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Hypogene violarite of exsolution origin from Mount Keith, Western Australia: field evidence for a stable pentlandite–violarite tie line

Published online by Cambridge University Press:  05 July 2018

B. A. Grguric
B. A. Grguric*
Affiliation:
Geology and Resource Evaluation Department, WMC Resources Ltd., Mount Keith Operation, P.O. Box 238, Welshpool Delivery Centre, W.A. 6986, Australia
*
*E-mail: [email protected]
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Abstract

In most documented occurrences, violarite (FeNi2S4) occurs as a product of the supergene alteration of primary pentlandite or millerite. Earlier experimental phase relations studies predicted the possible existence of a stable violarite–pentlandite tie line, though there has been little field evidence supporting this hypothesis, and the preferred topology in the Ni-Fe-S system involves a pyrite–millerite tie line. This paper documents the occurrence of violarite-pentlandite±pyrite assemblages which, on the basis of mineral chemistry and textural evidence, appear to be hypogene. Primary cobaltian violarite (with 2.1–13.2 wt.% Co) occurs as lamellae in pentlandite in the MKD5 nickel sulphide orebody at Mount Keith, central Western Australia. These lamellae are interpreted to be of exsolution origin. Cobalt is preferentially partitioned into violarite, resulting in high Ni:Co ratios in the associated pentlandite relative to pentlandite in violarite-free assemblages. Hypogene violarite-millerite±pentlandite assemblages were also noted. In all hypogene assemblages, violarite differs in both textural and mineral chemical characteristics from supergene violarite from the upper portions of the MKD5 orebody. The implications of the assemblages for the known low-temperature phase relations in the Ni-Fe-S-(Co) system are discussed.

Keywords

violaritepentlanditeNi-Fe-S systemMount KeithWestern Australia
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 2 , April 2002 , pp. 313 - 326
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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