The gas levels on January 8 caused a complete evacuation from the underground facility, while electricity was disconnected. The miners have not yet returned to their posts.

Oxbow officials told ILN late Wednesday that MSHA officials were on site at the western Colorado complex to help with manpower and equipment.

“Oxbow’s and MSHA’s management are dedicated to stabilizing the mine and getting Oxbow employees and MSHA personnel safely back to normal work assignments as soon as possible,” the company said.

“The plan was approved on January 15… the process of entering the mine and establishing communications and monitoring locations began today.”

Oxbow said the plan was to allow crews to install temporary isolation structures for the affected areas of the mine. The work should be completed by the end of the week, local time.

Once the impacted area is inert, regular seals will be places outby of the temporary structures. Once they have cured, mining activities outby will be cleared to restart.

Oxbow vice-president Mike Ludlow said a restart date could not be pinned down because too many variables were involved.

“Our belief is that it will be within a reasonable time frame,” he said, adding that a limited number of workers would be working intermittently to perform the seal work while the mine was idled.

A “significant proportion of the hourly workforce”, he added, remained unscheduled until the resumption of mining.

“We thank our miners for their patience and cooperation as we make every effort to get back to normal safe operations as soon as possible,” Ludlow said.

Oxbow, near Paonia, is neighbored by the Bowie and West Elk operations.

In all, there are a dozen coal operations in Colorado, including nine underground mines in Delta, Garfield, Gunnison, La Plata, Las Animas, Rio Blanco and Routt counties and three surface mines in Moffat and Montrose counties.