豫西东闯金矿床流体包裹体及稳定同位素研究

Fluid inclusions and stable isotope geochemistry of Dongchuang gold deposit in western Henan: Implications for genesis

东闯金矿床位于华北板块南缘的小秦岭金成矿带中部地区。矿体呈脉状、透镜状赋存于东西向压扭性断裂中,赋矿围岩为太古界太华群变质岩系。成矿作用可分为4个阶段,从早到晚,流体包裹体均一温度分别为296~342℃、257~341℃、250~314℃和175~267℃;对应流体盐度w(NaCleq)为5.23%~6.63%、1.63%~8.77%、3.38%~8.61%和8.55%~11.1%,以5%~9%为主,流体成分以H2O-NaCl-CO2为主。估算成矿压力为100~160MPa,静岩压力深度3.6~5.3 km。包裹体水的δDV-SMOW值为-49‰~80.2‰,多数在50‰~60‰之间,δ18O水计算值为3.33‰~7.88‰。碳酸盐矿物δ13CV-PDB为-5.1‰^-1.3‰,δ18OV-SM为9.9‰~15.29‰。矿石硫化物的δ34SV-CDT为-2.75‰~5.52‰,均值1.11‰,而其206Pb/204Pb=16.973‰~17.068‰、207Pb/204Pb=15.322‰~15.394‰、208Pb/204Pb=37.323‰~37.491‰。流体包裹体研究以及H-O、S、C、Pb同位素结果表明,东闯金矿床的成矿流体主要来自深部岩浆,矿质主要来自太华群地层。该矿床为低盐度、中成、中高温岩浆热液型金矿床。

The Dongchuang gold deposit is located in the central part of the Xiaoqinling gold metallogenic belt,which tectonically belongs to the southern margin of North China plate.Ore bodies occur as veins and lens within nearly EW-trending compresso-shearing faults,and are hosted by metamorphic rocks of Archaean Taihua Group.In accordance with paragenetic association of minerals and intercalation relationship of different veins,hydrothermal ore-forming period can be divided into 4 stages,and gold mineralization mainly occurred at stage Ⅱ and Ⅲ.The homogenization temperatures of fluid inclusions of the 4 stages are 296~342℃,257~341℃,250~314℃ and 175~267℃ respectively,with salinities of 5.23%~6.63%,1.63%~8.77%,3.38%~8.61% and 8.55%~11.1% accordingly（mainly between 5% and 9%）,and the hydrothermal fluids belong to the H2O-NaCl-CO2 system.The estimated ore-forming pressures of major mineralizing stages are from 100 MPa to 160 MPa,corresponding to the ore-forming depth of 3.6 km to 5.3 km.The calculated δ18O values of H2O in fluid inclusions in equilibrium with quartz is from 3.33‰ to 7.88‰,and the δDV-SMOW is from-49‰ to 80.2‰,mostly between 50‰ to 60‰.Moreover,the δ13CV-PDB and δ18OV-SM values of carbonate minerals（calcite） vary from-5.1‰ to-1.3‰ and from 9.9‰ to 15.29‰,respectively.Sulfide minerals in ores have a range of δ34SV-CDT values from-2.75‰ to 5.52‰,with the mean value being 1.11‰.However,206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios all vary within a narrow interval,from 16.973‰ to 17.068‰,15.322‰ to 15.394‰ and 37.323‰ to 37.491‰,respectively.Based on thermodynamic researches on fluid inclusions and comparisons of H,O,C,S and Pb isotopic compositions between ores,Taihua Group and Yanshanian granitic intrusions,it is concluded that ore-forming fluids originated from hypomagma,while Taihua Group offered ore-forming materials.The Dongchuang gold deposit is a magmatic hydrothermal type gold deposit characterized by low salinity formed under mesothermal-hypothermal and mesozonal conditions.