Halogen Stable Isotope Studies in Geological Processes

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Geochemistry and Geochronology".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 6593

Special Issue Editors


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Guest Editor
Eberhard Karls Universität Tübingen, FB Geowissenschaften, AG Petrologie, Wilhemstraße 56, 72074 Tübingen, Germany
Interests: stable isotopes of halgens; halogen geochemistry

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Guest Editor
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo, Japan
Interests: isotope geochemistry; experimental and theoretical study on the isotope effect

Special Issue Information

Dear Colleagues,

Over the last few years, interest in halogen (Cl and Br) stable isotopes has increased significantly. Thanks to improved analytical facilities, it is now possible to measure the chlorine isotope compositions, and increasingly, the bromine isotope compositions, of most existing geological samples. This has resulted in many studies, not only on terrestrial materials such as water and salt and, more recently, minerals and rocks, but also on extra-terrestrial materials such as meteorites and lunar rocks. These studies have increased the knowledge base on halogen isotope systematics immensely, providing a better understanding of the related systems. This is mostly the result of the fact that halogens, due to their characteristic chemistry, lack significant redox transitions and, consequently, show isotope characteristics that are very different from those of other isotope systems. In this Special Issue of Minerals, we aim to present a collection of papers showing recent developments in stable isotope studies of chlorine and bromine. These studies, while increasing our knowledge on halogen isotope systematics, will also result in a better understanding of the geological processes that take place. Collecting them in one place will also increase the visibility of this research and, as such, lead to interest in the further development of halogen isotope studies.

Dr. Hans Eggenkamp
Dr. Masaaki Musashi
Guest Editors

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Keywords

  • chlorine isotopes
  • bromine isotopes
  • mass spectrometry
  • fractionation
  • isotope effect
  • geochemistry
  • water
  • rocks
  • minerals

Published Papers (3 papers)

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Research

9 pages, 4864 KiB  
Article
Bromine Isotope Variations in Magmatic and Hydrothermal Sodalite and Tugtupite and the Estimation of Br Isotope Fractionation between Melt and Sodalite
by Hans G. M. Eggenkamp, Michael A. W. Marks, Pascale Louvat and Gregor Markl
Minerals 2021, 11(4), 370; https://doi.org/10.3390/min11040370 - 31 Mar 2021
Cited by 2 | Viewed by 1669
Abstract
We determined the bromine isotope compositions of magmatic and hydrothermal sodalite (Na8Al6Si6O24Cl2) and tugtupite (Na8Al2Be2Si8O24Cl2) from the Ilímaussaq intrusion in South [...] Read more.
We determined the bromine isotope compositions of magmatic and hydrothermal sodalite (Na8Al6Si6O24Cl2) and tugtupite (Na8Al2Be2Si8O24Cl2) from the Ilímaussaq intrusion in South Greenland, in order to constrain the Br isotope composition of the melt and hydrothermal fluids from which these minerals were formed. Early formed magmatic sodalite has high Br contents (138 ± 10 µg/g, n = 5) and low δ81Br values (+0.23 ± 0.07‰). Late stage hydrothermal sodalite has lower Br contents (53±10 µg/g, n = 5) and higher δ81Br values (+0.36 ± 0.08‰). Tugtupite that forms at even later stages shows the lowest Br contents (26 ± 2 µg/g, n = 2) and the highest δ81Br values (+0.71 ± 0.17‰). One hydrothermal sodalite has a Br concentration of 48 ± 9 µg/g and an exceptionally high δ81Br of 0.82 ± 0.12‰, very similar to the δ81Br of tugtupites. We suggest that this may be a very late stage sodalite that possibly formed under Be deficient conditions. The data set suggests that sodalite crystallises with a negative Br isotope fractionation factor, which means that the sodalite has a more negative δ81Br than the melt, of −0.3 to −0.4‰ from the melt. This leads to a value of +0.5 to +0.6‰ relative to SMOB for the melt from which sodalite crystallises. This value is similar to a recently published δ81Br value of +0.7‰ for very deep geothermal fluids with very high R/Ra He isotope ratios, presumably derived from the mantle. During crystallisation of later stage hydrothermal sodalite and the Be mineral tugtupite, δ81Br of the residual fluids (both melt and hydrothermal fluid) increases as light 79Br crystallises in the sodalite and tugtupite. This results in increasing δ81Br values of later stage minerals that crystallise with comparable fractionation factors from a fluid with increasingly higher δ81Br values. Full article
(This article belongs to the Special Issue Halogen Stable Isotope Studies in Geological Processes)
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23 pages, 2972 KiB  
Article
Stable Bromine Isotopic Composition of Coal Bed Methane (CBM) Produced Water, the Occurrence of Enriched 81Br, and Implications for Fluid Flow in the Midcontinent, USA
by Randy L. Stotler, Matthew F. Kirk, K. David Newell, Robert H. Goldstein, Shaun K. Frape and Rhys Gwynne
Minerals 2021, 11(4), 358; https://doi.org/10.3390/min11040358 - 30 Mar 2021
Cited by 1 | Viewed by 2334
Abstract
This study characterizes the δ37Cl, δ81Br, and 87Sr/86Sr of coal bed methane produced fluids from Pennsylvanian Cherokee Group coals of the Cherokee Basin in southeast Kansas, USA. The δ37Cl, δ81Br, and 87 [...] Read more.
This study characterizes the δ37Cl, δ81Br, and 87Sr/86Sr of coal bed methane produced fluids from Pennsylvanian Cherokee Group coals of the Cherokee Basin in southeast Kansas, USA. The δ37Cl, δ81Br, and 87Sr/86Sr values range between −0.81 and +0.68‰ (SMOC), −0.63 and +3.17‰ (SMOB), and 0.70880 and 0.71109, respectively. A large percentage of samples have δ81Br above +2.00‰. Two fluid groups were identified on the basis of K/Br, Br/Cl, and Ca/Mg ratios, temperature, He content, δ2H, δ18O, δ81Br, and 87Sr/86Sr. Both fluid groups have geochemical similarities to fluids in Cambrian, Ordovician, and Mississippian units. Lower salinity and higher temperature fluids from deeper units are leaking up into the Cherokee Group and mixing with a higher salinity fluid with higher δ81Br and more radiogenic 87Sr/86Sr. Variation in δ37Cl indicates an unknown process other than mixing is affecting the salinity. This process does not appear to be related to evaporation, evaporite dissolution, or diffusion. Insufficient data are available to evaluate halide–gas or water–rock interaction, but halide–gas interactions are not likely a significant contributor to high δ81Br. Rather, interactions with organically bound bromine and soluble chloride within the coal could have the strongest effect on δ37Cl and δ81Br values. Full article
(This article belongs to the Special Issue Halogen Stable Isotope Studies in Geological Processes)
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15 pages, 2140 KiB  
Article
Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment
by Takuma Hasegawa, Kotaro Nakata and Rhys Gwynne
Minerals 2021, 11(2), 208; https://doi.org/10.3390/min11020208 - 16 Feb 2021
Cited by 2 | Viewed by 2079
Abstract
For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key [...] Read more.
For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key pieces of evidence indicating a diffusion-dominant domain are the separation of components and the fractionation of isotopes by diffusion. To prove this, it is necessary to investigate the different diffusion coefficients for each component and the related stable isotope fractionation factors. Thus, in this study, through-diffusion and effective-porosity experiments were conducted on selected artificial materials and natural rocks. We also undertook measurements relating to the isotope fractionation factors of Cl and Br isotopes for natural samples. For natural rock samples, the diffusion coefficients of water isotopes (HDO and H218O) were three to four times higher than those of monovalent anions (Cl, Br- and NO3), and the isotope fractionation factor of 37Cl (1.0017–1.0021) was slightly higher than that of free water. It was experimentally confirmed that the isotope fractionation factor of 81Br was approximately 1.0007–1.0010, which is equivalent to that of free water. The enrichment factor of 81Br was almost half that of 37Cl. The effective porosity ratios of HDO and Cl were slightly different, but the difference was not significant compared to the ratio of their diffusion coefficients. As a result, component separation was dominated by diffusion. For artificial samples, the diffusion coefficients and effective porosities of HDO and Cl were almost the same; it was thus difficult to assess the component separation by diffusion. However, isotope fractionation of Cl and Br was confirmed using a through-diffusion experiment. The results show that HDO and Cl separation and isotope fractionation of Cl and Br can be expected in diffusion-dominant domains in geological formations. Full article
(This article belongs to the Special Issue Halogen Stable Isotope Studies in Geological Processes)
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