1. University of Michigan, Department of Earth
and Environmental Sciences, Ann
Arbor, Michigan 48109-1005, United States
2. University of Texas at Austin, Bureau of Economic Geology, Austin, Texas 78713-8924, United States
3. GEOTOP
and Département des sciences de la Terre et de l’atmosphére, Université du Québec á Montréal, succ. Centre-Ville, Montréal, Quebec CP8888, Canada