Comparative Study Of Caojiaba Skarn Tungsten Deposit And Longshan Gold-Antimony Vein Deposit,Central Hunan Province

In recent years,the breakthroughs of prospecting have been achieved in the Central Hunan area.A number of large-scale tungsten deposits have been discovered and important progress has been made in the exploration of the depth and margin area of old mine,which fully demonstrated the potential of mineralization in the Central Hunan area.Available data indicates that tungsten mineralization is associated with gold mineralization in the central Hunan and its adjacent areas.And the new discovered tungsten is associated with gold,where is an ideal region for us to study the separation of tungsten from gold in hydrothermal system.So based on detailed field investigation of the Caojiaba tungsten deposit and Longshan gold-antimony deposit,this study is focused on systematic microscope observation,electron microprobe analyses and in situ LA-ICP-MS analyses of the skarn minerals and scheelite,direct Ar-Ar isotope dating on muscovite collected from Longshan gold-antimony deposit,and sulfur isotope analyses of sulfides.Through all these works,we now obtain several achivevments and understandings,as follows:(1)Caojiaba tungsten deposit is a typical skarn tungsten deposit based on field geological characteristics.Systematically core drilling logging reveals that tungsten mineralization is closely related with skarn alteration.According to intersection relationships and mineral association,the ore-forming process can be fivided into three stages,such as: skarn stage,retrograde skarn stage and quartz-sulfide stage.And Longshan gold-antimony deposit mineralization can be divided into scheelite antimony gold stage,antimony arsenopyrite(pyrite)gold stage and pyrite(arsenopyrite)gold stage.(2)The systematic analyses of electron microprobe show that the garnets have two distinct stages,i.e.,early garnets are dominated by grossular with subordinate andradite,and ones during the late stage are grossular with minor almandine and spessortite.The pyroxene consists of mainly hedenbergite,with minor diopside,and the chlorites at Caojiaba belong to brunsvigite.Two stages of scheelite have identified,and early fined disseminated scheelite is intergrowth with prograde skarn,and late stage coarse grained scheelite coexists with quartz as fined vein.The CL imaging and LA-ICP-MS analyse show that early scheelite grain is heterogeneous.Based on its inhomogeneity,LA-ICP-MS analyses yield two different REE patterns.And the content of rare earth and distribution patterns show significant differences.(3)Two stages of scheelite of Longshan gold-antimony have identified,and early coarse grained scheelite is cemented by stibnite in the scheelite antimony gold stage,and late scheelite coexists with stibnite and quartz in the antimony arsenopyrite(pyrite)gold.The CL imaging and LA-ICP-MS analyse show that early stage scheelite grain is homogeneous while late stage scheelite scheelite grain is heterogeneous.And the content of rare earth of early stage scheelite is significant higher than late stage scheelite.(4)The Ar-Ar isotope dating on muscovite of Longshan gold-antimony deposit shows that the plateau age is 162.0±1.2Ma.Combined with the hydrothermal zircon(U-Th)/He age(160.7±7.3Ma)of No.5 gold-antimony lode in Longshan gold-antimony deposit and the early stage calcite Sm-Nd isochron age(155±1.1Ma)of Xikuangshan antimony deposit,it is suggested that the mineralization of the Longshan gold-antimony deposit is temporally and genetically related to the hydrothermal mineralization event in this area in 155?162Ma.(5)The sulfide isotope composition of sulfides of Caojiaba tungsten and Longshan gold-antimony deposit show the characteristisc of magmatic hydrothermal.Moreover SR-Nd isotopic characteristic of scheelite of Caojiaba tungsten deposit and Longshan gold-antimony shows that metallogenic material may be related to Baima Mountain pluton.Based on the geological characteristics,mineralogy,isotope and other aspects,this paper infers that Caojiaba tungsten deposit is a distal reduced skarn tungsten deposit and Longshan gold-antimony deposit is a hydrothermal deposit realted to magmatic activity.