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Insights into salty metamorphic fluid evolution from scapolite in the Trans-North China Orogen: Implication for ore genesis.

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Title: Insights into salty metamorphic fluid evolution from scapolite in the Trans-North China Orogen: Implication for ore genesis.
Authors: Qiu, Zhengjie1,2 (AUTHOR), Fan, Hong-Rui1,3,4 (AUTHOR) fanhr@mail.iggcas.ac.cn, Tomkins, Andrew2 (AUTHOR), Brugger, Joël2 (AUTHOR), Etschmann, Barbara2 (AUTHOR), Liu, Xuan5 (AUTHOR), Xing, Yanlu6 (AUTHOR), Hu, Yi7 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Jan2021, Vol. 293, p256-276. 21p.
Subjects: Bromine, Evaporites, Ores, Metamorphic rocks, Orogenic belts, Fluids, Schists
Abstract: • Rock and fluid buffering scapolite formation conditions are identifiable. • Br/Cl ratio of scapolite is a good tracer of deep fluid source and evolution. • Oxidized, S-rich, salty metamorphic fluid buffered by scapolite-rich rocks. • Evaporite-bearing orogenic belt facilitate for the base metal formation. Scapolite is abundant in medium to high grade metamorphic rocks with evaporitic calc-silicate bulk compositions, and because it can be Cl− and SO 4 2− rich, is able to provide a unique view into the evolution of deep brines during orogenic cycles. In the Zhongtiao Mountains, part of the Trans-North China Orogen (TNCO), scapolite occurs in two distinct mineralogical associations; scapolite-I in carbonate-bearing biotite schist and scapolite-II in amphibolites. Initially, metamorphic Cl-rich scapolite-I formed in the schist at low fluid-rock ratio and peak pressure (meionite content = 32–37%, Cl = 2.34–2.75 wt.%). This observation, together with high molar Cl/Br ratios (Cl/Br = 973–2236), implies a halite-bearing evaporitic protolith. During a second stage of scapolite formation in the calc-silicates, rims overgrew scapolite-I with distinct compositions (Me% = 31–32, Cl = 2.64–3.0 wt.%, Cl/Br = 408–892). The lower molar Cl/Br ratios in scapolite-I rims imply that the later fluid was distinctly different to the earlier metamorphic fluid, and may have evolved through a stage of halite saturation induced by phase separation. Halite saturation would drive Br enrichment in the remaining fluid because Cl is preferentially sequestered in halite. Also at this time, amphibolites were subjected to intense open system fluid-rock interactions resulting in formation of scapolite-II (Me% = 30–32, Cl = 2.74–2.97 wt.%, Cl/Br = 291–1426), similar to that of the scapolite-I. S6+/∑S ratios in scapolite obtained via synchrotron XANES indicate that equilibration between fluid and scapolite would buffer the fluid to oxidized conditions, with oxygen fugacity (log f O 2) beyond −15. The scapolitic rocks in this region were thus able to play a key role in controlling the salinity and oxidation state of the deep metamorphic fluid, thereby creating enhanced potential for scavenging of a range of metals within the metamorphic terrane and promoting syn-orogenic hydrothermal ore formation. [ABSTRACT FROM AUTHOR]
Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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DbLabel: Engineering Source
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  Label: Title
  Group: Ti
  Data: Insights into salty metamorphic fluid evolution from scapolite in the Trans-North China Orogen: Implication for ore genesis.
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  Data: <searchLink fieldCode="AR" term="%22Qiu%2C+Zhengjie%22">Qiu, Zhengjie</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Fan%2C+Hong-Rui%22">Fan, Hong-Rui</searchLink><relatesTo>1,3,4</relatesTo> (AUTHOR)<i> fanhr@mail.iggcas.ac.cn</i><br /><searchLink fieldCode="AR" term="%22Tomkins%2C+Andrew%22">Tomkins, Andrew</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Brugger%2C+Joël%22">Brugger, Joël</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Etschmann%2C+Barbara%22">Etschmann, Barbara</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Liu%2C+Xuan%22">Liu, Xuan</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Xing%2C+Yanlu%22">Xing, Yanlu</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Hu%2C+Yi%22">Hu, Yi</searchLink><relatesTo>7</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Jan2021, Vol. 293, p256-276. 21p.
– Name: Subject
  Label: Subjects
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  Data: <searchLink fieldCode="DE" term="%22Bromine%22">Bromine</searchLink><br /><searchLink fieldCode="DE" term="%22Evaporites%22">Evaporites</searchLink><br /><searchLink fieldCode="DE" term="%22Ores%22">Ores</searchLink><br /><searchLink fieldCode="DE" term="%22Metamorphic+rocks%22">Metamorphic rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Orogenic+belts%22">Orogenic belts</searchLink><br /><searchLink fieldCode="DE" term="%22Fluids%22">Fluids</searchLink><br /><searchLink fieldCode="DE" term="%22Schists%22">Schists</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: • Rock and fluid buffering scapolite formation conditions are identifiable. • Br/Cl ratio of scapolite is a good tracer of deep fluid source and evolution. • Oxidized, S-rich, salty metamorphic fluid buffered by scapolite-rich rocks. • Evaporite-bearing orogenic belt facilitate for the base metal formation. Scapolite is abundant in medium to high grade metamorphic rocks with evaporitic calc-silicate bulk compositions, and because it can be Cl− and SO 4 2− rich, is able to provide a unique view into the evolution of deep brines during orogenic cycles. In the Zhongtiao Mountains, part of the Trans-North China Orogen (TNCO), scapolite occurs in two distinct mineralogical associations; scapolite-I in carbonate-bearing biotite schist and scapolite-II in amphibolites. Initially, metamorphic Cl-rich scapolite-I formed in the schist at low fluid-rock ratio and peak pressure (meionite content = 32–37%, Cl = 2.34–2.75 wt.%). This observation, together with high molar Cl/Br ratios (Cl/Br = 973–2236), implies a halite-bearing evaporitic protolith. During a second stage of scapolite formation in the calc-silicates, rims overgrew scapolite-I with distinct compositions (Me% = 31–32, Cl = 2.64–3.0 wt.%, Cl/Br = 408–892). The lower molar Cl/Br ratios in scapolite-I rims imply that the later fluid was distinctly different to the earlier metamorphic fluid, and may have evolved through a stage of halite saturation induced by phase separation. Halite saturation would drive Br enrichment in the remaining fluid because Cl is preferentially sequestered in halite. Also at this time, amphibolites were subjected to intense open system fluid-rock interactions resulting in formation of scapolite-II (Me% = 30–32, Cl = 2.74–2.97 wt.%, Cl/Br = 291–1426), similar to that of the scapolite-I. S6+/∑S ratios in scapolite obtained via synchrotron XANES indicate that equilibration between fluid and scapolite would buffer the fluid to oxidized conditions, with oxygen fugacity (log f O 2) beyond −15. The scapolitic rocks in this region were thus able to play a key role in controlling the salinity and oxidation state of the deep metamorphic fluid, thereby creating enhanced potential for scavenging of a range of metals within the metamorphic terrane and promoting syn-orogenic hydrothermal ore formation. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Geochimica et Cosmochimica Acta is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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    Identifiers:
      – Type: doi
        Value: 10.1016/j.gca.2020.10.030
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 21
        StartPage: 256
    Subjects:
      – SubjectFull: Bromine
        Type: general
      – SubjectFull: Evaporites
        Type: general
      – SubjectFull: Ores
        Type: general
      – SubjectFull: Metamorphic rocks
        Type: general
      – SubjectFull: Orogenic belts
        Type: general
      – SubjectFull: Fluids
        Type: general
      – SubjectFull: Schists
        Type: general
    Titles:
      – TitleFull: Insights into salty metamorphic fluid evolution from scapolite in the Trans-North China Orogen: Implication for ore genesis.
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            NameFull: Qiu, Zhengjie
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            NameFull: Fan, Hong-Rui
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              Text: Jan2021
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              Y: 2021
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              Value: 293
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