The Research Of The Metallogenic Regularity Of Stratabound Zinc-Lead Deposits From Sinian-Cambrian In The Western Hunan And Eestern Hubei

The Northwestern Hunan and Western Hubei area is located at the middle of the Yangtze plate. It is north to the Qinling orogenic belt, south to the Xianggui block, east to the Jianghan-Dongting depression basin, and is an important component of the Yangtze plate. It hosts many Pb-Zn deposits. In this paper, the Bingdongshan Pb-Zn deposit, the Aozigang Pb-Zn deposit and the Shizishan Pb-Zn deposit are detailed studied. On the basis of fluid inclution and isotopic analysis, ore-forming fluids, ore-forming materials and metallogenic regularity have been evaluated.In the Northwestern Hunan and Western Hubei area, Mesoarchean-Paleoproterozoic crystalline basement, Mesoproterozoic metamorphic volcanic sedimentary rock, Neoproterozoic-Middle Triassic marine sedimentary rocks and Late Triassic-Cenozoic continental sedimentary rocks are exposed. Jinning movement,Caledonian movement,Indosinian-Yanshan movement and Himalayan movement have been experienced in these area, NE and NNE trending faults are well developed.The Bingdongshan deposit is hosted in the dolomite. The fluid inclusions in the dolomite have low homogenization temperature (146℃to193℃), and intermediate salinity (17.74%to17.92%NaCl). Three main types of fluid inclusions in the sphalerite are recognized:(1) two-phase gas-rich inclusions,(2) monophase vapor inclusions, and (3) monophase liquid inclusions, with low homogenization temperature (80℃to235℃), and intermediate salinity (6.44%to20.43%NaCl). In the main mineralizing stage, two-phase inclusions are well developed. And they have homogenization temperature of109℃to193℃), and intermediate salinity13.99%to21.95%NaCl. Fluid pressures are ca.22MPa to ca.44MPa. It belongs to the NaCl-CaCl2-H2O hydrothermal system, with a small amount of CH4and N2. Measured δ34S values for sulfide minerals range from13.03%o to34.57%o, suggesting the S source from the strata, result of hermochemical sulfate reduction (TSR). The sphalerite Rb-Sr isochron ages are506±14Ma(MSWD=2.00) and510±33Ma(MSWD=1.90), with (87Sr/86S)1is0.70926±0.00018 and0.70916±0.00044, respectively. These indicate the ore-forming materials source of underlying strata. The Bingdongshan Pb-Zn deposit is similar to MVT deposit.The fluid inclusions of the Aozigang Zn deposit have well studied. Three main types of fluid inclusions in the sphalerite are recognized:(1) monophase vapor inclusions,(2) monophase liquid inclusions,(3) two-phase inclusions. In the main mineralizing stage, the fluid inclusions in the dolomite have homogenization temperatures and salinities varying from110℃to190℃,12.00%to32.31%NaCl equivalent. Fluid pressures are ca.26MPa to ca.56MPa. It belongs to the NaCl-CaCl2-H2O hydrothermal system, with a small amount of CH4. Most sulfur isotope values of the sulfides give a δ34S interval of4.97%o to14.52%o, and some have a high δ34S interval of26.43‰to27.42%o. On the207Pb/204Pb vs206Pb/204Pb diagram and Δβ vs Δγ diagram, the samples plot in the mixing area. Measured δ13C values for dolomite range from1.76%o to3.77%o, with a average δ13C value of2.16%o. The green sphalerite Rb-Sr isochron age is434±15Ma(MSWD=0.19), while the red sphalerite Rb-Sr isochron age is409.6±9.7Ma(MSWD=0.95). The deposit belongs to the epithermal deposit.The Shizishan Pb-Zn deposit is strictly controlled by algal limestone. Three main types of fluid inclusions in the sphalerite and calcite are recognized:(1) monophase vapor inclusions,(2) monophase liquid inclusions, and (3) two-phase inclusions. The homogenization temperatures of these fluid inclusions range from120℃to170℃and their salinities range from12%to26%NaCl equivalent. Fluid pressures are ca.25MPa to ca.45MPa. The compositions of fluid inclusions are mainly H2O, Ca2+, Mg2+, Na+, K+, Li+, Cl-and Br-.The values of Na+/Br-and Cl-/Br-are5to18and11to41, respectively. On the207Pb/204Pb vs206Pb/204Pb diagram and Δβ vs Δγ diagram, the samples plot near the upper crust area. Measured834S values for sulfide minerals range from20.32%o to34.66%o, suggesting the S source from the strata, result of hermochemical sulfate reduction (TSR). Measured δ13C values and δ18O values range from-5.32%o to1.35%o and-12.45%o to-5.63%o, respectively. The sphalerite Rb-Sr isochron age is412±12Ma(MSWD=2.2), suggesting the deposit formed in the early Devonian. And the deposit belongs to the epithermal deposit.Though these research above, I propose that the carbonate platform edge is one of the most important ore-bearing area, intersections of fold and fault are conducive to mineralization. The ore-forming is relate to the low homogenization temperatures, high salinity brine. And these deposits in the Northwestern Hunan and Western Hubei area, such as the Bingdongshan Pb-Zn deposit, the Aozigang Pb-Zn deposit and the Shizishan Pb-Zn deposit, are similar to the MVT. Fluids boiling and hermochemical sulfate reduction (TSR) are happened during the ore-forming process.Two-stage metallogenic model of the Pb-Zn deposits in this area have been put forward in this paper. The early stage is the ore-bearing fluid formation stage, forming in a basin buried and compressed setting. Fluid-rock interaction and fluids mixing happened during this stage. The late stage is hydrothermal migration stage, forming in a extensional setting. In the late stage, the aqueous transport and Pb, Zn position at the carbonate platform edge.