gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1994.58A.1.260 Composition of the Early Precambrian Atmosphere and Hydrosphere Thermodynamic Constraints from Mineral Deposits Krupp R. E. Oberthür Th. Hirdes W. Bundesanstalt für Geowissenschaften und Rohstoffe, Postfach 510153, D-30631 Hannover, Germany 8 1994 58A 1 499 500 Copyright © 1994, The Mineralogical Society 1994