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TitleProtracted Paleoproterozoic gold history at the Archean BIF-hosted Meliadine Gold District, Nunavut
AuthorLawley, C J M; Creaser, R A; Jackson, S; Yang, Z; Davis, B; Dubé, B; Mercier-Langevin, P; Pehrsson, S; Vaillancourt, D
SourceGeological Survey of Canada, Open File 7743, 2015, 23 pages, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
NTS55J/13; 55K/16; 55N/01; 55O/04
AreaRankin Inlet
Lat/Long WENS-92.5833 -91.4167 63.7500 63.1250
Subjectsgeochronology; economic geology; paragenesis; sulphides; sulphide deposits; arsenopyrite; iron formations; gold; mineral deposits; mineral occurrences; Archean; uranium lead dates; uranium lead dating; uranium lead ratios; osmium; faults; Churchill Province; Meliadine gold district; Tiriganiaq Deposit; Pyke Break; Trans-Hudson orogeny; rhenium; Precambrian
Illustrationslocation maps; photographs; plots; photomicrographs
ProgramTargeted Geoscience Initiative (TGI-4), Gold Ore Systems
Released2015 03 12
AbstractThe Meliadine Gold District, Nunavut, represents one of Canada's largest emerging greenstone- and BIF-hosted gold districts (reserves of 2.8 Moz Au, plus indicated and inferred resources of 5.8 Moz Au). Most known gold deposits are co-spatial with the Pyke Break, which cuts Meso to Neoarchean (ca. 2.66 Ga) supracrustal and igneous rocks and represents an E-W trending fault associated with a NE-SW trending trans-cratonic fault network. The latter cuts the Western Churchill Province and records a complex and protracted reactivation history that spans at least four Paleoproterozoic orogenic episodes. Gold occurs as inclusions within idioblastic arsenopyrite crystals, at sulfide crystal boundaries and/or as sulfide fracture fills. Arsenopyrite crystal boundaries and domains adjacent to late fractures are variably recrystallized and relatively enriched in precious- and base-metals. In contrast, inclusion-free arsenopyrite crystals and overgrowths along with arsenopyrite domains devoid of fractures are relatively gold-poor. Clusters of gold and galena that correspond with recrystallized arsenopyrite domains and at contacts between disparate arsenopyrite generations suggest that sulfide recrystallization liberated gold and was remobilized, at least locally, into low-strain micro-textural sites along with precious- and base-metals during late fluid-assisted and deformation/metamorphic-driven remobilization. New U-Pb xenotime ages at ca. 1.86 Ga, coupled with previously reported U-Pb hydrothermal monazite ages, post-date arsenopyrite recrystallization, which suggests that gold remobilization was concomitant with the Trans-Hudson orogeny (1.9¬-1.8 Ga). New Re-Os arsenopyrite model ages range from 2.3-1.8 Ga and document a hitherto unrecognized and complex pre-1.86 Ga hydrothermal and sulfide history. The range of Re-Os model ages tends to support partial open-system behaviour and/or mixing of disparate arsenopyrite generations that are evident from micro-textures and in situ element mapping. Replicate analyses of the two most Re-rich and homogeneous arsenopyrite samples yield Re-Os model ages at ca. 2.27 and 1.90 Ga, which are broadly concurrent with the Arrowsmith (2.4-2.3 Ga) orogeny and the earliest phase of the Trans-Hudson orogeny (known locally as the Snowbird orogeny; ca. 1.9 Ga), respectively. These Re-rich samples also tend to be gold-poor and likely yield ages that pre-date gold remobilization and subsequent enrichment along arsenopyrite crystal boundaries and fractures at 1.86 Ga. We speculate that the bulk of the gold was initially introduced at 2.27 Ga and/or 1.90 Ga along with idioblastic arsenopyrite crystals and was subsequently re-mobilized, coupled with arsenopyrite recrystallization, during the Trans-Hudson orogeny.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Presentation delivered at the Yellowknife Geoscience Forum (November 25 to 27, 2014). Presentation summarizes age dating results at the Meliadine Gold District as part of TGI-4. New ages suggest that gold was introduced earlier than previously thought. Later faulting likely explain the current geometry of high-grade ore zones.