DENVER - Two miners who died in a gold and silver mine in Colorado over the weekend were killed when they were exposed to fatal levels of carbon monoxide following an explosion, federal safety officials said on Monday.
At least 19 other miners were sickened in the incident in the Revenue-Virginius mine in Ouray County in southwestern Colorado early on Sunday morning. All have since been released from two area hospitals.
Amy Louviere, a spokeswoman for the US Mine Safety and Health Administration, said it was not yet clear if the explosion was set off intentionally as part of a blasting operation or was an accident.
Louviere said according to preliminary information it appeared that after the explosives were detonated one of the miners entered the area and did not come back out.
"When he did not emerge, the shift foreman went in to search for him," she said. "Eventually they were both found by other miners working in the area, and those miners immediately evacuated the mine."
Mine rescue teams entered the mine and found the bodies of the two men, she said, detecting fatal levels of carbon monoxide inside the mine during the recovery operation.
Louviere said the agency would conduct a thorough investigation and ordered the mine operator to submit a plan for rescue teams to re-enter the mine to determine if it was properly ventilated and that all harmful gases had been removed.
The facility, about 330 miles (531 km) southwest of Denver, is owned by Star Mine Operations, LLC of Denver. A spokesman could not immediately be reached for comment on Monday.
The Colorado Division of Reclamation Mining and Safety, which regulates environmental impacts at state mines, said in a statement that Star Mine obtained a permit to mine silver, gold and sulfide materials in February.
"All mining at the site is conducted underground via drill and blast methods," the statement said.
The facility was last inspected in September to certify that an underground ore-processing mill complied with state regulations, the agency said.
The dead men were identified as Colorado residents Nick Cappanno, 34, and Rick Williams, 59.
The Revenue-Virginius mine was first claimed in the 19th century, and is located at an elevation of 12,000 feet (3,700 meters) along the so-called Governor Basin in the rugged San Juan Mountains.