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Mo isotope composition in Mo-rich high- and low-T hydrothermal systems from the Swiss Alps

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Title: Mo isotope composition in Mo-rich high- and low-T hydrothermal systems from the Swiss Alps
Authors: Greber, Nicolas D.1,2 greber@geo.unibe.ch, Hofmann, Beda A.2, Voegelin, Andrea R.1, Villa, Igor M.1,3, Nägler, Thomas F.1
Source: Geochimica et Cosmochimica Acta. Nov2011, Vol. 75 Issue 21, p6600-6609. 10p.
Subjects: Molybdenum isotopes, Metal complexes, Molybdenite, Temperature effect, Precipitation (Chemistry), High temperatures
Geographic Terms: Alps, Swiss (Switzerland), Switzerland
Abstract: Abstract: We analyzed the molybdenum (Mo) isotope compositions (IC) of 59 samples from two molybdenite mineralizations (Alpjahorn and Grimsel) and from a Mo-rich hydrothermal breccia (Grimsel) from the Aar Massif, Switzerland. The formation temperature of the Late Paleozoic Mo mineralizations (300–600°C) is much higher than that of the Pliocene breccia (100–160°C). The Mo IC of the molybdenites varies over 1.35‰. Even in a single hand specimen it spans 0.45‰, indicating that fractionation processes during molybdenite precipitation can vary on a cm scale. The Mo IC of most molybdenites analyzed here are significantly heavier than that of the host rock (δ 98/95Mo=(0.05±0.1)‰) and show a bimodal distribution centered around δ 98/95Mo≈1.1‰ and 0.2‰. This result rules out single stage Rayleigh fractionation as the relevant formation mechanism and instead, redox variations are suggested to be a main factor controlling the Mo IC of the studied high-temperature Mo deposits. The range of the Mo IC in one single deposit, the Alpjahorn, overlaps with the variation range of almost all other published values for Mo IC in Mo deposits. Compared to the molybdenites, the breccia shows an even wider variation of 3.0‰ (δ 98/95Mo between −1.6‰ and +1.4‰). In contrast to the high-T molybdenite deposits, here the Mo was transported via oxidized surface waters into the breccia system, where it was reduced and precipitated. This indicates that oxidation and reduction of Mo complexes may lead to highly variable Mo IC in hydrothermal systems. [Copyright &y& Elsevier]
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.)
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DbLabel: Engineering Source
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  Data: Mo isotope composition in Mo-rich high- and low-T hydrothermal systems from the Swiss Alps
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  Data: <searchLink fieldCode="AR" term="%22Greber%2C+Nicolas+D%2E%22">Greber, Nicolas D.</searchLink><relatesTo>1,2</relatesTo><i> greber@geo.unibe.ch</i><br /><searchLink fieldCode="AR" term="%22Hofmann%2C+Beda+A%2E%22">Hofmann, Beda A.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Voegelin%2C+Andrea+R%2E%22">Voegelin, Andrea R.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Villa%2C+Igor+M%2E%22">Villa, Igor M.</searchLink><relatesTo>1,3</relatesTo><br /><searchLink fieldCode="AR" term="%22Nägler%2C+Thomas+F%2E%22">Nägler, Thomas F.</searchLink><relatesTo>1</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Nov2011, Vol. 75 Issue 21, p6600-6609. 10p.
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  Data: <searchLink fieldCode="DE" term="%22Molybdenum+isotopes%22">Molybdenum isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Metal+complexes%22">Metal complexes</searchLink><br /><searchLink fieldCode="DE" term="%22Molybdenite%22">Molybdenite</searchLink><br /><searchLink fieldCode="DE" term="%22Temperature+effect%22">Temperature effect</searchLink><br /><searchLink fieldCode="DE" term="%22Precipitation+%28Chemistry%29%22">Precipitation (Chemistry)</searchLink><br /><searchLink fieldCode="DE" term="%22High+temperatures%22">High temperatures</searchLink>
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  Data: <searchLink fieldCode="DE" term="%22Alps%2C+Swiss+%28Switzerland%29%22">Alps, Swiss (Switzerland)</searchLink><br /><searchLink fieldCode="DE" term="%22Switzerland%22">Switzerland</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Abstract: We analyzed the molybdenum (Mo) isotope compositions (IC) of 59 samples from two molybdenite mineralizations (Alpjahorn and Grimsel) and from a Mo-rich hydrothermal breccia (Grimsel) from the Aar Massif, Switzerland. The formation temperature of the Late Paleozoic Mo mineralizations (300–600°C) is much higher than that of the Pliocene breccia (100–160°C). The Mo IC of the molybdenites varies over 1.35‰. Even in a single hand specimen it spans 0.45‰, indicating that fractionation processes during molybdenite precipitation can vary on a cm scale. The Mo IC of most molybdenites analyzed here are significantly heavier than that of the host rock (δ 98/95Mo=(0.05±0.1)‰) and show a bimodal distribution centered around δ 98/95Mo≈1.1‰ and 0.2‰. This result rules out single stage Rayleigh fractionation as the relevant formation mechanism and instead, redox variations are suggested to be a main factor controlling the Mo IC of the studied high-temperature Mo deposits. The range of the Mo IC in one single deposit, the Alpjahorn, overlaps with the variation range of almost all other published values for Mo IC in Mo deposits. Compared to the molybdenites, the breccia shows an even wider variation of 3.0‰ (δ 98/95Mo between −1.6‰ and +1.4‰). In contrast to the high-T molybdenite deposits, here the Mo was transported via oxidized surface waters into the breccia system, where it was reduced and precipitated. This indicates that oxidation and reduction of Mo complexes may lead to highly variable Mo IC in hydrothermal systems. [Copyright &y& Elsevier]
– 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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      – Type: doi
        Value: 10.1016/j.gca.2011.08.034
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      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 10
        StartPage: 6600
    Subjects:
      – SubjectFull: Molybdenum isotopes
        Type: general
      – SubjectFull: Metal complexes
        Type: general
      – SubjectFull: Molybdenite
        Type: general
      – SubjectFull: Temperature effect
        Type: general
      – SubjectFull: Precipitation (Chemistry)
        Type: general
      – SubjectFull: High temperatures
        Type: general
      – SubjectFull: Alps, Swiss (Switzerland)
        Type: general
      – SubjectFull: Switzerland
        Type: general
    Titles:
      – TitleFull: Mo isotope composition in Mo-rich high- and low-T hydrothermal systems from the Swiss Alps
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              M: 11
              Text: Nov2011
              Type: published
              Y: 2011
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