Relative and absolute timing of supracrustal deposition, tectonothermal activity and gold mineralization, West Meliadine region, Rankin Inlet greenstone belt, Nunavut, Canada

The West Meliadine area of the Neoarchean Rankin Inlet greenstone belt is underlain by complexly deformed, greenschist to amphibolite facies mafic volcanic and sedimentary rocks that have been intruded by Neoarchean and Paleoproterozoic felsic and mafic plutonic rocks. The dominant geological feature is the Pyke Break, an east to southeast-trending, several kilometre wide high strain zone characterized by strong fabrics and associated D2 and D3 shear zones. Orogenic lode-gold deposits are hosted in second-order shear zones and gold-bearing quartz-carbonate veining developed at favourable physical and chemical traps. Gold occurs in both greenschist and amphibolite facies host rocks but the most significant deposits occur in greenschist settings. Gold deposits hosted in greenschist facies rocks are interpreted as forming post-peak metamorphism and deposits hosted in amphibolite facies rocks likely formed syn-peak metamorphism.; Field and geochronological evidence (40Ar/39Ar, U-Pb zircon and SHRIMP monazite) indicate regional metamorphism, deformation and gold mineralization occurred between 1900 and 1850 Ma. Two Paleoproterozoic rnafic dyke swarms (ca. 2450 and 2190 Ma) are crosscut by both D2 and D3 fabrics and shear zones. 40Ar/39Ar data provide evidence for >500°C regional temperatures until ca. 1800 Ma. SHRIMP-determined ages on hydrothermal monazite indicate orogenic gold-bearing quartz veining occurred at ca. 1850 Ma. A minimum age for deformation and metamorphism is constrained by the intrusion of undeformed and unmetamorphosed lamprophyre dykes that were emplaced between 1850 and 1820 Ma.; Neoarchean supracrustal belts normally host only Neoarchean orogenic gold deposits. Evidence for younger Proterozoic gold mineralizing events within Neoarchean belts is typically considered to be a result of remobilization of pre-existing Neoarchean ores or later thermal re-setting of less robust dating systems. Field relations and highly concordant and robust (>600°C closure temperature for monazite) SHRIMP geochronology suggest "new" gold was formed as a result of Paleoproterozoic tectonothermal re-working of the western Churchill Province associated with the bounding Thelon and Trans-Hudson orogens. These observations do not preclude the presence of Neoarchean gold occurrences in the Rankin Inlet greenstone belt, but no "early" deformed ores can be linked to gold-bearing veins introduced at ca. 1850 Ma, suggesting remobilization was not a factor in forming gold deposits at ca. 1850 Ma.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat.