Incipient metal and sulfur extraction during melting of metasomatised mantle

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dc.contributor.authorRielli, Aen_AU
dc.contributor.authorTomkins, AGen_AU
dc.contributor.authorNebel, Oen_AU
dc.contributor.authorBrugger, Jen_AU
dc.contributor.authorEtschmann, BEen_AU
dc.contributor.authorEvans, KAen_AU
dc.contributor.authorWykes, JLen_AU
dc.contributor.authorVasilyev, Pen_AU
dc.contributor.authorPaterson, DJen_AU
dc.date.accessioned2025-01-10T01:13:52Zen_AU
dc.date.available2025-01-10T01:13:52Zen_AU
dc.date.issued2022-12-01en_AU
dc.date.statistics2024-11-28en_AU
dc.description.abstractA long-standing debate on the genesis of magmatic-hydrothermal Cu-Au deposits is whether the elevated oxygen fugacity (fO2) and metal endowment of their parental magmas are inherited from the mantle source or acquired during fractionation within the crust. This debate is built mainly on the composition of magmas emplaced into the upper crust that underwent varying degrees of differentiation and assimilation, which inevitably obscure their relationship to mantle processes. Here, we approach this debate from a new perspective by studying melt generation directly in mantle samples. This opportunity is provided by xenoliths from Lake Bullen Merri (Australia), which record partial melting of a pre-existing metasomatic assemblage. Melting occurred when the xenoliths were incorporated in hot basalts and carried towards the surface, where quenching upon eruption froze-in the melt-restite relationships. These samples preserve patches and interconnected networks of silicate glass along grain boundaries, caught in the act of undergoing melting and melt extraction. Melting consumed mainly metasomatic hornblende, phlogopite, and clinopyroxene, generating shoshonitic compositions that can be sulfide-rich, or have negligible sulfide content. We use four independent approaches to estimate the fO2 of glass, including sulfide content, oxybarometry based on spinel-olivine pairs, Fe3+/Fetot of glass determined by synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, and Cu/Fe ratio of the sulfide assemblage. Sulfide-rich melt had higher fO2 compared to the sulfide-poor melt, and these characteristics were inherited from the metasomatic assemblage; the oxidation state of the melts controlled their sulfide content. Subduction-modified mantle can thus store elevated oxidation state, sulfur, and metal content for hundreds of millions of years before low-degree partial melting generates oxidised, sulfur- and metal-enriched high-K/shoshonitic melts in post-collisional settings. © 2022 Elsevier B.V.en_AU
dc.description.sponsorshipWe thank A. Berry for providing the glass standards. Part of this research was undertaken on the X-ray Fluorescence Microscopy beamline at the Australian Synchrotron, part of ANSTO. A.R. acknowledges the Australian Government Research Training Program Scholarship and the funding support from the International Association of GeoChemistry (IAGC) through a PhD Student Research Grant. A.G.T. acknowledges ARC Future Fellowship (FT180100533). The authors thank C.-T. Lee and two anonymous reviewers for constructive comments which helped to improve the manuscript.en_AU
dc.identifier.articlenumber117850en_AU
dc.identifier.citationRielli, A., Tomkins, A. G., Nebel, O., Brugger, J., Etschmann, B., Evans, K. A., Wykes, J. L., Vasilyev, P., & Paterson, D. J. (2022). Incipient metal and sulfur extraction during melting of metasomatised mantle. Earth and Planetary Science Letters, 599, 117850. doi:10.1016/j.epsl.2022.117850en_AU
dc.identifier.issn0012-821Xen_AU
dc.identifier.journaltitleEarth and Planetary Science Lettersen_AU
dc.identifier.urihttps://doi.org/10.1016/j.epsl.2022.117850en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15892en_AU
dc.identifier.volume599en_AU
dc.languageEnglishen_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectMetalsen_AU
dc.subjectSulfuren_AU
dc.subjectExtractionen_AU
dc.subjectMeltingen_AU
dc.subjectEarth mantleen_AU
dc.subjectLakesen_AU
dc.subjectGlass industryen_AU
dc.subjectMineralsen_AU
dc.subjectOxidationen_AU
dc.subjectGlassen_AU
dc.subjectCopperen_AU
dc.subjectOxygenen_AU
dc.subjectSynchrotronsen_AU
dc.subjectSpinelsen_AU
dc.titleIncipient metal and sulfur extraction during melting of metasomatised mantleen_AU
dc.typeJournal Articleen_AU
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