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

Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, 7514 AE Enschede, The Netherlands
Department of Earth Sciences, Utrecht University, 3584 CB Utrecht, The Netherlands
Author to whom correspondence should be addressed.
Minerals 2018, 8(6), 259;
Received: 30 April 2018 / Revised: 14 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
Although the composition of chlorite group minerals 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 composition while for the metamorphic samples the original bulk chemistry determines the current composition of the rock. View Full-Text
Keywords: chlorite; NIR-spectroscopy; metasomatism; basalts; magnesium number chlorite; NIR-spectroscopy; metasomatism; basalts; magnesium number
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Kamps, O.M.; Van Ruitenbeek, F.J.; Mason, P.R.; Van der Meer, F.D. Near-Infrared Spectroscopy of Hydrothermal versus Low-Grade Metamorphic Chlorites. Minerals 2018, 8, 259.

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