Arch is planning to mine 173 million tons of coal from 1,700 acres of the 5,800-acre Sunset Roadless Area in Gunnison County.

But the moratorium on new coal mines does not apply to pending leases that have received a final decision by a federal landlord and that includes leases “undergoing re-evaluation after having been vacated by judicial decision”, according to the Interior Department's announcement of a comprehensive review of potential reforms to the nation's coal program.

Last week Arch filed for bankruptcy as it struggled under the weight of $US4.5 billion debt load and declining coal prices.

Arch expects its mining operations and customer shipments to continue uninterrupted throughout the Chapter 11 reorganization process, its chairman and CEO John W. Eaves said.

“After carefully evaluating our options, we determined that implementing these agreements through a court-supervised process represents the best way to solidify our financial position and strengthen our balance sheet,” he said.

“We are confident that this comprehensive financial restructuring will further enhance Arch's position as a large-scale, low-cost operator.”

Eaves said that since the market downturn, Arch has taken steps to enhance the efficiency of its operations and to strengthen its asset base.

“As a result, all of our operating segments were cash flow positive during the first three quarters of 2015,” he said.

“We will continue to provide our customers with exceptional service as we move through this process, while maintaining and further reinforcing our position as an industry leader in safety, environmental stewardship and productivity.”