Walter Energy spokesperson Michael Monahan confirmed to ILN that the Jim Walter Resources No. 7 operation had restarted at 11am local time Wednesday. In the meantime, a review into the incident has been started.

“The area of the mine under investigation is a non-production area of the mine and has been roped off pending the conclusion of the investigation,” he said, adding that he expects the investigation to continue into next week.

“Initial media reports, citing MSHA, blamed lack of oxygen as the cause of death. While this has not been ruled out, we believe it is premature to speculate on the cause of death until the investigation is complete.”

Monahan declined to identify the killed worker or those admitted to hospital, but local media reported that James Chaney, 53, had died while examining the mine’s bleeder and that his co-worker, 59-year-old Milton Etheridge, had been released from an area medical center Wednesday afternoon.

In all, the Birmingham News said, eight miners were treated for heat exhaustion. Monahan verified that all injured workers had now been discharged.

US Mine Safety and Health Administration spokesperson Amy Louviere told ILN a federal investigation would begin at JWR No. 7 on Monday.

Jim Walter Resources employs 1400 staff. As of September 30, the No. 7 mine had produced 2.6 million tons via a longwall and active continuous mining sections.