| The Xincheng gold deposit is one of the large"Jiaojia Type"gold deposits, lies in Jiaojia gold ore belt.The gold mineralization divided into 4 processes: coarse grained pyrite-quartz(I); fine-grained pyrite-sericite-quartz(â…¡);quartz-polymetallic sulfide(â…¢); quartz-carbonate(â…£) . Through the research on the fluid inclusions of different gold mineralization processes by petro-graphic,microscopic differential thermometry,geochemical,I get the following cognitions about the evolution and mechanism of the ore-forming fluid:(1)There are mainly gas-liquid fluid inclusions in the metallizing period,the uniform temperature is 190℃～310℃,the salinity is 2.56～10.74wt%NaCl.eqv,the density is 0.647～0.971g/cm3,which belongs to low density, low salinity fluid. The parameters of petro-graphic of processâ… ,â…¡,â…¢:the uniform temperature is 260℃～310℃, 230℃～270℃,190℃～230℃,which presents degressive tendency;The salinity is 6.14～10.24wt%,3.56～9.7wt%,2.56～6.29wt%.(2) The main gas phase composition of fluid inclusions is H2O and CO2,and little Ar,H2S,SO2,N2,C2H6,etc. In the Liquid phase composition, the cation is mainly to Na+ and K+ ,and Na+ is the highest, K+ followed, the content of Mg2+ and Ca2+ is very low; at the sane time, the anions is mainly to SO42-and Cl- ,and ore-forming fluids belong to the Na+(K+, Ca+)-Cl- (SO42-, F-)-H2O system. From the Mineralization stageâ… toâ…£, with the increasing of SO42-, Cl- decreased. In the mineralization stageâ…£,the content of Na+ and K+ decreased compared with the first three stages(3)In the test results of hydrogen and oxygen isotopes in fluid inclusions, theδ18OH2O-δDH2O projection points of samples in the mineralization stageâ… drop in just below the primary magma hydrotherm, it may indicate that the ore-forming fluids come from the deep; from the ore stageâ…¡, a tendency of a drift to atmospheric water may suggest the addition of atmospheric water in the ore-forming process.(4)Analyzing the synthesize results of gas-liquid phase ingredient of inclusion enclave, hydrogen and oxygen isotopes and isotopeδ34S , it is think that the ore- forming fluid of Xincheng gold deposits is come from magmatic hydrothermal. With the evolution of ore-forming stage, a large number of meteoric water mixed with ore-forming fluid, reflecting the precipitation mechanism of ore-forming fluids is the migmatization of deep fluid and meteoric water, which is the main reason for gold precipitation.
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