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TitreLithogeochemistry and sulfur isotopic composition of hydrothermal mudstones associated with the Lemarchant volcanogenic massive sulfide (VMS) deposit, Tally Pond belt, central Newfoundland
AuteurLode, S; Piercey, S J; Devine, C A; Layne, G D; Piercey, G
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 36, 2013 p. 131,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140465
ÉditeurGAC MAC
RéunionGAC-MAC 2013; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Winnipeg; CA; mai 22-24, 2013
Documentpublication en série
Mediaen ligne; numérique
Lat/Long OENS-56.7500 -56.5833 48.6667 48.5000
Sujetsgîtes minéralogiques; gisements minéraux; gîtes volcanogènes; minéralisation; zinc; plomb; cuivre; argent; or; sulfures; gîtes sulfureux; barytine; sphalérite; pyrite; chalcopyrite; bornite; tétrahédrite; tennantite; stroméyérite; galène; faciès; altération; gisements stratiformes; Zone de Dunnage ; Ligne de Red Indian ; minéralogie; géologie économique; Paléozoïque; Cambrien
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
The Cambrian precious metal-bearing bimodal felsic Lemarchant Zn- Pb-Cu volcanogenic massive sulfide deposit has a close association of hydrothermal sedimentary rocks to mineralization. Metalliferous mudstones occur immediately above and distal to mineralization - either stratigraphically on top of the massive sulfide deposit, or as interflow mudstones within hanging wall basaltic units. The mudstones range from samples that have hydrothermal signatures (high Fe/Al and basemetal values), to those with minor detrital input (lower Fe/Al and base metal values). When normalized to upper crustal shales, redoxsensitive positive Ce- and Eu-anomalies (Ce/Ce* and Eu/Eu* 1) and the redox-independent Y/Ho-ratio ~27 of the Lemarchant mudstones, suggest that they precipitated from reduced, high-T hydrothermal fluids with a short residence time in the hydrothermal plume and thus, a vent proximal setting. A second group of Lemarchant mudstones have negative Ce-anomalies, which may represent stronger mixing with seawater and REE-scavenging onto iron-oxyhydroxide particles, implying a more vent distal deposition. In-situ analyses by secondary ion mass spectroscopy (SIMS) of various sulfides from the mudstones (euhedral and framboidal pyrite, anhedral chalcopyrite and pyrrhotite, and euhedral arsenopyrite) yielded 34S values from -38 to -8‰ indicating a predominantly diagenetic-biogenic sulfur source and precipitation of the secondary sulfides under open system conditions. The absence of hydrothermal sulfur signatures suggests the potential for reduced vent fluid sulfur having been removed immediately after mixing with the seawater at or below the seafloor as the massive sulfides were formed. The predominance of biotic signatures in the sulfides suggests that most of the sulfides in the mudstones formed during diagenesis and are not primary, hydrothermal sulfides. It is proposed that the hydrothermal mudstones formed via deposition as black smoker plume fall-out - after mixing of hot, reduced and metalrich vent fluids with cold, oxidized, sulfate-rich ambient seawater; initially as amorphous iron-oxyhydroxide particles and silicagels, which were subsequently altered during diagenetic and hydrothermal alteration. Based on our study, lithogeochemical and sulfur isotope data show potential as an indicator of the proximity to massive sulfide mineralization within a mudstone-bearing host sequence.