Geology And Mineralization In Mujicun Porphyry Cu-Mo Deposit, Northern Taihang Mt.,China

Mujicun porphyry copper-molybdenum deposit, located in the northern section of Taihang Mt., is animportant ore district of the Taihang tectonic-magmatic-metallogenic belt. This article describes itsgeological, alteration and mineralization characteristics. Based on detailed study, we recognized the primaryalteration zonation and their spatial distribution characteristics, identified the magmatic and hydrothermalevents which caused the alteration and mineralization. It figures out the dating of diagenesis andmetallogeny by studying the isotope chronology and geochemistry, and probe genesis of ore-formingporphyry and geological significance. By means of the micro-thermometry, Raman component analysis offluid inclusions and H-O, S-Pb, He-Ar isotope tracers, it also discusses the ore-forming fluids and mineralprecipitation mechanism, and further probes into the metallogenic constraints in order to establish thegenetic model of Mujicun porphyry copper-molybdenum deposit.Mujicun diorite-porphyry copper-molybdenum deposit displays a typical alteration-mineralizationpattern. From the center to the edge, it respectively develops silification, K-silicate, beresitization as well asprophylitization. The deposit mainly has three phase hydrothermal fluids （A/B/D veins）. Silification in thecore of the deposit with the potassium in the periphery is closely related to A veins formed in the early stage.The pyrite phyllic alteration zone is characterized by pyrite-chlorite–sericite which due to superposition ofmulti-stage alteration. The isotopic dating yields a LA-ICP-MS zircon U-Pb age of144.7±1Ma forcrystallization of diorite porphyry that hosts the Cu-Mo mineralization, five Re-Os molybdenite ages give aweighted average of140.3±3.9Ma, which suggests that the magmatism, porphyry-type and skarn-typemineralization should form in the continuous process. The ore-bearing porphyry and adakites have similargeochemical properties, and Isotopic Lu-Hf data all implies that the magma and mineralized elementsshould be mainly resulted in partial melting of lower crust.Isotopic S-Pb data implies that the mineralized elements should be mainly from lower crust, the Cuelement may from low crust and exchanged material with the upper mantle, and the Mo element resulted inpartial melting of the lower crust; isotopic He-Ar, H-O results show the ore-forming fluids envolved fromthe primary magmatic water in the early stage, then from the meteoric water in the late stage. The evidenceof the fluid inclusions shows that the early fluid exsolved from ancient depth magma chamber （thetemperature>590℃）. As the fluid intruded into the bottom of porphyry, when the temperature decreased toabout392℃, A vein formed, which belongs to the high temperature and high salinity H₂O-CO₂-NaClsystem. There were a lot of boiling inclusions in the fluid of principle metallogenic stage （B vein）, whichbelongs to the middle temperature, middle salinity H₂O-NaCl system. The inclusions in the late stage （Dvein）, with only broad water peak in the gas phase composition, show the features of H₂O-NaCl systemwith low temperature, low salinity and high density. We conclude that the additional deep source fluidswhich caused a series of mineralization intensify the water-rock interaction, bring heat source and mineralsfor the hydrothermal system, the fluids boiling at a shallow lever induces the precipitation of ore-formingelements, eventually forming the Mujicun porphyry copper-molybdenum deposit.