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A silver-palladium alloy from the Bahia lateritic gold deposit, Carajas, Brazil

Published online by Cambridge University Press:  05 July 2018

Weisheng Zang ,
William S. Fyfe  and
Robert L. Barnett
Weisheng Zang
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
William S. Fyfe
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
Robert L. Barnett
Affiliation:
Department of Geology, University of Western Ontario, London, Ontario, Canada N6A 5B7
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Abstract

A silver-palladium alloy with structural formula close to AgPd has been found in laterite from the Bahia lateritic gold deposit. The alloy occurs in a void of an iron oxide nodule, associated with goethite and hematite. The angular shape and protuberances of the alloy grains suggest crystal growth in a lateritic environment, indicating that the alloy is a secondary mineral precipitated during lateritisation. The oxidation of sulphides of the parent rocks probably favoured the migration of palladium and silver as transient thiosulphate and sulphite complexes. Destruction of the thiosulphate and sulphite ligands could result in precipitation of both palladium and silver as an alloy. Eh-pH phase diagrams for Pd-H2O-C1 and Ag-H2O-C1 systems show that both palladium and silver are stable in lateritic environments under lower redox potentials. Such an environment may exist at the top of the ferruginous zone due to the abundant organic matter near the surface.

Keywords

silver-palladium alloythiosulphate complexchloride complexlateriteBahia gold depositBrazil
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 382 , March 1992 , pp. 47 - 51
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

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