【作者】 段其发；

【导师】 张克信；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2014， 博士

【摘要】 湘西-鄂西地区位于扬子陆块中部,北部以襄(樊)-广(济)断裂带为界与秦岭造山带相邻,东南以安化-溆浦断裂带为界与湘桂陆块相邻,往南止于湖南与贵州交界,西部与四川盆地以齐岳山断裂带为界,东与江汉-洞庭坳陷相邻。该区是扬子陆块重要组成部分,亦是我国重要的铅锌多金属成带之一。区内铅锌矿床(点)多、面广,成矿地质条件优越。本文在系统分析成矿地质背景的基础上,通过典型矿床解剖,探讨了盆地演化与成矿作用的关系,初步总结了区域成矿作用特点,应用流体包裹体和多种同位素示踪技术对铅锌矿成矿流体和成矿物质来源进行了详细研究,探讨了成矿流体和成矿元素的迁移富集规律,采用Rb-Sr法开展了成矿时代研究,建立了湘西-鄂西地区铅锌矿区域成矿演化模式。湘西-鄂西地区具有以中太古代-早元古结晶基底和中元古代变质沉积-火山岩系组成的过渡性基底(褶皱基底),新元古界-中三叠统的海相沉积盖层和上三叠统-新生界陆相沉积盖层构成的“双基双盖”结构。自新元石代以来,该区经历了晋宁运动、加里东运动、印支-燕山运动和喜马拉雅运动等构造变形,形成了以北东、北北东向为主的构造。通过对震旦系陡山沱组中的冰洞山铅锌矿床、灯影组中的凹子岗锌矿床和下寒武统清虚洞组中的狮子山铅锌矿床研究,发现赋矿围岩差异明显,冰洞矿床产于黑色岩系所夹的白云岩中,凹子岗矿床则产于发育古岩溶孔隙的白云岩中,狮子山矿床严格受藻灰岩控制,但是它们都具有明显的后生充填、交代特点,而且均含有沥青、发育热液矿床的典型矿石组构和低温热液成因的矿物组合。冰洞山矿床底板黑色岩系形成时有热水参与,赋矿白云岩为埋藏白云岩化的产物；流体包裹体分析表明：闪锌矿以气相流体包裹体为主,次为单相盐水溶液包裹体和两相盐水溶液包裹体,显示富气相和富液相的包裹体共生组合特点,均一温度(Th)为80～235℃,盐度为(6.44～20.43)%NaCleq;围岩白云石Th为146～193℃,盐度为(17.74～17.92)%NaCleq,主成矿期脉石矿物白云石和石英以两相盐水溶液包裹体为主,Th为109～193℃,盐度为(13.99-21.95)%NaCleq。流体密度为(0.880～1.103)g/cm3,属中等密度流体,成矿压力为22～44MPa,成矿深度0.82～1.63km。成矿流体为含少量CH4、N2的NaCl-CaCl2-H2O体系。铅同位素组成相对均一,为上地壳与造山带铅的混合铅,与赋矿地层的铅同位素组成明显不同；硫化物的δ34S值在13.03‰～34.57‰之间,平均为26.07‰,具有明显富重硫的特点和双峰式特征,硫主要来源于地层中的硫酸盐,是海水硫酸盐热化学还原反应的产物。流体包裹体水的δ18OH2O(SMOW)值为9.14%o～17.19‰,显示有大气水的参与。闪锌矿Rb-Sr等时线年龄为(506±14)Ma(MSWD=2.00),相应的Sr初始值(87Sr/86S)i为0.70926,地质时代为中寒武世。Sr初始值大于陡山沱组白云岩的87Sr/86Sr值,暗示成矿物质可能主要源自下伏地层或基底岩石。该矿床为后生浅成低温热液矿床,与MVT矿床相似。凹子岗锌矿床闪锌矿中发育单相盐水溶液包裹体、两相盐水溶液包裹体和单气相包裹体,以单相类型为主,两相包裹体含量低。主成矿期脉石矿物白云石的包裹体与闪锌矿相似,以单相类型为,同时还出现了含石盐子矿物包裹体,偶见气相烃包裹体；围岩白云石以两相盐水溶液包裹体主。包裹体的气相成分以水蒸汽为主,激光拉曼光谱分析,显示有CH4。白云石流体包裹体Th主要集中于110～190℃,盐度多为12%～32.31%NaCleq,流体密度为0.939-1.107g/cm3,矿床形成压力为26-56MPa,矿床形成深度为0.95-2.08km,平均深度为1.60km。成矿流体属含CH4的NaCl-CaCl2-H2O体系。在207Pb/204Pb-206Pb/204Pb图解和△p—△γ图解样品点比较分散,显示出混合铅特征,反映源区可能为黄陵基底。硫化物的δ34S值在4.97%‰-14.52%‰之间,以低正值为特点,同时,闪锌矿的δ34S还存在26.43%-27.42%0高值。白云石的δ13c值为1.76%o～3.77‰,平均为2.16‰,δ18O值为-6.04%‰～-12.63%‰,平均为-11.29‰；白云石化流体的δ18OH2O(SMOW)为3.42‰±12.42%‰,显示有大气水的加入。白色脉状白云石的87Sr/86Sr为0.71064±0.71165,平均为.071091,反映白云石化流体可能来自下伏地层和基底。绿色闪锌矿的Rb-Sr等时线年龄为(434±15)Ma(MS WD=0.19),地质时代为早志留世早期；红色闪锌矿的Rb-Sr等时线年龄为(409.6±9.7)Ma(MSWD=0.95),地质时代为早泥盆世晚期。为后生浅成低热液矿床。狮子山铅锌矿床产于藻灰岩中,闪锌矿与方解石均发育为两相盐水溶液包裹体、单相盐水溶液包裹体和单气相包裹体,其中以前者为主。闪锌矿Th主要为120～170℃,盐度为14%～21%NaCleq,方解石的Th为100～170℃,盐度为12%-26%NaCleq,属低温中高盐度流体。流体密度为0.771～1.125g/cm3,成矿压力为25-45MPa,平均压力为35MPa,成矿深度为0.94±1.68km,平均深度为1.28km。成矿流体中阳离子以Ca2+为主,其次为Mg+、Na+同时含少量的K+、Li+等,Na+/K+比值为11～18,平均为15,Na+/(Ca2++Mg2+)比值为0.07±0.50,属典型的热卤水成因。Na/Br值和C1/Br值分别为5-18和11～41。在矿田内铅位素组成比较一致,207Pb/204Pb-206Pb/204Pb图上,样品点分布于造山带与上地壳演化线之间,在△p-△γ图上,样品点靠近上地壳铅区域,μ值介于9.43～9.75之间,平均为9.60,显示铅主要来源于基底浅变质地层。黄铁矿的δ34s值为26.87‰～34.66‰,平均为30.81‰,闪锌矿的634s值介于20.32‰～33.88‰,平均为31.02%‰,方铅矿的δ34S值为22.40‰～27.35‰,平均为25.23‰,重晶石的634s值为31.13%-31.55%‰,平均为31.36%‰。矿石硫主要来源于盆地热卤水萃取下伏地层中的硫化物/硫酸盐,通过TSR形成H2S和CO2,提供给矿床形成硫化物的硫源和部分方解石的碳源。δ13C值和δ18O值的变化范围分别为-5.32‰～1.35%‰和-12.45‰～-5.63%‰,平均值为-0.24%‰和-9.43！,δ13C值和δ18O值均低于赋矿围岩藻灰岩的813C值(0.46‰)和δ18O值(-9.09‰),成矿流体的δ18OH2O(SMOW)介于0.38%‰～11.70‰；主成矿期闪锌矿的Rb-Sr等时线年龄为(412±12)Ma(MSWD=2.2),地质时代为早盆世中期,(87Sr/86Sr)i为0.70916。为后生浅成低热液矿床。研究认为,区域上碳酸台地边缘是最重要的赋矿部位；在矿田内,岩性和地层对铅锌矿有明显控制作用,褶皱与断层的交汇部位最有利于形成富矿。湘西-鄂西地区铅锌矿床的形成与低温高盐度热卤水活动有关,成矿时代晚于赋矿围岩,属后生浅成低温热液矿床,与MVT矿床相似,区域成矿作用发生于加里东期,且具有多期性,成矿与伸展断陷构造环境有关。成矿过程中普遍发生过TSR反应和流体沸腾现象。在典型矿床成矿模式分析的基础上,提出了湘西-鄂西地区铅锌矿的两阶段成矿模式,即成矿流体形成阶段和成矿热液运移富集阶段。成矿流体形成阶段发生于盆地埋藏和构造挤压时期,大气降水、地层水与深部流体混合,并发生广泛的水/岩反应,形成富含成矿物质的热卤水；成矿流体运移富集阶段发生于伸展构造环境,成矿流体发生大规模迁移,并在台地边缘等有利部位沉淀富集成矿。更多还原

【Abstract】 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.更多还原