Study On The Geological Features And Metallogenic Model Of Sandaowanzi Gold Deposit, Heilongjiang Province

The Sandaowanzi gold deposit is located in the connection between Daxing'anling and Xiaoxing'anling, in the Northwest of Xiaoxing'anling. Geotectonically, the deposit lies at the north of the Yanshannian Daxing'anling copper, pyrite, lead, zinc, gold, silver metallogenic belt. It is affected by the geological developing and evolvement of Central Asia-Mongolia Plate and Pacific Plate. The structure is complicated in the diggings. The nearly EW trend fold and fault are the basement structures. Pacific Plate subduct to Eurasia Continent, which formed the NE trend volcanical belt and brittle fault, maily is NNE and NE trend, secondly is NW, NNW and SN trend.The strata outcopping in the area include Mesozoic which are late Jurassic Tamulangou formation, low Cretaceous Guanghua formation and Cenozoic which is Quaternary. The gold-bearing quartz-veins are hosted by trachyandesite of Tamulangou formation.Ore bodies lie in NW trend fault fragmentized zones mostly. NE trend deep fault is the ore-leading and rock-leading structure. It controlled the magmatic activities and hydrothermal fluid movement in the diggings. NW trend fault which is the sub-structure is the main ore-controlling structure. we speculate that the two NNW trend dextrorotatory-normal-fault cut the whole vein into three parts. It is concluded that a buried ore body exists in the west of the I2. The intrusive rock outcopping in the area mainly is T3Sd, which is formed before the mineralization. Vein rocks are well developed and filled in the fractured zones. The main rock types are sillite and rhyolite porphyry. Sillite macroscopically cut ore bodies and gold-bearing quartz-vein, oblique crossing with them.The types of ore mainly is quart vein with poor sulfide in Sandaowanzi gold deposit. The texture of the ores are semi-euhedral granular texture and fine grain-dissemination texture. The main structure of the ores are vein structure and stockwork structure. The ores and minerals combination is simple. Besides pyrite and chalcopyrite, Optical Microscope and Scanning Electron microscope analyses with EDX indicate that tellurium-bearing gold mineral assemblage is the dominant gold-bearing minerals present in the ore vein.Tellurides include calaverite, hessite, petzite and so on. And they play a decisive role in the formation of high-grade gold ores with Au-Te association in quartz vein orebodies. Gangue is quartz and calcite ect. There are many types of wall-rock alteration, such as silicification, sericitization, epidotization and carbonatization. Mineralized silicification is linear distributed and controlled by structure. It is closely related to gold mineralization.According to the systematic study on fluid inclusions, we got some important metallogenic physico-chemical parameters. The types of the inclusion are simple. Aqueous two-phase and pure fluid phase are found, while aqueous two-phase primary fluid inclusions dominate in quartz-veins, the vapor/liquid ratio is commonly from 10% to 20%. The ore-forming fluid has characteristics of low salinity and low density, low-medium ore-forming temperature and low pressure. The homogenization temperature ranges from 152.2℃to 335.2℃. The metallogenic temperature is estimated to be 205℃~285℃. The salinity main value is from 1.2wt%NaCl to 1.8wt%NaCl, The main value of density is between 0.70 and 0.86g/cm3. The average value of pressure is 17.3MPa. On the base of the relationship between depth and pressure (Sun Fengyue et al, 2000), a 1.7km average metallogenic depth is worked out. The metallogenic fluid were meteoric water-dominated. All the characteristics show that the deposit belongs to typical low sulfuration epithermal deposit.The Sandaowanzi gold deposit underwent four ore-forming stages:Ⅰquartz-pyrite stage;Ⅱquartz-sulfide stage, forming a little chalcopyrite, blende;Ⅲquartzt-gold-bearing telluride-sulfide stage, widespread gold mineralization stage, composing the main gold ore bodies, which tellurides offen occure in the mid-late metallogenic stage;Ⅳquartz-carbonate stage, non-mineralization stage.The Sandaowanzi gold deposit developed three ore veins which isⅠ,Ⅱ,Ⅲvein. The ore-controlling faults are Sinistral-diagonal distributed.Gold-bearing veins filled in the fault generally arrange parallely, appear in groups and show anti-S type slightly in plane. Their extension along NW-SE strike is indentation, and there are obviousily orebody NW lateral extension rules. TheⅠ2 ore body is the main ore bodies in the diggings with the strike of 40°and the dip of 58°-77°. They all present multistage activities and compressional-extension torsion . The morphology of ore body mainly is nervation and lenticular.Gold mianeralation in quartz veins expand and shrink along strike and dip, with orebodies enrichment and dilution.The mafic-intermediate sillites are found to be fore-metallogenic vein rock, not post-metallogenic vein rock as formerly suggested.We speculate ore-bearing hydrothermal solution flow from west deep to east shallow part. The sillites stop the moving of ore forming fluid and control the formation of oreshoot. The oreshoot were found in the 130 level middle section, then predicting the deep has another one.On the base of the summarizion and study on the ore-forming condition and the rule of enrichment, effective method is adopted to prognosticate ore bodies in deep (side)in the diggings. Ore bodies lie in gold-bearing quartz vein mainly with poor sulfide and low polarizability. There is no apparent polarizability anomalies, so our aims are looking for high resisitivity geologic bodies. According to the measure of induced polarization and geochemical survey in S, E, B, W section, the part of high resisitivity and fragmentation zones consistent with soil anomaly were found, which can be tested by a further engineering confirmation. The primary halo analysis about samples got fromⅠ,Ⅲore veins show that there is still bigger potential of prospective in the deep ofⅠvein.