MELBOURNE, Aug 28 (Reuters) - Australia's Fortescue board made a mutual decision with metals division CEO Fiona Hick that she would step down on Aug. 27, energy division CEO Mark Hutchinson said on Monday. The departure of Hick after less than six months in the role has caught analysts off guard as Fortescue logged a $726 million impairment with its annual results. (Reporting by Melanie Burton; Editing by Jacqueline Wong)