Timescales of magmatic-hydrothermal activity at the giant San Rafael tin deposit (Peru)

Recent research suggests that protracted magmatic activity may play a critical role in forming large metal endowments in magmatic-hydrothermal deposits. Here, we test whether this concept applies to tin systems associated with peraluminous (S-type) granites, focusing on the intrusive complex at San Rafael (Peru) that hosts the world’s largest and highest-grade primary Sn deposit (>1.5 Mt of Sn at 3.7 %). We obtained a comprehensive (n = 187) set of high-precision U-Pb zircon dates from granites and mafic rocks that both pre- and post-date the cassiterite Sn ore according to crosscutting relationships. Individual granites exhibit large date dispersions (up to 1.7 Myr), which we evaluate in the context of magmatic and hydrothermal zircon origins, possibility of unmitigated Pb loss, and cryptic inclusion of older zircon cores. By integrating zircon compositions with field observations, we reconstruct 200–400 kyr of magmatic evolution in the crust – from 24.402 ± 0.019 Ma to final emplacement at shallow levels between 24.177 ± 0.004 Ma and 24.027 ± 0.028 Ma. Younger ages found in one sample of the ore-stage cassiterite (23.80 ± 0.25 Ma) and all samples of hydrothermal adularia (∼22.72–22.43 Ma) suggest that the mineralizing fluids were most likely not related to the cooling of the exposed intrusive complex, but instead to one or more younger magma pulses outgassing at depth. The duration of the magmatic build-up prior to Sn mineralization at San Rafael appears significantly shorter than in the largest porphyry copper systems, although we recognize that longer timescales may be resolvable in the unexposed portions of the system. Finally, we compared the metal tonnage and computed volumes of metal-sourcing melt at San Rafael (1.5 Mt of Sn and 77 km³ of melt) with the largest porphyry copper systems in magmatic arcs (112 Mt of Cu and >1000 km³ of melt) to propose that more limited and episodic melt supply, alongside with restricted water availability in (post-)collisional S-type systems may limit the maximum endowments of Sn systems.