Geochemical Characteristics And Mineralization Model Of Gold-Antimony Polymetallic Deposits In The Gudui Area,Tibet

The Gudui area in the Gangdise-Himalayan orogenic belt is located in the Gyangze-Longzi gold-antimony polymetallic ore belt in the southern Tibet,and its mineralization potential is huge.The geological work of this area is not enough,the exploration degree of the polymetallic deposits is low,and the geochemical characteristics and ore-forming fluids of the typical polymetallic deposits are lacking,the summary and research of the regional metallogenic regularity are also lacking.The polymetallic deposits in the study area are closely related to the second,third Nieru groups of Triassic and Zhela group of Jurassic,the lithology is dominated by muddy,it is more favorable to the ore-forming strata with the higher carbon content and the limestone,iron-silicon nodule,It is advantageous to infer that the sedimentary environment is a progressive strata of underwater fan deposits under different elevations.Near EW,NE and NW-trending faults and secondary fracture interbeds formed by stacking and extensional strata formed by collision orogeny and detachment extension are favorable metallogenic and ore-controlling structures.The granites from 40 Ma of the Paleogene are closely related to the polymetallic mineralization of the gold and antimony.The granite of the Neogene 20 Ma is closely related to the antimony plumbum and zinc.The results of this study are as follows:(1)The type of fluid inclusions are mainly aqueous solution inclusions(W type),CO2-H2 O inclusions(C type),small amount of gas inclusions,non-sub-mineral heterogeneous inclusions.The average temperature of the three typical deposits is 170-220?,the average salinity is 6.82%,the mineralization pressure is 50-55 MPa,and the mineralization depth is 1.5-2.5km,which can be judged as belonging to the superficial and low temperature hydrothermal deposit.The gas composition of ore-forming fluids is dominated by CO2,and it is deduced that the Au-Cu hydrothermal system is a low-temperature and lowsalinity NaCl-H2 O hydrothermal system.(2)H-O-S-Pb isotopic compositions show that the ore-forming fluids are mainly composed of metamorphic water and mixed water.Sulfur has the characteristics of deep source magmatic sulfur,and plumbum has the tendency to evolve from the orogenic belt to the crustal plumbum,forming the same plumbum isotopic composition with the surrounding rock.(3)The genesis of deposits is analyzed and the metallogenic model of the study area is established.It is concluded that the magmatic activity of the Dhalar rock mass provides the initial heat source and the transport power of the ore-forming material,the upwelling of the mantle hydrothermal and the intrusion of the medium acidity sub-volcanian,bring out the dynamic hydrothermal metamorphism and absorb a variety of ore-forming elements,so that activated into ore hydrothermal fluid,and migration,precipitation,in the region a series of near EW trending to the main fracture and near SN trending to secondary fracture enrich to form the mine.