The Petrogenesis Of Magmatic Rocks In Pujue Polymetallic Deposit In Tibet And Its Implication For Mineralization

The Pujue copper polymetallic deposit in the middle part of Gangdese porphyry metallogenic belt is located in the south margin of The Lhasa block.It is one of the new porphyry deposits found in the western part of Gangdese porphyry metallogenic belt.The intrusive rocks in The General Jae mining area are varied in lithology and age,including the biotite monzonite which constitutes the main of the large batholith,as well as numerous angular gabbro,diorite,coarse porphyry,granite diorite and hornblorite distributed in or around the large batholith in the form of dike or rock stock.The mineralization of Pujue copper polymetallic deposit is mainly tungsten-antimony mineralization and cu-Mo mineralization.The alteration is mainly clay alteration and proteinization with large area distribution,and a large number of crust epithermal quartz is developed.Potassium feldspar-quartz alteration,biomicization,ferric sericization,chloritization and opalite-pyrite-actinite alteration are developed in the deep part,and there are superposition and cut among different alteration.The alteration mineralization in Pujue mine is closely related to the coarse porphyry in time and space,which accords with the characteristics of typical porphyry deposit.This paper mainly analyzes and studies the coarse porphyry granodiorite,granodiorite and hornbeam granodiorite in the mine area.The U-Pb ages of zircons in granodiorite,granodiorite and hornblende granodiorite were 16.39±0.2Ma,24.2±0.23Ma,and 155.7±1.1Ma,respectively.Granite diorite porphyry is shoshonite series,alkaline granite,with losses of high field strength elements Nb,Ta,P,Ti,Zr and Hf,enrichment of large ion lithophile elements Pb,Th,U,Rb,and the characteristics of K and alkaline rock geochemical properties of heavy rare earth elements in rare earth element distribution curve of the characteristics of the loss,the product of partial melting of eclogitic.Coarse porphyry granite is a series of high-potassium-calc-alkaline granites,which has the characteristics of deficient high-field elements and enriched large-ion lithophile elements similar to granodiorite porphyry.The distribution curve of rare earth elements inclines to the right.The?Hf?t?value of its zircons is between-2.25 and+3.37,and the Hf isotope crustal model age T_DMC is among 887 to 1244Ma,indicating that the newly formed lower crust is partially melted and mixed with some old crustal materials.Granodiorite porphyry has high MgO,K₂O,Cr and Ni,showing the characteristics of ultrapotassic rock mixing.According to the covariance diagram of main trace elements,it is found that granodiorite porphyry and coarse granitic porphyry have different proportions of ultrapotassic rock mixing.Hornblende granodiorite belongs to high potassium calc alkali granite series is pomegranate subduction environment the product of partial melting of crust under amphibolite facies.Compared with porphyry deposits in the eastern part of the Gangdese porphyry metallogenic belt,the Hf isotopes of the coarser porphyry granitic porphyry are relatively enriched,which is due to mixing with the ancient lower crust of Lhasa.Through calculation of the zircon trace elements of Ce⁴⁺/Ce³⁺,Eu/Eu*and zircon Ti temperature show that the coarse spot granite porphyry and granite diorite porphyry has high oxygen fugacity and lower temperature of the magma?the majority in the 600⁷00°C?,the fitting with the eastern metallogenic characteristics of porphyry,the capability of migration and enrichment of ore-forming metals,that's sleep porphyry deposit with large porphyry deposit metallogenic potential.In addition,the low zircon Ce⁴⁺/Ce³⁺of the late Jurassic hornblende granodiorite indicates the possibility of sulfide accumulation in the lower crust during the Jurassic period.So in about 24 Ma,super potassic rock at the bottom of the lithosphere mantle partial melting under the assault to the lower crust and water make partial melting of crust produce rough spots granite porphyry magma and increase the oxygen fugacity and water content of magma to activate and sulfide accumulated a large number of lower crust,and enrichment of metal fluid of the magma assault on the first of the earth's crust release deposit fluid and metal forming;Subsequently,the ultrapotassic rocks continue to invade into the coarse porphyry granitic porphyry magma chamber and mix to produce granitic diorite porphyry.