SPOKANE, Wash. — A rock burst that injured seven miners underground may have been triggered by seismic activity in Idaho’s Silver Valley, the mining company said Friday.
All the injured miners were expected to fully recover from the injuries they suffered Wednesday. The two most serious injuries were a broken arm and a broken pelvis.
The mine remained closed and the federal Mine Safety and Health Administration is investigating.
Hecla Mining Co. said a small earthquake helped trigger a similar rock burst last month in the same area of the Lucky Friday Mine, one of the deepest mines in the nation.
The latest rock burst was unrelated to two separate accidents earlier this year that killed two miners at the Lucky Friday, Hecla president and chief executive officer Phil Baker said.
Hecla said that on Nov. 16, a small seismic event triggered by blasting in the mine caused a rock burst at roughly the same location as the latest accident 5,900 feet below the surface of the silver mine. No one was injured in that incident, Hecla said.
A rock burst is a common mining accident in which excessive pressure causes a rock to fracture or explode.
There was no blasting in the mine for 24 hours prior to Wednesday’s rock burst, Hecla said. That raised the possibility that a seismic event alone caused the burst.
“We need more information about what triggered this rock burst,” Baker said.
There were 25 Hecla employees and 18 contractor employees underground at the time of the rock burst, and most were not in the vicinity of the mishap, Hecla said. All were immediately evacuated.
The Lucky Friday has produced silver for more than a century. It is located near Mullen, Idaho, 90 miles east of Spokane. More than 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 collapsed in a tunnel more than a mile underground and trapped Larry Marek. Crews recovered his body nine days later.
In a report following an 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 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.
With 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.
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