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Peer Reviewed Literature
Authors

Erik Oerter, Michael Singleton, Lee Davisson

日期
十月 22nd, 2023
Abstract

The hydrogen and oxygen stable isotope composition (δ2 H and δ18O values) of mineral hydration waters can give information on the environment of mineral formation. Here we present and validate an approach for the stable isotope analysis of mineral hydration waters based on coupling a thermogravimetric analyzer with a laserbased isotope ratio infrared spectroscopy instrument (Picarro L-2130i), which we abbreviate as TGA-IRIS. TGAIRIS generates δ2 H and δ18O values of liquid water samples with precision for δ2 H of ± 1.2‰, and for δ18O of ± 0.17‰. For hydration waters in goethite, precision for δ2 H ranges from ± 0.3‰ to 1.6‰, and for δ18O ranges from ± 0.17‰ to 0.27‰. The ability of TGA-IRIS to generate detailed water yield data and δ2 H and δ18O values of water at varying temperatures allows for the differentiation of water in varying states of binding on mineral surfaces and within the mineral matrix. TGA-IRIS analyses of hydrogen isotopes in goethite yields δ2 H values that reflect the hydrogen of the OH− phase in the mineral and are comparable to that made by IRMS and found in the literature. In contrast, δ18O values on goethite reflect the oxygen in OH− groups bound to Fe (Fe-OH group), and not the oxygen bound only to Fe (Fe-O group) in the mineral crystal lattice, and may not be comparable to literature δ18O values made by IRMS that reflect the total O in the mineral. TGA-IRIS presents the possibility to isotopically differentiate the various oxygen reservoirs in goethite, which may allow the mineral to be used as a single mineral geothermometer. TGA-IRIS measurements of hydration waters are likely to open new avenues and possibilities for research on hydrated minerals.