Petrology,Geochemistry,Chronology And Significance Of Uranium-bearing Granite Porphyries In North Of Xiangshan

In this paper,we selected the granite porphyry in Hengjian,Youfang,Shazhou and Yunji of northern part of Xiangshan as the research object.Through the method means of field geological survey,lithology,main and trace element,Sr-Nd-Pb isotope,LA-ICP-MS zircon U-Pb dating and so on,Systematically studies the characteristics of rock mineralogy,geochemistry and chronology,and discusses the relationship between rock formation type,tectonic environment,magmatic material source and uranium mineralization.It is found that the granite porphyry in the northern part of the Xiangshan is mainly exposed to the areas of Hengjian,Youfang,Sha zhou,Baquan,Wangnikeng and Yunji.The Hengjian rock mass was north-south distribution,intermittent in the surface exposed;The Youfang rock mass was north-west to the curved display,intermittent in the surface exposed,deep together.The Shazhou rock mass was east-west distribution,continuous exposure.The Yunji rock mass in the surface was north-south distribution,continuous exposure.The granite porphyry in the northern area of the Xiangshan is mainly controlled by NE and EW to two groups of fault structures.The granite porphyry rock with the characteristics of rich silicon?SiO₂=64.50% 75.68%?,rich alkali?ALK=6.99%⁸.91%?,AR = 2.43 4.03),A/CNK = 0.90¹.32?quasi-aluminum-peraluminous?,DI=74.54⁹4.14?average value 83.51?,???=1.52³.47?average value 2.53?.The contents of Al2O3,CaO,MgO,TiO2 and P2O5 in the main elements decrease with the increase of SiO₂ content,and the characteristics of continuous evolution are continuous.Trace elements Th,U,Pb,La,Rb,Nd and other elements enrichment,P,Ti,Sr and other elements of the loss and ?Eu negative anomalies,With a similar trace element spider web and rare earth partition pattern;Rock ?REE is higher than the ?REE value of the crust,LREE is obviously enriched,Light and heavy rare earth fractionation is obvious,rare earth distribution pattern shows the right type.The compositions of isotope of granitie porphyry of?87Sr/86Sr?i=0.71584⁰.71830,values are belong to the continental crust,and the value of ?Nd?t?varies from-8.3 to-7.3,TDM2 is 1521¹599Ma,the average is 1560 Ma,close to the mainland crustal age;206Pb/204Pb=18.434¹8.832,207Pb/204Pb=15.618¹5.645,208Pb/204Pb=38.848³9.044,which is closely related to the melting ancient crustal material.The results of LA-ICP-MS zircon U-Pb dating showed that the weighted average of 206Pb/238 U age of the granite porphyry of Hengjian,Youfang,Shazhou and Yunji were 135.6±1.3Ma?MSWD=0.45,n=26?,136.2±1.3Ma?MSWD=1.2,n=21?,133.4±1.1Ma?MSWD=0.67,n=24?and 134.3±1.1Ma?MSWD=0.88,n=25?,Which represent the formation age of the original rocks in each region,and the age of uranium granite porphyry in each region shows a consistent result within the error range,which is between 132 Ma and 137 Ma,which belongs to the Early Cretaceous period.It is concluded that the type of granite porphyry in the northern part of Xiangshan is between the A-type granite and the S-type granite,which belongs to the transitional type between the two.The granitic porphyry magma originated from the Paleoproterozoic crust and the crustal material as the main component involved in the formation of granite porphyry.The formation of the environment for the plate tectonic environment,the output environment for the extension system,may be due to the Pacific plate subduction after the plate due to the role of the formation of magma invasion of the results.