Geology, fluid inclusion and fluorite geochemistry constraints on the genesis of the large-scale Guancun fluorite deposit, Zhejiang Province, Southeast China

• The Guancun fluorite deposit exhibits two distinct stages of mineralization. • Integrated fluid inclusion analyses indicate that fluid mixing served as the predominant mechanism of fluorite. • Systematic variations in trace element compositions between these two stages provide critical constraints on both the coloration of fluorite and its precipitation mechanisms. The large-scale Guancun fluorite deposit is situated within the Yangtze Block in northwestern Zhejiang Province. Mineralization occurs predominantly along an unconformity between the Cretaceous Laocun Formation and the Permian Qixia Formation and is intimately associated with silicified alteration zones, with minor stockwork and breccia type mineralization hosted in the Permian Qixia Formation. Based on detailed field and petrographic observations, the mineralization at Guancun can be divided into at least five stages: Stage I is characterized by the formation of early fluorite (Fl-1) in vein and breccia cement in both unconformity and limestone-hosted orebodies; Stage II is marked by the precipitation of barite (Brt-1); Stage III is characterized by quartz (Qz-1) crystallization, which rims the earlier barite; Stage IV represents the deposition of rhythmically banded fluorite (Fl-2) and stage V signifies the termination of mineralization with the formation of crustified quartz and minor pyrite. Fluid inclusion studies in fluorite and quartz reveal the evolutionary history of the ore-forming fluids and precipitation mechanisms. Liquid-rich two-phase inclusions are the dominant fluid inclusion type across all stages. Fluid inclusions in Fl-1 exhibit homogenization temperatures of 164–375 °C and salinities of 0.18–7.59 wt% NaCl equiv., with the broad ranges interpreted to reflect mixing between magmatic-hydrothermal fluids and meteoric water. Subsequently, type L inclusions in stage III quartz (140–250 °C and 1.57–3.87 wt% NaCl equiv.) show features inherited from the final mixed fluid in stage I fluorite, implying declined meteoric water mixing during quartz precipitation. Fluid inclusions in Fl-2 (130–227 °C and 0.18–0.70 wt% NaCl equiv.) record further decreases in temperature and salinity, indicating further fluid mixing and second episode of ore formation. The geochemical signatures of fluorite, particularly its rare earth element (REE) patterns, provide critical insights into elemental behavior, fluid evolution, and mineralization conditions. LA-ICP-MS data of fluorite indicate a genetic relationship between the Guancun fluorite deposit and concealed granites in the region. Trace elements, especially REEs, exert a significant control on the color zonation of fluorite. Higher REE contents in colored varieties, with specific Ce and U correlations for green and purple respectively, alongside elevated Fe in late-stage zones, identify these elements as key determinant governing both the initiation and intensity of coloration. Variations in elemental concentrations, along with Eu and Ce anomalies, suggest mineralization under fluctuating temperature and redox conditions consistent with microthermometric results. Taken together, mixing between ascending deep F-bearing magmatic fluid and calcium-rich meteoric or underground water is proposed as the principal mechanism for fluorite mineralization. Additionally, water–rock interaction between F-bearing fluids with carbonate host rocks may represent another important mechanism for fluorite precipitation.