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TitlePyrite and pyrrhotite in a prograde metamorphic sequence, Hyland River region, SE Yukon: implications for orogenic gold
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorPadget, C D W; Pattison, D R M; Moynihan, D P; Beyssac, O
SourceTargeted Geoscience Initiative 5: grant program final reports (2018-2020); by Targeted Geoscience Initiative Coordination Office; Geological Survey of Canada, Open File 8755, 2021 p. 169-200, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in Targeted Geoscience Initiative 5: grant program final reports (2018-2020)
RelatedThis publication is related to Genesis of orogenic gold in SE Yukon: linking metamorphic fluid generation with gold and trace element mobility at the pyrite-pyrrhotite transition
File formatpdf
NTS105H/06; 105H/07; 105H/08; 105H/09; 105H/10; 105H/11; 105H/14; 105H/15; 105H/16
AreaHyland River
Lat/Long WENS-129.1306 -128.2794 61.8961 61.2731
Subjectseconomic geology; geochemistry; tectonics; igneous and metamorphic petrology; Science and Technology; Nature and Environment; mineral deposits; gold; vein deposits; ore mineral genesis; mineralization; pyrite; pyrrhotite; tectonic environments; metamorphism, prograde; deformation; metamorphic zones; isograds; pressure-temperature conditions; phase equilibria; modelling; spectrometric analyses; thermal analyses; thermodynamics; fluid dynamics; trace element geochemistry; sulphides; bedrock geology; lithology; metamorphic rocks; metasedimentary rocks; greenschist-amphibolite facies; structural features; faults; folds; anticlinoria; petrographic analyses; mineral assemblages; thin section microscopy; whole rock geochemistry; mass spectrometer analysis; Hyland River Suite; Tay River Suite; Tungsten Suite; Anderson Anticlinorium; Tintina Fault; Yusezyu Formation; Phanerozoic; Mesozoic; Cretaceous; Paleozoic; Devonian; Silurian; Ordovician; Cambrian; Precambrian; Proterozoic
Illustrationslocation maps; geoscientific sketch maps; tables; photographs; photomicrographs; plots; profiles; ternary diagrams; phase diagrams
ProgramTargeted Geoscience Initiative (TGI-5) Knowledge Management Coordination
Released2021 10 27
AbstractThe distribution of pyrite and pyrrhotite is documented within an andalusite-sillimanite type (high-temperature, low-pressure) metasedimentary succession exposed in the Hyland River region of southeastern Yukon, Canada. The following metamorphic zones are recognized: chlorite, biotite, cordierite/staurolite (porphyroblast-in), andalusite, sillimanite, and K-feldspar + sillimanite. Pyrite occurs in the chlorite zone through the biotite zone, while pyrrhotite occurs from the chlorite zone to K-feldspar + sillimanite zone. The pyrite-pyrrhotite transition, therefore, occupies an interval in the chlorite and lower biotite zones that is terminated upgrade by a pyrite-out isograd in the upper part of the biotite zone or lowest grade part of the cordierite/staurolite zone. Pressure and temperature conditions of the rocks were estimated from phase equilibrium modelling and from Raman spectroscopy of carbonaceous material (RSCM) thermometry. Modelling indicates pressures of 3.7-4.1 kbar with temperatures of ~425 °C at the biotite isograd, 560-570 °C for chlorite-out/porphyroblast-in, ~575 °C for andalusite-in, 575-600 °C for the sillimanite isograd, and 645-660 °C at the K-feldspar + sillimanite isograd. RSCM temperatures are greater than or equal to 420 °C in the Chl zone, 500 °C at the Bt isograd, 525-550 °C for porphyroblast-in isograd, ~550 °C at the And isograd, and 580 °C at the Sil isograd. These results suggest the pyrite-pyrrhotite transition occurs from less than or equal to 420°C to ~560 °C. Thermodynamic modelling shows 0.6 wt. % H2O is released during metamorphism over the ~140 °C interval of the pyrite-pyrrhotite transition. The gradual release of fluid in the biotite zone is interpreted to have broadened the pyrite-pyrrhotite transition compared to other studies that predict a small interval of vigorous fluid release associated with volumetric chlorite consumption. Samples from the pyrite-pyrrhotite transition zone contain lower whole rock and pyrite Au values than samples from unmetamorphosed/lower rocks, suggesting that Au was removed from the rock at conditions below the pyrite-pyrrhotite transition (<420 °C). The chlorite zone and higher-grade metamorphic rocks of the Hyland River area do not appear to be a plausible source region for orogenic gold.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques, which will result in more effective targeting of buried mineral deposits. This compendium is the result of the TGI Grant Recipients 2018-2020.

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