Study On The Fluid Inclusions Of Xiejiagou Gold Deposit

The Xiejiagou gold deposit is located between Jiaojia fault belt and Zhaopingfault belt in the eastern Shandong province. The fault structure is very complicated.The ductile-brittle fracture zone provided advantaged spatial condition for themineralization and controlled the occurrence of ore bodies. Pyrite-phyllic alterationrock is the dominant ore type. The metalogenic processs can be further divided intofive stages, i.e. (â… )quartz-pyrite stage;(â…¡)quartz-pyrite-chalcopyrite stage;(â…¢)quartz-multi-metal sulfide stage;(â…£) quartz-carbonate-pyrite stage;(â…¤) (without Au)stage;and most gold occurs in the former three stages.The homogeneous temperature of the inclusion from I～III stages are mainlyconcentrated 260～340℃, indicating the deposit is a mesothermal deposit. Thecorresponding salinity and density of the three stages are 2.07～9.08wt%NaCl.eqv and0.57 ～ 0.97g/cm3 respectively, which shows the ore-forming fluid belongs tolow-salinity and density fluid system. The capture pressure of fluid inclusions is2.66bar ～ 212.71bar. The ore-forming depths is about 748.52m, so it is ashallow–seated deposit.The gas component of fluid inclusions is dominated by H2O and CO2, and alsohave little Ar,H2S,SO2,N2,C2H6 etc. From Ⅰ～Ⅲ to IV stage, the content ofH2O increases, and the content of CO2 decreases correspondingly. The positive ions influid inclusions are mainly Na+ and K+;and the main negative ions are Cl-and SO₄^2-.That is to say, the sample of Ⅰ～Ⅲ-stage, the ore-forming fluids are generallycharacterized by Cl-> SO₄^2- and Na+> K+, belonging to Na+-Cl-type fluid. But for thesample of IV-stage, Na+ 4^2-, belonging to K+-SO₄^2- type fluid.In I, II, III stage, the δ18O average value of quartz is 10.98‰ equal to themineral-bearing the biotite granite and the Guojialing granite which occurs in the deepof the Xiejiagou gold ore district. The corresponding δ18OH2O average values of waterare 4.15‰. The δDH2O average values are -86.68‰. The plots of ore fluid in goldmineralization stage (I^III stages) falls in the area below the metamorphic water, nearthe magmatic water and move to the meteoric water line. The δDH2O value of the fluidinclusions in the fluorite formed after metallogenesis is -122.71‰, being identicalwith the Mesozoic meteoric water .Therefore the H-O isotopic characteristics indicatethat the ore-forming fluid was derived from magmatic water, and was mixed by someatmosphere water in the late stage of metallogenesis.The assemblage of different fluid inclusions and evolution of fluid show thatblend is the key element for mineralization.