Multi-aliquot method for determining (U+Th)/He ages of hydrothermal hematite: Returning to Elba

Wu, L.-Y., Stuart, F. M. , Di Nicola, L., Heizler, M., Benvenuti, M. and Hu, R.-Z. (2019) Multi-aliquot method for determining (U+Th)/He ages of hydrothermal hematite: Returning to Elba. Chemical Geology, 504, pp. 151-157. (doi: 10.1016/j.chemgeo.2018.11.005)

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We have used a multi-aliquot method to obtain precise (U+Th)/He ages of hydrothermal hematite and to assess the extent to which He loss from fine-grained hematite caused by diffusion and recoil. Hematite (n=6) from the Rio Marina mine, Elba (Italy) yields (U+Th)/He ages that range from 5.36 ± 0.33 to 5.64 ± 0.11 Ma, giving a weighted mean age of 5.53 ± 0.14 Ma and an isochron age of 5.25 ± 0.20 Ma. 40Ar/39Ar data from cogenetic adularia yield flat age spectra with analytically indistinguishable plateau ages (5.575 ± 0.008 and 5.583 ± 0.013 Ma). An additional adularia has a more complex spectrum and yields an interpreted age of 5.64 ± 0.03 Ma. The hematite (U+Th)/He ages overlap the 40Ar/39Ar ages, albeit they are less precise (2-6% vs. 0.2-0.5%). This indicates that the loss of in situ radiogenic 4He from complex fine-grained hematite, either by diffusion and recoil, is insignificant. The study shows that multi-aliquot method has the potential to reliably deliver precise and accurate ages for iron oxide mineralisation that has not suffered significant post-crystallisation thermal perturbation.

Item Type:Articles
Additional Information:This work was financially supported by SUERC, the National Key Research and Development Program of China (2016YFC0600207), the Strategic Priority Research Program (B) of Chinese Academy of Sciences (XDB18000000) and National Natural Science Foundation of China (41773048). We thank two journal reviewers for comments that improved this work.
Glasgow Author(s) Enlighten ID:Di Nicola, Dr Luigia and Stuart, Professor Fin
Authors: Wu, L.-Y., Stuart, F. M., Di Nicola, L., Heizler, M., Benvenuti, M., and Hu, R.-Z.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Chemical Geology
ISSN (Online):0009-2541
Published Online:20 November 2018
Copyright Holders:Copyright © 2018 Elsevier
First Published:First published in Chemical Geology 504:151-157
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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