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Phase-equilibrium constraints on the magmatic origin of laurite + Ru-Os-Ir alloy

David R. A. Andrews and James M. Brenan
Phase-equilibrium constraints on the magmatic origin of laurite + Ru-Os-Ir alloy
The Canadian Mineralogist (December 2002) 40, Part 6: 1705-1716

Abstract

Experiments to assess the effects of T and fS (sub 2) on phase relation in the system Ru-Os-Ir-Cu-S found that at constant fS (sub 2) of 10 (super -1) atm, the two-phase field of laurite + alloy is restricted to the most Ru-rich bulk compositions (X (sub Ru) > 0.85) at 1250 degrees C and slightly expands to encompass the more Ru-poor composition (X (sub Ru) > 0.6) at 1200 degrees C; at this fS (sub 2) , laurite remains very close to pure RuS (sub 2) . An increase in fS (sub 2) led to the expansion of the two-phase field, with both laurite and alloy dissolving more Os + Ir. The compositions of both laurite and IPGE alloy defined by high-fS (sub 2) experiments show remarkable similarity to coexisting PGM compositions in natural chromitite from several localities. If such phases result from entrapment at the magmatic stage, then high-fS (sub 2) conditions are inferred. Limits on the fO (sub 2) of magmas that may precipitate alloy-laurite pairs stem from the requirement that such magmas remain sulphide-liquid-undersaturated, at least until PGM are trapped in their phenocryst host. Calculations suggest that for this to occur at high fS (sub 2) , laurite + IPGE alloy precipitation requires the involvement of relatively oxidized, low-FeO magmas.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 40, Part 6
Title: Phase-equilibrium constraints on the magmatic origin of laurite + Ru-Os-Ir alloy
Affiliation: University of Toronto, Department of Geology, Toronto, ON, Canada
Pages: 1705-1716
Published: 200212
Text Language: English
Summary Language: French
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 31
Accession Number: 2003-050676
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Update Code: 200316
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