Study On The Fluid Inclusions Of The Bolong Copper Deposit,Tibet

The Bolong porphyry copper deposit was recently discovered by the No.5Geological Team of the Bureau of Tibetan Geology and Exploration in2000。The Bolong copper deposit is one of the typical large-scaled porphyry deposit,lies in Duolong deposit area of eastern Bangongco metallogenic belt,Tibet.The object study that Geological background of mineralization(stratum, structure, magmatite and metamorphic rocks), ore deposit geological characteristics (the ore-bearing rock characteristics, orebody characteristics, ore texture and structure, mineral composition, wall rock alteration and mineralization stages and the fluid inclusions within quartz and anhydrite in the different stages of mineralization Through systematical study in geology character, homogenization temperature, oxygen and hydrogen isotope composition, we discussed the character and genesis of ore-forming fluid and the mineralization and precipitation process. The result of research shows as fllowing:The ore body is generally concealed and half concealed, the ore body is not exposed in surface.The ore body of mother rock is granodiorite porphyry. The major elements of the allgovite are characterized by high Al2O3, rich K2O,poor Na2O and CaO; The allgovite have low content ofEE, a weak positv Eu anomaly or no Eu anomaly, Chondrite-normalized REE diagrams show LREE-enriched patterns; traceelements are characterized by enrichments in LILE (Cs、Rb、K and Nd) and depletments in HFSE(Ba、U、Ta、Nb、Sr and Ti).The structure of ore are vein-impregnation,vein and impregnation;the texture include crystal, solid solution separated,metasomatic texture. Dominanent metallic minerals are pyrite and chalcopyrite,secondary are pyrrhotite, bornite, stibnite, magnetite, hematite. Ore chemical composition shows thatAu the average grade of Cu is0.49%, the average grade of Au is0.20g/t, the average grade of Ag is1.3g/t, the average grade of S is1.2%, the average grade of Ga is17.0×10-6,the average grade is200.1×10-6.The associated elements are Au,Ag,S,Ga.According to the geological information,we divided the metallogenic process of Bolong deposit into three stage,which are magma-advanced atage,hydrotherm ore forming stage and supergene stage. We partitioning hydrotherm ore forming stage to three period also,which are magnetite-molybdenite period, chalcopyrite-pyrite period and anhydrite-pyrite period.There are four types of fluid inclusions in this deposit, mainly are pure gasphase,liquid phase,gas-liquid phases and the multiphase fluid inclusions with NaCl and(or) metal sulfide daughter minerals. The ore-forming environment is middle-high temperature (232℃～549℃), middle-high pressure (1.40×105～234.41×105Pa), shallow depth (0.01～0.78km).The ore fluid system is typically middle-high salinity (28.65～52.16wt%NaCl)、middle-high density (1.0683～1.1598g/cm3). Form quartz phenocrysts to magnetite-molybdenite period to chalcopyrite-pyrite period to anhydrite-pyrite period, the homogenization temperature pressure and salinity are gradually reduce.On the contrary,the density is gradually rise.The8D of fluids change from-91.5‰to-72.2‰, Average is-125.89‰. The δD values of quartz are from9.5‰to16.3‰, Average is11.8‰. Theδ18OH2O values are form5.4‰to9.9‰, Average is7.1‰. Hydrogen and oxygen isotopes study shows that:the fluids may be derived from magmatic water,parts of fluids may be the underground hot water.The stude that Bolong,Duobuza,Qulong,Chongjiang,Bangpu,Jiama,Yulong, Dexing, La aridad、Rosario、Butte、Oyu Tolgoi、Endeavour26North、Bajo de la Alumbrera porphyry copper deposit, we discussed that the types of fluid inclusions, temperature, pressure, salinity, density are very similar.It suggest Bolong copper deposit has a good ore-forming potentia.