Fluid inclusions and hydrogen-oxygen isotope geochemical characteristics of the Kayakedeng fluorite deposit in the eastern Kunlun Mountains

The newly discovered large hydrothermal vein-type fluorite deposit in Kayakedeng is located in the western section of the East Kunlun Mountains in Qinghai Province. The industrial ore bodies are mainly distributed along the contact zone between the Paleoproterozoic gneiss and marble, and are controlled by the Early Devonian K-feldspar granite, faults and fractures. The main types of ores are calcite-fluorite veins and quartz-fluorite veins. The mineral composition mainly consists of fluorite, quartz and calcite. The ore shows a medium-coarse grain structure, with blocky, banded, reticulate and brecciated textures. The analysis of fluorite inclusions indicates that the fluid inclusions during each mineralization stage have similar characteristics, with the majority being two-phase liquid-rich inclusions. The homogenization temperature of the fluid inclusions ranges from 90 ℃ to 220 ℃, the salinity is 2.07% to 3.87%, and the density is 0.84 g/cm3 to 1.01 g/cm3. This indicates that the ore-forming fluid is a low-temperature, low-salinity and low-density NaCl-H2O hydrothermal system. The hydrogen and oxygen isotope analysis of fluid inclusions indicates that the composition of the inclusion water lies between the atmospheric precipitation line and the magmatic water range, and is closer to the atmospheric precipitation line, suggesting that the ore-forming fluids mainly originated from atmospheric precipitation, with a small amount of magmatic water participating. It is speculated that the initially formed rich F-bearing hydrothermal fluid after the magma period rose along the fractures and mixed with atmospheric precipitation at the shallow surface. It then leached and extracted the Ca components in the surrounding marble, forming ore-bearing fluids. The fluids containing F and Ca fill and metasomatize the surrounding rocks in favorable positions of the fracture-crevice structural zone, forming calcite-fluorite veins and quartz-fluorite vein-type deposits.