Richard Gates, the lead investigator for the federal Mine Safety and Health Administration, made the disclosure in a briefing for a state commission that is looking into whether Utah should return to the business of regulating coal mines after a 20-year hiatus.
Kevin Stricklin, MSHA's administrator for coal-mine safety, said Cleveland-based Murray Energy Corp. sealed the Crandall Canyon mine's three main passageways with walls of concrete block in early October.
The decision did not represent any loss of hope for recovering the men's bodies, he said, although the possibility of that appears to remain distant. The walls can be removed in the event of a new effort to recover the bodies, he said.
The miners were trapped in a cave-in Aug. 6. Ten days later, another collapse killed three people and injured six others trying to dig their way toward the trapped men.
Gates displayed a series of grim photographs of the collapsed mine. They showed splintered chunks of coal packed tightly in tunnels, deformed roofs and caved-in walls.
One photograph, taken after the collapse that killed three rescuers, showed only the bumper of their continuous mining machine buried in loose rubble - still 2,000 feet from the presumed location of the trapped miners.