Fluid Mixing Metallogenic Mechanism Of Huize Superlarge Lead-Zinc Deposits In Northeast Of Yunnan Poly-metallic Mineralization Domain

By choosing a representative deposit, Huize Pb-Zn deposit in the ore concentration area of northeast of Yunnan province in poly-metallic metallogenic domain of Sichuan-Yunnan-Guizhou, based on the previous research results and detailed field geological survey, we revealed the mechanisms for the migration and precipitation of elements, and explained the characters of these deposits which are "rich, large, strong and zonation by studying on geochemistry of fluid inclusion, geochemistry of isotope, geological and geochemical thermodynamics and geochemistry of experiment. The conclusions are as follows:(1)Studying on the fluid-inclusion geochemistry showes that:Moreover, there are two kinds of fluids with different salinity(fluid A and fluid B) participated in the hydrothermal ore-forming process. From the hydrothermal mineralization stage Ii â†'stageI2â†'stage â…¡ â†'sstageâ…¢â†'stage â…£, the ore-forming fluid has obvious regularity characteristics on the homogenization temperature and salinity. Evolution process of ore-forming fluid are as follow:The salinity increases after decompression boiling of the high temperature high salinity of fluid in Ii stage in which precipitation part of sphalerite. Then it mixed with the other high salinity cryogenic fluid. With mixing, sulfide precipitate continuously. From the â… 2â†'â…¡â†'>â…¢â†'â…£ stage, the salinity of fluid decrease and the temperature fell slightly. Only a temperature drop is more obvious in late stage.The pH value calculation results show that ore-forming fluid is acidic in migration stage (pH<3.6). Lead and zinc migrated mainly by chlorine complex.(2)Isotope geochemical studies indicate that two fluid mixed in the ore-forming process; The acidic fluid A of high temperature and low salinity comes from the basement which is rich in heavy sulfur and lighter C, O isotopes. The Kunyang Groupe provides ample source for it. The fluid B of low temperature and high salinity is the formation brine which is the fluid of atmospheric precipitation leaching carbonate rock and extraction reduction of sulfur of pyrite and sulfate (gypsum) in formation.lt is rich in lighter S and heavier C-O, H-O isotopic composition.(3) The geological and thermodynamic studies showed that T and pH values determine the precipitation interval of sulfides in the fluids, the loga values are more related to the scale and grade of deposits, and the logfo2 and logfs2 values are still the key factors to control the mineral zonation of the lead-zinc paragenesis and differentiation.(4) The experimental geochemical study shows that acid effect is the primary factor to control the precipitation reaction. Acid and alkali barrier is the main ore-forming geochemical barrier of these deposits. In fluid mixing mode, lead and zinc ion react with HS- to precipitate to sulfide, rather than H2S or S2-.(5) Through the comprehensive research, it has established the migration and precipitation of in Huize Pb-Zn deposit. The oxidation acidic sulfate fluid (lead and zinc as chloride complex form) from the basement and the local reduction fluid which contain reducing fluid migrated driven by the tectonic power on their way into the interlaminar fracture. They mixed and precipitated after boiling. It demonstrates the mechanisms of supernormal enrichment of elements and huge amount of accumulation from diagenetic mineralization experiment, macro and micro research. It illustrate characteristics in this kind deposit which are "rich, large strong and zonation".The new mechanisms of supernormal enrichment of elements and huge amount of accumulation were put forward, the thermodynamics of constraints on mineral assemblage zoning was illustrated and the process of evolution of ore-forming fluid was further refined by this paper.It is not only important innovation in the field of cutting-edge research in the HZT type Pb-Zn deposits, but also a guiding significance and application prospect for ore concentration area in northeast Yunnan even the Sichuan-Yunnan- Guizhou metallogenic domain of fluid geochemistry, deposit geochemistry and experimental geochemistry and geological prospecting exploration.