Richard Klingaman, meanwhile, reassumed his board chairman title so the Colorado-based miner keeps a dual CEO and board chairman governance, said officials. Klingaman was also chairman from 2009 to 2013, and has served as lead independent director since Q2 2013. Robert King has become president of U.S. operations.

On completion of the Sherritt transaction, Alessi will become interim president for Canadian operations, too, directly overseeing the Canadian business transition.

Westmoreland is one of the oldest independent coal companies in the U.S. Its portfolio includes subbituminous coal in the Powder River Basin in Montana and Wyoming, with lignite mining in Montana, North Dakota and Texas.