Single-grain detrital muscovite 40Ar/39Ar geochronology was performed on eight siliciclastic samples from the Mackenzie Mountains and Mackenzie Plain of the Northwest Territories. The rocks encompass two separate sample suites: the Neoproterozoic Mackenzie Mountains Supergroup and the Devonian Imperial Formation. A majority of the muscovite sample ages (1200-875 Ma) from the Neoproterozoic strata suggest derivation from a Grenvillian-aged source to the east. Detrital ages from individual samples serve to refine the poorly constrained stratigraphic ages for formations within the supergroup. Single-grain ages from the Imperial Formation range between 650-350 Ma, with a 425-400 Ma mode corresponding to the timing of collision between ancestral North America and a northern landmass throughout the Devonian. These new data allow re-evaluation of current understanding of both the post-Grenvillian and pre-Ellesmerian source to sink pathways for siliciclastic strata of the Mackenzie River corridor.
The TGI-4 Lode Gold project, which comprises numerous site-specific and thematic research activities, covers the entire spectrum of crustal settings for lode gold deposits, from orogenic banded iron formationhosted and greenstone-hosted quartz carbonate vein-type gold deposits formed deep in the crust (>5 km), to intrusion-related deposits that are formed at shallower crustal levels (~2-5 km), and to deposits formed at or near the seafloor. Herein we synthesize a number of important project contributions that have significant implications for on-going mineral exploration for hidden deposits. Among the key findings is a newly established link between major faults, their early evolution, syntectonic magmatism and synorogenic sedimentary basin evolution, and gold metallogenesis in various greenstone belts. The revised model incorporates a phase of tectonic extension-a distinct feature recognized in gold-rich settings worldwide-that is applicable to mineral exploration targeting across the Canadian Shield. Importantly, the simultaneous multidisciplinary study of a number of large banded iron formation-hosted gold deposits and districts allows for the development of a unifying genetic model for such deposits that integrates critical structural, stratigraphic, hydrothermal, and metamorphic elements. Several key features that are common to all of the studied deposits, but elements specific to dominantly banded iron formation-hosted gold deposits or to deposits that are only partly hosted in banded iron formation, were also established. The Lode Gold project also bridges a major knowledge gap by characterizing a spectrum of "unusual" or "atypical" gold deposits in the Superior Province. The new and revised models incorporate synvolcanic as well as pre-deformation and synorogenic synmagmatic or intrusion-related gold deposits that represent a large part of the newly discovered resources in the Canadian Shield in both "brownfield" and "greenfield" exploration environments.
Secondary ion mass spectrometry (SIMS) U-Pb depth profiles of unpolished detrital zircon were used in an attempt to resolve the timing of metamorphism and mineralization in the North Caribou greenstone belt of northern Ontario, which hosts the Musselwhite gold mine. Eleven samples located 10-75 km from the mine site were collected from metasedimentary rocks adjacent to structures that may have promoted hydrothermal fluid flow. Zircon rim material is commonly characterized by decreased Th/U concentrations (up to an order of magnitude), as well as generally possessing concordant ages. Rim ages obtained via this technique range from 2788-2703 Ma, up to 250 m.y. younger than zircon cores. The timing of zircon rim recrystallization overlaps with the timing of potassic alteration in the surrounding plutons, as well as regional gold mineralization in the North Caribou Superterrane. These zircon rims may represent the timing and potential distribution of Au-bearing fluids within and regional to the Musselwhite deposit.
Orogenic Au deposits require a trigger to transport auriferous fluids from their deep-seated source regions to their depositional site in the mid- to upper-crust. Defining the tectonic trigger of Au ore systems requires precise age constraints. Herein we address that knowledge gap with new Re-Os sulphide (arsenopyrite and pyrite) and U-Pb detrital zircon geochronology results from the Lynn Lake greenstone belt of the Paleoproterozoic Trans-Hudson Orogen, Manitoba, Canada. We document an early-stage of Au-rich veins (ca. 1.82 Ga) that are coeval with syenitic magmatism (1.83-1.82 Ga) and immediately post-date new ages for the opening and closure of synorogenic basins (1.84-1.83 Ga) and late-stage arc magmatism (1.84-1.83 Ga). Together these data point to the importance of stalled subduction and upwelling asthenosphere as possible triggers for fluid release during the earliest stages of continental collision between the Hearne, Superior, and Sask cratons. New dating further documents a second, overprinting generation of auriferous fluids (ca. 1.78 Ga) that post-dates peak metamorphism (ca. 1.81 Ga). These late-stage fluids were driven by a second thermal pulse (ca. 1.78 Ga), which, based on the timing of coeval, crustally derived pegmatitic dykes, may be related to crustal thickening and/or another unrecognized subcrustal heat source. Mineral exploration should focus on the large-scale architecture that is required to focus multiple pulses of auriferous fluids to the same depositional trap over the lifespan of an orogen.
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