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TitleContrasting halogen geochemistry of barren and mineralized breccias of the Sudbury Igneous Complex, Ontario
AuthorStewart, R C; Hanley, J J; Ames, D EORCID logo
SourceMineralogical Magazine vol. 75, 2011 p. 1943
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20140504
MeetingGoldschmidt conference; Prague; CZ; August 2011
Mediapaper; on-line; digital
File formatpdf
Lat/Long WENS -81.5000 -80.5000 46.7500 46.2500
Subjectseconomic geology; geochemistry; igneous and metamorphic petrology; metallic minerals; igneous rocks; indicator elements; elements; rock analyses, trace elements; hydrothermal alteration; hydrothermal deposits; hydrothermal systems; halides; breccia deposits; groundwater; geothermal fluids geochemistry; metasomatic deposits; Igneous Complex; Mineralized Breccias; Sulphide Saturation
ProgramTargeted Geoscience Initiative (TGI-4), Mafic-Ultramafic Ore Systems
AbstractThe potential for the halogen elements (Cl, Br, I) to be used as geochemical indicators for contact -style Ni-Cu-PGE mineralization along the lower contact of the Sudbury Igneous Complex (SIC) has been investigated. Two environments-one barren, and the other containing economic magmatic sulphide ore systems-were compared.The studied host rocks to these deposits are polymict igneous-textured breccias, formed by partial melting of the Archean country rocks (gneisses).
No significant differences in bulk major and trace element geochemistry of rocks between the environments aside from the halogen elements were observed. Two major differences in halogen geochemistry were recognized:
First, mineralized breccias show marked enrichment in I. This is thought to have resulted from the leaching of I from brecciated sulphides by hydro thermal fluids released during contact metamorphism and partial melting of the country rocks, and is unique to those breccias that host sulfides. The anomalous I can be detected for distances of up to several 100 metres from mineralized samples. This observation is consistent with experimental studies which show that I is the most compatible halogen in sulfide liquids [1] leading to I enrichment in environments where sulfide liquids crystallize.
Second, analysis of the soluble fraction (from fluid inclusions) of the halogens reveal that two distinct fluid end-members were trapped in the matrix of the breccias during their crystallization (as mixtures in primary fluid inclusions): a high Cl-/Br-fluid phase of probable magmatic origin (exsolved from the SIC), and a low Cl-/Br-fluid phase derived from fluid released during dehydration of hydrous minerals in the country rocks. Mineralized breccias contain a much higher proportion of the non-magmatic fluid end-member. This would suggest that footwall partial melting was a critical component to deposit development, possibly promoting sulfide saturation in this local environment or the transportation of ore metals in high salinity fluids of non-magmatic origin (e.g. groundwater, metamorphic fluid).

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