Geochemical Characteristics And Genesis Of Mesozoic Intrusive Rocks In Taipingchuan Mo-Cu Deposit,Inner Mongolia

The Taipingchuan deposit is located in the northeastern of Inner Mongolia,the north section of the Deerbugan metallogenic belt.The Deerbugan metallogenic belt has always been an important area for strategic prospecting and evaluation of mineral resource in China.More than 40 super large-scale deposits have been found in neighboring Russia and Mongolia,which shows the great metallogenic potential of the metallogenic belt.However,since the discovery of a large number of large polymetallic deposits such as Unugetu and ErenTolgoi in the south of the metallogenic belt in the 1950s and 1960s,there have been no major prospecting breakthroughs in the following decades.After entering the 21st century,some potential deposits and ore spots have been discovered in the central and northern part of the metallogenic belt.The Taipingchuan deposit,as a large Mo-Cu deposit,may be the breakthrough point for prospecting in the central and northern part of the area.In the paper,we report results of zircon U-Pb isotope dating,geochemical analysis.zircon Lu-Hf isotope studies and mineralogical studies of Mesozoic granites in the area to solve the problems of the period of Mesozoic magmatic activity,the nature of the Mesozoic intrusive magmatic source,the physical and chemical conditions of diagenetic magma,the relationship between magma and mineralization,and the Mesozoic tectonic evolution process in this area.There are two magmatic events recorded in the Mesozoic in Taipingchuan deposit.The earlier magmatic event(Indosinian)occurred during the middle Triassic to the Late Triassic(240 Ma?23 1 Ma),and is represented by granodiorite(240.2±3.0 Ma)and quartz monzodiorite(231.0±4.6 Ma);the later magmatic event(Yanshanian)occurred in the early Jurassic(192 Ma-190 Ma),and is represented by biotite monzogranite(191.8±1.6 Ma)and granodiorite porphyry(1 90.5±2.6 Ma).Contents of major elements and trace elements in intrusions indicate that the two intrusions are all I-type granites,and the magma source of the intrusions are different.The initial magma of granodiorite could be derived from subduction oceanic crust;The initial magma of quartz monzodiorite is a mixture of magma derived from the crust the depleted mantle,in addition to mixing fluids from subduction zones;The monzogranite and ore-forming granodiorite porphyry could be derived from partial melting of juvenile crustal material,which differentiated from the mantle in Mesoproterozoic,mixing ancient lower crust group in the later rising process.During the middle Triassic to the Late Triassic,the magmatic episode in Taipingchuan is related to the southward subduction of the Mongol-Okhotsk oceanic plate,and the magmatic event in the early Jurassic is related to the collision orogenic process after the closure of the Mongol-Okhotsk ocean.The low crystallization temperature and high emplacement depth of granodiorite porphyry in Taipingchuan are not conducive to cause Mo-Cu mineralization,which may be one of the reasons for the scale of Taipingchuan.The monzogranite has the potential for mineralization.