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TitleApplication of molybdenum and thallium isotopes as indicators of paleoredox conditions and genesis of hyper-enriched black shale deposits, Peel River, Yukon, Canada
AuthorCrawford, I; Layton-Matthews, D; Peter, J MORCID logo; Gadd, M GORCID logo; Voinot, A; Leybourne, M I; Pufahl, P
SourceCanadian Mineralogist vol. 59, no. 5, 2021 p. 1085-1110,
Alt SeriesNatural Resources Canada, Contribution Series 20210229
PublisherMineralogical Association of Canada
Mediapaper; digital; on-line
File formatpdf; html
NTS106E/09; 106E/10; 106E/11; 106E/12; 106E/13; 106E/14; 106E/15; 106E/16; 106F/11; 106F/12; 106F/13; 106F/14; 106K/03; 106K/04; 106K/05; 106K/06; 106K/11; 106K/12; 106K/13; 106K/14; 106L; 116H/09; 116H/10; 116H/11; 116H/12; 116H/13; 116H/14; 116H/15; 116H/16; 116I
AreaPeel River
Lat/Long WENS-138.0000 -133.0000 67.0000 65.5000
Subjectseconomic geology; geochemistry; Science and Technology; Nature and Environment; mineral exploration; exploration methods; mineral deposits; sulphide deposits; stratiform deposits; nickel; molybdenum; zinc; gold; ore mineral genesis; mineralization; depositional environment; paleoenvironment; bedrock geology; lithology; sedimentary rocks; black shales; stable isotope studies; sedimentary basins; geochemical analyses; bulk composition; Selwyn Basin; Road River Group; Canol Formation; Richardson Trough; platinum group elements; Phanerozoic; Paleozoic; Devonian; Silurian; Ordovician; Cambrian
Illustrationslocation maps; geoscientific sketch maps; photographs; stratigraphic columns; tables; geochemical profiles; plots; schematic models
ProgramTargeted Geoscience Initiative (TGI-5) Volcanic and sedimentary systems - volcanogenic massive sulphide ore systems
Released2021 10 07
AbstractHyper-enriched black shale (HEBS) deposits in northern Yukon, consist of thin (<10 cm), laterally extensive (tens of thousands of km2) stratiform sulfide mineralization layer(s) that are hyper-enriched in Ni, Mo, Zn, platinum group elements, Re, and Au. The genesis of HEBS deposits and the ambient paleoenvironment in which they formed are the subject of vigorous debate. Non-traditional stable isotopes, particularly molybdenum and thallium, are robust paleoredox indicators and we have employed these isotope systems in this study of Yukon HEBS. Systematic sampling and Mo and Tl isotopic analysis of a continuous 200 m stratigraphic section through the Yukon HEBS mineralization and footwall and hanging-wall strata at the Peel River north and south bank showings (spaced five km apart) give delta-98Mo -1.24 to -0.53 permille and -8.1 to -5.2 epsilon-units for the mineralization and -0.70 to 0.60 permille and -6.5 to -2.0 epsilon-units for the unmineralized strata. These values preclude a hydrothermal origin and strongly suggest that redox processes were responsible for the Yukon HEBS mineralization. The isotopic compositions, together with rare earth element (REE) systematics (REE profile, Y positive anomalies, Ce negative anomalies, and Y/Ho values) and other bulk geochemical redox indicators (Mo, V, Re/Mo, Ni/Co, U/Th, and V/Cr) indicate that the Peel River HEBS mineralization formed because of metal scavenging from seawater in a quiescent, euxinic basinal paleoenvironment.
Summary(Plain Language Summary, not published)
Samples of polymetallic black shales and the enclosing (non-mineralized) host rocks from Peel River, Yukon were subject to novel stable metal isotopic analyses. These analyses revealed critical information about the formation of the metallic deposits at Peel River, indicating that the mineralization was a product of protracted, seawater-derived metal enrichment. This is a major departure from the prevailing hypothesis that invoked hydrothermal discharge at or near the seafloor; however, our new hypothesis accounts for the salient geochemical features preserved in these rocks.

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