Geochemical Characteristics Of Granite Porphyry From Juyuan Tungsten Deposit In Central Of Jiangxi Province And Its Geological Implications

Juyuan granite porphyry is located in central Jiangxi province,and its geotectonic position is on the east of the joint zone between Cathaysian plate and Yangtze plate.The granite porphyry from the deposit is believed to be closely related to the formation of scheelite deposit of quartz vein type.This study applied multiple methods of petrography,geochronology,geochemistry and isotope geochemistry to investigate petrogenesis and diagenetic environment of granite porphyry from Juyuan.Juyuan granite porphyry is present as porphyritic texture and massive structure,in which the phenocrysts are mainly composed of potassium feldspar,quartz,plagioclase or small amount of biotite.The structure of phenocrysts enclosed by fine-grained quartz crystals is common.The minor minerals are consist of zircon,monazite,apatite,xenotime,thorite,Rutile,magnetite,ilmenite,allanite,Pyrite,etc.,the charactersitics of which resemble the tungsten bearing granite in south China.Some Nb-Ti-Y-U-W-HREE oxides are discovered to be enclosed in crystals of albite,potash feldspar and quartz,or coexist with scheelite.According to the results of EPMA,the chemical compositions of the mineral fit in the crystal chemical formula [A1-xB2+x(O,OH)6 or A1+xB2-x(O,OH)6],where A is occupied by Fe2+?Y3+?REE3+?Ca3+?U4+ or Th4+,and B is occupied by Nb5+?Ti4+?Si4+ or W6+,x shows the ratio of vacancies in A-site.The zircon U-Pb age of Juyuan granite porphyry by LA-ICP-MS method is 152.36±0.97 Ma,consistent with the age of tungsten bearing granite in south China,suggesting that the granite porphyry is the product of large-scale magmatic activities during the Mesozoic(Middle Yanshan)period in south China.Part of the points obtained about 160 Ma test results,show that features of the rock in the early stage is not fully assimilated.The results of geochemical analysis show that for major elements,Juyuan granite porphyry contains high contents of SiO2,K2 O,Alk,Al2O3,TFeO(Fe*=0.95~0.97),and low contents of CaO,P2O5.For trace elements,the rocks show enrichment of Rb,U,Th,Sm etc.,and strong negative anomalies of P,Ti,Zr,Ba,Sr.Based on calculations,the granite porphyry has high ratios of(K2O+Na2O)/CaO,TFeO/MgO and Ga/Al,which is typical characteristics of A1 type granite.The diagenetic temperature for granite porphyry is estimated to be from 978?to 995?,calculated from the zirconium saturated thermometer.The content of W is very high in granite porphyry,with an average concentration of 11.4 ppm,suggesting that the W enriched in granite porphyry is probably the main material sources for the scheelite deposit.The average ISr value of granite porphyry is 0.715,?Nd(t)of granite porphyry and ?Hf(t)values of zircons are-8.8~-8.1 and-12.0~-9.3,The Nd model ages(T2DM)are 1.60~1.66 Ga,The Hf model ages(T2DM)are 1.78~1.95 Ga,implying that the granite porphyry is originated from partial melting of paleoproterozoic crust.