Metallogenesis Of Juno Porphyry Cu(Mo-Au)Deposit,Angren,Tibet,China

More than 30 million tons of Cu resource was produced in the Gangdese belt,Tibet,China.It is one of the important mineral reserve resources in China.Juno porphyry copper deposit,the copper reserve of which is over 2 million tons,was newly found in the most western of the Gangdese belt.It is located in the western part of the northern Gangdese,north to Shigatse forearc basin.The administrative division is Xuru village,Yamu town ship,Ngamring county,Tibet,China.Juno porphyry copper deposit was formed in the post collision extentional tectonic setting,it was called the type of continental collision porphyry Cu?-Mo-Au?deposit.The number I,II and III orebodies are included in Juno,but the number I is the most important one.Two magmatic activities happened in Juno,the Eocene quartz diorite porphyry?51.89Ma?and the Miocene porphyry?16.28¹3.97Ma?which are composed of biotite granodiorite,biotite monogranite,quartz porphyry,granite porphyry,diorite porphyry,lamprophyre veins and andesite veins.The biotite granodiorite,the minerliazation porphyry,formed about 14Ma,was at the same age of other porphyry deposits in Gangdese which were formed about 13¹5Ma.The mineralization and alteration of Juno deposit happened in and around the biotite granodiorite and its contacts.The economic Cu and Mo resources are 2.3million tons,with average grade of 0.57%and 40 thousand tons,with average grade of 0.017%respectively.The main ore types are disseminated chalcopyrite ore and fine vein chalcopyrite ore.The structure of the ore is densely disseminated,sparsely disseminated,fine vein and net vein.The texture of the ore is idiomorphic,hypidiomorphic-idiomorphic,metasomatic,solid solution separation and so on.The mineralization of orebody it's grade are inhomogeneous.The mineralization of Mo is at the bottom of ore body while the Cu at the top.The Eocene and Miocene porphyries are high K calc-alkaline series,their REE model is characterized by enrichment in light REE and Eu anomaly,Light REE fractionation is strong,while fractionation of heavy REE is not obvious.The trace elements were significantly depleted in high field strength elements?HFSE?,enrichment of large ion light elements and Pb.The Sr-Nd-Hf isotopic characteristics showed that the two stage magmas were composed of Lhasa terrane?melt of Paleoproterozoic or more ancient crust?,Tibetan lower crust and arc magnism residue of oceanic subduction of Neo-Tethyan.This was the same as the result of Pb isotope.And the Miocene ore-forming stock displayed adakite-like affinities which is the same as other porphyry copper deposits in Gangdese belt.The hydrothermal alteration in Juno area is potassic alteration,phyllic alteration and prophylitization.The types of hydrothermal are early biotite sulfide veins,early bare or weak mineralization quartz veins,quartz molybdenite?±chalcopyrite±pyrite?veins,quartz chalcopyrite?±molybdenite?veins,molybdenite veins,chalcopyrite veins,pyrite veins,calcite veins and late quartz veins,late quartz sulfide veins and prophylitic veins.We inferred the source of S and metal elements was from deep magma from the?S_V-CDTS-CDTS isotope in Juno ranging from-1.8¹.5.The radiative characteristics of isotope Pb suggested that the contribution of crust Pb is more than the mantle.The low-middle density fluid,exsolved continuously from magma chamber,was the transporter and source of the metal elements.The molybdnite precipitation was collected with the depression of the pressure and the escape of CO₂,while the copper mineralization was related to boiling.Juno hydrothermal system was rich in water and sulfer and has high fugacity of O₂,The continuously exsolved fluid and metal elements from the deep magma chamber was the major factor to form the Juno porphyry copper deposit.The copper mineralization conditions were the same as the accessary mineral rutile,they all were formed in 400⁷00?,a few hundredMPa,oxygen fugacity of NNO+1.3 and water rich environment.The Juno ore-forming stock was controlled by the west-east and south-north rift structure.And the Miocene porphyry stretches in north-north east direction.The malachite,gossan,depressions and all kinds of alterations on the surface are the indicator for mine.When the rutile is used for looking for mine,the content of V₂O₃and Nb₂O₅ in rutile should be higher than 0.20%.And the higher content of WO₃should also be concerned.