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Chalcophile and platinum-group element distribution in the Ultramafic series of the Stillwater Complex, MT, USA — implications for processes enriching chromite layers in Os, Ir, Ru, and Rh

Barnes Sarah-Jane, Pagé Philippe, Prichard Hazel Margaret, Zientek M.L. et Fisher Peter C.. (2016). Chalcophile and platinum-group element distribution in the Ultramafic series of the Stillwater Complex, MT, USA — implications for processes enriching chromite layers in Os, Ir, Ru, and Rh. Mineralium Deposita, 51, (1), p. 25-47.

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URL officielle: http://link.springer.com/article/10.1007/s00126-01...

Résumé

All of the rocks from the Ultramafic series of the Stillwater Complex are enriched in PGErelative tomostmafic magmas. Furthermore, the chromite layers are particularly enriched in IPGE (Os, Ir, and Ru) and Rh. This enrichment appears to be a common characteristic of ultramafic rocks from many types of settings, layered intrusions, ophiolites, and zoned complexes. We have carried out a petrological, mineralogical, and geochemical study to assess how the enrichment occurred in the case of the Stillwater Complex and applied our results to the chromite layers of the Bushveld and Great Dyke complexes. The minerals that now host the PGE are laurite and fine-grained intergrowths of pentlandite, millerite, and chalcopyrite. The laurite occurs as inclusions in chromite, and mass balance calculations indicate that it hosts most of the Os, Ir, and Ru. The sulfide minerals occur both as inclusions in chromite and as interstitial grains. The sulfides host much of the Pd and Rh. The IPGE and Rh correlate with Cr but notwith S or Se, indicating that these elements were not collected by a sulfide liquid. Palladium, Cu, and Se correlate with each other, but not with S. The low S/Se (<1500) of the whole rock and magnetite rims around the sulfides indicate some S has been lost from the rocks. We conclude that to account for all observations, the IPGE and Rh were originally collected by chromite, and subsequently, small quantities of base metal sulfide liquid was added to the chromite layers from the overlying magma. The IPGE and Rh in the chromite diffused from the chromite into the base metal sulfides and converted some of the sulfides to laurite.

Type de document:Article publié dans une revue avec comité d'évaluation
ISSN:0026-4598
Volume:51
Numéro:1
Pages:p. 25-47
Version évaluée par les pairs:Oui
Date:2016
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:Platinum-group elements, Selenium, Chromite, Laurite, Ultramafic series, Stillwater Complex
Déposé le:17 juin 2016 15:20
Dernière modification:09 déc. 2016 15:40
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