Patriot said mining operations had ceased Friday after one measurement in an abandoned area of the mine was found to be out of compliance during routine testing in accordance with the mine's ventilation plan.

As a result, the company is making further refinements to its ventilation plan to address the conditions.

Patriot planned to review the refinements with the US Department of Labor, Mine Safety and Health Administration as soon as possible in order to resume production at the mine.

Federal originally suspended mining activity on February 18 when potentially adverse atmospheric conditions were found.

It resumed production Wednesday last week, only to suspend operations again Friday.