The Geological Charateristics And Genesis In Wangershan Gold Deposit Of Laizhou Shandong

The Wangershan gold deposit in Shandong Province is located in Shangzhuang-Wangershan fault zone,Zhaoping metallogenic belt,and to the east of Yishu fault zone.The strata exposed in the mining area are relatively simple,which is mainly composed of Neoarchean metamorphic rocks of the Jiaodong Group and a small number of Quaternary strata.The main structure in the mining area is fault system,mainly for NE and NNE.Intense magmatism mainly comprisesLinglong granites accompanied by lamprophyre dikes before mineralization,which is dated to be 162.74±0.47Ma in this paper by zircon U-Pb method.The ore bodies are mainly emplaced in linglong granites as veins,which is strictly controlled by fault.The ore minerals mainly comprise chalcopyrite,pyrite,tellurium-bismuth ore,natural gold,silver gold and gold and silver ore,etc.Gangue minerals are mainly composed of quartz,potassium feldspar,sericite,chlorite,epidotite and carbonate.The ore textures include grains,cataclastic,interstitial,solid solution separation,metasomatic and crushingtextures.The ore structures are veined,disseminated,net-veined and banded structures,etc.The alterations of surrounding rock include potash feldspathization,sericitization,sericitization,silicification,chlorinization,epidotization and carbonation,etc;and gold mineralization is closely related to sericitization and silicification.It is confirmed that the Wangershan gold deposit mainly experienced two metallogenic periods,namely the hydrothermalperiod and the supergene oxidation period.The hydrothermal period can be divided into four stages:quartz-pyrite stage;gold-quartz-pyrite stage;quartz-gold-polymetallic sulfide stage?pure sulfide veins?;and quartz-carbonate stage.Through the investigations of the geological characteristics,conbined withthe analysis of a large number of fluid inclusions in the ore bodies,it is shown that the ore-forming fluid of the wangershan gold deposit is NacCl-CO₂-H₂O system.Ore-forming fluid show low salinity?7.0-9.5%NaCl?and low density?0.85-0.0.95 g/cm³?,the temperature of the mineralization focuses on 270-320?within the medium temperature range.The metallogenic pressure range is 68-108mpa,and the corresponding depth is 6.7-8.6km.The results of carbon,hydrogen,oxygen isotopes show that the ore-forming fluid is mainly derived from mantle primary water with a little atmospheric water.The results of lead and sulfur isotopes show that the mineralization materials are mainly derived from the mantle.During the transition period from collision to extension in the late Yanshanian,the lithosphere thinningoccurred through delamination,which induce large-scale volcanic eruptions and the intense upwelling of the mantle material and energy,from which the mineralization elements?Te,Au,Cu,etc.?in the upper mantle were taken out;then the ore-bearing thermal fluid concentrated unloading in the brittle fracture mineralization.The discovery of tellurium-bismuth ore in the mining area and its close relationship with gold mineralization,as well as the widespread development of lamprophyres,support the understanding of mantle derived fluxion gold mineralization model in jiaodong region proposed by FengyueSun et al.?1995?from the perspectives of mineralogy and petrology.In conclusion,the genetic type of wangershan gold deposit is determined to be mesothermal vein type gold deposit.