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TitreMultiple sources of selenium in ancient seafloor hydrothermal systems: Compositional and Se, S, and Pb isotopic evidence from volcanic-hosted and volcanic-sediment-hosted massive sulfide deposits of the Finlayson Lake District, Yukon, Canada
AuteurLayton-Matthews, D; Leybourne, M I; Peter, J M; Scott, S D; Cousens, B; Eglington, B M
SourceGeochimica et Cosmochimica Acta vol. 117, 2013 p. 313-331,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20090191
Documentpublication en série
Mediapapier; en ligne; numérique
Formatspdf; html
Lat/Long OENS-131.0000 -130.5000 61.7500 61.5000
Sujetsselenium; plomb; soufre; gîtes volcanogènes; sulfures; gîtes sulfureux; events hydrothermaux sous-marins; éléments en trace; géochimie des éléments en trace; géochimie; géologie économique
Illustrationslocation maps; plots; tables; histograms; cross-sections
ProgrammeProjet de recherche en zones profondes IGC-3, Initiative géoscientifique ciblée (IGC-3), 2005-2010
ProgrammeÉtude des gîtes de sulfures massifs volcaniques, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
Volcanic-hosted massive sulfide (VHMS) and volcanic-sediment-hosted massive sulfide (VSHMS; i.e., hosted by both volcanic
and sedimentary rocks) deposits in the Finlayson Lake District, Yukon, Canada, provide a unique opportunity to study
the influence of seafloor and sub-seafloor hydrothermal processes on the formation of Se-poor (GP4F VHMS deposit; 7 ppm
Se average), intermediate (Kudz Ze Kayah - KZK VHMS deposit; 200 ppm Se average), and Se-enriched (Wolverine VSHMS
deposit; 1100 ppm Se average) mineralization. All three deposits are hosted by mid-Paleozoic (~360 - 346 Ma) felsic volcanic
rocks, but only the Wolverine deposit has voluminous coeval carbonaceous argillites (black shales) in the host rock package.
Here we report the first application of Se isotope analyses to ancient seafloor mineralization and use these data, in conjunction
with Pb and S isotope analyses, to better understand the source(s) and depositional process(es) of Se within VHMS and
VSHMS systems. The wide range of d82Se (-10.2%per-mille to 1.3%per-mille, relative to NIST 3149), d34S (+2.0%per-mille to +12.8%per-mille CDT), and elevated Se contents (up to 5865 ppm) within the Wolverine deposit contrast with the narrower range of d82Se (-3.8%per-mille to -0.5%per-mille), d34S (9.8%per-mille to 13.0%per-mille), and lower Se contents (200 ppm average) of the KZK deposit. The Wolverine and KZK deposits have similar sulfide depositional histories (i.e., deposition at the seafloor, with concomitant zone refining). The Se in the KZK deposit is magmatic (leaching or degassing) in origin, whereas the Wolverine deposit requires an additional large
isotopically negative Se source (i.e. ~-5%per-mille d82Se). The negative d82Se values for the Wolverine deposit are at the extreme
light end for measured terrestrial samples, and the lightest observed for hypogene sulfide minerals, but are within calculated
equilibrium values of d82Se relative to NIST 3149 (~30%per-mille at 25 °C between SeO4 and Se2-). We propose that the most negative
Se isotope values at the Wolverine deposit record the d82Se of the Se-source, and that the wide range in d82Se values
results from the combined effects of thermal and chemical degradation and Se-loss from the carbonaceous argillite source
to a hydrothermal fluid (including magmatic Se i.e., leached and/or magmatic-hydrothermal) with deposition at or near
the paleoseafloor. Pristine unaltered black shales show little variation in d82Se relative to bulk earth; Se accumulation and