Email this article Separation of salts NaCl and CaCl2 in aqueous-carbon dioxide deep fluids
- Authors: Ivanov M.V.1, Bushmin S.A.1
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Affiliations:
- Institute of Precambrian Geology and Geochronology RAS
- Issue: Vol 32, No 2 (2024)
- Pages: 245-254
- Section: Articles
- URL: https://journals.rcsi.science/0869-5903/article/view/259775
- DOI: https://doi.org/10.31857/S0869590324020076
- EDN: https://elibrary.ru/DCGBLX
- ID: 259775
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Abstract
The possibility of changing the ratio of the concentrations of NaCl and CaCl2 salts in fluid phases formed as a result of heterogenization of the H2O–CO2–NaCl–CaCl2 fluid with a decrease in P-T parameters has been studied. A well-known experimental fact regarding the ternary systems H2O–CO2–NaCl and H2O–CO2–CaCl2 is the greater tendency of the H2O–CO2–CaCl2 system to separate into coexisting predominantly aqueous-salt and aqueous-carbon dioxide phases compared to the similar system H2O–CO2–NaCl. This experimental fact can be interpreted as a greater affinity of NaCl for CO2 compared to CaCl2. Using a recently developed numerical thermodynamic model of the H2O–CO2–NaCl–CaCl2 quaternary fluid system, it was possible to identify geologically significant consequences of this difference in the interaction of NaCl and CaCl2 with CO2. Multistage heterogenization of the H2O–CO2–NaCl–CaCl2 fluid with a significant decrease in P-T parameters ultimately leads to the formation of aqueous-carbon dioxide fluid phase f2, the salt component of which is significantly enriched in NaCl and depleted in CaCl2 compared to the initial fluid. The fluid phase f1 formed at each stage of heterogenization has a predominantly water-salt composition with the ratio of the mole fractions of NaCl and CaCl2 salts, differing little from that in the initial fluid. However, the total mole fraction of salt in the f1 phase, as a rule, significantly exceeds that in the original fluid. The density of phase f1 significantly exceeds the density of phase f2. During the process of multistage heterogenization of the fluid phase f1, there is no formation of a fluid with a significant enrichment of CaCl2 compared to the initial ratio of the mole fractions of NaCl and CaCl2. At the same time, successive multiple separation of the f2 phase leads to the enrichment of its salt component in NaCl. Under favorable conditions, this process can lead to the formation of a fluid with almost pure NaCl salt. Changes in the salt composition of the fluid H2O–CO2–NaCl–CaCl2 are considered in application to the evolution of fluid composition along the regressive branch of the P-T trend of HP metamorphism and syngranulite metasomatism in the Lapland granulite belt.
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About the authors
Mikhail V. Ivanov
Institute of Precambrian Geology and Geochronology RAS
Author for correspondence.
Email: m.v.ivanov@ipgg.ru
Russian Federation, Sankt-Peterburg
Sergei A. Bushmin
Institute of Precambrian Geology and Geochronology RAS
Email: s.a.bushmin@ipgg.ru
Russian Federation, Sankt-Peterburg
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