Ore Genesis And Tectonic Setting Of Badaguan Copper-molybdenum Deposit In Erguna Region, Inner Mongolia

The Badaguan deposit, discovered in1950’s in Erguna area, is one of medium-sizedcopper-molybdenum deposits in the Great Hinggan Range of Inner Mongolia. It is locatedwithin Erguna Massif and the northwest part of the Tayuan-xiguitu fault, eastern segmentof the Central Asian Orogenic Belt. The ore bodies mainly occur in the contact zonebetween the Triassic quartz diorite porphyry intrusion and dark green tuffaceous sandstoneof the Carboniferous Hongshuiquan Formation, and obviously controlled by NE-trendingfaults. The deposit is featured by typical wall-rock alteration zoning which is divided intothe quartz-sericite zone, phyllitization zone, transition zone, propylitization zone from thecenter of the metallogenic quartz diorite porphyry to outward, and the major mineralizationtype is veinlet-disseminated type.Petrography and microthermometry of fluid inclusions in the quartz grains formed inthe main mineralization stage show that primary fluid inclusions include liquid-rich phase,vapor-rich phase, CO2-bearing three-phase and CO2-pure phase, which are captured fromthe boiling fluid. Ore-forming fluid of the main metallogenic stage is a low density(0.52~0.94g/cm3), the low salinity (2.59~20wt%NaCleqv), medium-high temperature(240~400℃), hypabyssal (0.43~1.73km) of NaCl-H2O-CO2(±CH4) fluid system. H-Oisotope data agree the conclusion that the ore-forming fluid of the main metallogenic stageis featured by the mixture of magmatic and atmospheric water. Through comprehensiveanalysis, we can draw an conclusion that Badaguan deposit is a typical porphyrycopper-molybdenum deposit. Isotopic dating data show that the weighted mean U-Pb age of zircons from themetallogenic quartz diorite porphyry of Badaguan deposit is (217.6±2.6) Ma(MSWD=1.17,probability=0.27,95%conf.) and the Re-Os model age of the molybdenite collected fromores is (222.4±3.3)Ma, which indicates that the metallogeny took place in the Late Triassicperiod, and the deposit was resulted from the Indosinian tectonic-magmatic event.The metallogenic quartz diorite porphyry is rich in LREE and depleted of HREE,featured by positive Eu anomalies, depletion in large ion lithophile elements (LILE) suchas Ba and Sr, enrichment in high field strength elements (HFSE) of Pb, Th, U, Zr, Hfexcept Ti, indicating that the material source of the intrusion is the deep-derived magma.Combined with the test results of S, Pb, Re isotope, this thesis suggests that both diageneticand metallogenic materials were originated from the upper mantle contaminated by thecrust.According to geochemical characteristics of the metallogenic porphyry, by thetectonic discrimination diagrams, an conclusion can been drawn that the metallogenicquartz diorite porphyry was formed in the active continental margin-volcanic arc with thesubduction of Ocean Plate. Combined with geochronological data of this deposit, it’sindicated that the Badaguan porphyry copper-molybdenum deposit was formed under thetectonic settings of the southward subduction of the Mongolia-Okhotsk Ocean Plate inTriassic.