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Smectite quantification in hydrothermally altered volcanic rocks

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, 1 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) measurement, by back-titration of the Coppertriethylenetetramine(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 measurements 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/100g.
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https://hal-insu.archives-ouvertes.fr/insu-03043134
Contributor : Bruno Lanson <>
Submitted on : Monday, December 7, 2020 - 10:26:04 AM
Last modification on : Monday, July 5, 2021 - 3:20:03 PM
Long-term archiving on: : Monday, March 8, 2021 - 6:28:18 PM

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Léa Lévy, Thráinn Fridriksson, Nathaniel Findling, Bruno Lanson, Bernard Fraisse, et al.. Smectite quantification in hydrothermally altered volcanic rocks. Geothermics, Elsevier, 2020, 85, pp.101748. ⟨10.1016/j.geothermics.2019.101748⟩. ⟨insu-03043134⟩

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