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TitleSEDEX Deposits in the Cordillera: Current concepts on their geology, genesis, and exploration
AuthorParadis, S; Goodfellow, W
SourceGeological Survey of Canada, Open File 7144, 2012, 11 pages, (Open Access)
PublisherNatural Resources Canada
MeetingProspectors and Developers Association of Canada (PDAC), International Convention, Trade Show and Investors Exchange; Toronto; CA; March 6th, 2012
Documentopen file
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia; Yukon
NTS82F; 82G; 82J; 82K; 82M; 82N; 94D; 94E; 94L; 104H; 104I; 105A; 105B; 105C; 105E; 105F; 105G; 105J; 105K; 105L; 105M; 105N
Areasoutheastern British Columbia; Howard's Pass; Gataga; MacMillan's Pass
Lat/Long WENS-121.0000 -114.0000 53.0000 49.0000
Lat/Long WENS-130.0000 -125.0000 59.0000 56.0000
Lat/Long WENS-138.0000 -128.0000 64.0000 60.0000
Subjectseconomic geology; sedimentary ore deposits; mineral deposits; zinc; lead; mineralization; tectonic setting; sedimentary basins; basin analysis; basin formation; morphology; alteration; Sullivan Deposit; North Star Deposit; Kootenay King Deposit; Selwyn Basin; Faro Deposit; Grum Deposit; Vangorda Deposit; DY Deposit; Swim Deposit; Howard's Pass deposits; Kechika Trough; Cirque Deposit; Driftpile Deposit; Akie Deposit; Tom Deposit; Jason Deposit; SEDEX deposits; Paleozoic; Cambrian; Silurian; Proterozoic; Devonian
Illustrationslocation maps; block diagrams; photographs; stratigraphic columns; cross-sections
ProgramTargeted Geoscience Initiative (TGI-3), 2005-2010, Southern Cordillera TGI-3
ProgramTargeted Geoscience Initiative (TGI-4), Sedimentary Exhalative Ore Systems
Released2012 09 20
SEDEX (SEDimentary EXhalative) deposits are important resources of Zn and Pb. In addition to Zn and Pb, other potentially economic commodities are: Ag, Au, Cu, Cd, Sb, Sn, and barite. Major metallogenic districts in the Canadian Cordillera that host SEDEX deposits are:
Mesoproterozoic Sullivan district in southeastern British Columbia, which hosts the world-class Sullivan deposit and other smaller deposits such as North Star and Kootenay King.
Late Cambrian Anvil district in the Selwyn Basin of central Yukon, which hosts the Faro, Grum, Vangorda, DY, and Swim deposits.
Early Silurian Howard's Pass district in the Selwyn Basin of the northeastern Yukon, which hosts the world-class Howard's Pass deposits (XY, Brodel, HC, Don, Anniv, OP, Pelly North).
Late Devonian Gataga district of the Kechika Trough (southern extension of Selwyn Basin) in northeastern British Columbia, which hosts the Cirque, Driftpile, and Akie deposits.
Late Devonian MacMillan's Pass district in the Selwyn Basin of northeastern Yukon, which hosts the Tom and Jason deposits.
The Sullivan deposit and two deposits of the Anvil district (i.e., Faro and Grum) are past-producers. Other deposits have seen or are undergoing intensive exploration and development work (e.g., Howard's Pass, MacMillan's Pass, Drifpile, Akie, and Cirque).
SEDEX deposits are defined as being predominantly composed of Zn and Pb hosted in sphalerite and galena that were deposited at or near the seafloor from basinal metalliferous fluids discharged into rift-controlled anoxic sedimentary basins. They consist of vent-distal and vent-proximal facies. The former is composed of interbedded sphalerite, galena, iron sulphides and clastic sediments, and the latter of variably veined, infilled and replaced bedded sulphides.
Cordilleran SEDEX deposits occur in intracratonic and epicratonic rifts within reduced marine basins. The architecture of sedimentary basins is characterized by rapid syn-rift subsidence and clastic sedimentation that is overlain by fine-grained clastic and carbonate sediments that accumulated during a post-rift sedimentation phase. Marine turbidites with interlayered mafic sills of the syn-rift phase host the Sullivan deposit, whereas organic-rich carbonaceous shales/mudstones of the post-rift phase host deposits of the Selwyn Basin. The deposits most likely formed at or just below the sea floor from warm to hot (~100° up to 300°C), saline (10 to 20% NaCl equiv.) basinal brines that ascended along basin-controlling synsedimentary faults. Deposition and sequestration of metals occurred by precipitation of sulphide minerals as a result of mixing of metal-transporting brine with locally derived H2S produced by bacterial (and perhaps thermochemical) reduction of local seawater sulphate.
Important exploration vectors include the presence of:
Deep-seated synsedimentary faults expressed as abrupt changes in facies and isopachs, intraformational breccias, slumps, debris flows, and fault scarp talus.
Recognition of local fault-controlled paleoenvironments that represent restricted and stratified basins with anoxic H2S-rich bottom waters.
Organic-rich sediments with >1% Corg.
Anomalous concentrations of redox-sensitive trace elements (e.g., V, Tl, Cd, U, V/Mo, and Re/Mo).
Widespread hydrothermal alteration (muscovite, carbonates, and silicates).
Laterally and vertically extensive distal sediments that are mineralogically and chemically zoned around seafloor vents.