago. At the time of Wednesday night's rock burst, miners were erecting a system of mesh material that is designed to contain such bursts, Hennessey said.
The cause of the rock burst has yet to be established, Hennessey said.
But there had been no blasting in the mine in the previous 24 hours, so the burst does not appear related to mining activity, Hennessey said. Rock bursts can also be caused by natural seismic activity, she said.
"We are thankful that all employees are out of the mine and have been accounted for," Hecla president and chief executive Phil Baker said in a press release. "We will be investigating the cause of the seismic activity."
The Lucky Friday is one of the nation's deepest mines, and has produced silver for more than a century. It is located near Mullen, Idaho, 90 miles east of Spokane, Wash. About 300 people work at the mine, making some of the best wages in a depressed region.
At the Lucky Friday, holes are drilled into the walls of the mine, charges are placed and detonated, and the resulting rubble is collected and hauled to the surface for processing.
In April, a roof collapse in a tunnel more than a mile underground trapped Larry Marek. Crews recovered his body nine days later.
In a report following their investigation, Mine Safety and Health Administration regulators criticized Hecla for safety failures that led to Marek's death. They cited Lucky Friday management for failing to install adequate ground support systems and neglecting to test the stability of the area where the collapse that killed Marek occurred.
Last month, miner Brandon Gray was buried in rubble after trying to dislodge a jammed rock bin. He died from his injuries two days later.
Because of the high price of silver, the mine is currently undergoing a $200 million project to deepen it to nearly 9,000 feet to increase access to deeper silver deposits. Hecla officials expect the project to be completed by 2014.