The Fluid Inclusion Characteristics And Genetic Significanceof The Keyue Plumbum-polymetallic Deposits, South Tibet, China

The Keyue Lead multi-metal mines is located in northwest of Longzi countytown in the shannan area of Tibet about4kilometers, and in north-east direction of thenoted Lead multi-metal mines of Zhaxikang. It’s geo-structure is a part of first-ordertectonic units of the Himalayan block in the Gangdise-Himalaya mountains, whilemain part belongs to the Laguigangri passive continental margin basin. It’sstratigraphy is geared to the KangMa-LongZi stratigraphic in the Himalayanstratigraphic area. It have happened long tectonic-sedimentary-Magmatic evolution,especially including orogenesis by the Himalayan landmass colliding with theGangdise landmass and Large scale extensional Detachment-slip, This cause widemetamorphic magmatic activities of the region, mainly manifesting for the fold, theEW trending faults, Zangnan detachment, north-south rift.Keyue Lead multi-metal mines is the typical Lead multi-metal mines in theZangnan antimony (gold) Metallogenic belt, It’s a newly discovered poly-metallicdeposits, Mining Company focused on Calculating the amount of resources, and do alittle research on the genesis of the mining, Therefore the research degree is relativelylow. The thesis is study the fluid inclusions of Keyue ore, Through systematicobservation and studies of ore fluid inclusions, Reveal the nature, formation andevolution of the ore-forming fluids, Discuss migration mechanism and mineralcrystalline precipitate of fluid, Provide some reliable basic data for research genesis ofthe deposit, Provide technical support for the exploration of deep and peripheral.Based on the systematic collection of the resources and studies made by thepredecessors, systematically conducted field geological survey about the KeYuedeposit. The main emphasis of the survey are quantity, size, shape of ore body in thisdeposit and how many contain vein it has. I kept overall observation and sample bothon the earth and in the gallery, and finally found out ore body geologic characteristic,ore bearing stratum and wall-rock alteration.KeYue Lead multi-metal mines located in the middle of the area, and the gutter isin RiDang group of Lower Jurassic. Lithology is mainly composed of black carboncontaining calcareous slate, slate, calcareous slate, shale siltstone and argillaceous limestone containing dolomite, while the boundaries of mineral ore and adjacent rockis clear. KeYue deposit consists of No.1mineral ore (main) and No.2mineral ore,occurrence in the North-South and high-angle-tension shear fault zone, and mineralore is strictly controlled by the faults. The mineral ore is vein, bedded and lenticular.Mineral ore along the fault is continuously, with thinning, swelled, branch andcomplex phenomenon.The main alteration type in area are silicate、pyritization、Carbonation andLimonitization，followed by a little chloritization、sericitization and argillation.Studies like observation, identification and photographing of an amount ofpolished flakes, polished, Inclusions tablets with the microscope are made indoor in asystematical way, which defined texture and structure of the ore.Ore structure are self-shaped crystal structure, half shape texture, containingtexture, interstitial texture, inclusion texture, skeletal texture and emulsion texture；The main structure of the ore are massive structure, banded structure, disseminatedstructure and vein-like structure;Metal minerals in deposit have galena, sphalerite,jamesonite, chalcopyrite, stibnite, mispickel, pyrite, siderite and so on. Metallizingphase of KeYue deposit can be divided into three periods: hydrothermal sedimentaryperiod, low to moderate temperature hydrothermal stage and supergene weatheringperiod, including low temperature hydrothermal stage is the main metallogenic period,which can be divided into the following five stages: ferromanganese carbonate stage(Ⅰ), quartz-mispickel stage(II), quartz-sphalerite-galena-orepyrite stage(Ⅲ),quartz-stibnite stage (IV), quartz-calcite stage (V).Inclusion types in KeYue deposit have gas-liquid phase aqueous inclusion（L+V）、liquid phase aqueous inclusion（L）and gas phase CO2aqueous inclusion（V），and inthe test mainly choose gas-liquid phase aqueous inclusion which is massivelydistributed. Conducted a uniform temperature and freezing point measurement,Calculated salinity, density, pressure of inclusions. Roughly calculate the depth ofmineralization.Through the homogenization temperature of inclusion test, homogenizationtemperature peak of KeYue deposit metallogenic stages are: erromanganese carbonatestage stage21~230℃, quartz-mispickel stage220~250℃, quartz-sphalerite-galenaand pyrite stage240~260℃, quartz stibnite ore stage200~240℃quartz-calcite stage,210~220℃. As can be seen, inclusion homogenization temperature changes little fromearly to late stages, with a tendency of decreasing in general; Each stage Mainlydistributed salinity range (NaCl eq) of each stage is5.1~6.9%,4.3~7.1%,2.9~5.0%, 4.0%~5.0%,2.6%~4.5%, which is low but slightly higher than the seawater salinity;Fluid density in each stage of mineralization are roughly equal, respectively0.88~0.95g/cm3,0.80~0.90g/cm3,0.70~0.91g/cm3,0.85~0.92g/cm3,0.81~0.89g/cm3, with little change. Mineralizing fluid in KeYue deposit belongs tomedium-low temperature, low salinity, low density of NaCl-H2O system.Mineralizing fluid pressure is between9.9and78MPa, postulated the metallogenicdepth ranged from0.37Km to2.91Km, which is the shallow depth of mineralization.The macroscopic and microscopic features and the characters of fluid inclusionsof KeYue deposit indicate that its mineralization is comparatively complex byshowing its ore forming for several periods and times. A preliminary deduction is thatKe Yue deposit is Shallow-super shallow hydrothermal fluid type plumbumpoly-metallic deposit by packing means. The main ore-controlling factors is faults,Mineralization processes roughly: Early for the submarine volcano eruption andhydrothermal sedimentary, metallogenetic element in the layer Preliminary enrichedand form original provenance layer, which laid the material foundation for the latermineralization. Due to changing regional stress field，South-North rift was formed inthe main mineralizaton period. Magmatic activity area formed gas and waterhydrothermal solution, which happened infiltration metasomatism with surroundingrock along diaclase. The original mineral formed mineral-bearing hydrothermal fluidby activation, which migrated along diaclase. mineral-bearing hydrothermal fluid iscontinue to diffusion and osmosis along the fracture surface of surrounding rocks, andfinally deposited and concentrated mineralised in structural weak zonebroken, such asthe tensile shear fracture zone and fractured zone. Because of extension in theZangnan area sustainable, mineral ore in the late period was uplifted to the shallowerparts and formed oxidized mine by the eluviation of atmospheric precipitation andhypergene oxidation.