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Sperrylite saturation in magmatic sulfide melts: implications for formation of PGE-bearing arsenides and sulfarsenides

Bai Liping, Barnes Sarah-Jane et Baker Don R.. (2017). Sperrylite saturation in magmatic sulfide melts: implications for formation of PGE-bearing arsenides and sulfarsenides. American Mineralogist, 102, (5), p. 966-974.

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URL officielle: https://doi.org/10.2138/am-2017-5631

Résumé

Sperrylite (PtAs2) is one of most common Pt minerals, but the processes whereby it forms are not clearly established. Most commonly it is associated with the major-component base metal sulfide minerals (pyrrhotite, pentlandite, and chalcopyrite), which are believed to have crystallized from magmatic sulfide melts. Hence, sperrylite is thought to have formed by crystallization from a sulfide melt or by exsolution from sulfide minerals. However, sperrylite is also found associated with silicate and oxide minerals where it is thought to have formed by crystallization from the silicate magma. To investigate the conditions under which sperrylite could crystallize from magmatic sulfide melt we investigated sperrylite saturation in Fe-Ni-Cu-S sulfide melts under controlled fO2 and fS2 at 910–1060 °C and 1 bar. The As and Pt concentrations in the sulfide melt at sperrylite saturation increase from 0.23–0.41 to 2.2–4.4 wt% and from 0.36–0.65 to 1.9–2.8 wt%, respectively, as the iron concentration in the sulfide melt decreases from 50 to 36 wt% at 910–1060 °C. We show that transitional metal concentrations, particular iron and nickel, as well as sulfur and oxygen fugacities influence As and Pt concentrations in the sulfide melt at sperrylite saturation. These intensive variables appear to effect sperrylite solubility by influencing the oxidation state of As in the sulfide melt. The measured concentrations of As and Pt in sperrylite-saturated sulfide melts produced in our experiments are much higher than that in most natural sulfides, implying that arsenides and sulfarsenides will not reach saturation in natural magmatic sulfide melts at high temperatures unless the magma has been contaminated with an exceptionally As-rich rock. This suggests that the observed arsenides and sulfarsenides in natural sulfide ores were not formed by crystallization from unfractionated sulfide melts at high temperatures above 900 °C, but might form at low temperatures below 900 °C.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:102
Numéro:5
Pages:p. 966-974
Version évaluée par les pairs:Oui
Date:2017
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:Sperrylite, PGE, magmatic sulfide melt, arsenide, sulfarsenide
Déposé le:02 avr. 2019 23:49
Dernière modification:02 avr. 2019 23:49
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