The Indication Of Wolframite And Hydrothermal Mica For Mineralization In Jiaoxi Tungsten Deposit In The Western Part Of Bangong-Nujiang Belt

The Jiaoxi tungsten deposit is the first quartz vein type tungsten deposit discovered in the Bangong-Nujiang metallogenic belt.The formation of the deposit can be divided into oxide stage,sulfide stage and fluorite carbonate stage.The ore minerals are wolframite and a small amount of scheelite.In this paper,through the analysis of electron probes and trace elements of wolframite of different depths and mica of different stages,reveal the characteristic and evolution process of the ore-forming fluids during the formation of the minerals and to explore the W Precipitation mechanism.Specific understanding of the following points:?1?Electron probe analysis of wolframite at different depths in the borehole shows that the content of MnO in wolframite is almost higher than that of FeO,indicating that the whole deposit is formed in an acidic metallogenic environment.The Fe/Mn of wolframite has a certain correlation in depth.The ratio of iron to manganese increases with the decrease of the output depth.The type of wolframite changes from iron-bearing tungsten-manganese ore to iron-tungsten ore.And as the depth is closer to the surface,the Fe/Mn ratio is closer to 1.It shows that the redox state of the ore-forming fluid changes during the upward migration.The fluid in the deep oxidized state undergoes a redox reaction with the reduced argillaceous slate during the upward migration process,which causes the fluid to over-transform from the oxidized state to the reduced state.The proportion of FeO in the wolframite in the shallow part of the surface increases.?2?The trace element analysis results of wolframite indicate that the Sc element content in Jiaoxi wolframite is relatively enriched(average value is 31.15×10^-6),and the ore-forming fluid of Jiaoxi tungsten deposit has low pH and Eh and is rich Features with F^-and/or PO₄^3-.The electron probe analysis of the mica in the oxide and fluorite carbonate stages of the deposit showed that the mica in the Jiaoxi tungsten deposit is single in composition,mainly muscovite and polysilicon muscovite,and is rich in F,Al₂O₃,K₂O,and poor in TiO₂,MgO,FeO.After the greisenization,[WO₂F₄]^2-ions in the flui decompose into WO₄^2-continually and combine with Fe and Mn ions to form wolframite.In addition,the Fe³⁺-Fe²⁺-Mg²⁺diagram shows that the oxygen fugacity of ore-forming fluids gradually decreases after the greisenzation,which is another key factor that promotes the formation of wolframite.