Geological, Geochemical Characteristics And Genesis Of The Mengya'a Lead-Zinc Deposit, Tibet

The Mengya'a lead-zinc deposit, located 18km southeast in Rongduo Town of Lhari County, Tibet Autonomous Region, is a very important and typical skarn deposit in the Menba-Jinda Pb-Zn-Ag-Cu-Mo polymetallic ore district of Gangdise-Nyainqentanglha metallogenic belt. The Mengya'a deposit belongs to the eastern section of Longge'er-Nyainqentanglha Mesozoic island chain in the central part of Gangdise-Nyainqentanglha plate in structure. Based on analyzing the geological conditions of deposit formation, the fluid inclusion and geochemistry of this deposit have been in-depth studied in this paper, while the ore-forming fluids and material sources of this deposit are revealed. Meanwhile, combining with the regional tectonic evolution history and mineralization chronology information, the genesis of this deposit is discussed, and its corresponding genetic model is initially established.The studies of fluid inclusion in quartz showed that: the ore-forming fluids have characteristics of middle temperature and low salinity; Based on the study of H-O and C-O isotopic compositions of Mengya'a deposit, the writer presumed that the ore-forming fluids are dominated by magmatic water in its early stage while are mixed with a lot of precipitation in the later phase; The Eu anomalies of different performances about the rare earth of metal sulfides reflected that, the physical and chemical properties of fluids have occurred different degrees of change during the mineralization process.The results of stable isotopic geochemistry showed that: the carbon of mineralization hydrothermal mainly comes from the magma with deep sources, with a small amount from the carbonate rocks, and the magmatic rocks happen strong oxygen isotopic exchange with the formation of wall rocks; The sulfur isotope of ores generally has the characteristic of magmatic sulfur with deep source, and the sulfur is mainly from the magmatic source; After beening determined, the lead of the Mengya'a ore belongs to the normal common lead. The characteristic about highμvalues of lead isotope and the tectonic evolution model diagram of Zartman Pb isotope, as well as the investment positions of sample illustrated in the△γ-△β genetic classification diagram, all suggested that material sources of ore-forming metals come from the upper crust (crystalline basement), and the activation of lead has close relationship with early Cretaceous granite.The history of regional tectonic evolution showed that the thermal events of Cretaceous granite have been developed extensively, and the different sizes of mineralization have been formed; The ore-forming age analysis of typical skarn deposit in the mineralization belt suggested that the Mengya'a Pb-Zn deposit is likely formed in the late Yanshan, has a close relationship with Yanshan acid magmatic events and is a typical skarn deposit.