Founding shareholder O'Rourke will leave the company on June 1, although will remain as non-executive chairman and a director on the board.
Clausen will join Copper Mountain after he finishes working on the acquisition of Brio by Leagold Mining.
He has more than 30 years' experience in the base and precious metals industry, most recently as CEO of Brio Gold (from 2014) and before that as CEO of Augusta Resources from its birth in 2005 until it was taken over by HudBay Minerals in 2014.
Prior to this he also held senior positions at Washington Group International and Stillwater Mining.