Ore-forming Timing And Material Source Of The Tongshanling Pb-Zn-Cu Polymetallic Deposit In Southern Hunan Province

The Tongshanling Pb-Zn-Cu polymetallic deposit is located in the collage part between one depression of southern Hunan Province-northeastern Guangxi Province inthe Yangtze Block and another depression of northern Guangdong Province depression in the Cathaysia Block.It is one of the representative deposits in metallogenic province of the Nanling.Based on previous studies,this dissertation clarified the ore deposit's geological and ore geological characteristics and carried out researches of Sm-Nd isotope geochronology,Pb isotope geochemistry and fluid inclusions in minerals.The main results are as followings:Garnets in the mineralized skarn are measured for Sm-Nd isotopes,with the isochrone value of 173 ± 3 Ma(MSWD =1.3).This value is earlier than the results from the Lu et al.(2015),and as well earlier than the most granitic complex and the other polymetallic deposits in the southeastern Hunan Province.However,they all belong to the products of the magmatism during the early Yanshanian.This indicates that the Tongshanling deposit is probably formed through mineralization more than once,and the 173 Ma is likely to the initial mineralized event.Metal sulfide minerals are measured for 206Pb/204 Pb,207Pb/204 Pb and 208Pb/204 Pb,with their means of 18.602,15.701,38.729,respectively,which indicate that the radiogenic Pb is obvious.In addition,the ? value with 9.64 is higher than normal lead;Th/U with 3.81 is lower than normal lead.All these features indicate that ore-forming material is mainly derived from relatively uranium lead-enriched and slightly thorium lead-defected Upper Crust.In the diagram of(207Pb/204Pb)i-(206Pb/204Pb)i,date of sulfide minerals are mainly distributed in the region of hosted granodiorite,indicating the hosted granodiorite is an important material source.Fluid inclusions from three petrogenesis and mineralization stages(skarn,quartz-sulfide and carbonate)for the Tongshanling deposit has been done,with the results that ore-forming hydrothermal fluid has the characteristics of middle-high temperature,middle-low salinity and low density,and its ore-forming surroundings is hypabyssal and low pressure.Part of the overlap in the diagram of homogenization temperature-salinity for fluid inclusions from quartz-sulfide phase and carbonate phase,indicates that there is a successive evolution between the hydrothermal fluids from those two phases.Apart from that,some data are near the meteoric water religion in that diagram,demonstrating that hydrothermal fluid is probably suffered from the meteoric water.Petrography and microthermometry characteristics demonstrate that fluid inclusions from skarn stage and quartz-sulfide phase may be captured from inhomogeneous fluid,representing the feature of fluid immiscibility.In addition,some typical water-rock interactions are common such as potash feldspathization and sericitization,which is also a great factor for urging the aggregation and precipitation for the metal elements.