Westmoreland Coal has also agreed to supply coal to the nearby San Juan generating station.
Under the agreement, Westmoreland would take over mine operations in early 2016. The coal-supply deal with the power plant expires in 2022, with an option by the facility’s owners to extend it.
The agreements are subject to internal approvals, Westmoreland said.
Westmoreland Coal CEO Keith Alessi said: "We look forward to working with the ownership of San Juan and BHP Billiton in assuring a smooth transition on or about January 1, 2016.
"The San Juan mine is a well-run operation with an excellent workforce that fits extremely well with our mine mouth, contracted business model."
Earlier this year, Westmoreland Coal acquired Buckingham Coal as well as Oxford Resources, a pair of Ohio firms involved in the coal business.
Westmoreland’s coal operations include sub-bituminous and lignite coal mining in the Western US and Canada,
The company also operates a char production facility, and a 50% stake in an activated carbon plant.
