The Ore-forming Processes And Mineralization Of Badaguan Porphyry Cu-Mo Deposit, Inner Mongolia

The Badaguan porphyry Cu-Mo deposit is one of the typical porphyry Cu-Mo deposits of the Greater Hinggan Range, China, locating the Erguna Massif’ s Cuogang-Derbugan upwarping region, eatern segment of the Central Asian Orogenic Belt. The orebodies are mainly hosted within Indo-chinese epoch Granodiorite porphyry, and the contact zone between indo-chinese epoch granitic porphyry and Granodiorite porphyry. Badaguan Cu-Mo deposits exhibits the feature of a typical porphyry alteration zoning, which in turn develops the potassic zone, quartz-sericite alteration zone, sericitization zone and propylite zone from the center of porphyry rock to outward, mineralization closely related to alteration. Mineralization is dominated by copper and molybdenum, the molybdenite in the quartz veins mainly distributing within quartz-sericite alteration zone and the chalcopyrite of disseminated and veinlet disseminated mostly closely connecting with sericite alteration zone, a few in quartz-sericite alteration zone.In this paper, systemically sampled major intrusive rocks of the Badaguan ore district, the microscopic identification results reveal that the primary lithology is biotite granite, granite, granitic porphyry, moyite, granite porphyry and granodiorite porphyry; LA-ICP-MS zircon U-Pb age of intrusive rocks is are mainly concentrated in (243-243Ma) and (231-229Ma), which suggest that the instrusive rocks are closely related to the tectonics and magma activities of Indo-chinese epoch. Besides, Re-Os isotopic age of seven molybdenite yield a weighted average model age of228.7±3.1Ma that is concordant with the diagenetic age (about230Ma) within the error, which suggests that the Badaguan Cu-Mo deposit is formed in the Middle Triassic, belonging to indo-China epoch mineralization.The geochemical results of intrusive rocks show that the rocks are characterized by relative high SiO2and rich Al2O3, poor MgO and TFe2O3. Rich in LREE、LILE but poor in HREE、 HFSE, Weaker negative Eu anomalies, all suggest that they are familiar with island arc granites in subduction setting. Combined with the Hf isotopic research of zircon in intrusive rock, the conclusion can been drawn that the primitive magma of intrusive rocks during Indo-chinese epoch originated from partial melting of the juvenile crust which derive from depleted mantle in the early neoproterozoic, fully assimilating a certain degree of crustal material during evolution and rising period. The study of fluid inclusion shows that there are many types of fluid inclusion in Badaguan Copper-molybdenum Deposit, which mainly include vapor-rich phase fluid inclusion, liquid-rich phase inclusions, multiphase inclusions including daughter mineral and CO2-bearing three-phase inclusions. Evolution process of ore-forming fluid is divided into early, middle and late stages. Homogeneous temperatures in the early, middle and late stage are mainly between238℃and572℃, and the salinities are between0.42and63.13%NaCleqv. The features of high temperature and high salinites reflect the characteristics of magmatic hydrothermal. The precipitation of copper and molybdenum occurs mainly in middle stages while their precipitation mechanism has decoupling. Precipitation of the large amount of Molybdenite is mainly related to boiling that induced by reduced pressure, but precipitation of chalcopyrite closely related to the fall of temperature.According to the study of Petrographic and analysis of Laser Raman probe, fluid inclusions in the early and middle stage of ore-forming fluid contain CO2and a few of N2except for H2O, and the daughter minerals identified that have been include halite, anhydrite, hematite and sulfides; There is nothing but H2O in aqueous fluid inclusions in late-stage. The ore-forming fluid evolved from H2O-CO2-NaCl system to H2O-NaCl fluid system gradually. H-O-S isotope data agree the conclusion that the ore-forming fluid mostly derives from magmatic hydrothermal and limited mixture of atmospheric water, and metallogenic material is mainly derive from the mantle.In Indosinian period, the study area is mainly under the tectonic background of the southward subduction of the Okhotsk ocean to the China-Mongolia joint plate. According to the geochemical characteristics of the intrusive rocks and Hf isotopic analysis results, this paper argues that badaguan Cu-Mo deposit formed under the tectonic environment of transition of Okhotsk ocean subduction closing to collision in late indo-chinese, meanwhile dynamic metamorphism of regional scale suggest that the closing of Mongolia Okhotsk in erguna region may develop in the late indosinian period.