Fluid mixing as primary trigger for cassiterite deposition: Evidence from in situ δ18O-δ11B analysis of tourmaline from the world-class San Rafael tin (-copper) deposit, Peru

Article Article scientifique Article Fluid mixing as primary trigger for cassiterite deposition: Evidence from in situ δ18O-δ11B analysis of tourmaline from the world-class San Rafael tin (-copper) deposit, Peru eng 2021 author Harlaux Matthieu 870797 author Kouzmanov Kalin 0000-0002-7327-8949 529239 author Gialli Stefano 735615 author Marger Katharina author Bouvier Anne-Sophie author Baumgartner Lukas P. author Rielli Andrea author Dini Andréa 827083 author Chauvet Alain 828138 author Kalinaj Miroslav author Fontboté Lluís 26840 Lluis Fontboté 10.1016/j.epsl.2021.116889 0012-821X https://linkinghub.elsevier.com/retrieve/pii/S0012821X21001485 We present a high-resolution in situ study of oxygen and boron isotopes measured in tourmaline from the world-class San Rafael Sn (-Cu) deposit (Central Andean tin belt, Peru) aiming to trace major fluid processes at the magmatic-hydrothermal transition leading to the precipitation of cassiterite. Our results show that late-magmatic and pre-ore hydrothermal tourmaline has similar values of δ18O (from 10.6‰ to 14.1‰) and δ11B (from −11.5‰ to −6.9‰). The observed δ18O and δ11B variations are dominantly driven by Rayleigh fractionation, reflecting tourmaline crystallization in a continuously evolving magmatic-hydrothermal system. In contrast, syn-ore hydrothermal tourmaline intergrown with cassiterite has lower δ18O values (from 4.9‰ to 10.2‰) and in part higher δ11B values (from −9.9‰ to −5.4‰) than late-magmatic and pre-ore hydrothermal tourmaline, indicating important contribution of meteoric groundwater to the hydrothermal system during ore deposition. Quantitative geochemical modeling demonstrates that the δ18O-δ11B composition of syn-ore tourmaline records variable degrees of mixing of a hot Sn-rich magmatic brine with meteoric waters that partially exchanged with the host rocks. These results provide thus direct in situ isotopic evidence of fluid mixing as a major mechanism triggering cassiterite deposition. Further, this work shows that combined in situ δ18O and δ11B analyses of tourmaline is a powerful approach for understanding fluid processes in dynamic magmatic-hydrothermal environments. Dewey 550 Swiss National Science Foundation S19053_169901 CH 42 Département des sciences de la Terre 154 false 692 Mineral Resources and Geofluids Earth and Planetary Science Letters 563 116889 71e492eb-879e-4f1f-ad5e-a85bc0d96686 Article (Published version) Public HarlauxEPSL2021tourmalineSR.pdf 2589329 application/pdf CC BY-NC-ND openAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

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Fluid mixing as primary trigger for cassiterite deposition: Evidence from in situ δ¹⁸O-δ¹¹B analysis of tourmaline from the world-class San Rafael tin (-copper) deposit, Peru	Earth and Planetary Science Letters			2021	329	285

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Chauvet, Alain