The reasons for large-scale fluorite mineralization in South China during the Mesozoic-Cenozoic

South China is a globally significant concentration area of fluorite deposits. Significant genetic differentiation is observed in fluorite deposits across different tectonic units due to variations in their associated mineral assemblages, yet their metallogenic dynamic settings and material sources remain unclear. A research team investigated typical fluorite deposits in the western margin of the Sichuan Basin (associated with lead-zinc deposits), its eastern margin (associated with barite), and the Zhejiang-Jiangxi region (associated with quartz). The research team, by integrating Sm-Nd geochronology, microthermometry of fluid inclusions, H-O-S-Sr-Pb isotopic tracing, and in-situ LA-ICP-MS trace element analysis, aimed to reveal why large-scale fluorite mineralization occurred in South China.

In the Zhejiang-Jiangxi region, fluorite is often associated with quartz, and the mineralization age is concentrated in the Late Cretaceous to Early Cenozoic. The ore-forming fluids were predominantly meteoric water, characterized by low temperature and low salinity. Rare earth elements and isotopic signatures indicate that the ore-forming materials were mainly derived from water-rock reactions involving fluorine-rich volcanic rocks and basement metamorphic rocks. Mineralization was controlled by extensional faults triggered by the retreat of the Pacific Plate. The eastern margin of the Sichuan Basin hosts widely developed MVT-type barite-fluorite deposits, which formed mainly during the Late Cretaceous. The tectonic setting is related to regional extension caused by the subduction of the Paleo-Pacific Plate. The ore-forming fluids were a mixed system of basin brines and meteoric water. Sr isotopes and rare earth elements suggest that the ore-forming materials were derived from Cambrian carbonate rocks, black shales, and Ordovician limestones. The western margin of the Sichuan Basin is a key area where fluorite is associated with lead-zinc deposits. Mineralization occurred mainly during the Late Triassic, related to the Indosinian orogeny following the closure of the Paleo-Tethys Ocean. The ore-forming fluids exhibited medium-low temperature and medium-low salinity characteristics. The coexistence of high- and low-salinity fluid inclusions, along with H-O isotopic data, indicates that the fluids were a mixture of basement metamorphic water, basin brines, and meteoric water. Sr-Pb isotopes and rare earth element characteristics show that the ore-forming materials were mainly sourced from Precambrian basement rocks and Cambrian sedimentary strata (e.g., black shales).

In summary, fluorite deposits in South China mainly formed during the Mesozoic–Cenozoic, with mineralization ages generally exhibiting a trend of being older in the west and younger in the east. The ore-forming fluids were dominated by meteoric water or basin brines, and the ore-forming materials were derived from fluorine-rich volcanic rocks and sedimentary strata, respectively. Tectonically, mineralization was controlled by two major dynamic systems: the closure of the Paleo-Tethys Ocean (western margin) and the subduction of the Paleo-Pacific Plate (eastern margin and Zhejiang-Jiangxi region).