Gravitational Fractionation of Isotopes and Dissolved Components as a first-order process in crustal fluids

Paul D. Bons*, Enrique Gomez-Rivas

*Corresponding author for this work

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The origin of ore-forming hydrothermal fluids and mechanisms of ore formation are commonly inferred from chemical and isotopic signatures. Fluid mixing and fluid-rock interaction are well-known processes that modify and produce these signatures, respectively. We propose that gravitational fractionation is an additional, hitherto not considered process that can significantly affect fluid signatures. Gravitational fractionation is the tendency for heavier components in a fluid to concentrate at the base of a reservoir. In stagnant fluids, gravitational fractionation can lead to significant changes in isotopic signatures, but also halogen ratios, within tens of millions of years. Rising fractionated fluids can give the same signatures that are classically and potentially erroneously interpreted as indicating mixing of surface-derived and deeper fluids. Recognition of gravitational fractionation as an additional first-order process affecting fluid composition necessitates a thorough reevaluation of models for crustal fluid flow, especially for the formation of unconformity-related hydrothermal ore deposits.

Original languageEnglish
Pages (from-to)1195-1201
Number of pages7
JournalEconomic Geology
Volume108
Issue number5
DOIs
Publication statusPublished - Aug 2013

Cite this

Gravitational Fractionation of Isotopes and Dissolved Components as a first-order process in crustal fluids. / Bons, Paul D.; Gomez-Rivas, Enrique.

In: Economic Geology, Vol. 108, No. 5, 08.2013, p. 1195-1201.

Research output: Contribution to journalArticle

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abstract = "The origin of ore-forming hydrothermal fluids and mechanisms of ore formation are commonly inferred from chemical and isotopic signatures. Fluid mixing and fluid-rock interaction are well-known processes that modify and produce these signatures, respectively. We propose that gravitational fractionation is an additional, hitherto not considered process that can significantly affect fluid signatures. Gravitational fractionation is the tendency for heavier components in a fluid to concentrate at the base of a reservoir. In stagnant fluids, gravitational fractionation can lead to significant changes in isotopic signatures, but also halogen ratios, within tens of millions of years. Rising fractionated fluids can give the same signatures that are classically and potentially erroneously interpreted as indicating mixing of surface-derived and deeper fluids. Recognition of gravitational fractionation as an additional first-order process affecting fluid composition necessitates a thorough reevaluation of models for crustal fluid flow, especially for the formation of unconformity-related hydrothermal ore deposits.",
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note = "This study was carried out within the framework of DGMK (German Society for Petroleum and Coal Science and Technology) research project 718 “Mineral Vein Dynamics Modelling,” which is funded by the companies ExxonMobil Production Deutschland GmbH, GDF SUEZ E&P Deutschland GmbH, RWE Dea AG and Wintershall Holding GmbH, within the basic research program of the WEG Wirtschaftsverband Erd{\"o}l- und Erdgasgewinnung e.V. We thank the companies for their financial support and their permission to publish these results. We thank B.Ph. van Milligen and N.H.S. Oliver for scrutinizing the theory and numerical model. We thank Vincent van Hinsberg and an anonymous reviewer for their critical but helpful reviews.",
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