The Ore-forming Fluid Characteristics And Mineralogenetic Epoch Of The Dayin’gezhuang Gold Deposit In Jiaodong Region

Eastarn Shandong gold deposit eluster is the most important gold Province inChina. Sanshan island fracture zone, Jiaojia fault zone and Zhaoping fault zone is themost important metallogenic belt located in Eastarn Shandong gold deposit eluster.The Dayin’gezhuang gold deposit is a typical rotten-rock gold deposit which occurswithin the central Zhaoping fault belt. The gold deposit includes26ore bodies inwhich the main ore bodies are No. Ⅰ and Ⅱ. No. Ⅱ ore body isthe research object ofthis paper. No. Ⅱo re body which has a strike of20°to NE, a dip of28°～53°to NW,is distributed in66-84exploration line, and-80～-570m elevation. The ore bodyaverage gold grade is2.56×10-6.The ore type mainly is beresitization rock, and fractured granodioriticsericitization rock, composed of pyrite, sphalerite, chalcopyrite etc metal sulfideminerals, and quartz, sericite, carbonate minerals etc nonmetallic minerals．Thetextures of ores are predominant in crystalline-granular texture, cataclastic texture andmetasomatic textures texture．The structures of ores are dominated by nodularstructure, disseminated structure, vein structure and brecciaed structure. The types ofwall rock alteration include potassic alteration，pyrite-sericite-quartz alteration，sericite-quartz alteration， silicification， pyritization， carbonatization andchloritization． The mineralization stages contain beresitization, pyrite-quartz,quartz-pyrite, polymetallic sulfides, and quartz-pyrite-siderite and quartz-carbonatestages.Thermometry of fluid inclusions shows that the inclusions of the gold deposit arebasically I1types with aqueous vapor+aqueous liquid, which mainly concentrated in1～4um in diameter, and a few can reach6um. The homogeneous temperature of I1types inclusions is between155.7～325.5℃, which mainly concentrated in220～280℃. The paper applies traditional mineralogy methods to calculate the equilibriumtemperature of potash feldspar, which include Barth geothermometer, J.C.Stormergeothermometer and X-ray powder diffraction. The potash feldspar samples comefrom hydrothermal potassium feldspar metallogenic period, and the equilibrium temperature is400±50℃,415±30℃, and422℃, respectively. Combine the actualconditions, the equilibrium temperature which apply traditional mineralogy methodsis better than using thermometry of fluid inclusions.Carbon and oxygen isotopes analysis shows δ13C V-PDB‰ranges from-3.5~-5.3. The results suggest that the source of Carbon isotope comes from the mantle,and there may be have hydrothermal metasomatic reaction between fluids and wallrocks. The ore forming fluid evolution is influenced by atmospheric water. Thepotassium feldspar Ar-Ar age is118.5±1.0Ma (2σ), which is close to other golddeposit in Eastarn Shandong gold deposit eluster. The potassium feldspar comes frompyrite-quartz-potassium feldspar mass. According to the ore-forming age, thecrystallization of potassium feldspar mass from rotten-rock in the gold deposit(hydrothermal alteration events) is no direct relation with the emplacement events ofGuojiadian biotite monzogranite. Metallogenic Microscopic evidence andOre-forming age show that The Dayin’gezhuang gold deposit is an Orogenic-like typegold deposit.