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Smectite quantification in hydrothermally altered volcanic rocks

Lévy, Léa LU ; Fridriksson, Thráinn ; Findling, Nathaniel ; Lanson, Bruno ; Fraisse, Bernard ; Marino, Nicolas and Gibert, Benoit (2020) In Geothermics 85.
Abstract

In volcanic environments, the presence of smectite may indicate recent hydrothermal circulations. Smectite is also responsible for enhanced rock electrical conductivity, as well as mechanical weakening. Therefore, quantifying smectite is important in geothermal exploration. Smectite identification requires X-ray diffraction (XRD) but quantification based on XRD is time-consuming and not always accurate. In the present study, we investigate the use of an optimized unbuffered Cation Exchange Capacity (CEC) determination, by back-titration of the Copper-triethylenetetramine(II) “Cu-trien” molecule, to quantify the smectite content of altered volcanic rock samples. We establish that a satisfying trade-off between the instrument uncertainty... (More)

In volcanic environments, the presence of smectite may indicate recent hydrothermal circulations. Smectite is also responsible for enhanced rock electrical conductivity, as well as mechanical weakening. Therefore, quantifying smectite is important in geothermal exploration. Smectite identification requires X-ray diffraction (XRD) but quantification based on XRD is time-consuming and not always accurate. In the present study, we investigate the use of an optimized unbuffered Cation Exchange Capacity (CEC) determination, by back-titration of the Copper-triethylenetetramine(II) “Cu-trien” molecule, to quantify the smectite content of altered volcanic rock samples. We establish that a satisfying trade-off between the instrument uncertainty and an independant systematic error is theoretically reached for a fraction of reactants consumed of about 30% at the end of the exchange reaction. We suggest a modification to classical protocols to fall in that range. Finally, we show that optimized CEC determination by Cu-trien are a direct measure of the smectite weight fraction in altered volcanic samples, with an average CEC of pure smectite of 90 ± 5 meq/100 g.

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type
Contribution to journal
publication status
published
subject
in
Geothermics
volume
85
article number
101748
publisher
Elsevier
external identifiers
  • scopus:85075473775
ISSN
0375-6505
DOI
10.1016/j.geothermics.2019.101748
language
English
LU publication?
no
additional info
Funding Information: This work was supported by the IMAGE FP7 EC project (Integrated Methods for Advanced Geothermal Exploration, grant agreement No. 608553) and by a PhD grant from Paris Sciences et Lettres granted to Léa Lévy. Funding Information: L.L. thanks Sigurdur Sveinn J?nsson, Helga Margr?t Helgad?ttir and Bjarni Gautason for their help with identifying primary and alteration minerals in XRD patterns, thin sections and microscopic observations. L.L. thanks Heimir Ingimarsson, Christina Guenther and Ester Inga Eyj?lfsd?ttir for their help with the CEC determinations, as well as Iwona Monika Galezka and Kristinn I. Gudmundsson for ICP determinations and discussion of the results. L.L. also thanks Freysteinn Sigmundsson for critical reading of the manuscript, which helped improve much its quality. The authors thank Christophe Nevado, Doriane Delmas and Khaled Oubellouch for high-quality polished thin sections and Jacinthe Caillaud for electron probe data collection and analysis. The authors are also grateful to Landsvirkjun, and especially ?sgr?mur Gudmundsson, for providing rock samples used in this work. Finally, the authors thank editor Halldor ?rmannsson, as well as Reiner Dohrmann and another anonymous reviewer for their remarks and suggestions, which very much helped improve the manuscript. Publisher Copyright: © 2019 Elsevier Ltd
id
602e562a-4681-4615-8f58-02a888514e9a
date added to LUP
2021-12-14 11:58:23
date last changed
2022-04-27 06:38:44
@article{602e562a-4681-4615-8f58-02a888514e9a,
  abstract     = {{<p>In volcanic environments, the presence of smectite may indicate recent hydrothermal circulations. Smectite is also responsible for enhanced rock electrical conductivity, as well as mechanical weakening. Therefore, quantifying smectite is important in geothermal exploration. Smectite identification requires X-ray diffraction (XRD) but quantification based on XRD is time-consuming and not always accurate. In the present study, we investigate the use of an optimized unbuffered Cation Exchange Capacity (CEC) determination, by back-titration of the Copper-triethylenetetramine(II) “Cu-trien” molecule, to quantify the smectite content of altered volcanic rock samples. We establish that a satisfying trade-off between the instrument uncertainty and an independant systematic error is theoretically reached for a fraction of reactants consumed of about 30% at the end of the exchange reaction. We suggest a modification to classical protocols to fall in that range. Finally, we show that optimized CEC determination by Cu-trien are a direct measure of the smectite weight fraction in altered volcanic samples, with an average CEC of pure smectite of 90 ± 5 meq/100 g.</p>}},
  author       = {{Lévy, Léa and Fridriksson, Thráinn and Findling, Nathaniel and Lanson, Bruno and Fraisse, Bernard and Marino, Nicolas and Gibert, Benoit}},
  issn         = {{0375-6505}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Geothermics}},
  title        = {{Smectite quantification in hydrothermally altered volcanic rocks}},
  url          = {{http://dx.doi.org/10.1016/j.geothermics.2019.101748}},
  doi          = {{10.1016/j.geothermics.2019.101748}},
  volume       = {{85}},
  year         = {{2020}},
}