US Mine Safety and Health Administration spokesperson Amy Louviere confirmed that production on the longwall section was stopped last Monday to allow for additional support to be installed in the headgate travelways following the collapse of mine roof.

“That was done … and the longwall went back into production and continues,” she said.

“They are systematically installing additional support outby as they mine.”

Signal Peak president John DeMichei told local news outlet the Billings Gazette a buildup of pressure caused the collapse.

Following the incident, he said, repair crews were sent in to shore up the roof and an unidentified worker sustained a minor head injury while installing a beam.

That individual was treated and released, and he told the paper late Wednesday that he had been cleared to return to work.

The underground Bull Mountain No.1 operation near Roundup operates a longwall and one continuous mining machine development section in the Mammoth seam.

It has 197 employees and produces about 3650 tons daily, according to 2010 federal data.