The Genesis And Prospecting Direction Of The Mengya'a Pb-Zn Deposit In Tibet

This contribution analyses gensis and prospecting direction of Mengya'a Pb-Zn deposit in the Tibet.Based on the field work,detailed lab research and the analyses to the former data and references,this paper summarizes the detailed geology and metallogenic conditions of the Mengya'a Pb-Zn deposit and provides theoretical basis for further exploring direction.The Mengya'a Pb-Zn deposit is located in the east of Nyainqentanglha metallogenic belt.The Laigu Formation of the Upper Carboniferous to Lower Permian and The Luobaduizu Formation of the Middle Permian,which rich in lead and zinc mineralization elements,are major ore source bed.Near east-west faults,north-west faults and south-north faults provided route ways and ore-hosting sites for ore-forming.The magmatic rocks are mainly composed of granite porphyry.The ore bodies are layered and veined,spreading along the main faults and their two sides and provided with typical skarn minerals and alteration.On the base of zircon U-Pb geochronology,rock ages of granite porphyry in the research area is the Miocene(13 to 20Ma).Combine with the mica Ar-Ar geochronology,molybdenite and pyrrhotite Re-Os geochronology,this paper constraints the major metallogenic time of The Mengya'a Pb-Zn deposit is 49-66 Ma.Two main Pb-Zn mineralizing periods are the Paleocene and the Eocene and granite porphyry are post-metallogenic rocks.The geochemical characteristics of strata and ore reveal that Laigu formation and Luobadui formation provide some metallogenic materials and the ore-forming fluid shows the reduction characteristic as a whole with the reduction tendency from east to west.The detailed mineralogical study shows that the Mengya'a Pb-Zn deposit is a typical skarn deposit.The fluid inclusion and C-H-O isotope datum showed that the ore-forming fluid was a mixture of magmatic water and meteoric water.A large amount of meteoric water was involved in the later period.The temperature and salinity gradually decreased from east to west,which may be the mechanism of mineral deposition.S-Pb isotope datum show that ore-forming materials are crust-mantle mixing,which may be related to the remelting of the crystalline basement of Nyainqentanglha metallogenic belt.Laigu Formation and Lobadui Formation strata provided part of ore-forming materials.Based on the geologicalcharacteristics and the study of diagenesis-metallogenic epoch,it is inferred that the formation of the Mengya'a deposit is related to magmatic activity during the main collision period between India and Eurasia and belongs to the distal skarn type deposit.Geological,geophysical,geochemical,remote sensing anomalies and short-wave infrared spectroscopy data show that the southwestern part of the mining area is located in Lobadui formation of Laigu formation with large faults,having a large number of magnetic anomalies with high anomalies,exists obvious Pb-Zn-Cu-Ag combination anomalies with high anomaly intensity and some iron-stained anomalies,and it is similar to the metallogenic environment of other known ore bodies in the mining area.Possibly it has big metallogenic potential.