The additional 7,160 acres will add about nine additional years to the Musselshell County mine’s lifespan.

Bull Mountain, which currently employs 325, is projected to generate more than $127 million in revenue from royalties and state taxes on the expansion property alone during the coming nine years; the agency said that the growth will ensure a workforce of about 200 to 250 at the complex.

The Montana Department of Environmental Quality gave their approval to the mine expansion in October 2013, and the year prior the leasing of the federal coal reserves tied to the expansion was approved by the U.S. Bureau of Land Management.

The Signal Peak operation, which has recoverable coal reserves both above and below ground — 109 million tons and 431 million tons, respectively — produced 8.7 million tons of coal last year.