BILLINGS, Mont. (AP) — A 977-acre expansion of Spring Creek Mine was approved in Montana for the state's largest coal mine, located near the Wyoming border, regulators said.

The Montana Department of Environmental Quality gave its final approval of the expansion on Monday, extending the life of the mine by four years to 2031, the Billings Gazette reported.

The expansion includes about 72 million tons (65 million metric tons) of coal and is expected to keep production at about 18 million tons a year during the extension, department officials said. The project is also expected to produce up to $59.5 million in taxes for the state, and employ up to 340 workers, officials said.

The decision also includes more than $105,000 for 615 acres of lost habitat for endangered sage grouse. The money would be given to the Montana Sage Grouse Oversight Team’s Stewardship Fund.

Navajo Transitional Energy Company bought the 275-worker Spring Creek strip mine and two mines in Wyoming last year from bankrupt Cloud Peak Energy. The transition was complicated because the company and state officials were unable to resolve demands the company waive its immunity as a tribal entity from future lawsuits.

The mine shut down briefly in October when the dispute over sovereignty first emerged. A sovereign immunity waiver was provided by the company March 12 and cleared the way for the permitting process.

Montana Gov. Steve Bullock had said he was “satisfied the limited waiver protects the rights of Montanans” and directed “all agencies of the State of Montana to accept the waiver," the Navajo company said in a statement.