Genesis of the Late Cretaceous fluorite mineralization surge in Zhejiang, South China, using geochronological, isotopic, and geochemical evidence from the Hengkengping fluorite deposit

• Fluorite Sm − Nd isotopic age of 80 Ma indicates ore formation during Late Cretaceous. • A new metallogenic model for the Hengkenping fluorite deposit. • South China fluorite mineralization was driven by Late Cretaceous Paleo-Pacific Plate rollback and extension. Large-scale fluorite mineralization occurred in the South China Block during the Late Cretaceous, but its genesis and tectonic setting remain unknown. The Hengkengping fluorite deposit, a representative large-scale hydrothermal vein-type monomineralic fluorite deposit in the Zhezhong–Wuyi minerogenetic belt in South China, is characterized by high-grade ore and substantial reserves. Most orebodies occur in NE-trending fractures within early Cretaceous porphyroclastic lava controlled by NE-striking faults along Mesozoic volcanic faulted basins. In this study, the timing and genesis of mineralization were systematically investigated through integrated methods, including cathodoluminescence imaging, fluid inclusion microthermometry, in situ laser ablation inductively coupled plasma mass spectroscopy (LA–ICP–MS) microanalysis, H–O isotope tracing, and Sm–Nd isotope dating. Ore textures and cathodoluminescence features revealed the following three mineral types (stages): purple veinlet/breccia-type fluorite, green massive fluorite, and colorless vein-replacement fluorite. The trace and rare earth element signatures of fluorite indicated a multistage growth history involving dissolution–reprecipitation–recrystallization, with characteristics of homologous medium- to low-temperature hydrothermal products. Sm–Nd isochron dating yielded an age of 80 ± 3 Ma, which coincides with terminal Late Cretaceous volcanism. The low εNd (80 Ma) values suggested crustal derivation of ore-forming materials. The δD and δ 18 O values of the ore-forming fluids indicated dominant meteoric water involvement. The fluid inclusion data revealed homogenization temperatures ranging from 100 to 190 °C and the occurrence of low-salinity H 2 O–NaCl fluids, corresponding to a shallow mineralization depth (∼0.9 km). The ore-forming system involved geothermal fluids derived from deeply circulated meteoric water heated by Cretaceous magmatic activity. Water–rock interactions between geothermal fluids and F-rich volcanic rocks generated weakly reduced, F-enriched medium- to low-temperature hydrothermal fluids. These F-bearing fluids, mobilized from Jurassic–Cretaceous pyroclastic sequences, precipitated large-scale fluorite deposits through cooling and decompression during their ascent along fault zones. In this study, it is proposed that Late Cretaceous extensional tectonics and volcanism, driven by Paleo-Pacific Plate rollback, provided critical controls on the surge in fluorite mineralization in the South China Block by providing F-rich materials, thermal energy, fluid dynamics, and structural traps for the formation of fluorite deposits.