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TitleLinks between seawater paleoredox and the formation of sediment-hosted massive sulphide (SHMS) deposits - Fe speciation and Mo isotope constraints from Late Devonian mudstones
AuthorMagnall, J M; Gleeson, S A; Poulton, S W; Gordon, G W; Paradis, S
SourceChemical Geology vol. 490, 2018 p. 45-60, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20160280
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf; html
AreaMacmillan Pass
Lat/Long WENS-132.0000 -130.0000 64.0000 63.0000
Subjectseconomic geology; geochemistry; mineral deposits; sulphide deposits; ore mineral genesis; mineralization; metals; lead; zinc; basin evolution; drillholes; iron geochemistry; isotopic studies; molybdenum geochemistry; uranium geochemistry; phosphorus geochemistry; bedrock geology; lithology; sedimentary rocks; mudstones; olistostromes; structural features; faults; mineral enrichment; alteration; pyritization; sea water geochemistry; hydrothermal systems; submarine hydrothermal vents; burial history; host rocks; Ancestral North America; Selwyn Basin; Earn Group; Portrait Lake Formation; Richardson Trough; sediment-hosted massive sulphide (SHMS) deposits; redox; anoxia; euxinic conditions; total organic content (TOC); chemical traps; Phanerozoic; Paleozoic; Devonian
Illustrationsgeoscientific sketch maps; schematic cross-sections; stratigraphic charts; correlation sections; photographs; tables; geochemical profiles; histograms; geochemical plots; geochronological charts
ProgramTargeted Geoscience Initiative (TGI-4), Sedimentary Exhalative Ore Systems
Released2018 05 09
AbstractMany models of sediment hosted massive sulphide (SHMS) deposit formation invoke basin restriction events that resulted in long-term stagnation and anoxia, in which sulphidic (euxinic) conditions ultimately prevailed. Euxinic conditions are then thought to provide a chemical trap for hydrothermally exhaled base metals. Here, we present Fe speciation and Mo isotope data for organic-rich mudstones from two drill-holes intersecting Upper Devonian strata, deposited along the passive margin of ancestral North America. One drill-hole intersects a 35m thick sequence of SHMS mineralisation, while the other intersects correlative, un-mineralised strata. All samples have high Fe(HR)/Fe(T) values (> 0.38), indicating water-column anoxia. For the majority of samples in the unmineralized drill-hole, the levels of pyritisation fall below the threshold typically used to define euxinic conditions (Fe(PY)/Fe(HR)
Summary(Plain Language Summary, not published)
The paper presents Fe speciation and Mo isotope data for organic-rich mudstones hosting sulphide deposits from two drill-holes done in Late Devonian strata, Selwyn Basin, Yukon. Collectively, the data suggest that local seawater was dominantly ferruginous (anoxic, non-sulfidic), consistent with evidence for relatively low seawater sulfate. In the absence of water column euxinia, high primary productivity and enhanced organic carbon burial were the key variables for promoting sulfate reduction in the sub-surface and trapping metals.