(Recasts with quotes, details; changes dateline to CHICAGO) CHICAGO, Aug 10 (Reuters) - Three construction workers were killed on Friday while digging a shaft for an underground coal mine in Princeton, Indiana, authorities said, the second serious accident at a U.S. coal mine in less than a week. "There was an accident with fatalities," said Bob Pond of Frontier-Kemper Constructors Inc., which was drilling a new shaft for the Gibson County Coal mine. The deaths were not caused by an explosion or cave-in, a police detective told CNN. "Three fatalities are confirmed," Detective Mike Hunt said by telephone. "We're not sure if it was an equipment problem or what at this point." He said no more deaths were expected to be reported. "There are people trying to retrieve the bodies and we know there was no explosion," Hunt said. The mine -- owned by Alliance Resource Partners LLP, the fourth-largest coal producer in the eastern United States -- was opened in 2000 and has a capacity of 700 tons an hour. The accident in Indiana followed a collapse on Monday at a coal mine in Utah that trapped six miners underground. It is not yet known whether those miners are alive or dead.
