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TitleMineralogy, metal zoning and genesis of the Cambrian-Ordovician Zn-Pb-Cu-Ag-Au Lemarchant volcanogenic massive sulphide (VMS) deposit, Newfoundland
AuthorGill, S B; Piercey, S J; Layton-Matthews, D
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 102-103
LinksOnline - En ligne
Year2014
Alt SeriesEarth Sciences Sector, Contribution Series 20140463
PublisherGeological Association of Canada
PublisherMineralogical Association of Canada
MeetingGAC-MAC 2014; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Fredericton; CA; May 21-23, 2014
Documentserial
Lang.English
Mediaon-line; digital
File formatpdf
ProvinceNewfoundland and Labrador
NTS12A/10
AreaRed Indian Lake
Lat/Long WENS -56.7500 -56.5833 48.6667 48.5000
Subjectsmineralogy; economic geology; mineral occurrences; mineral deposits; volcanogenic deposits; mineralization; zinc; lead; copper; silver; gold; sulphides; sulphide deposits; barite; sphalerite; pyrite; chalcopyrite; bornite; tetrahedrite; tennantite; stromeyerite; galena; facies; alteration; stratiform deposits; Dunnage Zone; Red Indian Line; Lemarchant volcanogenic massive sulphide deposit; Tally Pond belt; Paleozoic; Cambrian
ProgramVolcanogenic Massive Sulfide Ore Systems, Targeted Geoscience Initiative (TGI-4)
AbstractThe Lemarchant deposit, located in the Tally Pond volcanic belt, Newfoundland, is a bimodal felsic volcanogenic massive sulphide (VMS) deposit with anomalous gold, silver, and epithermal suite elements (i.e. As, Sb, Ba, Ge). Currently, the deposit has a geological resource of 2.58 Mt at 0.49% Cu, 4.51% Zn, 1.01% Pb, 54.62g/t Ag, and 1.00 g/t Au. The roughly stratiform massive sulphide zone and underlying stockwork zone comprising the Lemarchant deposit are hosted in footwall rhyolite breccia, flows and volcaniclastic rocks, and are overlain by a dominantly exhalative pyritic mudstone. The stratiform massive sulphides are divided into 3 mineral assemblage types. Type 1 mineralization consists of barite, massive red (high-Fe, <7 mole%) to white (low-Fe, <1 mole%) sphalerite, recrystallized fine-grained pyrite, galena and chalcopyrite. Type 2 mineralization cross-cuts the lower type 1 mineralization and is subdivided into thin Type 2a bornite-galena-stromeyerite stringers and thick Type 2b bladed barite-coarsegrained tetrahedrite-galena-colusite-electrum stringers. Type 3 stockwork mineralization is found below type 1 and type 2 assemblages and consists of orange sphalerite-chalcopyriteeuhedral pyrite stringers. Sulphur isotope values (?34S) are relatively lower in galena, pyrite and chalcopyrite from the type 2 assemblages than the upper type 1 and type 3 assemblages. Type 2 assemblages are enriched in trace elements relative to type 1 and type 3 assemblages, and are zoned from proximal As-Cu-bearing sulphosalts to more distal Sb-Ag-bearing sulphosalts. Lead isotopes in galena indicate that lead in the hydrothermal fluid was derived from a mixture of eroded continental crust and depleted mantle material. Paragenetically, deposition began with type 1 sulphides, followed by deposition of type 2a and penecontemporaneous type 2b mineral assemblages. Type 3 sulphides were deposited last, with coincident zone refinement and recrystallization of the stratiform massive sulphides. The low-Fe sphalerite, low ?34S sulphides and epithermal suite sulphide mineral assemblage (i.e. tetrahedrite, bornite, colusite, electrum) in type 1 and type 2 assemblages suggest that mineralizing fluids were likely low temperature (<250°C), oxidized and had high sulphur activity; hydrothermal fluid conditions especially suitable for gold transport and deposition. The type 3 assemblage is indicative of relatively higher fluid temperatures (>300°C). A direct contribution of magmatic volatiles to the hydrothermal fluid may have been responsible for the contribution of lead isotopes to the Lemarchant deposit from a depleted mantle source and for trace element enrichment of the type 2 assemblages, and might provide an explanation for the lower ?34S values found in these assemblages.
GEOSCAN ID295872