The deal involves about 450 workers at the Navajo surface mine and the San Juan longwall operation and will expire at the end of January 2018.

No details of the agreement were disclosed.

“Approval of this agreement is a positive step for the viability of NMC’s surface operations, including the Navajo mine, the continued delivery of coal to our customers, as well as the continued employment and safety of our employees and contractors,” BHP Billiton New Mexico Coal president Pat Risner said.

“We commend the union leadership and company representatives for their diligence and steadfastness in reaching an agreement.”

“With the ratification of this new five-year agreement by our membership, the union is confident that this agreement supports the Navajo mine into the future, not only for our members and the company but for the community as well,” IUOE Local 953 business manager Pat Vigil said.

BHP confirmed last December it had reached an initial agreement to sell its Navajo operation to the Navajo Nation.

Under a memorandum of understanding, BHP will continue operating the mine for the tribe until July 2016 should the transfer come to fruition.