Unexplained "noxious gases" killed two miners and injured 20 others in an accident at a Colorado mine Sunday morning, the mine's manager said.
All but two of the injured miners were treated and released from area hospitals, authorities said Sunday night.
The accident occurred at 7:20 a.m. (9:20 a.m. ET) at the Revenue-Virginius silver, lead, zinc, copper and gold mine near Telluride in Ouray County, officials said.
Rory Williams, the mine's project manager, told NBC station KUSA of Denver that he didn't know what might have led to the release of the fumes, which he said was very rare. The U.S. Mine Safety and Health Administration was investigating, he said.
Williams, who said he was "saddened" by the deaths, wouldn't release the victims' names, saying that was up to their families.