136562 - B- and O-isotopic compositions - author version.pdf (1.71 MB)
B- and O-isotopic compositions of tourmaline constrain late-stage magmatic volatile exsolution in Tasmanian tin-related granite systems
journal contribution
posted on 2023-05-20, 09:17 authored by Wei HongWei Hong, Fox, N, David CookeDavid Cooke, Lejun ZhangLejun Zhang, Fayek, MThe 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.
Funding
Australian Research Council
AMIRA International Ltd
BHP Billiton Ltd
Newcrest Mining Limited
History
Publication title
Mineralium DepositaVolume
55Pagination
63-78ISSN
0026-4598Department/School
School of Natural SciencesPublisher
SpringerPlace of publication
GermanyRights statement
Copyright Springer-Verlag GmbH Germany, part of Springer Nature 2019Repository Status
- Open