Metallogenesis And Metallogenic Prognosis Of Gold-Copper Polymetallic Deposits In Qibaoshan Orefield,Wulian County,Shandong Province

The Qibaoshan orefield,including Jinxiantou gold-copper deposit,Diaoyutai pyrite deposit,Qibaoshan lead-zinc deposit and some other deposits,is located in the southwest of the Jiaolai depression within Wulian county,Shandong Province.In 2009,molybdenum mineralization has been found in the deep part of the Jinxiantou gold-copper deposit.On the basis of systematic field geological investigation,combined with the results involved in fluid inclusions,stable isotopes,and geologic ages,this paper discusses the geologic features,ore-forming fluids and materials,and ore genesis of Cu-Au deposits,and carries out the comprehensive information metallogenic prediction of geology and physicochemical exploration in Qibaoshan orefield.Our study contributes to a better understanding of these deposit,which might be helpful for future prospecting of new deposits in the orefield.The main achievements are listed as follows.1.Mineralization and geological characteristics of Au-Cu and Pb-Zn deposits in the Qibaoshan orefield.The jinxiantou Au-Cu deposit is located in the south of the Orefield,in which the orebodies mainly occur in cryptoexplosion breccia pipe hosted in granodiorite porphyry,quartz diorite porphyrite,diorite and andesite porphyrite.The deposit displays two types of mineralization as breccia pipe mineralization and veinlet-dissemination mineralization in the deep.Based on field observations,cross-cutting relationships and mineral paragenetic associations,mineralization can be divided into five stages:(I)pyrite-quartz,(II)molybdenite-(pyrite)-quartz,(IIIa)specularite-quartz-carbonate,(IIIb)specularitepyrite-chalcopyrite-quartz-carbonate,(IV)pyrite-chalcopyrite-quartz,and(V)late carbonate.Qibaoshan Pb-Zn deposit consisted of Changgou,Hongshigang,and Xingshanyu ore blocks is located in north part of the Orefield,which includes hydrothermal quartz-(calcite)vein and alteration rock types mineralization.The orebodies mainly occur in the andesitic porphyrite and volcanic rocks of Qingshan Group.Two stages of mineralization,(I)galena-sphalerite-quartz-(calcite)and(II)quartz-calcite,have been recognized in the Qibaoshan Pb-Zn deposit.2.Based on our study,we conclude that the Jinxiantou Au-Cu deposit is a porphyry deposit related to granodiorite porphyry,while the Qibaoshan Pb-Zn deposit can be classified into mesothermal hydrothermal vein type deposit involved in high-level emplacement of andesitic porphyrite.3.Based on petrography and magmatic zircon LA-ICP-MS U-Pb dating,this paper established the emplacement sequence of magmatic rocks in the Qibaoshan orefield: pyroxene diorite(I period: 175Ma±),Qingshan Group volcanic rocks(II period: 134Ma±),pyroxene andesite porphyrite-hornblende andesite porphyrite-granodiorite porphyritequartz diorite porphyrite(III period: 129~125Ma),andesite porphyrite-dioritic porphyrite(IV period: 112Ma±).We propose that the formation of I period pyroxene diorite is related to environment of collision and extensional transformation of the Sulu orogenic belt.According to the tectonic environment discrimination diagrams of Sr/Y-Y,Rb/30-Hf-3Ta,Rb-Yb+Ta,Rb-Y+Ta,II-IV periods of magmatic rocks formed in the volcanic arc tectonic environment related with B-type subduction of the Pacific plate.4.Based on the tectonic background of magmatic intrusions and the genesis of different types of deposits,we establishes mineralization model of Au-Cu polymetallic Orefield.The Sulu ultrahigh pressure metamorphic belt was formed during collision orogenesis of North China and the South China plates.The earliest intrusive pyroxene diorite in the Qibaoshan orefield was the product of transformation from compression to extension of the orogenic belt.Then the Wulian area was during the stage of intraplate volcanism,the eastern part of the North China that contains the whole Jiaodong region Craton was dominated by the Pacific tectonic domain during the Cretaceous.The formation of the main part of Qibaoshan complex was related to the subduction of the Pacific plate.The migration and emplacement took placed after the convergence of the ultramafic magmas from mantle wedge in the favorable position.The ore-forming fluids of Au-Cu mineralization in the Qibaoshan orefield was centered on the quartz diorite porphyrite and radially expanded outwards.The mineralization shows spatially and temporally an evolution tendency from the south east to the north west,Xingshanyu ?Hongshigang?Changgou.The superposition of two periods of mineralization occurred in the Changgou ore block.5.Metallogenic prediction has been carried out:1)According to the ore-forming geological conditions and geophysical and geochemical anomaly characteristics within the Orefield,the metallogenic prediction is carried out,and five metallogenic prospect areas are delineated;2)The deep metallogenic potential of the jinxiantou gold copper deposit has been evaluated and it is predicted that the deep of the south-east ore-breccia tube contains potential to find vein disseminated type of ore body.3)Using the OPIS methods,structural control and deep metallogenic prediction has been carried out to the ?-vein of the Changgou ore block and the?-vein of the Hongshigang ore block.The research has delineated advantageous of the deep rospecting to the veins.It provides an important basis for further exploration and prospecting of the ore deposits and the orefield.