Sandfire Resources American CEO John Shanahan was only 58. Local Montana media reported he died on Saturday of natural causes.
The company extended its condolences to Shanahan's family and expressed its gratitude for his leadership and contribution.
"John was both well respected and well liked within Sandfire and the wider mining industry," Sandfire America chairman Matthew Fitzgerald said.
"His sudden passing is a great shock and a tragic loss, and our thoughts are with his family at this distressing time."
Australian-born Shanahan has been the CEO of Sandfire America since June 2016 and lived in Montana close to the company's Black Butte development project.
Before joining Sandfire, Shanahan was president and CEO of Revett Mining Compa...