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    Decoupling of Au and As during rapid pyrite crystallization

    Access Status
    Fulltext not available
    Authors
    Wu, Y.
    Evans, Katy
    Hu, S.
    Fougerouse, Denis
    Zhou, M.
    Fisher, L.A.
    Guagliardo, P.
    Li, J.
    Date
    2021
    Type
    Journal Article
    
    Metadata
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    Citation
    Wu, Y. and Evans, K. and Hu, S. and Fougerouse, D. and Zhou, M. and Fisher, L.A. and Guagliardo, P. et al. 2021. Decoupling of Au and As during rapid pyrite crystallization. Geology. 49 (7): pp. 827-831.
    Source Title
    Geology
    DOI
    10.1130/G48443.1
    ISSN
    0091-7613
    Faculty
    Faculty of Science and Engineering
    School
    School of Earth and Planetary Sciences (EPS)
    Funding and Sponsorship
    http://purl.org/au-research/grants/arc/DE190101307
    URI
    http://hdl.handle.net/20.500.11937/91629
    Collection
    • Curtin Research Publications
    Abstract

    Gold (Au) is largely hosted by pyrite in a variety of hydrothermal systems, but the incorporation of Au into pyrite under disequilibrium conditions remains poorly understood. We integrate synchrotron X-ray fluorescence microscopy, electron backscatter diffraction, nanoscale secondary ion mass spectrometry, and laser ablation–multicollector–inductively coupled plasma–mass spectrometry to constrain the processes that sequester Au into zoned pyrite in the hydrothermal cement of breccia ores from the world-class Daqiao orogenic Au deposit, central China. Euhedral pyrite cores with oscillatory and sector zoning, variable δ34S values, and lower Au-As contents than the mantles are attributed to crystallization during oxidation of metal-depleted ore fluids with local variation in fluid conditions. The isotopically uniform colloform mantles are formed by pyrite crystallites separated by low-angle boundaries and are characterized by unusual decoupling of Au and As. Mantle formation is attributed to rapid disequilibrium precipitation from a metal-rich FeS2-supersaturated fluid. Incorporation of Au into the pyrite mantles was facilitated by abundant lattice defects produced by rapid nucleation. Gold-As–poor pyrite rims were deposited from an evolved ore fluid or other metal-depleted fluids. These results show that chemical variations recorded by fine layering within minerals can provide valuable insights into disequilibrium mass transfer and ore formation. The decoupling between Au and As in pyrite mantles indicates that As is not always a reliable proxy for Au enrichment in rapidly crystallized porous pyrite.

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