MSHA investigators are trying to determine what happened Sunday morning at the Revenue Virginius Mine near Ouray, Colo., where two miners died and 19 miners were injured in an accident there.
A preliminary coroner's reported indicated that miners Nick Cappanno, 34, and Rick Williams, 59, died from carbon monoxide poisoning, according to the Colorado Office of Emergency Management.
Of the 19 miners who were taken to various hospitals in southwestern Colorado, most were treated and released, according to the agency. A handful of them were admitted and were reported to be in fair condition.
The Ouray County Sheriff's Office has ruled out an explosion or mine collapse as a possible cause of the incident.
Star Mine Operations LLC, a division of Denver-based Silver Star Resources, operates the mine. The company received a permit in February to mine silver, gold and sulfide minerals from vein deposits in the mine, according to the Colorado Department of Natural Resources.
All mining at the site is done by underground drilling and blasting, according to the agency.
Around 7:20 a.m. local time on Sunday, the sheriff's office received a call from 9-1-1 dispatch indicating that there had been an accident at the mine.
While the other miners in the area were able to evacuate, Cappanno and Williams remained underground and had to be rescued, according to reports.
"Mine rescue teams were dispatched and brought the victims to the surface at 2 p.m.," an MSHA spokeswoman told Denver's ABC 7 News.