CHLORINE ENRICHMENT AND HYDROUS ALTERATION OF THE SUDBURY BRECCIA HOSTING FOOTWALL Cu Ni PGE MINERALIZATION AT THE FRASER MINE, SUDBURY, ONTARIO, CANADA

Abstract

An assemblage of hydrous, Cl-bearing alteration-induced minerals is present within 150 m of footwall-style Cu-Ni-PGE sulfide mineralization hosted by the Sudbury Breccia at the Fraser Copper zone, Fraser mine, Onaping-Levack area, Ontario. The pyroxene hornfels to hornblende hornfels contact-metamorphic aureole of the Sudbury Igneous Complex (SIC) contains less than 15 modal % hydroxysilicates. Near the mineralized areas, a diagnostic assemblage of secondary minerals of the albite-epidote hornfels facies is present in the matrix of the Sudbury Breccia; it contains 25 to 80% actinolite + chamosite as well as epidote + sodic plagioclase (An 2.8-42 ) + quartz ± titaniferous magnetite ± biotite ± K-feldspar ± titanite. The Cl content and Cl/(Cl + F) values of amphibole and biotite in this matrix are elevated within 150 m of mineralization, and increase toward known occurrences of sulfides. Parameters of K, Na, and A-site occupancy correlate with Cl content in actinolite in such matrix material. The value of Mg# is lower in biotite in the matrix near mineralized areas and is inversely correlated with Cl/(Cl + F) in the biotite, reflecting Mg-Cl or Fe-F avoidance. Calculated temperatures of amphibole-plagioclase equilibration for the diagnostic hydrous assemblage are between 442 to 540 ± 75°C. The assemblage formed during a retrograde metamorphic event during or after footwall Cu-Ni-PGE mineralization, and after passage of peak conditions of contact metamorphism at the base of the SIC. The enrichment of Cl in this assemblage was the result of the increased amounts of free Cl relative to F in the equilibrating fluid, and favorable cation proportions for incorporation of Cl into the structure of hydroxysilicate minerals. The Cl-bearing assemblage accounts for a significant portion of the bulk halogen content of Sudbury Breccia matrix. It is unique to zones of Sudbury Breccia that host mineralization, and hence may be used to identify prospective areas. SOMMAIRENous décrivons un assemblage de minéraux d'altération hydratés et contenant du chlore dans une auréole de 150 m autour des indices minéralisés (Cu-Ni-EGP, sulfures) dans le socle bréchifié sous le complexe igné de Sudbury, à la zone dite de Fraser Copper, exploitée à la mine Fraser, région de Onaping-Levack, en Ontario. Les hornfels à pyroxène et à hornblende de l'auréole de contact autour de ce complexe contiennent moins de 15% de ces silicates hydroxylés. Près des indices imnéralisés, en revanche, nous trouvons un assemblage distinctif de minéraux secondaires équilibrés dans le faciès des hornfels à albite-épidote, développés dans la matrice de la Brèche de Sudbury; sont présents de 25 à 80% d'un assemblage à actinolite + chamosite, de même que épidote + plagioclase sodique (An 2.8-42 ) + quartz ± magnétite titanifère ± biotite ± feldspath potassique ± titanite. La teneur en Cl et les valeurs du rapport Cl/(Cl + F) de l'amphibole et de la biotite dans cette matrice sont élevées à l'intérieur de cette auréole de 150 m autour des zones minéralisées, et augmentent d...

Effects of hydrous alteration on the distribution of base metals and platinum group elements within the Kevitsa magmatic nickel sulphide deposit

“…Gal et al (2011) describe PGE minerals associated with the products of Cl-rich late magmatic or hydrothermal fluids in contact rocks of the Duluth Complex, although no whole-rock concentrations were reported. Several PGE-rich ores of hydrothermal origin have also been described over the years, such as the PGE-rich ore formed within cross-cutting faults at the Fortaleza de Minas deposit in Brazil (De Almeida et al, 2007), the low-S Cu-Ni-PGE footwall ores at Sudbury in Canada (Farrow and Watkinson, 1997;Hanley and Mungall, 2003;Molnár et al, 2001aMolnár et al, , 2001bMolnár and Watkinson, 2001), the McBratney deposit in Canada (Bursztyn and Olivo, 2010), and the high Pt concentrations observed in dunite pipes in the Bushveld Complex which are generally regarded as being hydrothermal in origin (Schiffries, 1976). Elevated Pt and Pd contents are found in some porphyry Cu-Au systems (Augé et al, 2005;Economou-Eliopoulos, 1991;LeFort et al, 2011) and unconformitytype uranium deposits (Jaireth, 1992;Mernagh et al, 1994).…”

Evolution of Palaeoproterozoic mafic intrusions located within the thermal aureole of the Sudbury Igneous Complex, Canada: Isotopic, geochronological and geochemical evidence

“…Halogen-bearing fluids have been invoked to account for the outward migration (away from the basal SIC contact) and emplacement of Cu-PGE-enriched liquids deep into the footwall of the SIC (Farrow et al, 1994;McCormick et al, 2002;Hanley and Mungall, 2003). Cu/Ni ratios are shown in Figure 9 (e, j), demonstrating first that they provide no useful discriminatory information regarding provenance, but also showing some evidence for significant depletion in Cu in some of the Drury samples, producing Cu/Ni ratios as low as 0.09 in sample SPA-88-55 (Table 1).…”

Múltiplos estágios de alteração hidrotermal do depósito de óxido de ferro-cobre-ouro Furnas, Província Carajás: evolução paragenética e química mineral.

“…Os conteúdos de halógenos nos minerais se relacionam à proporção de cátions nesses minerais, temperatura de formação, composição do fluido e a processos de lixiviação posteriores à cristalização devido a interação com fluidos de mais baixa temperatura (Hanley & Mungall, 2003).…”

“…(Munoz, 1984) (Selby & Nesbitt,2000), de Cu-Ni-PGE (Hanley & Mungall, 2003) e do corpo Sossego (Monteiro et al,200x? )…”

“…Diagramas: a) IV (F/Cl) vs IV (F), comparando os campos associados a biotita do depósito Furnas com os campos definidos para o corpo Sossego, Cu-pórfiro, S-W-Be e Mo-pórfiro (Munoz, 1984). b) log (ƒHF)/(ƒHCl) vs log (ƒH2O)/(ƒHCl); c) log (ƒH2O)/(ƒHF) vs log (ƒH2O)/(ƒHCl), mostrando variações de halógenos no fluido em equilíbrio com a biotita a uma temperatura de 400ºC e comparações com depósitos de Cu pórfiro (Selby & Nesbitt,2000), de Cu-Ni-PGE (Hanley & Mungall, 2003) e do corpo Sossego (Monteiro et al,200x?). Valores referentes à biotita do depósito de Cu-Ni-PGE de Sudbury são disponibilizados para comparação.…”