Early Yanshan Granitic Magmatic-hydrothermal Evolution And Tungsten Deposits Mineralization In Southeast Hunan

Nanling region is an important area of non-ferrous metal resources in China,which lots of large or very large tungsten deposits are widely distributed in the area.Diagenesis of the Nanling granite and the relationship between Nanling granite andtungsten deposits have always received attention from academic circle. Since the1980s, the magmatic-hydrothermal metallogenic theory (MHMT) has made importantprogress, and with the theory of MHMT putting forward, studies on the nature ofmagmatic-hydrothermal fluid and mineralization have gradually attracted thegeologists attention. The mainstream history view considered that quartz vein, skarnmineralization were post-magmatic hydrothermal type ore-forming mode. In recentyears, a large number of liquid immiscibility phenomena has found in Yanshan periodgranite strains which had a close relationship with the tungsten deposits in southeastHunan province, including granie-hosted tungsten mineralization, ore chamber,greisens segregations, alkali-metasomatized veins, eye-shape segregations andpegmatitoides, and so on. Some immiscible geological phenomenons recorded thefeatures of magmatic-hydrothermal evolution processes. For example, the core of agreisens segregation shows the textures in hydrothermal stages and it is comprisedmainly of quartz and mica, whereas the rim shows magmatic texture. And the centerof an alkali-metasomatized veins are granitic materials, while the margins are alwayscomprised of K-feldspar and fluorite veins.This thesis focuses on some typical tungsten ore deposits in southeast Hunan,including Yaogangxian, Shizhuyuan, Xiangdong and other quartz vein-type,skarn-type tungsten polymetallic deposits, and comparative study of the depositsmentioned above. Through detailed study of field geology, mineralogy, geochemistry,and so on, this thesis exponds the evolution of the high differentiation and evolvedgranite during the late stage of magmatic-hydrothermal transition and metallogenesis.The main results obtains in this paper are given in more detail below.1. A number of important geological phenomena which could represent the liquidimmiscibility of late-stage magma were found.2. The continuous evolution processes from granitic magmatic to hydrothermalwas constructed, and the quartz vein type and skarn type tungsten deposits belong tomagmatic-hydrothermal type deposits. In the magmatic-hydrothermal transition stage, some geological unites (e.g., greisen, greisen segregations,alkali-metasomatized veins and garnet skarns) widely host melt-fluid inclusions. Thestudies of fluid inclusions in greisen segregations and alkali-metasomatized veinsshows that the magmatic-hydrothermal evolution is a continuous process.3. The migration processes of ore-forming elements during the process ofmagmatic-hydrothermal evolution is recognized. Some elements can be concentratedduring the process of liquid immiscibility. Taking greisen segregations as example,from alkaline granite to margin and center of greisen segregations, the ore-formingelements (such as W, Mo,Bi, Pb, Zn, Nb and Ta), associated with volatile elements(Liand F) would be concentrated, meanwhile, the LREE/HREE ratios and δEu aredecreasing. The concentrations of each element are continuous and directional, forexample, W is much more concentrated in center, whereas Mo is much moreconcentrated in margin of the greisen segregations.4. The metallogenic models of both quartz-vein-type and skarn-type tungstenpolymetallic deposits are build. The tungsten mineralization is strictly controlled bythe processes of evolution from the magmatic to hydrothermal stage. As forquartz-vein-type tungsten deposit, the granitic-type ore was derived from volatile-richmagma which separated out at the late magmatic stage, the greisen segregations werederived from liquid at the magmatic-hydrothermal transition stage, and theore-bearing quartz veins were always formed at the high-temperature hydrothermalstage. As for the skarn-type deposit, the early alkali-metasomatized veins shows thecharacteristics of the magmatic-hydrothermal transition stage, which gradualtransformed to the late stage alkali-metasomatized veins. The fluid was hydrothermalin late stage alkali-metasomatized veins and this period is the main mineralizationstage.