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Type: Journal article
Title: B- and O-isotopic compositions of tourmaline constrain late-stage magmatic volatile exsolution in Tasmanian tin-related granite systems
Author: Hong, W.
Fox, N.
Cooke, D.R.
Zhang, L.
Fayek, M.
Citation: Mineralium Deposita: international journal of geology, mineralogy, and geochemistry of mineral deposits, 2020; 55(1):63-78
Publisher: Springer
Issue Date: 2020
ISSN: 0026-4598
Statement of
Wei Hong, Nathan Fox, David R. Cooke, Lejun Zhang and Mostafa Fayek Mineralium Deposita
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. The δ11B 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 that the 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 S-type magmas during emplacement into the shallow crust. High degrees of fractional crystallization of the melt may have caused the exsolution of boron-rich hypersaline fluids from which the tourmaline orbicules and cavities formed. Bimodal δ11B populations (− 21.7 to − 12.7‰ and − 3.9 to + 4.0‰) imply that the granitic melts were mostly sourced from 10B-rich metapelitic rocks. The granites underwent fluid exsolution during the late magmatic stage that contributed to the widespread development of tourmaline-rich features and also to the formation of tin deposits associated with the Heemskirk Granite.
Keywords: B- and O-isotopes; tourmaline; volatile exsolution; tin mineralization; Tasmania
Rights: © Springer-Verlag GmbH Germany, part of Springer Nature 2019.
DOI: 10.1007/s00126-019-00885-5
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