Mining has resumed at the Signal Peak coal mine south of Roundup. Operations were suspended Dec. 1 because of high carbon monoxide levels.
Mike Dawson, spokesman for the Boich Cos. in Ohio, said Friday that carbon monoxide levels have decreased and that the federal Mine Safety and Health Administration has cleared the mine to resume operations.
Mining was suspended after carbon monoxide levels exceeding 125 parts per million were detected in a previously mined tunnel that had been sealed off. The problem area was 1.7 miles from where miners were working and where the levels were normal, Dawson said.
The gas sometimes migrates out of the coal seam; the coal also may oxidize after being exposed to air and water, Dawson said.
Workers performed other jobs during the temporary suspension of mining.