Study On Fluid Inclusions And Geochemical Characteristics Of Major And Trace Elements Of Fluorite In The Dabate Cu-Mo Deposit,West Tianshan,Xinjiang

The Dabate Cu-Mo deposit in West Tianshan,Xinjiang is located in the middle of the Sailimu block,between the Late Paleozoic Boluokenu Island arc and the Alatao continental margin basin.Predecessors still lack systematic research on the large amount of fluorite developed in the ore of the copper ore section of this deposit.This paper comprehensively utilizes research methods such as petrography,mineralogy,fluid inclusions,and major and trace element geochemistry,and based on the identification of the geological characteristics of the deposit,the nature of the ore-forming fluid was determined,and the source and evolution of the ore-forming material and the color mechanism of fluorite were discussed..The ore in the copper section of the Dabate Cu-Mo deposit contains a lot of fluorite.In the early stage,green fluorite and white fluorite are closely symbiosis with chalcopyrite and arsenopyrite,and in the late stage,purple fluorite is symbiotic with chalcopyrite,quartz and potash feldspar.The formation of white fluorite in early stage of fluorite is slightly later than that of green fluorite,and the order of formation is:green fluorite?white fluorite?purple fluorite.The study of fluid inclusions in fluorites of different colors at various stages shows that the ore-forming fluid related to the ore formation of the copper section of the Dabate Cu-Mo deposit is the F-rich H₂O-CO₂-Na Cl system,and the early-stage ore-forming fluids are high temperature,low salinity,medium-low density.The late-stage ore-forming fluids are medium-high temperature,low salinity and medium-low density.The precipitation mechanism of Cu in the early stage is dominated by fluid cooling,while the precipitation mechanism of Cu in the late stage is dominated by fluid mixing,and the higher CO₂ content in the two stages is also conducive to Cu precipitation.A systematic study of the geological background of the copper mineralization of the Dabate Cu-Mo deposit and the REE geochemical characteristics of fluorite,it shows that the rare earth element distribution curve of the early green and white fluorite is a typical"V"-shaped broken line with a slight right-leaning,with the characteristics of relatively enrichment of light rare earths and relatively depletion of heavy rare earths.The rare earth element distribution curve of late purple fluorite shows a slightly left-leaning"N"-shaped broken line,which has the characteristics of relatively depleted light rare earths and relatively enriched heavy rare earths.The early green and white fluorites all have negative Eu anomalies,and the late purple fluorites are not obvious negative Eu anomalies.It is speculated that the ore-forming fluids evolved from the early reducing environment to the late neutral environment when the fluorite deposits in this deposit.Green fluorite,white fluorite and purple fluorite have homology,and they are all of hydrothermal origin,which are separated and crystallized from ore-bearing hydrothermal fluid.The ore-forming fluid comes from pebbly rhyolite porphyry.The difference in?REE concentration is the reason for the different colors of green fluorite and white fluorite,and the color of fluorite changes from green to white as the concentration of?REE decreases.Crystal defects caused by elements such as Th⁴⁺,Na⁺and crystal plane damage,and the selective absorption and transmission of color by colloidal calcium are important reasons for late-stage fluorite to appear purple.