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Copper isotopic evidence of microbial gold fixation in the Mesoarchean Witwatersrand Basin.

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Title: Copper isotopic evidence of microbial gold fixation in the Mesoarchean Witwatersrand Basin.
Authors: Mathur, Ryan1 (AUTHOR) mathur@juniata.edu, Godfrey, Linda2 (AUTHOR), Frimmel, Hartwig E.3,4 (AUTHOR), Yee, Nathan2 (AUTHOR), Mossman, David5 (AUTHOR), Baran, Peter6 (AUTHOR), Valencia, Victor A.7 (AUTHOR) victor.valencia@wsu.edu
Source: Geochimica et Cosmochimica Acta. Jan2025, Vol. 388, p114-126. 13p.
Subjects: Great Oxidation Event, Copper isotopes, Copper, Sedimentary rocks, Hydrothermal alteration
Abstract: A comparison of the copper isotope composition of sedimentary rock strata spanning in age across the Great Oxidation Event (GOE) and that of pyrite, carbon, and native gold from the Mesoarchean Witwatersrand Basin reveal that an oxidative gradient triggered gold precipitation on biologic material, now present in the form of gold-rich carbon seams in the latter. Oxidative redox reactions are known to favor the heavier 65Cu isotope. A sequence of sedimentary rock strata on the Kaapvaal Craton records higher Cu isotope values before the start of the oxidation of the Proterozoic atmosphere in comparison to that of younger transitional-GOE strata. A similar increase in Cu isotope ratios was found in gold within carbon seams in comparison to the Cu isotope ratios in rounded pyrite in auriferous metaconglomerates of the ca. 2.9 Ga basal Central Rand Group. However, the Cu isotope ratios in the post-GOE sedimentary rocks of the Kaapvaal Craton and the pre-GOE native gold in the ca. 2.9 Ga carbon seams record different causes of oxidation. The gold in the carbon seams was not uniformly deposited across the lower Central Rand Basin but in isolated depositional environments. Changes in large-scale atmospheric oxidation, evident by the increase in δ65Cu in the pre and transitional-GOE sedimentary strata in the Kaapvaal Craton, cannot be tied to the elevated Cu isotope values in the carbon seams. Instead, the latter, which are higher than all other measured values (δ65Cu = +2.41 ± 0.24 ‰), mimics Cu isotope fractionation associated with acidophilic bacterial activity. Therefore, the significant difference in Cu isotope values of the carbon seams compared to those of detrital pyrite in the Witwatersrand metaconglomerates could be interpreted as a fingerprint of a microbial redox gradient that might have induced the precipitation of gold, thus having formed the richest known gold province in the world. [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.)
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  Data: Copper isotopic evidence of microbial gold fixation in the Mesoarchean Witwatersrand Basin.
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  Data: <searchLink fieldCode="AR" term="%22Mathur%2C+Ryan%22">Mathur, Ryan</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> mathur@juniata.edu</i><br /><searchLink fieldCode="AR" term="%22Godfrey%2C+Linda%22">Godfrey, Linda</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Frimmel%2C+Hartwig+E%2E%22">Frimmel, Hartwig E.</searchLink><relatesTo>3,4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Yee%2C+Nathan%22">Yee, Nathan</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Mossman%2C+David%22">Mossman, David</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Baran%2C+Peter%22">Baran, Peter</searchLink><relatesTo>6</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Valencia%2C+Victor+A%2E%22">Valencia, Victor A.</searchLink><relatesTo>7</relatesTo> (AUTHOR)<i> victor.valencia@wsu.edu</i>
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  Data: <searchLink fieldCode="JN" term="%22Geochimica+et+Cosmochimica+Acta%22">Geochimica et Cosmochimica Acta</searchLink>. Jan2025, Vol. 388, p114-126. 13p.
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  Data: <searchLink fieldCode="DE" term="%22Great+Oxidation+Event%22">Great Oxidation Event</searchLink><br /><searchLink fieldCode="DE" term="%22Copper+isotopes%22">Copper isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Copper%22">Copper</searchLink><br /><searchLink fieldCode="DE" term="%22Sedimentary+rocks%22">Sedimentary rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Hydrothermal+alteration%22">Hydrothermal alteration</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: A comparison of the copper isotope composition of sedimentary rock strata spanning in age across the Great Oxidation Event (GOE) and that of pyrite, carbon, and native gold from the Mesoarchean Witwatersrand Basin reveal that an oxidative gradient triggered gold precipitation on biologic material, now present in the form of gold-rich carbon seams in the latter. Oxidative redox reactions are known to favor the heavier 65Cu isotope. A sequence of sedimentary rock strata on the Kaapvaal Craton records higher Cu isotope values before the start of the oxidation of the Proterozoic atmosphere in comparison to that of younger transitional-GOE strata. A similar increase in Cu isotope ratios was found in gold within carbon seams in comparison to the Cu isotope ratios in rounded pyrite in auriferous metaconglomerates of the ca. 2.9 Ga basal Central Rand Group. However, the Cu isotope ratios in the post-GOE sedimentary rocks of the Kaapvaal Craton and the pre-GOE native gold in the ca. 2.9 Ga carbon seams record different causes of oxidation. The gold in the carbon seams was not uniformly deposited across the lower Central Rand Basin but in isolated depositional environments. Changes in large-scale atmospheric oxidation, evident by the increase in δ65Cu in the pre and transitional-GOE sedimentary strata in the Kaapvaal Craton, cannot be tied to the elevated Cu isotope values in the carbon seams. Instead, the latter, which are higher than all other measured values (δ65Cu = +2.41 ± 0.24 ‰), mimics Cu isotope fractionation associated with acidophilic bacterial activity. Therefore, the significant difference in Cu isotope values of the carbon seams compared to those of detrital pyrite in the Witwatersrand metaconglomerates could be interpreted as a fingerprint of a microbial redox gradient that might have induced the precipitation of gold, thus having formed the richest known gold province in the world. [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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      – Type: doi
        Value: 10.1016/j.gca.2024.11.018
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      – Code: eng
        Text: English
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        PageCount: 13
        StartPage: 114
    Subjects:
      – SubjectFull: Great Oxidation Event
        Type: general
      – SubjectFull: Copper isotopes
        Type: general
      – SubjectFull: Copper
        Type: general
      – SubjectFull: Sedimentary rocks
        Type: general
      – SubjectFull: Hydrothermal alteration
        Type: general
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      – TitleFull: Copper isotopic evidence of microbial gold fixation in the Mesoarchean Witwatersrand Basin.
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            – D: 01
              M: 01
              Text: Jan2025
              Type: published
              Y: 2025
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