Details
| Original language | English |
|---|---|
| Pages (from-to) | 499-519 |
| Number of pages | 21 |
| Journal | ACS Earth and Space Chemistry |
| Volume | 8 |
| Issue number | 3 |
| Early online date | 19 Jan 2024 |
| Publication status | Published - 21 Mar 2024 |
Abstract
To improve our understanding of the formation of sedimentary copper deposits, the reaction of cuprite with 0.2 m HAc-KAc or pure H2O solutions is studied systematically at 100-250 °C and 5-30 MPa. The experiments were carried out for periods of up to 72 h in a Parr autoclave, allowing for the in situ sampling of the fluid phase. The experiments conducted in this study demonstrate that cuprite (Cu2O) underwent a series of changes: (i) simple dissolution, (ii) Cu(I) disproportionation to native Cu and Cu(II), and (iii) subsequent oxidation into tenorite (CuO). In pure water, only (i) and (ii) steps can be discerned, whereas all three processes have been observed in an acetate-bearing system. In HAc-KAc solutions, the maximum dissolved Cu content correlates inversely with temperature, i.e., 378 to 168 μg/g at 100 and 200 °C, respectively. However, equilibrium has not been reached in our experiments and these values may be treated as minimum cuprite solubility. In situ Cu isotope analyses have been carried out by laser ablation combined with a multicollector inductively coupled plasma-mass spectrometer. The data imply that copper isotope fractionation during cuprite replacement reactions is small. Both the microscopic observations on cross sections and the analytical data support the idea that the mineral replacement reaction is controlled by a coupled dissolution-reprecipitation (CDR) mechanism. This applies to both the deposition of metallic copper and the formation of tenorite. As suggested by the formation of pore spaces in the deposited layers, only a portion of the dissolved copper is redeposited directly in situ. The isotopic analyses of the solution and solid phases show that the partial transfer of copper into the surrounding solution is not associated with a significant isotopic effect, e.g., a measured difference between Cu and Cu2O is within 0.32 ± 0.06‰. Our study indicates that acetate plays a dual role in copper transport and deposition. On one hand, the presence of acetate strongly enhances the Cu content in solution up to 400 μg/g, implying that acetate complexation can be responsible for metal transport in hydrothermal fluids. On the other hand, decarboxylation of acetate substantially decreases the dissolved Cu and aids the precipitation of tenorite. This may lead to the co-occurrence of Cu-bearing minerals with different oxidation valence states at low temperatures in a variety of geological settings such as supergene hydrothermal systems.
Keywords
- acetate, coupled dissolution and reprecipitation, Cu isotope fractionation, Cu(I) disproportion, cuprite, native copper, tenorite
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Atmospheric Science
- Earth and Planetary Sciences(all)
- Space and Planetary Science
Sustainable Development Goals
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In: ACS Earth and Space Chemistry, Vol. 8, No. 3, 21.03.2024, p. 499-519.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Experimental Study on the Reaction of Cuprite (Cu2O) with Acetate-Bearing Hydrothermal Fluids at 100-250 °C and 5-30 MPa
AU - Qi, Dongmei
AU - Behrens, Harald
AU - Lazarov, Marina
AU - Botcharnikov, Roman
AU - Zhang, Chao
AU - Ostertag-Henning, Christian
AU - Weyer, Stefan
N1 - Funding Information: This research was supported by the National Natural Science Foundation of China (41972055, 42002059), Open Project of Key Laboratory, Xinjiang Uygur Autonomous Region, China (2023D04067), the Key Research and Development Program of Xinjiang Uygur Autonomous Region, China (2022B03015-2), and the German Academic Exchange Service (DAAD-57076462). We thank U. Kroll, A. Reimer, and J. Feige for their technical support and D. Graskamp and J. Poggenburg for the gas chromatographic analyses. We are grateful to three anonymous reviewers, and the Associate Editor Sumit Chakraborty for their constructive comments and revisions that greatly improved the quality of the manuscript.
PY - 2024/3/21
Y1 - 2024/3/21
N2 - To improve our understanding of the formation of sedimentary copper deposits, the reaction of cuprite with 0.2 m HAc-KAc or pure H2O solutions is studied systematically at 100-250 °C and 5-30 MPa. The experiments were carried out for periods of up to 72 h in a Parr autoclave, allowing for the in situ sampling of the fluid phase. The experiments conducted in this study demonstrate that cuprite (Cu2O) underwent a series of changes: (i) simple dissolution, (ii) Cu(I) disproportionation to native Cu and Cu(II), and (iii) subsequent oxidation into tenorite (CuO). In pure water, only (i) and (ii) steps can be discerned, whereas all three processes have been observed in an acetate-bearing system. In HAc-KAc solutions, the maximum dissolved Cu content correlates inversely with temperature, i.e., 378 to 168 μg/g at 100 and 200 °C, respectively. However, equilibrium has not been reached in our experiments and these values may be treated as minimum cuprite solubility. In situ Cu isotope analyses have been carried out by laser ablation combined with a multicollector inductively coupled plasma-mass spectrometer. The data imply that copper isotope fractionation during cuprite replacement reactions is small. Both the microscopic observations on cross sections and the analytical data support the idea that the mineral replacement reaction is controlled by a coupled dissolution-reprecipitation (CDR) mechanism. This applies to both the deposition of metallic copper and the formation of tenorite. As suggested by the formation of pore spaces in the deposited layers, only a portion of the dissolved copper is redeposited directly in situ. The isotopic analyses of the solution and solid phases show that the partial transfer of copper into the surrounding solution is not associated with a significant isotopic effect, e.g., a measured difference between Cu and Cu2O is within 0.32 ± 0.06‰. Our study indicates that acetate plays a dual role in copper transport and deposition. On one hand, the presence of acetate strongly enhances the Cu content in solution up to 400 μg/g, implying that acetate complexation can be responsible for metal transport in hydrothermal fluids. On the other hand, decarboxylation of acetate substantially decreases the dissolved Cu and aids the precipitation of tenorite. This may lead to the co-occurrence of Cu-bearing minerals with different oxidation valence states at low temperatures in a variety of geological settings such as supergene hydrothermal systems.
AB - To improve our understanding of the formation of sedimentary copper deposits, the reaction of cuprite with 0.2 m HAc-KAc or pure H2O solutions is studied systematically at 100-250 °C and 5-30 MPa. The experiments were carried out for periods of up to 72 h in a Parr autoclave, allowing for the in situ sampling of the fluid phase. The experiments conducted in this study demonstrate that cuprite (Cu2O) underwent a series of changes: (i) simple dissolution, (ii) Cu(I) disproportionation to native Cu and Cu(II), and (iii) subsequent oxidation into tenorite (CuO). In pure water, only (i) and (ii) steps can be discerned, whereas all three processes have been observed in an acetate-bearing system. In HAc-KAc solutions, the maximum dissolved Cu content correlates inversely with temperature, i.e., 378 to 168 μg/g at 100 and 200 °C, respectively. However, equilibrium has not been reached in our experiments and these values may be treated as minimum cuprite solubility. In situ Cu isotope analyses have been carried out by laser ablation combined with a multicollector inductively coupled plasma-mass spectrometer. The data imply that copper isotope fractionation during cuprite replacement reactions is small. Both the microscopic observations on cross sections and the analytical data support the idea that the mineral replacement reaction is controlled by a coupled dissolution-reprecipitation (CDR) mechanism. This applies to both the deposition of metallic copper and the formation of tenorite. As suggested by the formation of pore spaces in the deposited layers, only a portion of the dissolved copper is redeposited directly in situ. The isotopic analyses of the solution and solid phases show that the partial transfer of copper into the surrounding solution is not associated with a significant isotopic effect, e.g., a measured difference between Cu and Cu2O is within 0.32 ± 0.06‰. Our study indicates that acetate plays a dual role in copper transport and deposition. On one hand, the presence of acetate strongly enhances the Cu content in solution up to 400 μg/g, implying that acetate complexation can be responsible for metal transport in hydrothermal fluids. On the other hand, decarboxylation of acetate substantially decreases the dissolved Cu and aids the precipitation of tenorite. This may lead to the co-occurrence of Cu-bearing minerals with different oxidation valence states at low temperatures in a variety of geological settings such as supergene hydrothermal systems.
KW - acetate
KW - coupled dissolution and reprecipitation
KW - Cu isotope fractionation
KW - Cu(I) disproportion
KW - cuprite
KW - native copper
KW - tenorite
UR - http://www.scopus.com/inward/record.url?scp=85183013368&partnerID=8YFLogxK
U2 - 10.1021/acsearthspacechem.3c00254
DO - 10.1021/acsearthspacechem.3c00254
M3 - Article
AN - SCOPUS:85183013368
VL - 8
SP - 499
EP - 519
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 3
ER -