The Associated Press
-- — OURAY, Colo. — Two workers were killed and 20 others injured Sunday in a mining accident near the southwestern Colorado town of Ouray.
Authorities said that the two who were killed died from carbon monoxide poisoning, the Denver Post reported.
The officials said at a nighttime news conference that the source of the gas was under investigation, with officials looking at whether a small explosion in the mining process might have caused it.
The 20 injured were taken to area hospitals, and all but two were treated and released, Ouray County spokeswoman Marti Whitmore said. The conditions of those two hospitalized workers haven't been released.
The Montrose Daily Press reported that 10 of them went to Montrose Memorial Hospital, where officials say they were treated for carbon monoxide exposure. It wasn't immediately clear if the remaining 10 also suffered from exposure to the gas.
Rory Williams, the operations manager for Denver-based Star Mine LLC, said all of the men are required to wear personal respirators and the two who died had them. He said that it doesn't appear to be an equipment malfunction, the Post reported.
Whitmore said that the Ouray County sheriff's office was called to the Revenue-Virginius mine at about 7:20 a.m. The miners were underground and were confirmed dead Sunday afternoon.
She said that mine owner Star Mine Operations has accounted for all of the workers at the site.
Though there was no word on the cause of the accident, Williams told the Ouray Watch newspaper that it wasn't related to a cave-in or mine collapse.
The U.S. Mine Safety and Health Administration is at the accident site, which is about 270 miles southwest of Denver.
The last major mining disaster in Colorado occurred on April 15, 1981, when an explosion killed 15 people at the Mid-Continent Dutch Creek No. 1 Mine near Redstone.
There have been eight mining deaths in the state since 2002, not including the two Sunday, according to the mine safety agency.
In 2011, a New Mexico contract worker died after being hurt at the West Elk Coal Mine in Somerset, in western Colorado. The agency found the 53-year-old slipped and fell from a beam at a tower construction site.
In 2012, a 25-year-old water truck driver died after losing control of his vehicle at Colowyo Mine in Moffat County.
The Watch reported that in its heyday, between 1876 and the late 1940s, the Revenue-Virginius mine produced more than 14.5 million ounces of silver, enough to weather the Silver Panic of 1893.
Star Mine Operations acquired the property in late 2011.