| Shuangwang gold deposit, located in the southwestern Taibai of Shaannxi province,is characterized by large size and low grade, with simple ore type amenable to miningand ore dressing. Its unique breccia type mineralization is different from other golddeposits. The deposits occur in the Devonian strata which locate in west Qinling area.In this paper, the features of fluid inclusions and isotope geochemical characteristicsof the No.5ore body (KT5) are discussed, based on which the mineralizationmechanism is considered, and getting the following standpoints.(1) There are4types of fluid inclusions: aqueous, CO2-H2O-NaCl, pure CO2, anddaughter-mineral-bearing multiphase inclusion.(2) The ore-forming fluid system is typically mesothermal (186~349℃), low salinity(average9.1wt%NaCleqv), reducibility and CO2-rich. The composition of gas phasein fluid inclusion are dominated by CO2, H2O, with minor CH4. Liquid phasecomposition are dominated by Na+, Cl-,and Mg2+, K+, with minor SO42-, F-. Theoxygen fugacity is decline from early ore-forming stage to the late one, the fluid’spH-value and Eh-value increase from early ore-forming stage to the late one.(3) The petrography, micro-temperature measurement and breccia type mineralizationof fluid inclusion suggested that the ore-forming fluid experienced boiling. Themetallogenic pressure is90~110MPa, and the mineralization depth is3.4~4.1km.(4) Carbon isotope illustrated that the carbon came from mantle, magma, and marinecarbonate, implying the complex source. Sulfur isotope exposited that the ore-formingmaterials might come from strata partly, which indicates a mixed feature of sulfurcoming from the magma and the crust. Lead isotope revealed that lead came from theupper crust mainly and mantle secondly with complex sources of mixed lead, whichreflected that the lead came from deep source and related to orogeny.(5) Gold is mostly transported in the form of chlorine complex. By the change of thephysical and chemical conditions, the pressure of the fluid decreased with boiling, thatmaking the gold deposited. |
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