Fluid Inclusion Studies Of The Tangge Cu-Pb-Zn Polymetallic Skarn Deposit, Tibet

The Gangdese metallogenic belt is one of the most important copper metallogenic belts in China. Tangge Cu-Pb-Zn polymetallic skarn deposit located in the volcanic-magma arc belts on southern margin of Gangdese. The only one large porphyry copper deposit in the western part of Gangdese metallogenic belt-Zhunuo,is about eight kilometers west of the Tangge deposit. This paper studied geological characteristics of deposit,the characteristics of the petrography, microthermometry, and Raman spectrum of fluid inclusions. We compared Tangge deposit with Zhunuo porphyry copper deposit through previous research results in fluid inclusion. Through the mineral composition, metasomatic alteration and the sequence relationship, we divided ore formation into skarn stage and quartz-sulfide stage, subdivided into wet skarn phase, dry skarn phase, quartz-iron-copper sulfide phase, quartz-lead-zinc sulfide phase, and quartz-carbonate phase. Mineralization mainly occurs in quartz sulfide phase. The stronger skarn lithification alterated(near marble), the richer of mineralization; The weaker skarn lithification alterated (as volcanic breccia), the poorer mineralization;Cracks and the lithologic mutations parts are the strong alteration parts,as well as the ore forming part. According to the petrography characters of the fluid inclusion at room temperature, it can be divided into three categories:(1) the liquid rich gas-liquid two-phase aqueous inclusions (LV);(2) the gas rich gas-liquid two phase aqueous inclusions (VL);(3) the pure liquid inclusions (L). Garnet and epidote are riched in LV type inclusions. Calcite and Wollastonite are full of LV and VL type inclusions.The Quartz is riched in inclusions of LV, VL, L types. Based on this, we carry out research on the laser Raman spectrum analyses. The liquid phase in Quartz composition mainly is water, part will contain a small amount of CH4; Gas phase composition is more complex. We can find C3H8, CH4, N2, CO2 from it. A small amount of gas phase of Calcite inclusion contains CH4. The ore forming depth of wet skarn phase, quartz-sulfide phase, quartz-carbonate phase were 2.5 km,1 km and 0.9 km. By the results of the microthermometry we can find the temperature and salinity gradually reduced with fluid evolution. Temperature decrease, pressure decrease and the increase of pH value, will make the ore forming fluid selective. The fluid with low temperature and low salinity is not suit for transporting the Cu2+. The existence of a pressure gradient just as fault will make the long transportation of Pb-Zn possible.The reduction of temperature is the most important reason for ore deposits’formation. The downgraded chloridion makes is the essence of mineral precipitation. The ore-forming fluid of Tangge Cu-Pb-Zn polymetallic skarn deposit show some similarity with Zhunuo porphyry copper deposit. The transformation of ore-forming fluid come from Zhunuo porphyry copper deposit.plays a big role in Tangge deposit’s formation.