Study On Deformation, Metamorphism And Carbonic Fluids Of The Dadonggou Lead-znic Deposit，altay

The Dadonggou Lead-Zinc deposit is one of the massive sulfide deposits inthe Devonian Kelang vocanic-sedmentary basin in the southern margin of ChineseAltaids. The orebodies, controlled by regional Abagong-Kurti Fault zone, occur inlayers in the second lithological unit of upper Kangbutiebao Formation whichconsists of calcareous sandstones, biotite schists and chlorite schists. DuringCarboniferous-Permian orogeny, the deposit has experienced regionaltectonic-hydrothermal metamorphism. This article focused on the deformation andmetamorphic characteristics of the host rocks and ores, and the carbonic fluidinclusion overprints. A detailed study was conducted using the methods includingfield surveys, petrology and mineralogy, SEM test, stable isotope research,microthermometry of fluid inclusions, Reman and SRXRF analysis. Mainconclusions were drawn as followings:Microscopic observation shows that the host rocks and ores have experiencedintensive deformation and metamorphism. Fish-shaped biotite can be commenlyfound, and quartz grains were stretched to lens, eye-ball shapes and so on;sphalerite and galena were often modified or cut by some metamorphic mineralssuch as biotite, chlorite and garnet. The structures of fracturing, pressure shadow,pressure solution and overgrowth in ore minerals were common. Based on thesephenomenons, two metallogenic periods can be identified. The first is marinevolcanic sedimentary period, and the second is metamorphic hydrothermal period.Fluid inclusions in the metamorphic quartz veins are mainly carbonic fluidinclusions(CO2-N2±CH4), mostly occurring as linear or planar, ribbon distribution.The microthermometry of carbonic fluid inclusions shows that Tm,CO2=-82.5℃～-59.4℃, Th,CO2=-40.2℃～+20.3℃, with densities ranging from0.75g/cm3to1.15g/cm3. The CO2-H2O fluid inclusions associated with carbonic inclusionshave209℃～459℃of homogeneous temperatures, and the minimum trappingpressures of carbonic fluid inclusions are estimated to be110MPa～540MPa. It issuggested that the carbonic fluid inclusions may be related to synorogenicmetamorphism and can’t be originated from submarine exhalation. CO2-richfluids might be the regional fluids derived from orogeny in Kelang Basin, whichwere active during the deformation and metamorphism in rocks and ores,espescially in gold mineralization. SRXRF analysis shows that Au in carbonic fluid is higher than that in the strata, and gold is high in orogenic chalcopyritesand pyrite tested by SEM. It is indicated that the carbonic fluid inclusions hadbrought gold superposed mineralization.Some research work on sulfur isotopes was done to speculate the origin ofore-forming materials in Kelang basin. The δ34S of Sulfides in the Sarekuobuorogenic gold deposit ranges from+4.31‰to+8.57‰, which means a deep-crustsource, while that of the Tiemuerte and Dadonggou VMS deposits ranges from-26.46‰～+3.95‰and+2.02‰～+7.65‰, respectively. It is indicated that thereare two sources of sulfur, the seawater sulfur related to VMS mineralization andthe deep magmatic sulfur related to metamorphic overprints.