Micro-Fourier Transform Infrared (FT-IR) and δD value investigation of hydrothermal vein quartz: Interpretation of fluid inclusion {delta}D values in hydrothermal systems

Gleeson, S.A., Roberts, S., Fallick, A.E. and Boyce, A.J. (2008) Micro-Fourier Transform Infrared (FT-IR) and δD value investigation of hydrothermal vein quartz: Interpretation of fluid inclusion {delta}D values in hydrothermal systems. Geochimica et Cosmochimica Acta, 72(18), pp. 4595-4606. (doi: 10.1016/j.gca.2008.06.014)

Abstract

Some recent studies have suggested that the hydrogen isotopic composition ({delta}D) of hydrothermal fluids, released <i>in vacuo</i> by thermal decrepitation of quartz, are not always accurately revealed. We report the results of a step-heating {delta}D value study of vein quartz, hosted by Lower Palaeozoic rocks in SW England, which was analyzed by micro-FT-IR for hydrogen speciation, before and after fluid extraction at temperatures between 750 and 1500°C. The {delta}D values of individual aliquots of released water vary between -3 ‰ and -208 ‰, with the lowest values generally corresponding to the highest temperature fractions and samples of relatively low yield. The data show significant departures from geologically reasonable {delta}D. Micro-FT-IR analyses show that a variety of OH species are present within the vein quartz, with significant intra and inter sample variation. Typically a broad absorption due to molecular water, in the region 3400 cm¹ is observed, along with bands attributed to Li-OH and Al-OH. On heating, the broad absorption due to molecular water is reduced, accompanied by a measurable loss of Li-OH species. The latter becomes more pronounced in the higher temperature fractions (>750°C). These data support earlier studies which indicated that contributions from the contrasting OH reservoirs in quartz can significantly influence the reported {deltA}D values. These new data also suggest that the incorporation of OH released from Li-OH sites in the quartz may be the most important factor in the generation of the anomalous values for these samples.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian and Fallick, Professor Anthony
• Authors: Gleeson, S.A., Roberts, S., Fallick, A.E., and Boyce, A.J.
• Subjects: Q Science > QE Geology; G Geography. Anthropology. Recreation > GE Environmental Sciences
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Geochimica et Cosmochimica Acta
• ISSN: 0016-7037