Ore-forming Intrusion Chronology And Geochemistry Of The Jiaduobule Skarn Fe-Cu Deposit In Tibet

Jiaduobule skarn Fe-Cu deposit is located 8km north of the Xietongmen city in the central of the Lhasa terrane.So far there's just a few reports about the intrusive rocks' epoch and petrogenesis,espencially it's relatively weak on Biotite monzonitic granite which has a close relationship with metallogeny Therefore,this study have done lots of work on the basic geology,geochemistry and geochronology to insure its' ore-forming intrusion and discussed the metallogenic background and its' forming.The most mineraization is magnetite,chalcopyrite and bornite,and minor is hematite.From south to north the mineralization types show as iron,iron and copper,copper in space.The gangue minerals mainly are andradite,grossular,diopside,hedenbergite,actinolite,epidote,chlorite,phlogopite,quartz and calcite.From south to north the garnet colors change from dark to shallow,what's more grossular content is decreasing,while andradite is as the opposite.These features display a fact that the southern monzonitic granite is related to mineralization instead of northern quartz monzonite.Zircon U-Pb chronology study shows that the age of biotite monzonitic granite is 53.82±0.60 Ma.So it is sure that the Jiaduobule skarn Fe-Cu deposit formed in the Eocene.Geochemistry shows that the host rock of metallogenic intrusive has the charactertics of high-K-Calc-alkali,A/CNK<1.1,middle negative Eu anomaly,which belongs to I-type granitoids.Large ion lithophile elements are enriched as Rb?Th?Nd,high field strength elements are depleted,such as Ta ? Nb ? P ? Ti.The Fe2O3/(FeO+Fe2O3)average is high as 0.42,which could indicate that the magma had a high oxygen fugacity.Biotite monzonitic granite is syn-collision granite and charactered by arc magma.The Hf and Pb isotopes analysis show that the host rock of metallogenic maga is the mixture of mantle-derived magma and the ancient crust molten lava.Combining with the regional tectonic background,Jiaduobule skarn Fe-Cu deposit was formed at the Eocene epoch.In the main collision of the Indian and Asian plate,the asthenosphere mantle fluid mixed with lithosphere magma influenced by the unreel of Neo-tethys.The mixture intrusive formed the biotite monzonitic granite and the Jiaduobule skarn Fe-Cu deposit after crystallization and differentiation.