The Study Of Geology, Geochemical And Mineralization Of Tangzhangzi Au Polymetallic Deposit, East Hebei Province

Tangzhangzi Au poly-metallic deposit is located 17 km from southeast Kuangcheng of East Hebei. Geotectonic position is in Yanshan folded fault belt of North Margin of the North China Craton. This study focuses on the diagenesis-mineralization relationship, fluid and metallic material origin and ore forming mechanism. Based on a series of experiments, i.e, magmatic zircon U-Pb dating, Hf isotope analysis, whole-rock geochemistry analysis, fluid inclusion micro-thermometry, H-O isotope composition analysis for fluid inclusion and S, He-Ar isotope composition analysis for metallic sulfide, we draw a series of conclusion below:Based on geologic feature of orebodies, mineral assemblages and cross-cutting of veins, 6 metallogenetic sub-stages which respectively belong to 2 main metallogenic stage are divided. One main metallogenic stage is molybdenite stage whicn includes potash feldspar sub-stage, molybdenite mineralization sub-stage and pyrite- carbonate sub-stage. The other one is Au- polymetallization stage which includes pyrite- quartz sub-stage, gold and polymetallic mineralization sub-stage and quartz-carbonate sub-stage.Gold precipitated in thick smoky quartz veins or associated with pyrite, chalcopyrite, sphalerite, galena. Electron probe microanalysis(EPMS) of polymetallic sulfide indicates that the gold is mainly hosted in pyrites of quartz-polymetallic sulfide veins and silver is primarily hosted in freibergite.We got two groups of LA-ICP-MS zircon ages, respectively 161.23±0.65Ma(A) and 173.0±5.5Ma(B) of granite porphyry from the main adit at an altitude of 370 meters. B group represents diagenetic age. Zircons of A group were considered to be altered by hydrothermal, resulting in a young age for losing radiogenic lead. The U-Pb dating indicates that the mineralization process was after 173.0±5.5Ma.In combination with tectonic setting of other researchers, and geochemical study of granite porphyry and dolerite, we consider that the mineralization process took place under the tensional intraplate tectonic setting.Fluid inclusions’ observation under microscope and micro-thermometry of different metallogenic stage demonstrate that the ore-forming fluid is H2O-CO2-Na Cl system. The homogenization temperatures of Au-polymetallic fluid inclusions are relative of statistical significance. The homogenization temperatures vary from 143.7℃ to 320℃ and most data are at 170℃ to 240℃. The salinities are between 4.96% and 11.7% and the densities are between 0.96 g/cm3 and 0.81 g/cm3.Hydrogen-Oxygen isotopic compositions indicate that the ore forming fluids are mainly from magma and only a little meteoric water was mixed in it. S, He-Ar isotopic compositions of metallic sulfide indicate that the ore forming materials were derived from crust source.