Geological Characteristics And Enrichment Regularities Of Mineralization Of Orogenic Gold Deposits In Beijie -Dahe District, Northwest Of Jiaodong Peninsula

Abstract:Beijie-Dahe district in the Northwest of Jiaodong Peninsula is located in the centralization zone of gold mine in Jiaodong Peninsula. Jiaodong region underwent a very important orogenic-metallogenic epoch in Mesozoic with Izanagi plate subducting under the Eurasia plate from southeast to northwest. Archaean metamorphic rock of Jiaodong group exists as major xenoliths in the study area. Magmatic rocks mostly crop out Linglong granite, Guojialing granodiorite and Luanjiahe granite. Thereinto, the Mesozoic crustal derived anatectite granites is widely distributed and genetically linked with mineralization. And they were affected by the subduction of Pacific Plate in Mesozoic. Such subduction induced crust temperature rising and mantle source upwelling. The multistage granitic pluton formed by selective melting provided source of rocks, heat and host rocks for gold mineralization in the study area.The area consist of major intermediate-basic dyke, minor lamprophyre and few acid dykes, which occurred widely in the study area.They occur closely with gold veins in temporal and spatial.Fault structures are developed in the study area.And the structure system is composed of the NE-NNE faults and EW basement structure, which supplied impetus, migration channels and metallogenic space for gold-bearing hydrothermal fluid.The fault system controlled not only outcrop of shape and occurence of three types of granitic complex,but also the distribution of gold ore bodies. Zhaoyuan-Pingdu,Sanshandao-Cangshang and Jiaojia-Xincheng faults belong to three pieces of major primary regional metaogenic structures, and Lingshangou-Beijie and Dahe faults are secondary ones. Systemic studying on the characteristics of gold ore bodies,ore composit-ion,ore texture and structure,wall-rock alteration and mineralization types etc about typical gold deposits in the study area, we thought these gold deposits associated with the orogensis belong to typical orogenic gold deposits, which have similar regularities and close genetic relations in spatial-temporal distribution and genesis, similar geological and geochemical characteristics. Gold deposits in this area are controlled by multi-order structural systems, whose distribution are controlled by deep regional faults and located in secondary fault systems.Ore components are simple and with low sulphide. T-he monocrastal minerals of gold consist of native gold and electrum, and pyrites and chalcopyrite are main auriferous minerals, in which the aurum exist as major inclusion one, a few intecrastalline and fracture ones.Ore texture and structure are various,mainly including euhedral-half euhedral granular, anhedral granular, poikilitic, typomorphic, replacement remanant, fracture filled and solid solution textures, and primary structures consist of block, brecciola, disseminated, veinlet, veinlet-disseminated, and mottled structures. Wall-rock alteration include dominant potassic alteration, silicifica-tio, silicification-sericitization and carbonatization. Based on studying on fluid inclusion,the quartz of different ore-forming stages contain three main types of fluid inclusions:CO2 enriched,CO2-H2O,and H2O inclusions.The CO2-H2O inclusion are relative plenty,the ore-forming fluidisa type of low-salinity H2O-CO2-CH4,CO2 is comparative plenty,and this three types of fluid inclusions are characterize by unmiscibility. The stable isotopic data of sulfur, carbon, hydrogen and oxygen from several typical gold deposits in this area shows that sulfur derive from the lower crust or mantle. The metallogenic fluids are composed of major magma-tic fluid, with meteoric and metamorphic water in a certain extent.