Denver Crumbling pillars in the Twentymile Mine near Hayden — Colorado's largest coal mine — have delayed production and will cost its owner, Peabody Energy Corp., $25 million to $75 million, according to the company.
The discovery in early April has limited activity at the mine while Peabody and the U.S. Mine Safety and Health Administration came up with a plan to address the risk.
Twentymile produced 7.2 million tons of coal in 2010 and employs 500 people. In 2009, the last year for which the Colorado Mining Association figures are available, the state produced 28.8 million tons of coal.
The mine has not been closed, as employees were shifted to other areas, Peabody spokeswoman Meg Gallagher said.
Peabody announced earlier this week that an interim remediation plan has been approved by federal mine safety officials.
The problem Peabody encountered was crumbling support pillars, said Allyn Davis, director of the federal mine safety administration's district office in Denver.
"There was no collapse, but the pillars were crushed a bit," Davis said.
Twentymile is a highly automated long-wall mine.
The coal seam is about 980 feet in length, according to Davis.
In long-wall mining, hydraulic jacks hold up the roof as shears cut across the face of the coal seam gouging out the coal, which is carried away on conveyor belts.
There is a gallery on either side of the long-wall that provides access to the equipment and emergency routes for workers. Pillars in this area were breaking down, Davis said.
The plan is to fortify pillars with concrete as the long-wall mining proceeds. "We've agreed to try it," Davis said. Federal mining engineers will monitor the activity.
If the cementing does not work, Peabody may have to pull all the equipment and start a new long-wall.
The lost production and new requirements will cost Peabody between $25 million and $75 million, Michael Crews, the company's chief financial officer, told stock analysts last week.
The cost will be lower if the remedial plan works, and higher if all the equipment must be removed, Crews said.
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