Geochronology, geochemistry and genesis of the Shanwang fluorite deposit in central Zhejiang, SE China: implications for hydrothermal evolution within a pre-existing caldera

Abstract

Southeast China hosts extensive Late Mesozoic metallogenic systems, including metallic and non-metallic deposits genetically linked to tectonic-thermal events. Central Zhejiang Province, a major fluorite-producing region in China, exhibits spatiotemporal relationships with the Cretaceous magmatic-hydrothermal activity. In this study, zircon U–Pb and fluorite Sm–Nd geochronology, whole-rock/mineral geochemistry, Sr–Nd–H–O–Ca isotopes, and fluid inclusion microthermometry were used to constrain the genesis of the Shanwang fluorite deposit in the Mazhai caldera, central Zhejiang. Fluorite orebodies are structurally controlled by intracaldera faults and contain fluorite–quartz–barite–pyrite–pyrophyllite assemblages. Geochronological data revealed that fluorite mineralization (77 Ma, Sm–Nd isochron age) postdated the Early Cretaceous caldera-forming volcanism (128–125 Ma, zircon U–Pb age). Fluid inclusion data indicated low-temperature (128–184 °C) and low-salinity (0.2–8.8 wt.% NaCl eqv.) hydrothermal conditions. Stable isotopes (δD_VSMOW = -101.8‰ to -64.9‰, δ¹⁸O_VSMOW = -10.4‰ to -6.9‰) confirm meteoric water-dominated fluids. Integrated Sr–Nd–Ca isotopes (fluorite δ^44/40Ca values = 1.29–1.35‰) and trace element characteristics demonstrate that ore-forming materials were primarily leached from volcanic rocks via meteoric water–rock interaction in a paleo-geothermal system, with subsequent migration along fault zones leading to fluorite precipitation. Mineralization is correlated with Late Cretaceous lithospheric extension driven by the Paleo-Pacific slab rollback beneath Southeast China.