Lumps of coal in a file photo.
The Spring Creek Mine in Big Horn County is operated by the Navajo Transitional Energy Company.
The expansion will allow 39.9 million tons of coal to be mined over the next 16 years.
The approval marks a victory for the Spring Creek mine, which has sought for nearly two decades to boost production. Its expansion plans were stymied by a court order mandating a fresh federal environmental review.
That analysis was published in January, days before Trump took office.
The NTEC, which is wholly owned by the Navajo Nation, bought the mine in 2019 from bankrupt Cloud Peak Energy.
NTEC was not immediately available for comment.
