West Virginia Office of Miners’ Health, Safety and Training spokesperson Leslie Fitzwater confirmed to ILN that the workers, whose names have not been released, were hurt July 30 at about 7pm local time at the Ohio County complex.

“A mantrip derailed on a downhill grade; nine people were onboard,” Fitzwater said, noting that one person was a Tunnel Ridge employee and the remaining eight were contractors.

Six of the injured workers were taken to the hospital immediately following the incident. Four were treated and released and the remaining two who were admitted have also since been released.

Further details on the cause were not available Monday, but the agency confirmed that it was working on its investigation.

A US Mine Safety and Health Administration spokesperson did not provide further details to ILN by press time, and owner Alliance Coal did not issue a public statement.

The Tunnel Ridge mine, under development to become one of the nation’s newest longwall operations, has been producing coal since last March. It now employs 160 and will have a staff of 300 when at full capacity.

At prime production, the mine is expected to produce 6 million tons annually from an estimated coal reserve of 97.4Mt.