The Characteristics Of Metallogenic Fluid And Genesis Of Yinkeng Porphyry-Mo Deposit In West Zhejiang Province

Yinkeng porphyry-Mo deposit in West Zhejiang province is restrained by Jiangshan-Shaoxing fracture belt locating in Huaxia plate. Fractures are well developed and the caldera structure is clear in Yinkeng mine area. Porphyry granite acts the major ore-bearing rock body. Mineralization mainly occurs in porphyry granite and appears disseminated.Different measurements are done to determine the characteristics of FIs and the temperature of various alteration belt in Yingkeng ore zone, therefore metallogenic periods of fluids the FIs and the metallogenic processes are withdrawn. The depth of the deposit is calculated and a three-stage metallogenic model is made.The type of fluid inclusions is plentiful and gas-rich inclusions, gas-fluid inclusions, crystal-included inclusions and CO2-three-phase inclusions are well discovered. Many crystal-included inclusions and gas-rich inclusions are symbiotic in quartz crystals. The types of FIs have obvious transition characteristics from the quartz crystals, quartz veins of early-stage to ore-bearing quartz veins. The homogeneous temperature gradually declines in FIs of crystals to quartz veins. The homogeneous temperature of gas-rich inclusions and crystal-included inclusions is mainly350～450℃,250～405℃as to the gas-fluid inclusions with a more distribution in305～405℃. High-T, high-Salinity FIs develops in early metallogeny with low-T, medium-salinity FIs in Late stage. The homogeneous pressure varies between1and36MPa. Based on detailed study of quartz crystals, ore-bearing quartz veins to ore-barren quartz veins, combined with geological characteristics of ore deposit, the FIs is divided into four stages, of which second and third stage is the principal mineralization stage with an obvious character of boiling.A-type granite acts the major metallogenic body and the fluid boiling and mixing process play an important role in metallogenic process. Capture pressure of39.6～49.4MPa is constrained by FIs and suggests a metallogenic depth of1.5～2.0km. The Yinkeng ore deposit is typically controlled by structure-magma-fluid system.Through the contrast of rock fabric, metallogenic era, tectonic settings, types of magma, character of FIs and compositions of FIs, two diverse metallogenic fluid systems and metallogenic process is withdrawn in West Zhejiang province.There exists two different metallogenic proccesses with Jiangshan-Shaoxing fracture zone as boundary. The first kind of magma planer distributed is early Yanshan period with I-type and S-type granites and the age appears younger from west to east. It is controlled by regional compressive stress. The other locates in the east to Jiangshan-Shaoxing fracture zone, with an age of Late Yanshan period and controlled by nearly east-westward extensional stress. The magma is major A-type and I-type and is linear distributed along regional fracture.