Study On Metallogenic Mechanism Of Qimudigou Gold Deposit In Songxian County,Henan Province

The Qimudigou gold deposit in Song County, Henan province, it is located in the southern margin of the North China Craton Xiongershan area. The presence of acidic volcano rock of mesoproterozoic Xiong’er group in the deposit, ore bodies are strictly controlled by the tectonic faulted zones of vein. mainly veinlike, quartz vein type is dominant in the ore, a small amount of corrosion becomes rock type; The main ore minerals as pyrite, a small amount of galena, sphalerite, chalcopyrite. Wall rock alteration silicification, sericitization, chloritization and carbonatization.Divided into three stages: Quartz-pyrite stage, pyrite-quartz-multi metal sulfide stage and quartz-calcite stage ore-forming process of from morning till night. Fluid inclusions in quartz and/or calcite in different stages of mineralization. Early stage and middle stage quartz CO₂ fluid inclusions in fluid inclusion body, NaCl-H₂O type, sub mineral fluid inclusions were developed. In the late stages of calcite mainly developed NaCl-H₂O type fluid inclusions. From early stage to late stage, homogenization temperature of fluid inclusions were 254℃-397℃, 221℃-397℃, 162 ℃ -237 ℃, salinity from early stage bimodal salinity values 3.52-21.88 wt.%NaCl.eqv and 34.95-45.33 wt.%NaCl.eqv, the bimodal phase salinity value of 0.42-13.83 wt.% NaCl.eqv and 29.11-42.48 wt.%NaCl.eqv, to late stage of salinity is 0.35-5.86 wt.%NaCl.eqv. CO₂ inclusion to estimate the trapping pressure for 93-199MPa, 47-169Mpa in early and main stage, Trapping pressure of W-type inclusions in the estimated 28-64MPa in late stage, 3.4-7.2km, 1.7-6.2km and 2.9-6.5km corresponding mineralization depth, indicating that the mineralization occurs in the earth’s crust uplift, the regional stress field from compression to extension transformation. Fluid boiling is the main mechanism of rapid precipitation of sulfide and gold and other mineral deposits. The evolution of the ore-forming fluid system is enriched by CO₂ to the poor CO₂ through the mixing of boiling and precipitation., and the fluid system is evolved from the metamorphic fluid to the atmosphere.We collect samples of fractured belt-alteration rock type and vein-type at different levels, and divide these samples into different mineralization stages. With the method of inductively coupled plasma mass spectrometry（ICP-MS）, trace element, rare earth element of the pyrites and whole rock in the samples are tested to inflect characteristics of ore fluids evolution. Compared to CI chondrite, LREE is more enriched than HREE in pyrites, Hf/Sm and Th/La are all less than 1, which indicates Cl- was enriched in the ore fluids while F- was lacking. Compared to continental crust, thiophil elements including Cu, Pb and iron group elements including Co, Ni were enriched in ore fluid. In each stage, pyrites show a weak Ce anomaly（δCe ranges from 0.60-1.08）, which indicates a reducing condition during the mineralization process. Eu2+ is apt to stay in the high temperature condition which leads to the normal anomaly, while Eu in the pyrite shows no exception. During the early stage, δEu ranges from 0.71-1.29, in some special cases, δEu is larger than 1, during the main stage, δEu ranges from 0.89-0.92, concentrating around 0.9, during the late stage, δEu ranges 1.13, which indicates that during the early mineralization stages, temperature of ore fluid was low, during the late mineralization stages, temperature of ore fluid was low, with high-temperature hydrothermal fluids entering. Y/Ho and Zr/Hf are stable in the stable hydrothermal systems, the wide range of Y/Ho and Zr/Hf of pyrites in Qimudigou gold deposit indicates the ore fluid changed when external hydrothermal fluids entered or reacting with the wallrocks.The average δ¹⁸Owater values changed from 5.8‰ in the early stage, through 3.5‰ in the middle stage, to-4.4‰ in the late stage, with the δD values ranging between-79‰ and-96‰. The δ13CCO₂ values of ore fluids are between-0.9‰ and-22.2‰, with an average of-13.0‰. The C-H-O isotope systematics indicate that the ore fluids forming the Qimudigou gold deposit were probably initially sourced from a process of metamorphic devolatilization, and with time gradually mixed with meteoric water.