OURAY, Colo. (AP) -- Authorities are trying to determine exactly what sort of accident occurred in a mine in southwestern Colorado that left two miners dead of carbon monoxide poisoning and injured 20 others.
The Ouray County sheriff's office was called to the Revenue-Virginius mine at 7:20 a.m. Sunday, Ouray County spokeswoman Marti Whitmore said.
The miners were underground and were confirmed dead Sunday afternoon.
Authorities said at a late night news conference that the two died from carbon monoxide poisoning, according to The Denver Post. But the source of the gas was under investigation.
Both the Montrose Daily Press and the Post reported that investigators are looking at whether a blast on Saturday played a role.
The 20 injured were taken to area hospitals, and all but two were treated and released, Whitmore said. There was no word on the conditions of the two hospitalized workers.
The 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.
Both newspapers identified the dead as 34-year-old Nick Cappanno of Montrose, Colo., and Rick Williams, 59, of Durango, Colo.
"I knew both of these individuals personally," said Rory Williams, who said he is no relation to Rick Williams. "They were hard-working men. They were great men. They will be remembered indeed."
Though the cause of the accident hasn't been determined, Rory 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 Post said that the company has a permit to mine silver, gold and sulfides. About 100 miners work at the site, which will be closed until the end of the investigation, Williams said.
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.