Transient tin mineralization from cooling of magmatic fluids in a long-lived system

Abstract Fertility and longevity of hydrothermal systems are key parameters required to improve our ability in predicting new deposits and directly extracting metals from metalliferous fluids. Reconstructing evolutional trajectories of metalliferous fluids with high temporal resolution is critical for pushing our understanding forward, but this is inevitably challenging because traditional approaches for obtaining this information either have poor temporal resolution and/or bear considerable uncertainties. We present a novel approach (translating texture-controlled information to temporal patterns) to reconstruct the thermal and isotopic history of the Weilasituo vein-type tin deposit (Inner Mongolia, China) at the millennial scale. In situ oxygen isotope thermometry of paragenetically constrained quartz and cassiterite reveals that tin deposition was accompanied by gradual cooling of pure magmatic fluids from ~500 °C to ~390 °C at lithostatic conditions, while fluid mixing and/or water-rock interaction were not required. The system then transitioned to hydrostatic conditions and permitted penetration of meteoric water and further cooling. Aluminum diffusion in quartz chronometry yields time scales of ~50 k.y., ~5 k.y., and ~200 k.y. for pre-, syn-, and post-ore stages, respectively. Our results highlight that the magmatic-hydrothermal system did not form ore minerals for most of its lifetime, with mineralization occurring only briefly (i.e., <5% of its lifetime). Hence, the rates and efficiency of ore formation may need significant revision. For magmatic-hydrothermal systems with felsic magmas being stored at high crystallinity after extensive volatile exsolution, the efficiency of scavenging metals from melts to fluids critically controls their fertility. To directly extract metals from metalliferous fluids, the key is targeting systems with a high degree of magma crystallization (e.g., higher metal contents in fluids) in warm crust (e.g., able to sustain long-lived systems).