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Chemical and physical transfers in an ultramafic rock weathering profile: Part 1. Supergene dissolution of Pt-bearing chromite

¹ Institut de Recherche pour le Développement (IRD), UMR 161 CEREGE, BP A5, 98848 Nouméa, New Caledonia
² Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement, (UMR CNRS 6635/UMR IRD 161), Aix-Marseille Université, Université Paul Cézanne, BP 80, 13545 Aix en Provence Cedex 4, France
³ EOST-Centre de Géochimie de la Surface (CNRS/ULP), Université Louis Pasteur, 1 rue Blessig, 67084 Strasbourg Cedex, France
⁴ UMR G2R/CREGU, Université Henri Poincaré 54506 Vandoeuvre-lès-Nancy, France

Correspondence: ^* E-mail: beauvais{at}cerege.fr

Chemical weathering and supergene dissolution processes of Pt-bearing chromite have been studied in a lateritic weathering profile developed on ultramafic rocks in New Caledonia (southwest Pacific). The chemical distributions of alkaline earth, transition metals, and precious metals (including Pt and Pd) were determined in a weathering profile varying from bedrock at the base upward through coarse and fine saprolites, and capped by a mottled zone and a lateritic colluvial nodular horizon. Chemical analyses and mass-balance calculations suggest that progressive weathering of the parent rock is characterized by an enrichment of Fe, Co, and Mn, a segregation of Ni at the boundary between the bedrock and the coarse sapolite and in the lower part of the fine saprolite, and a depletion of Mg, Ca, Si, Al, and Cr. The higher concentration of transition metals at the interface between the coarse and fine saprolite is due to vertical transfer and precipitation at the base of the weathering profile. In such a lateritic environment, the Pt-bearing chromite grains are progressively dissolved and the Pt-group minerals (PGM) are released in the weathering mantle with a preferential depletion of Pd with regard to Pt.

Key Words: Lateritic weathering • ultramafic rocks • mass-balance calculation • Pt-chromite • New Caledonia

This article has been cited by other articles:

				D. Traore, A. Beauvais, T. Auge, J. C. Parisot, F. Colin, and M. Cathelineau Chemical and physical transfers in an ultramafic rock weathering profile: Part 2. Dissolution vs. accumulation of platinum group minerals American Mineralogist, January 1, 2008; 93(1): 31 - 38. [Abstract] [Full Text] [PDF]