Characteristics, Genesis And Prospecting Criteria Of The Mesozoic Epithermal Gold Deposits In Yanbian Area

The study area is in Korean Autonomous Prefecture of Yanbian of China.Geotectonic position of the study area is in the eastern of central Asia orogenic belts,across the southern margin of Xing’an Mongolian orogenic belts and the north margin ofthe North China platform. It is suffered superposition reconstruction of the Pacifictectonic domain since Mesozoic.It is closely associated with mineralization that volcanic rock-subvolcanic rock inthe late Jurassic-early cretaceous of Mesozoic. Main rock type is the basalticandesite-andesite-dacite-rhyolite and volcanic rock body at the same time. Secondaryrock type is the combination of basaltic trachyteandesite-trachyteandesite-trachytedacite.The volcanic rock chemical composition is mainly medium potassium calc alkaline series,the second is high potassium calc alkaline series. It shows the characteristic of volcanicrocks formed in active continental margin environment.The calculation results show that western Pacific oceanic lithosphere in the deeptrench subduct the Eurasia continental lithosphere along benioff zone at5.5cm/yearclosing speed in the late Jurassic-early cretaceous of Mesozoic. The subduction ofoceanic crust leads to partial melting of overlying mantle wedge, to form basalticandesitic magma and andesitic magma in the area, magma invade along the fracture anddifferential evolution, and may be blended in part of the basal shell material, to formchangeable volcanic rocks-the subvolcanic rocks symbiotic combination. It is obvious that Spatial distribution of gold deposits in the area is controlled by thegeological background and the structure. It is divided into BaiCaoGou-JinCangstructure-volcanic depressions in the north, WuFeng-XiaoXiNanCha structure-volcanichorst In the middle, YanJi-HunChun structure-volcanic depressions in the southaccording to the boundary of East-West BaiCaoGou-JinCang fault zone and East-WestYanJi-HuncHun fault zone. It is divided into the three metallogenic belt from north tosouth: BaiCaoGou-JinCang metallogenic belt, WuFeng-XiaoXiNanCha metallogenic belt,YanJi-HunChun metallogenic belt according to the boundary of the above fault zone.The gold deposit (mineralization) to occurs north and south structure-volcanicdepressions is in the volcanic lava and volcanic clastic rock facies (such asWuFeng-WuXingShan gold deposits and CiWeiGou gold deposits). It is the gold depositsof (poor) sulphide-adularia-quartz-calcite vein type. The gold deposit (mineralization) tooccurs structure-volcanic horst is in the the subvolcanic body (porphyry), Volcanic neckfacies, Volcanic Explosive breccia facies(such as XiaoXiNanCha gold copper deposits,NaoZhi gold deposits, DuHuangLing gold deposits), it is Joint control of Volcanicinstitutions and regional structure. It is the gold copper deposits of (rich) sulphide-quartztype or Disseminate vein.Alteration characteristic of Deposit in the study area: propylitization-potassiumfeldspathization alteration in early metallogenic period; silicification-sericitization-pyritization alteration in metallogenic period; carbonatation-adularization-zeolitizationalteration in late mineralization period.Metallogenic physicochemical environment: The temperature of the metallogenicstage is169-285℃; pressure is142-241b; deepness is0.47-0.80km; density ofore-bearing hydrothermal is0.83-0.92g/cm3; the evolution is from reductionenvironment to oxidizing environment; the evolution of Ph is from alkaline to acid.The comparative study on the metallogenic conditions show that low sulfur golddeposits and high sulfur gold deposits is mainly controlled by oxidation-reductionenvironment of mineralization process. It is not obvious that is affected by thetemperature. Low sulfur gold deposits formed in the reduction environment-reductionenvironment, high sulfur gold deposits mainly formed in the weak oxidizing environment -oxidizing environment. low sulfur type gold deposit occurs in structure-volcanicdepressions, High sulphur gold deposits mainly formed in structure-volcanic horst on thespace. These features indicate that low sulfur and high sulphur types of gold deposits ismainly controlled by diagenetic environment, this paper argues that they are not theproducts of different stages in same ore-forming hydrothermal, may formed by evolutionin different environment in independent origin of ore-forming hydrothermal.Through the comprehensive analysis and summary of mineralization of Regionalgeological, spatial distribution of ore deposits, ore body occurrence regularity and itscontrol relation of volcanic structure and the regional faults, ore mineral combination,surrounding rock type, alteration characteristics, Established prospecting marks ofepithermal middle and low temperature hydrothermal gold deposits related to volcanismin the areas. It is favorable metallogenic space that many times, multi-type andmulti-attitude subvolcanic rock (porphyry) and the ring fissure, radial fissure andvolcanic pipes, volcanic neck and Volcanic Explosive breccia facies. Multiphasealteration superposition, Multi-stage forming quartz vein and quartz calcite veins (orbroken alteration zones)，A variety of sulfide mineral assemblage are three importantprospecting marks.The Regional geophysical anomalies, such as gravity gradient belt, jumpingmagnetic fields is the important sign of looking for this kind of gold deposits in this area.Regional geochemical, part of the elements (Such as gold, arsenic, antimony, nickel,molybdenum, cobalt, zinc, etc) in the study area showed high background values, thevariation is relatively large and distribution is nonuniform, this is an importantprospecting marks.Natural placer mineral of the gold deposits in the1river is>0.003g/T and at riversource>0.03g/T in high value anomaly. The abnormal area overlapping highersecondary copper dispersion halo anomalies, and the placer mineral in river appearelectrum, chalcopyrite, pyrrhotite, is important prospecting marks.Put forward the prospecting areas according to analysis of geological, geophysical,geochemical, remote sensing information in the study area in this paper:BaiCaoGou-JinCang region, XiaoXiNanCha region, WuFeng-WuXingShan region, NaoZhi region.