Origin of the Tongda fluorite deposit related to the Palaeo‐Pacific Plate subduction in southern Jiangxi Province, China: New evidence from geochronology, geochemistry, fluid inclusion, and H–O isotope compositions

Abstract

The southern Jiangxi Province is an important part of the fluorite mineralization belt in South China. Fluorite ore bodies are primarily in the contact zone between the Devonian Huitong granitic complex and the Late Cretaceous Ganzhou Formation, controlled by the NE‐trending faults. Zircon U–Pb dating of the Huitong granitic complex yields emplacement ages of 410.7 ± 1.4 Ma and 400.7 ± 4.6 Ma, while the Sm–Nd dating of the fluorite yields an isochron age of 94 ± 2 Ma, suggesting that the Huitong granitic complex is the host rock. Fluid inclusions in the fluorite show low homogenization temperatures (136–207°C), salinities (1.23–3.87 wt% NaCl), and densities (0.87–0.95 g/cm3), suggesting that the ore‐forming fluid is an NaCl‐H2O system of low temperature, salinity, and density. Raman spectroscopy showed that the fluid phase is dominated by water. The δDVSMOW values of the fluid inclusions in the Tongda fluorite ranged between −59.5 and −55.2‰, while the δ18OVSMOW values of the fluorite ranged from −7.2 to −5.6‰. Collectively, the ore‐forming fluid is dominated by meteoric water, possibly with a minor contribution of hydrothermal fluid. Both the interaction with host rocks and the cooling of hydrothermal fluids are the likely mechanisms of underlaying fluorite precipitation at low temperatures. The mineralization occurred in extensional faults during the Late Cretaceous related to the subduction of the Palaeo‐Pacific Oceanic Plate.