The Characteristics Of Hydrothermal Fluids And The Origin Of Metallogenic Materials In The Tongshanling Cu Polymetallic Deposit,South Hunan

The Tongshanling polymetallic deposit is located in the central-western part of the Nanling tectonic belt and is an important part of the Shuikoushan-Baoshan-Tongshanling metallogenic belt in Southeastern Hunan.The basic geology has been discussed by many researchers,but the division of skarn orebodies and quartz-vein orebodies needs to be improved,and the source,composition,and properties of the hydrothermal fluids are not clear.Based on the previous research,the geochemical characteristics of sulfides(sphalerite and chalcopyrite)and the fluid inclusion characteristics of quartz in skarn and quartz-vein orebodies were analyzed to compare the difference of hydrothermal fluids and determine the characteristics of hydrothermal fluids and the source of metallogenic materials.The main research achievements are as follows:By comparing the quartz H-O isotopes,and sulfide S isotope results,it is found that the isotopic characteristics of the two ore bodies are very similar,and the hydrothermal fluid is mainly derived from granodiorite,and a small amount of meteoric water was added in the late stage.The granodiorite provided massive ore-forming materials,and the δ34S value is similar to the typical Cu-polymetallic deposits in Southern Hunan.The temperature data of quartz fluid inclusions show a gradual downward trend from skarn stage(320°C)to early quartz-sulfide stage(290°C),to late quartz-sulfide stage(260°C),to post-mineralization stage(220°C).In the quartz-vein orebodies,the temperature gradually decreases away from the granodiorite(290℃→260℃),and the salinity also shows a slightly decreasing trend.The sphalerite precipitation temperature of skarn and quartz-veins from the early stage to the late stage has an obvious downward trend(330℃→260℃;310℃→270℃),and the exsolution minerals gradually decrease(chalcopyrite,tetrahedrite,pyrite → none;chalcopyrite→none).Both orebodies are formed in an environment of high sulfur fugacity,medium-low temperature,and medium-low salinity,and the temperature,salinity,and sulfur fugacity of skarn ore-forming fluid are relatively high.The contents of Pb,Bi,and Sb elements continue to increase in the fluids of skarn orebodies due to the continuous addition of sedimentary materials.Due to the substitute mechanism and incompatibility,the content of Sn element is increasing in sphalerite,but less in chalcopyrite,and the contents of Cd and Co is relatively high.However,the content of Cd,Co,Bi,and Sb in the quartz-vein orebodies is relatively low.In this paper,a detailed two-stage metallogenic model of Tongshanling is established.The hydrothermal fluids of the two orebodies were divided from one deep magma chamber,and both have the characteristics of medium-low temperature,low salinity,and high sulfur fugacity.Due to the participation of formation materials in the skarn orebodies,the main factors of mineral precipitation are fluid mixing and depressurization boiling.The contents of Pb,Bi,and Sb elements in the fluid are relatively high.The temperature of the hydrothermal fluid in the quartz-vein orebodies is relatively low,and the metal precipitation is mainly due to natural cooling and adding of meteoric water.The element contents of most metals decrease continuously with the transport of the fluid.This study provides a theoretical reference for the study of other granite-related skarn and vein composite deposits in southern Hunan.