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B- and O-isotopic compositions of tourmaline constrain late-stage magmatic volatile exsolution in Tasmanian tin-related granite systems

Hong, W, Fox, N, Cooke, DR ORCID: 0000-0003-3096-5658, Zhang, LJ and Fayek, M 2019 , 'B- and O-isotopic compositions of tourmaline constrain late-stage magmatic volatile exsolution in Tasmanian tin-related granite systems' , Mineralium Deposita: International Journal of Geology, Mineralogy, and Geochemistry of Mineral Deposits, vol. 55 , pp. 63-78 , doi: 10.1007/s00126-019-00885-5.

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Abstract

The Devonian Sn-mineralized Heemskirk and barren Pieman Heads granites of western Tasmania (southeast Australia)contain abundant tourmaline-rich features, including orbicules, patches, cavities, and veins within their roof zones. Theδ11B and δ18O compositions of tourmaline from these texturally different features range from − 21.7 to + 4.1‰ (average− 4.7 ± 4.0‰, n = 127), and from + 6.5 to + 14.9‰ (average + 10.7 ± 1.8‰, n = 38), respectively. These data suggest thatthe tourmaline-rich assemblages precipitated mostly from magmatic-hydrothermal fluids derived from their host plutons,mixed with minor external components sourced from metasedimentary, meta-ultramafic rocks, and/or meteoric water.The B-isotopic values increase sequentially from tourmaline patches to orbicules and/or cavities in both granites,probably caused by progressive volatile exsolution and systematic fluxing of aqueous boron-rich fluids from the Stypemagmas during emplacement into the shallow crust. High degrees of fractional crystallization of the melt may havecaused the exsolution of boron-rich hypersaline fluids from which the tourmaline orbicules and cavities formed. Bimodalδ11B populations (− 21.7 to − 12.7‰ and − 3.9 to +4.0‰) imply that the granitic melts were mostly sourced from 10Brichmetapelitic rocks. The granites underwent fluid exsolution during the late magmatic stage that contributed to thewidespread development of tourmaline-rich features and also to the formation of tin deposits associated with theHeemskirk Granite.

Item Type: Article
Authors/Creators:Hong, W and Fox, N and Cooke, DR and Zhang, LJ and Fayek, M
Keywords: B- and O-isotopes, tourmaline , volatile exsolution, tin mineralization, Tasmania
Journal or Publication Title: Mineralium Deposita: International Journal of Geology, Mineralogy, and Geochemistry of Mineral Deposits
Publisher: Springer
ISSN: 0026-4598
DOI / ID Number: 10.1007/s00126-019-00885-5
Copyright Information:

Copyright Springer-Verlag GmbH Germany, part of Springer Nature 2019

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