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TitleSEDEX mineralisation, Macmillan Pass (Yukon): petrography, mineralogy and bulk geochemistry of the Tom and Nidd deposits
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AuthorMagnall, J M; Gleeson, S A; Paradis, S
SourceGeological Survey of Canada, Open File 7457, 2014, 37 pages, https://doi.org/10.4095/293105 (Open Access)
Image
Year2014
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia; Yukon
NTS105F; 105G; 105H; 105I; 105J; 105K; 105N; 105O; 105P
Areasoutheastern British Columbia; Howard's Pass; Gataga; MacMillan's Pass
Lat/Long WENS-133.0000 -128.0000 63.0000 61.0000
Subjectseconomic geology; mineralogy; geochemistry; sedimentary ore deposits; mineral deposits; zinc; lead; mineralization; paragenesis; sedimentary basins; basin analysis; basin formation; morphology; alteration; deformation; sedimentary rocks; shales; silts; conglomerates; mudstones; petrography; electron probe analyses; trace element analyses; trace element geochemistry; major element analyses; major element geochemistry; minor element geochemistry; Tom Deposit; Nidd Deposit; Jason Deposit; Selwyn Basin; Earn Group; Lake Formation; Macmillan Pass Member; SEDEX deposits; Paleozoic; Cambrian; Silurian; Proterozoic; Devonian
Illustrationslocation maps; stratigraphic columns; photographs; tables; ternary diagrams; plots; photomicrographs
ProgramSedimentary Exhalative Ore Systems, Targeted Geoscience Initiative (TGI-4)
Released2014 01 23
AbstractSedimentary exhalative (SEDEX) deposits formed in the Selwyn Basin coeval with 3 magmatic episodes in the Cambrian, Silurian and Late Devonian. At Macmillan Pass, the Tom, Jason and Nidd deposits are hosted by Late Devonian strata and have well preserved vent complexes beneath overlying stratabound sulphide and sulphate facies.
Drill core has been sampled from the vent complexes at Nidd and Tom. Detailed petrography (reflected and transmitted light, cathodoluminescence, back-scatter electron imaging) has developed a paragenesis and, at Tom, critically assessed textural relationships between the vent facies and the overlying stratabound sulphide and sulphate facies. The mineral chemistry of major phases has been determined from quantitative electron microprobe analyses in the vent and stratabound ore from Tom. The geochemical signatures of the hydrothermal vents (Tom, Nidd) are comprehensively characterized through bulk rock geochemical analysis of vent facies material for major, minor and rare earth elements.
Detailed petrography has highlighted subtle feeder veins that preferentially replaced laminations leading to the formation of pseudo-bedded sulphide-rich layers in the grey facies rocks at Tom. This provides an important link between the vent and the overlying stratabound facies. Within the vent, main stage sulphide minerals succeeded destructive carbonate alteration, and were overprinted by pulses of sulphide minerals coeval with, and replacing, siderite, Ba-carbonate and barite. Aside from the ore components (Pb, Zn and Ba), vent facies samples are enriched above upper crustal values in Au, Ag, As, Cd, Cu, Ge, In, Mo, Sb, Sn and Ta. Notably, Au in two samples from Tom exceeds 100 ppb. Rare-earth element profiles broadly track the composition of un-mineralised shale in the area but have a positive Eu anomaly, likely attributable to the presence of Ba feldspar in the samples. This highlights the potential importance of the compositions of underlying strata in controlling the geochemistry of the hydrothermal fluids.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Tom, Jason and Nidd Sedimentary exhalative (SEDEX) deposits at Macmillan Pass (Yukon) are hosted by Late Devonian sediments and they have well preserved vent complexes (Nidd, Tom and Jason) beneath overlying bedded sulphides (Tom and Jason). Drill core has been sampled from the vent complexes (Nidd and Tom) and bedded sulphides (Tom). Detailed petrography of the vent facies and overlying bedded sulphides has highlighted examples of subtle feeder veins preferentially replacing laminations leading to the formation of pseudo-bedded sulphide-rich layers in the grey facies ore at Tom. Aside from the ore components (Pb, Zn and Ba), the vent facies samples have enrichments above upper crustal values in Au, Ag, As, Cd, Cu, Ge, In, Mo, Sb, Sn and Ta.
GEOSCAN ID293105