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TitleTracing gold mobility using in situ Pb isotope geochemistry of early and remobilized sulphide minerals, Meliadine gold district
AuthorLawley, C J M; Jackson, S E; Yang, Z; Davis, W J; Creaser, R A; Mercier-Langevin, P; Dubé, B
SourceGeological Survey of Canada, Scientific Presentation 51, 2017, 39 pages,
PublisherNatural Resources Canada
Mediaon-line; digital
File formatpptx
NTS55J/11; 55J/12; 55J/13; 55J/14; 55K/09; 55K/10; 55K/15; 55K/16; 55N/01; 55N/02; 55O/03; 55O/04
AreaMeliadine Gold District; Rankin Inlet
Lat/Long WENS -92.5167 -91.1333 63.2333 62.6667
Subjectseconomic geology; geochemistry; igneous and metamorphic petrology; geochronology; Archean; mineral deposits; hydrothermal deposits; modelling; ore mineral genesis; metals; gold; sulphides; ore grades; tectonic setting; orogenesis; metamorphism; intrusions; quartz veins; remobilization; recrystallization; precipitation; isotope geochemistry; lead isotope ratios; porphyroblasts; arsenopyrite; pyrite; host rocks; source rocks; structural features; faults; shear zones; bedrock geology; lithology; greenstone belts; ultramafic rocks; igneous rocks; intrusive rocks; gabbros; granites; tonalites; volcanic rocks; metamorphic rocks; quartzites; sedimentary rocks; iron formations; mass spectrometer analysis; radiometric dating; uranium lead dating; Churchill Province; Rankin Inlet Greenstone Belt; ore systems approach; banded iron formations (BIFs); rhenium-osmium dating; Precambrian
Illustrationsphotomicrographs; photographs; location maps; geological sketch maps; lithologic sections; plots; sections; stereonets; models; schematic cross-sections; Concordia diagrams
ProgramGold Ore Systems, Targeted Geoscience Initiative (TGI-4)
Released2017 02 14
AbstractThe late timing of gold is a characteristic feature of orogenic gold deposits. For many of these deposits, gold and other metals were liberated from the host greenstone belt and/or early sulfides concomitant with the syndeformational and fluid-assisted metamorphic transition of pyrite to pyrrhotite and remobilized into late, high-grade ore shoots. However, this metamorphic-driven gold-upgrading model is usually inferred, at least in part, from mineral textures, which can be equivocal in the absence of geochemical and/or isotopic constraints. Herein, we report new bulk mineral separate and in situ Pb isotope results for minerals in key textures in the Paleoproterozoic Meliadine gold district. Arsenopyrite and pyrite porphyroblasts occur in Paleoproterozoic quartz ± ankerite veins and are enveloped by remobilized pyrrhotite, chalcopyrite, and galena crystals that accompany gold in late, microtextural sites, a texture that forms the basis for the gold-upgrading model. Early, sieve-textured arsenopyrite and pyrite are gold rich and tend to yield the least radiogenic Pb isotope compositions (high 207Pb/206Pb and 208Pb/206Pb ratios), suggesting these relict domains escaped complete recrystallization during later reworking. Late, inclusion-free arsenopyrite and pyrite overgrowths scatter to more radiogenic Pb isotope compositions (low 207Pb/206Pb and 208Pb/206Pb ratios) and are typically gold poor, which we attribute to reworking and precipitation from a younger and more radiogenic fluid prior to and/or during the precipitation of free gold in variably plunging high-grade ore shoots at 1.90 to 1.85 Ga. Remobilized sulfides are the youngest sulfide phases, but locally yield low 206Pb/204Pb and 207Pb/204Pb ratios and, thus spurious old model “ages,” which overlap with the least radiogenic, sieve-textured arsenopyrite/pyrite domains. The isotopic signature of these remobilized sulfides was likely inherited from Pb liberated during reworking of early arsenopyrite and pyrite and a second, crustal Pb source that was introduced during late remobilization. Our results highlight the importance of element recycling from early sulfides and/or the Neoarchean deposit host rocks during significantly younger Paleoproterozoic reworking and gold remobilization. The in situ Pb isotope results of early and remobilized sulfides document the transition of gold from source to sponge to sink, which is likely a feature that occurred during the formation of other orogenic-style gold deposits.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI) 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. Metamorphosed volcanic rocks represent an important host for some of the world's largest concentrations of gold. TGI-4 is focused on improving models and targeting for these metamorphosed deposits. In this contribution, we report new lead isotope geochemistry results for sulphide minerals from a package of metamorphosed rocks near Rankin Inlet that host one of Canada's largest emerging gold districts (Meliadine). Our results allow us to constrain the timing and processes responsible for gold deposit genesis.