Near-Infrared Spectroscopy of Hydrothermal versus Low-Grade Metamorphic Chlorites

O.M. Kamps (Corresponding Author), Frank Van Ruitenbeek, Paul Mason, Freek Van Der Meer

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Abstract

Although the composition of chlorite groupminerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed under low-grade metamorphic conditions. Both sets of samples were collected from the Pilbara Craton,Western Australia. Near-infrared (NIR) spectroscopy was used to determine if spectral differences record compositional differences between chlorites from the two geological environments. The spectra showed a significant difference in the Mg-OH absorption wavelength, near 2350 nm, with the hydrothermal group showing longer absorption wavelengths than the metamorphic one. A comparison of the spectral data with geochemical analyses showed a relation between the absorption wavelength and the magnesium-to-iron ratio (magnesium number) of chlorite, as well as the bulk rock composition. Metamorphic rocks have a higher magnesium-to-iron ratio than the hydrothermal ones, predominantly explained by differences in the degree of metasomatism. In the hydrothermal system,mass transfer changes the bulk rock compositionwhile for themetamorphic samples the original bulk chemistry determines the current composition of the rock.

Original languageEnglish
Article number259
Pages (from-to)1-12
Number of pages12
JournalMinerals
Volume8
Issue number6
DOIs
Publication statusPublished - 19 Jun 2018

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Near infrared spectroscopy
infrared spectroscopy
chlorite
Magnesium
near infrared
Rocks
Wavelength
magnesium
Chemical analysis
Metamorphic rocks
Iron
hydrothermal system
wavelength
rock
Mass transfer
iron
metasomatism
metamorphic rock
craton
mass transfer

Keywords

  • ITC-ISI-JOURNAL-ARTICLE
  • ITC-GOLD

Cite this

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abstract = "Although the composition of chlorite groupminerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed under low-grade metamorphic conditions. Both sets of samples were collected from the Pilbara Craton,Western Australia. Near-infrared (NIR) spectroscopy was used to determine if spectral differences record compositional differences between chlorites from the two geological environments. The spectra showed a significant difference in the Mg-OH absorption wavelength, near 2350 nm, with the hydrothermal group showing longer absorption wavelengths than the metamorphic one. A comparison of the spectral data with geochemical analyses showed a relation between the absorption wavelength and the magnesium-to-iron ratio (magnesium number) of chlorite, as well as the bulk rock composition. Metamorphic rocks have a higher magnesium-to-iron ratio than the hydrothermal ones, predominantly explained by differences in the degree of metasomatism. In the hydrothermal system,mass transfer changes the bulk rock compositionwhile for themetamorphic samples the original bulk chemistry determines the current composition of the rock.",
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Near-Infrared Spectroscopy of Hydrothermal versus Low-Grade Metamorphic Chlorites. / Kamps, O.M. (Corresponding Author); Van Ruitenbeek, Frank; Mason, Paul; Van Der Meer, Freek.

In: Minerals, Vol. 8, No. 6, 259, 19.06.2018, p. 1-12.

Research output: Contribution to journalArticleAcademicpeer-review

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N2 - Although the composition of chlorite groupminerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed under low-grade metamorphic conditions. Both sets of samples were collected from the Pilbara Craton,Western Australia. Near-infrared (NIR) spectroscopy was used to determine if spectral differences record compositional differences between chlorites from the two geological environments. The spectra showed a significant difference in the Mg-OH absorption wavelength, near 2350 nm, with the hydrothermal group showing longer absorption wavelengths than the metamorphic one. A comparison of the spectral data with geochemical analyses showed a relation between the absorption wavelength and the magnesium-to-iron ratio (magnesium number) of chlorite, as well as the bulk rock composition. Metamorphic rocks have a higher magnesium-to-iron ratio than the hydrothermal ones, predominantly explained by differences in the degree of metasomatism. In the hydrothermal system,mass transfer changes the bulk rock compositionwhile for themetamorphic samples the original bulk chemistry determines the current composition of the rock.

AB - Although the composition of chlorite groupminerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed under low-grade metamorphic conditions. Both sets of samples were collected from the Pilbara Craton,Western Australia. Near-infrared (NIR) spectroscopy was used to determine if spectral differences record compositional differences between chlorites from the two geological environments. The spectra showed a significant difference in the Mg-OH absorption wavelength, near 2350 nm, with the hydrothermal group showing longer absorption wavelengths than the metamorphic one. A comparison of the spectral data with geochemical analyses showed a relation between the absorption wavelength and the magnesium-to-iron ratio (magnesium number) of chlorite, as well as the bulk rock composition. Metamorphic rocks have a higher magnesium-to-iron ratio than the hydrothermal ones, predominantly explained by differences in the degree of metasomatism. In the hydrothermal system,mass transfer changes the bulk rock compositionwhile for themetamorphic samples the original bulk chemistry determines the current composition of the rock.

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