Metallogenic Mechanism In The MingZe-PaNan Porphyry Molybdenum Deposits In The East Of South Gangdese,Tibet

Porphyry molybdenum deposits which lies in the southern edge of the eastern section of Gangdese is the main object of study.Two detailed anatomies of MingZe and PaNan molybdenum deposits in DangZe area have been done.Geological characteristics,ore body characteristics,ore types,alteration zonation and mineralization stage are identified,as well as the evolutionary sequence of magmatic rocks within the mining area.With the research in petrography,mineralogy and geochemistry,the magmatic source,the evolution process of the magma and the magma deep dynamic process are recognized.In addition,the mineralization age is regulated with the accurate Re-Os isotope tracing and dating in PaNan molybdenum deposits.MingZe molybdenum deposit mineralization is closely related to the two-feldspar granite porphyry.The porphyry shows the characteristics of full mineralization,and the ore is principally veinlet-disseminated mineralization,and straight vein mineralization also develops.Strong mineralization is usually accompanied by strong hydrothermal alteration,and obvious sub-band phenomenon happens,from deep to shallow showing potassic-zone,quartz-sericite-zone and mud-zone.The mineralization of metal components of the ore body has obvious banding phenomenon,and Mo mineralization produced in the lower potassic-zone while Cu mineralization produced in the upper zones.These characteristics are in line with the properties of porphyry mineralization.PaNan deposit is similar to MingZe deposit in mineralization and sub-band.Both mineralized porphyries are two-feldspar granite porphyry and strong hydrothermal alteration in the region happened.Geochemical studies indicate that the porphyry of two porphyry molybdenum deposit is two-feldspar granite porphyry which is highly fractionated.Detailed zircon U-Pb age data shows that the porphyry intrusive age is 30Ma.Rocks are enriched in SiO2,K2O,and depleted of Fe,Mg,Ti.The MREE are significant loss and have a weak negative Eu nanomaly,which reflect that the Mo porphyry may be the resulted of fractional crystallization of MREE-rich amphiboles and Eu-rich plagioclase of Adakitic magma.The whole rock Sr-Nd-Pb isotopic and zircon U-Pb dating and Hf isotope show that the quartz monzonite,K-feldspar granite and two-feldspar granite porphyry are actually the same set in the acidic magma experienced complex crystallization differentiation,magma mixing and crust-mantle contamination.The isotope data show that the mafic xenoliths are from the enriched lithospheric mantle and the host rocks derive from the lower crust which are mixed by a large number of mantle materials.Mineralogical evidence suggests that magma mixing happened in study area and the mixing should occur in the middle-upper crustal scale.Zircon U-Pb and molybdenite Re-Os dating show that the porphyry Mo mineralization in metallogenic belt occurs mainly in the 32.5-30.0Ma,and in this age India-Asia plates collision was ending.The mineralization may be mainly related to the magmatism induced by asthenospheric upwelling induced by the initial delamination of lithosphere and mantle in southern Tibet.