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TitreTracing gold mobility using in situ Pb isotope geochemistry of early and remobilized sulphide minerals, Meliadine gold district
TéléchargerTéléchargements
AuteurLawley, C J M; Jackson, S E; Yang, Z; Davis, W J; Creaser, R A; Mercier-Langevin, P; Dubé, B
SourceCommission géologique du Canada, Présentation scientifique 51, 2017, 39 pages, https://doi.org/10.4095/299668
Année2017
ÉditeurRessources naturelles Canada
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.4095/299668
Mediaen ligne; numérique
Formatspptx
ProvinceNunavut
SNRC55J/11; 55J/12; 55J/13; 55J/14; 55K/09; 55K/10; 55K/15; 55K/16; 55N/01; 55N/02; 55O/03; 55O/04
Lat/Long OENS -92.5167 -91.1333 63.2333 62.6667
SujetsArchéen; gisements minéraux; gisements minéraux hydrothermaux; établissement de modèles; genèse des minerais; métaux; or; sulfures; qualités des minerais; cadre tectonique; orogenèse; métamorphisme; intrusions; filons de quartz; remobilisation; recristallisation; précipitation; géochimie isotopique; rapports des isotopes de plomb; porphyroblastes; arsénopyrite; pyrite; roches hôtes; roches mères; caractéristiques structurales; failles; zones de cisaillement; géologie du substratum rocheux; lithologie; ceintures de roche verte; roches ultramafiques; roches ignées; roches intrusives; gabbros; granites; tonalites; roches volcaniques; roches métamorphiques; quartzites; roches sédimentaires; formations ferrifères; analyse par spectromètre de masse; datation radiométrique; datation au uranium-plomb; Province de Churchill ; géologie économique; géochimie; pétrologie ignée et métamorphique; géochronologie; Précambrien
Illustrationsphotomicrographs; photographs; location maps; geological sketch maps; lithologic sections; plots; sections; stereonets; models; schematic cross-sections; Concordia diagrams
ProgrammeÉtude des gîtes d'or, Initiative géoscientifique ciblée (IGC-4)
Diffusé2017 02 14
Résumé(disponible en anglais seulement)
The 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.
Résumé(Résumé en langage clair et simple, non publié)
L'Initiative géoscientifique ciblée (IGC-4) est un programme géoscientifique fédéral de collaboration qui fournit à l'industrie les connaissances géoscientifiques et les techniques novatrices de prochaine génération dont elle a besoin pour mieux détecter les gîtes minéraux enfouis, réduisant ainsi certains risques liés à l'exploration. Les roches volcaniques métamorphisées sont des hôtes de première importance pour certaines des plus grandes concentrations d'or au monde. L'IGC-4 se concentre sur l'amélioration des modèles et le ciblage de ces gisements métamorphisés. Dans la présente contribution, nous présentons de nouveaux résultats d'analyses géochimiques des isotopes du plomb pour des minéraux sulfurés provenant d'un assemblage de roches métamorphisées situé près de Rankin Inlet, l'un des plus vastes districts aurifères émergents du Canada (Meliadine). Nos résultats nous permettent d'établir les limites de la chronologie et des processus responsables de la genèse des gisements d'or.
GEOSCAN ID299668