Geological, Geochemical Characteristics And Metallogenic Model Of Jin Chang Super-large Gold Deposit, Dongning, Heilongjiang Provinces

Jinchang gold deposit is located in uplift belt between Zhangguangcai ling and Taiping Ling mountain.Huangsongqun group of upper proterozoic is the oldest strata in this area. The intrusive rocks are dominated by Intermediate-acid intrusives,such as granodiorite,adamellite,diorite(porphyrite) etc .They occur in batholith, stocks and veins.Regional tectonic history indicates that the area was in the process of Central Asian from Mongolia Ocean ,Collisional Orogeny to consolidating before Trias; After Trias,the district transformed from Pale-Asian ocean to Peri-Pacific tectonic domain, with intense volcanic eruption.The area developed strongly folds and fractures of NE-NNE trending, while TaipingLing anticlinoria and Suiyang deep fault affected magma activities and ore deposits-forming.The geological features of mining area show that: gold mineralization is divided into cryptoexplosive breccia type,fissure filling type,fracture alteration type; there are plenty of mine types such as Cu-Au orebody,Au orebody,Pb-Zn oredody ect,but mainly breccia-type Cu-Au orebody and Au orebody; the wall rocks ore-bearing are dominated byplagioclase,granite,granodiorite,granite-porphyry,diorite,diorite.porphyrite.ect;Kaolinization,sericitization,silicification are common alteration phenomena,and a few of potassic alteration,chloritization,carbonatization;crystal texture is the chief ore texture,secondly cataclastictexture,replacement texture,zonal structure,framework,solid solution-sepatation structure;ore texture are breccia shape,dissemination shape,vein shape,ect.On the base of these ,we divided into four mineralization stages:K-feldspar-quartz-pyrite stage, quartz-pyrite stage, and quartz-multimetallic sulfide stage, quartz-calcite stage.Research on fluid inclusions in quartz show that : fluid inclusion types: volatile-rich , aqueous-biphase , aqueous polyphase fluid inclusions with daughter minerals and few of melt inclusion, pure liquid fluid inclusions; Homogenization temperature range is 150 to 600℃; The compositon of the volatiles are mainly H2O, CO2 and a few N2, C4H6, H2; These fluid inclusions characterize the salinity between 2.57 and 73.96% (ωNaCl), that is, high temperature high salinity (35.99 to 73.96%), high temperature high-mesosalinity (38.94 to 57.09%), and high-meso temperature meso-low sainity (2.57 to 19.05%); Halite, sylvine, anhydrite, and chalcopyrite were found in polyphase fluid inclusions; the depth at which orebodies formed is about 3Km, that is epizonal magma meothermal to high-meothermal; the temperatures of ore-forming range from 310 to 400℃; the ore-forming fluids deriving from mantle posses the characters of high oxide , high temperature, high salinity,high mental content.The result about S and Pb stable isotope indicates that metallogenetic materials which show characteristics of a deep or mantle source originate from lower crust and upper mantle; the study of H and O isotope has shown ore-forming fluid is mainly composed of magmatic water,and with mixed meteoritic water.The intrusive rock is categorized as calc-alkaline series ,mainly belonging to high-potassium and shonshonite series; Rare elements are characterized by delpeting in HREE and Y , high Sr, as well as enriching LREE and very weak negative Eu anomaly. These features are similar to adakite rock, suggesting that they are formed in an active continental margin .According to above conclusions and metallogenic epoch (203Ma),we get a primalary metallogenic model :the area was in compression environment because of pale-pacific subduction;Oxide magma fluids derived from lower crust and upper mantle asised; In the process, fluid crystallized and evolved uninterruptly ;when reaching 3Km, fluid boiling led to coming into being high salinity fluid , at the same time , magnetite crystallization resulted in forming of deoxidized S; with the decompression of dense fissure and the decrease of temperature, the fluids crystallzied and precipitated to form copper-gold orebodies, while breccia gold deposits may indicate the mixed result between boiling fluid and meteoric water; until nearly metallogenic end, Calcite and a series of low temperature minetal combinations such as chloritization ,kaolinization caming into being, with decreasing of solution salinity and acidity, as well as lack of Au element, then mineralization process was over.