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TitlePetrography, mineralogy and initial fluid inclusion results from the Jason, Tom, and Nidd SEDEX deposits, Macmillan Pass District, Yukon
AuthorMagnall, J M; Gleeson, S A; Paradis, S; Blamey, N J F
SourceGeological Survey of Canada, Open File 7599, 2017, 31 pages, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
ProvinceYukon; British Columbia
NTS95A; 95B; 95C; 95D; 95E; 95F; 95G; 95H; 95I; 95J; 105F; 105G; 105H; 105I; 105J; 105K
AreaCanadian Cordillera; Macmillan Pass
Lat/Long WENS-133.0000 -128.0000 63.0000 61.0000
Subjectseconomic geology; geochemistry; igneous and metamorphic petrology; mineralogy; mineral deposits; sedimentary ore deposits; stratiform deposits; volcanic exhalitive zone; base metals; zinc; lead; ore mineral genesis; mineralization; hydrothermal systems; volcanic vents; sulphides; fluid inclusions; drill core analyses; petrographic analyses; thermal analyses; mass spectrometer analysis; stable isotope studies; carbon isotopes; oxygen isotopes; sulphur isotope ratios; gas analyses; carbon dioxide; nitrogen; argon; helium; fluid flow; stockworks; veins; carbonates; alteration; iron; pyrite; gangue minerals; phase relations; magmatism; temperature; salinity; sodium chloride; sphalerite; galena; weathering; bedrock geology; lithology; sedimentary rocks; mudstones; sandstones; conglomerates; shales; siltstones; clastics; paragenesis; Selwyn Basin; Earn Group; Portrait Lake Formation; Macmillan Pass Member; Tom Deposit; Nidd Deposit; Jason Deposit; sedimentary exhalative deposits (SEDEX); vent complexes; microthermometry; Phanerozoic; Paleozoic; Devonian; Silurian; Cambrian
Illustrationsgeoloigcal sketch maps; stratigraphic charts; photographs; photomicrographs; charts; tables; geochemical plots; histograms
ProgramTargeted Geoscience Initiative (TGI-5), Volcanic and sedimentary systems
Released2017 06 13
AbstractSediment-hosted base metal mineralization in the Selwyn Basin occurs during 3 time intervals in the Cambrian, Silurian and Late Devonian, coeval with magmatic episodes. At Macmillan Pass, the Tom, Jason and Nidd showings are hosted by Upper Devonian sediments and have well preserved vent complexes beneath overlying bedded sulphides (Tom, Jason).
Core was sampled from the vent complexes at Tom, Jason, and Nidd. Detailed petrography (reflected and transmitted light and cathodoluminescence), was conducted to characterize the mineralogy within the vent complex, and the relationship of fluid inclusion bearing mineral phases to base metal sulphides. Microthermometry (Tom and Nidd) and bulk incremental fast scan gas mass spectrometry (Nidd) was performed on fluid inclusion samples. Carbon, oxygen and sulphur isotopes were analysed on mineral separates to determine the source of these components in each system.
The petrography indicates that for all three localities, fluid flow in the vent can be split in two distinct stages. Stage 1 is dominated by extensive stock-work style iron carbonate veining, along with destructive carbonate and pyrite alteration. Base-metal sulphides are deposited during Stage 2, in association with a volumetrically minor gangue assemblage (siderite, quartz ± barite, barytocalcite and quartz). Initial fluid inclusion results indicate the presence of a CO2-bearing assemblage at Nidd, which has preserved evidence of phase immiscibility. The N2-Ar-He bulk composition of these samples suggests the involvement of a deep calc-alkaline magmatic reservoir. Microthermometric results from Tom indicate the presence of low (120-130°C) and intermediate (170-235°C) temperature fluids; only one salinity measurement was obtained from the intermediate temperature fluid, which yielded a value of 7.9 wt.% NaCl. Delta-34S (VCDT) values have a broad range from -12.6 permille to 20.5 permille, and two sphalerite-galena pairs suggest equilibrium fractionation may have occurred between 366-388°C; delta-13C (V-PDB) have a restricted range from -0.5 permille to -8.6 permille, apart from two groups of outliers that are either highly negative (-20 permille and -12.4 permille) or highly positive (13.3 permille and 14.3 permille); delta-18O (V-SMOW) range between 13.6 permille to 20.5 permille.
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. Samples from the vent complexes and the stratabound sulphides of the sediment-hosted base metal Tom, Jason, and Nidd deposits are studied to define their mineral composition, the sources of sulphur, carbon and oxygen, and the composition of the mineralizing fluid(s) that generated these deposits. Two mineralizing stages are defined: 1) stockwork iron carbonate veining with destructive carbonate and pyrite alteration; and 2) base metal mineralization. Initial geochemistry indicates the presence of low (120-130°C) and intermediate (170-235°C) temperature fluids of moderate salinity (~7.9 wt.% NaCl).