Ore-forming Fluid And Metallogenic Mechanism Of The Qiyugou Gold Deposit, Henan Province, China

The Qiyugou Au deposit is 18 kilometers from the county, which located in the Xiong'er shan area, southern margin of the North China Craton. This mineral deposit is a typical of breccia hosted Au deposit. Xiongershan-Waifangshan region is an important gold mineralization region where assemble numerous Au, Mo, W, and Ag-Pb-Zn deposits.Every breccias of the Qiyugou Au deposit is not far from each other, actually, mineralization situation of every breccias are different:J2 breccia has gold ore, J4 breccia has copper and gold ore, J2 breccia has gold ore, J7 breccia has molybdenum and gold ore.On the basis of the field work and microscopic observations, four stages of mineralization have been recognized:the Quartz-Potash Feldspar stage (Ⅰ), the Quartz-Pyrite stage (Ⅱ), the Gold-Complex sulfide stage (Ⅲ), and the Quartz-Carbonate stage (Ⅳ).The mineralization mainly occurred in phaseⅡandⅢand gold mostly enriched in the late paragenesis of stage III. The ore minerals consist mainly of pyrite, chalcopyrite, electrum and gold, less significantly, galena, sphalerite, magnetite and hematite. The dominate gangue minerals are quartz, sericite, epidote, clacite, chlorite, biotite, plagioclase and amphibole.Hydrothermal alteration is well developed,such as silicification, sericitization, chloritization, and carbonatization, in addition,silicification being closely related to mineralization.The mineral stone structure include mainly of massive structure, disseminated structure, brecciated structure, mesh-vein structure and vein structure. The textures of ores consist mainly of crystal structure, deformational texture and replacement texture.Fluid inclusions study of calcite and quartz has revealed that liquid rich two-phase fluid inclusions, daughter minerals bearing inclusions and CO2-rich three-phase inclusions are dominate all mineralization stages. The primary fluid inclusions are grouped close together, and minority primary fluid inclusions appear in isolation. The shapes of fluid inclusions are round, oval, negative form and irregular.The size of fluid inclusions is from11μto 35μ. The experimental results indicate that:Daughter minerals bearing inclusions(S type), gaseous fluid inclusions (V type) and two-phase fluid inclusions(L+V type) are locally present in minerals of stageⅠ. Every types of fluid inclusions(S type, L+V type, C type, V type) are locally present in minerals of stageⅡ,Ⅲ.Two-phase fluid inclusions (L+V type) and pure liquid fluid inclusions are locally present in minerals of stageⅠ. Daughter minerals bearing inclusions(S type) appeared in all phases of hydrothermal period. Daughter minerals include Hematite, chalcopyrite, pyrite and calcite.The fluid inclusions in several types of rocks in the Qiyugou were systematically investigated in the aspects of petrography and temperature of phase change show that the homogeneous temperatures of the inclusions from stageⅠto stageⅣare 409.3～506.3℃, 303.6～442.8℃,251.6～344.0℃, and 121.8～254.6℃, respectively, while the calculated salinities of the ore fluids are17.08～20.89 wt.% NaCl equiv.,6.16～20.07 wt.% NaCl equiv.,1.4～17.17 wt.% NaCl equiv., and1.4-12.85wt.% NaCl equiv., respectively. Both homogenization temperatures and salinities are progressively decreasing from stageⅠto stageⅣLaser Raman spectrometer is applied to the identification of single fluid inclusion.20 samples come from J4 breccia to test. Liquid ingredients of V+L type is H2O, moreover, gas is CO2 and N2. By analyzing the data of group fluid inclusion, gas are H2O, CO2, O2, N2 and CH4.Furthermore, Na+, K+, Ca2+, Mg2+, Cl-, SO42-, F-and NO3-are existence.QYG-155, QYG-157, QYG-166 and QYG-122 had obvious mineralization, which also had abundant Cl-. So there is the possibility, Cl- is a great media of extract metallogenic material, in other words, migration of Au depend on chloric complex.The granite porphyry is dated to be 153.6±2.4Ma by LA-ICPMS zircon U-Pb, which surround J4 breccia. The contents of trace element in ore are complex.The characteristics of rare earth elements and sulfur, hydrogen and oxygen isotope indicate that gold mineralization are closely related with granites. The comibined fluid inclusion and stable isotope data support previous proposals for a genetic relationship between the Qiyugou ores and magmatic fluids. The ore-forming-fluid, which derive from magma, is near-saturated supercritical fluid and came from the magmatic exsolution with rich volatile constituent. Supercritical fluid is rich in CO2 and focus appearance in stageⅡ.It seldom the number of appearance in stageⅠ. Estimate for metallogenic pressure was 24MPa-37MPa.There is minerogenic mechanism of the Qiyugou deposit:Emplacement of granite magma was high oxygen fugacity.In Magma chamber, near-saturated supercritical fluid was gathering more and more so that stresses inside was increases. As the pressure inside higher than increases exterior pressures, crypto-explosion was happen. Then Ore-forming material transport and produce breccias. With the reduce of temperature and pressure, the supercritical fluid was Change to vapor phase with low salinity (CO2-H2O System) and liquid phase with high salinity (H2O-NaCl System).Cryptical blasting, fluid-boiling and meteoric water-mixing are reasons of gold deposition in the deposit, forming cement type and vein type mineralization. It has been found that the mineralization and enrichment by hydrothermally altered. Then the meteoric water-mixing change the fluid inclusion into liquid phase with low salinity...