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TitreEvidence from fluid inclusion microanalysis and stable Cl isotopes for the interaction of magmatic fluids with saline groundwater at the Sudbury Igneous Complex, Ontario: a revised model for footwall-style mineralization
AuteurHanley, J J; Ames, D E; Barnes, J; Sharp, Z; Guillong, M
SourceL'Association géologique du Canada-L'Association minéralogique du Canada, Réunion annuelle conjointe, Recueil des résumés vol. 34, 2011 p. 88,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140503
RéunionSpecial session on Precambrian Metallogeny SEG-GAC-MAC; Ottawa; CA; mai 25-27, 2011
Documentpublication en série
Mediapapier; numérique; en ligne
Lat/Long OENS -81.5000 -80.5000 46.7500 46.2500
Sujetsinclusions fluides; isotopes; études des isotopes stables; minéralisation; magmatisme; écoulement de la nappe d'eau souterraine; géologie économique; pétrologie ignée et métamorphique
ProgrammeÉtude des gîtes magmatiques de Ni-Cu-EPG, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
Along the northern margin of the 1.85 Ga Sudbury Igneous Complex (SIC), Canada, veins and dikes of a granitic rock type known as the footwall granophyre preserve evidence of the interaction of magmatic fluid and groundwater. Textures and cross-cutting relations show that the emplacement of the footwall granophyre created favourable sites for the later deposition of footwall-style (high Cu, Pd, Pt) sulfide veins. Geochemical modeling shows that the rock type represents a mobilized (injected) silicate melt residue from the crystallizing SIC. Primary fluid inclusions in the footwall granophyre contain mixtures of a high salinity (44-70 wt% Na-Cl eq), metal-poor Na-rich aqueous magmatic fluid and a lower salinity, Ca- and Sr-rich groundwater. The magmatic end-member is considered to be an SIC-derived volatile phase. Estimates of the mixing proportions show that primary and secondary inclusions in the footwall granophyre contain 60-100% and 20-70% of the magmatic end-member by mass, respectively. The chlorine isotope composition of biotite in the footwall granophyre shows 37 Cl enrichment (d 37 Cl = 0.98‰ to 1.61‰). In contrast, biotite from the Archean country rocks (d 37 Cl = -0.88 to -0.53‰) and associated groundwater are 37 Cl-depleted.
The results of this study lead to two important conclusions concerning genetic and exploration models for the footwall ore zones. First, early magmatic fluids introduced into the footwall contained very little Cu (<100 ppm), the main ore metal in footwall ore deposits. This result is in contradiction with existing hydrothermal models for footwall ore formation that hypothesize that Cu and other ore metals were remobilized from sulfide deposits along the SIC contact by saline fluids and redeposited in the footwall. Rather, the data presented here supports the emplacement of sulfide liquids as the main mechanism of footwall ore development. Second, although stable Cl isotope and fluid inclusion analyses confirm that magmatic fluid was introduced into the footwall, this magmatic end-member fluid was common to both mineralized and barren segments of the footwall. Therefore, detection of this magmatic component alone will not serve as a useful exploration method for sulfide deposits. In contrast, mapping the distribution and abundance of the footwall granophyre rock type may be ore-predictive since its emplacement and higher abundance in mineralized areas appears to have been a structural and textural
prerequisite for footwall ore development.