Fluid Evolution Characteristics Of Wunugetushan Porphyry Cu Mo Deposit In Inner Mongolia

The wunugetushan porphyry copper and molybdenum deposit(hereinafter referred to as"wushan"deposit)is located at the interface between the erguna post-baikal fold system and the da-hinggan mountain fold system,the relative uplift of the helar Mesozoic continental volcanic belt,and the proximal axis of the ushan anticline,which is controlled by the volcanic mechanism.Based on the systematic field investigation and laboratory study,the auther choosed sufficient samples from ore-bearing rock-bodies,ore minerals and gangue minerals of the Badaguan Cu-Mo deposit to conduct geochemical analyses including rock geochemistry,geochronology,isotopic geochemistry and fluid inclusion.Finally the paper discussed mineralization mechanism and main ore controlling factors.Fluid evolution of Wunugetushan large porphyry Cu-Mo deposit,where Cu and Mo orebodies are spatially separated,was studied through crosscutting relationship and alteration minerals of various quartz veins,petrographic observation,microthermometric,laser Raman spectroscopic and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)analyses of fluid inclusions to explore the possible parameters influencing the Cu and Mo decoupling.Hydrothermal activities experiences four stages:(1)early Mo mineralization stage,fluids are intermediate-densities(11.0-17.3 wt.%Na Cl equivalent),CO₂-rich and high-temperatures(540-580?),accompanied with biotitization;(2)late Mo mineralization stage,fluids are characterized by high-densities(up to 77.0 wt.%Na Cl equivalent),intermediate temperatures(380-470?),oxidized,neutral,and CO2-bearing,associated with K-feldspathization,sericitization and illization alterations;(3)Cu mineralization stage,fluids are low-temperatures(230-380?),high-densities(up to 45.6 wt.%Na Cl equivalent),slightly reduced,acidic and CO₂-rare,related to sericitization and illization alterations.(4)Cu-Zn-Pb mineralization stage,fluids are low-temperatures(144-211?),densities(up to 11.7wt.%Na Cl equivalent),related to sericitization and illization alterations.Fluid evolution follows the typical path in porphyry mineralization system,from Mo mineralization stage to Cu mineralization stage,fluids are gradually more reduced and acidic after the amounts of crystallization of K-feldspar,biotite,anhydrite and hematite,loss of CO₂ during cooling and decompression of magma bodies.Given that the possible effects of redox,p H,pressure,and temperature on the separation of Cu and Mo,we concluded that separation of the two metals is possibly controlled by the brine-vapor immiscibility.