Gold and arsenic deposition on pyrite surfaces from hydrothermal solutions : G.B. Arehart (Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA) S.L. Chryssoulis (Surface Science Western, London, Ont. N6A 5B8, Canada) and C.S. Eldridge (Research School Earth Science, Australia National University, GPO Box 4, Canberra, A.C.T., Australia)