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

We present a high-resolution in situ study of oxygen and boron isotopes measured tourmaline from the world-class San Rafael Sn (–Cu) deposit (Central Andean tin belt, Peru) aiming to trace major fluid processes at magmatic-hydrothermal transition leading precipitation cassiterite. Our results show that late-magmatic pre-ore hydrothermal has similar values δ18O (from 10.6‰ 14.1‰) δ11B −11.5‰ −6.9‰). The observed variations are dominantly driven by Rayleigh fractionation, reflecting crystallization continuously evolving system. In contrast, syn-ore intergrown with cassiterite lower 4.9‰ 10.2‰) part higher −9.9‰ −5.4‰) than tourmaline, indicating important contribution meteoric groundwater system during ore deposition. Quantitative geochemical modeling demonstrates δ18O-δ11B composition records variable degrees mixing hot Sn-rich magmatic brine waters partially exchanged host rocks. These provide thus direct isotopic evidence as mechanism triggering Further, this work shows combined analyses is powerful approach for understanding dynamic environments.