Mineralization And Evolution Of Magmatism And Fluid In Baoshan Cu-Pb-Zn Polymetallic Deposit,Hunan Province

The Baoshan Cu-Pb-Zn polymetallic deposit,located at the convergence area of the Cathaysian and Yangtze plates,is located in the central Nanling mineralization zone.Based on the gained achievement and detailed field geological investigation,this paper conducted a integrated research on both the revolution of magma-fluid and the its metallogenic relationship of Cu-Pb-Zn polymetallic deposit of Baoshan with 3 primary methods,among which are the study of characteristics of fluid inclusions,isotope geochemistry and alteration zoning.Then a discussion was hold on the genetic mechanism of the ore deposit combined with previous regional tectonic evolution and geochronology data.The Cu-Mo ore body in Cu-Pb-Zn polymetallic deposit of Baoshan is produced in the contact zone consisted of inrmediate-acid intrusive rocks and carbonate rock in Yanshanian,while the Pb-Zn-Ag ore body is in the fracture zone and the surrounding rocks formed in Carboniferous.Obvious is the horizontal zoning characteristic of Baoshan ore deposit,in the middle of which is the high-thermal ore body contained the elements such Cu and Mo.The surroundings is the low-thermal Pb-Zn-Ag ore body with the periphery low-thermal Au or Mn.Based on the study od the petrography,mineralogy and rock geochemistry,we find that the magmatic rock is formed od upper crust remelting magma.The ore-forming magmatic rocks are granodiorite and grinite porphyry featured with a high concentration of Al and K while low of Na.And it has the feature of I type magmatic rock.The positive physical and chemical characteristic of the surrounding rocks accommodating ores can not only be a qualified transferable access for thermal liquid,but in which the hazel in Ceshui Formation is a favorable protective layer as well to provide a prerequisite for the enrichment and mineralization resulted from thermal liquid.The mineral characteristics of garnet and diopside in skarn are similar to those of typical Cu skarn all over the world.The REE distribution pattern of intermediate to acidic-acidic volcanic rock in Baoshen is characterized with slight negative anomaly of Eu.Studies of H-O isotopes indicate that the early staged thermal liquid for ore forming is magmatic water.As the ore forming processed,large amount of precipitation has been involved in the process.Analysis of the characteristics of fluid inclusions shows that the ore-forming thermal fluid is mainly the moderate-high temperature and medium density thermal liquid typed H2O±Co2±CH4±N2±C2H6.The concentration of Na? was lower than that of K? in early ore-forming fluid,while the ration reserved in later process.There existed two times of fluid boiling during the evolution of fluid.One occurred in skarnization,while the other one occurred in sulfurization.The analysis of thermal liquid alteration zoning shows a zoning mode that Cu/Mo ratio is low in rock body and high in endoskarn which located in the hanging wall of rock body.Zn/Pb ratio of ore body and Fe/(Zn+Fe)ratio of sphalerite show that the ratio increases from NW to NE along F21 Fault.F0 Fault is the channel for uranium migration in skarnization while F21 Fault is the channel for uranium migration in sulfurization.And F21Fault formed later than FO Fault.It indicates that the mineralization process of Cu-Mo and Pb-Zn may occur in different geological processes.The cluster analysis graph of the altered rock mass also suggests that Cu have less relationship with Pb,Zn,Ag,Hg,Sb,As which are chalcophile elements.This further explain that the mineralization process of Cu-Mo and Pb-Zn may occur in different geological processes.Through the research and previous data,draw follow conclusion,there exists two different deposit types in Baoshan.One is post-magmatic hydrothermal Cu-Mo deposit,the other is filling-metasomatic Pb-Zn deposit.The magmatic process provided the source for material,water and heat.The feature of horizontally zoning is resulted from the transportation and revolution of thermal liquid.There is a close connection between magma-fluid and mineralization in the deposit.