Thermodynamic Formation Conditions And Genesis Of The Baiyangping Pb-Zn Polymetallic Deposit,Yunnan

Lanping basin,located in the south of Sanjiang area,the western boundary is the Lancang River zone and the eastern boundary is the Jinsha River zone,which gradually vanishes to the north and is fan-shaped.The structural belt of the basin is well developed,which provides favorable conditions for the formation of orebodies.There are a large number of common Pb-Zn deposits in Lanping area.At present,there is still some controversy about the conclusion of the genesis of these Pb-Zn deposits,especially the thermodynamic study of carbonate ore-bearing Pb-Zn deposits developed in Lanping basin.The thermodynamic study of Pb-Zn polymetallic deposits in Lanping basin is of great significance for the enrichment of the metallogenic theory of metallogenic belt and sedimentary rock-bearing Pb-Zn deposits in Lanping basic.Combined with and referring to the previous research results of Baiyangping Pb-Zn polymetallic deposit,the author uses various geological means.The author makes a further study on the ore-forming physicochemical conditions,ore-forming material sources and deposit genesis of the Baiyangping copper-lead-zinc polymetallic deposit in Lanping area by means of mineralogical and petrological research and analysis,geochemical research and thermodynamic phase diagram of mineral assemblages.The main achievements of this study are as follows:Baiyangping deposit is located in the northern part of Lanping basin.The regional tectonic evolution in the basin provides geological conditions for the formation of orebodies.Most of the orebodies occur in the secondary fault zone of the structural belt in the basin.According to the conclusion of sulfur isotope study,the material carried by ore-forming fluid comes from deep and has the characteristics of crust-mantle mixing.The common cobalt mineral in Baiyangping mining area is arsenite.The common Ag mineral is silverite.Co mineralization is related to As element anomaly.The change of element regularity indicates that the ore-forming temperature is about 300?.Next,the thermodynamic study on the symbiotic mineral assemblage of the Baiyangping Pb-Zn polymetallic deposit is carried out.First of all,the typical mineral symbiotic assemblage of the deposit and the division of metallogenic stages are determined.We selected pyrite,chalcopyrite,galena and sphalerite,which are symbiotic under the microscope,to calculate the thermodynamic equilibrium.Then,we get the thermodynamic phase diagrams of lg[Cu²⁺]-pH,lg[HS^—]-pH and Eh-pH were drawn by selecting the characteristic equations of mineral symbiosis at 400 K,500K and 600 K.It shows that the mechanism of mineral migration and precipitation and the formation of mineral symbiotic assemblage in ore-forming fluid are closely related to the temperature,ion activity,pH,Eh and other factors of ore-forming fluid.The metallogenic model of the deposit is established on the basis of thermodynamic phase diagram,combined with the tectonic setting of the mining area and sulfur isotopes.