gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.1.214 The Effect of Organic Matter on Chemical Weathering: Study of a Small Tropical Watershed: Nsimi-Zoétélé Site, Cameroon Dupré B. Oliva P. Viers J. Fortune J. P. Laboratoire de Géochimie, OMP, UMR-CNRS 5563, 38 rue des 36 ponts, 31400 Toulouse, France Braun J. J. Robain H. ORSTOM TOA, BP 1857, Yaoundé, Cameroun Martin F. Laboratoire de Géochimie, OMP, UMR-CNRS 5563, 38 rue des 36 ponts, 31400 Toulouse, France 1998 62A 1 405 406 Copyright © 1998, The Mineralogical Society 1998