【作者】 孙省利；

【导师】 曾允孚； 何知礼；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2002， 博士

【摘要】 西成矿化集中区位于甘肃省西和县、成县和徽县一带，矿化集中区铅锌（银）矿床和金矿床类型多，规模大，是我国重要的铅锌基地之一。矿化集中区内主要的矿床类型是热水沉积型和热水沉积改造型，其中热水沉积成矿作用形成的厂坝-李家沟矿床为超大型矿床，热水沉积-改造型矿床有毕家山和邓家山等大型铅锌（银）矿床，矿床与中泥盆统地层整合产出，并同步褶曲。 对成矿区带或矿化集中区用系统论的观点进行分析研究，已成为矿床学研究的热门课题。论文应用现代海底热水沉积成矿研究成果、层序地层学、地幔热柱或热点理论及矿床成矿系列理论等，对本区热水沉积型铅锌（银）矿床、热水沉积-改造型铅锌（银）矿床和金矿床进行了详细的地质地球化学研究。从层序地层分析着手，分析热水沉积成矿时的沉积环境、海平面变化及陆源沉积输入对热水沉积成矿的影响，研究热水沉积岩的地质特征和地球化学特征、矿床地质特征对比、矿床地球化学、成矿物理化学条件等，最终建立了该区的成矿系列。 通过对该区矿床成矿作用的综合分析研究，取得了如下一些成果和认识： 1)应用层序地层学理论，首次系统论述了该区泥盆系层序地层的特征，识别出13个不完整的三级层序，并进行了区域对比。层序地层分析发现海底热水沉积型矿床和海底热水沉积-改造型矿床的赋矿部位是两个层序的过渡部位，既高水位体系域向海侵体系域过渡。厂坝式矿床主矿体产在碳酸盐台地相向盆地相过渡处，盆地水体相对较深；毕家山式矿床赋存在生物滩相向盆地相的过渡部位。在从高水位体系域向海侵体系域的盆地相迅速转化时，盆地内断裂构造活动强烈，断裂沟通不同部位的热水流体，使成矿烃碱流体沿断裂上升，在海底沉积成矿。 2)对热水沉积岩进行了系统的分类，研究了热水沉积岩的地质地球化学特征，提出了热水沉积岩的定义。区内的热水沉积岩主要有硅质岩、钠钾长石岩、重晶石岩、透闪石岩、碳酸盐岩、绿泥石岩和铁白云石斑点千枚岩，它们往往与热水沉积矿体紧密伴生。热水沉积岩化学组成复杂，以高含量的Si、Ba、U、Th为特征，个别岩类中K、Na、Mg的含量增高。从热水沉积岩的（SiO₂／Al₂O₃）-[（CaO+Na₂O）／K₂O]和Si-Mg图解中可看出，它们的化学组成均位于正常沉积岩的过渡区或正常沉积岩与火成岩的过渡区，表明热水沉积岩有不同于正常沉积岩的物质来源。硅质岩的硅同位素δ³⁰Si_NRS-28分布于-0.1～－0.6‰之间，均为负值，表明其主要来源于下伏地层柱。硅质岩的⁸⁷Sr ／⁸⁶Sr比值变化于0.70985～-0.72812之间、热水沉积灰岩的⁸⁷Sr ／⁸⁶Sr比值分布在0.70994～0.71811内、绿泥石岩的⁸⁷Sr ／⁸⁶Sr比值较高，分布在0.71112～0.71242，均明显高于海洋锶的组成，分布在陆壳锶与海洋锶之间。热水沉积岩的地球化学研究结果认为，热水沉积岩的形成是在海底盆地中进行的，但它的物质来源不是陆源沉积物，而是来源于地壳的内部，即形成方式和环境具外生特征，物质来源具内生特点。 3)详细研究了矿床的分类、各类的特点。把铅锌（银）矿床分为热水沉积型、热水沉积-改造型、热液型和岩浆热液型4类，把金矿划分为热水沉积-改造型、热液型、氧化次生富集型和沙金矿4类。首次对厂坝式矿床按照矿床在海底沉积成矿距离热水流体喷口的远近进行了划分，分别为流体通道中的脉状矿化（黄厂、黑谭沟矿床），距离喷口较近、流体温度较高洼地中沉积矿化（硬碗沟矿床），以富含磁黄铁矿的似层状、浸染状矿化为特点，其次为厂坝-李家沟矿床，以中-厚层状、似层状矿化为特征，最远的是朱安沟矿床，以薄-纹层状矿化为主。同时，论述了金矿与铅锌（银）矿在空间上的伴生关系，热水沉积-改造型金矿无一例外的赋存在热水沉积-改造型铅锌银矿床的上部层位-海侵体系域沉积。 4)矿石铅同位素组成与地层铅同位素组成及火成岩铅同位素组成差异较大，但与基底 西寓岭坍笼戾西成 桑中MM泳冰磁矿系剜地层铅同位素组成相似。在铅同位素‘07PM“Ph‘06PbP“Ph构造模式图上，矿石铅同位素均位于地馒与上地壳之间的造山带铅演化曲线附近，斜切造山带铅同位素演化曲线。铅同位素研究结果表明，成矿物质主要来源于下伏基底地层，并有深源铅的加入，铅同位素组成系以壳源为主的壳慢混合铅。 矿石硫同位素组成以富集重硫为特征，与地层中硫化物硫同位素组成及火成岩的硫同位素组成有显著的差异。厂坝式矿床的 6’‘S值集中分布在 l(＞2％。间，毕家山式矿床在集中分布在 5—18％0之间，小沟里式金矿和小湾里岩浆热液矿床的6’‘S值比较低，分别为2．06－13．66％和－8．5～12．74％．矿床硫同位素组成 5’‘S值呈现从厂坝式到岩浆热液矿床逐渐变小之趋势。不同期矿石的5吨值不同，热水沉积期条带状矿石的 6’‘S值明显高于后期形成的矿石。硫主要来源于泥盆纪海水硫酸盐，次为深源硫。不同矿床类型深源硫参合比例不同，深源硫参与成矿比例从大到小的顺序是热水沉积型铅锌（银）矿床（厂坝式）－热水沉积－改造型铅锌（银）矿床（毕家山式）一热水沉积－改造型金矿床（小沟里式）。海水硫酸盐是?更多还原

【Abstract】 Xicheng concentrated mineralization area is located in Xihe, Chengxian and Huixian county, Gansu province, western Qinling. In the concentrated mineralization area ,there are many types of Pb-Zn-(Ag) deposits and gold deposits , it is one of bases of lead-zinc in china. In this area seafloor hydrothermal sedimentary ore deposits and hydrothermal sedimentary-rebuilded ore deposits are predominated. All lead-zinc-(silver) and gold deposits hosted in Devonian sedimentary rocks, and orebodies of seafloor hydrothermal sedimentary deposits and hydrothermal sedimentary-rebuilded deposits draped in phase with stratum.Applying System theory to study mineralized belt or concentrated area has been a hot topic recently. This paper applied new theory of modern seafloor hydrothermal sedimentary minerlization,sequence stratigraphy, mantle plume or hotspot and metallogenic series to study systematacially characteristic of geology and geochemistry of seafloor hydrothermal sedimentary deposits and hydrothermal sedimentary-rebuilded deposits and gold deposits. Begining with analysis of sequence stratigraphy of stratum ore hosted, this paper analysed structure of basin, variation of sea level and terrigenous sedimentation input rate which impacted on seafloor hydrothermal sedimentary mineralization, then through the study of characteristics of hydrothermal sedimentary rocks ,ore deposit geochemisty and geology, metallogenic series are established.Through synthetically study, some achievements are made as follows:1.Based on the application of sequence stratigraphy, for the first time the characteristics of sequence stratigraphy in the Xicheng concentrated mineralization area are discussed systematically and 13 three graded imperfect sequences of Devonian stratum are recognized.The result shows that hydrothermal sedimentary mineralized type and hydrothermal sedimentary-rebuilded mineralized type ore deposits occur in intergrade between two sequence, as well as occur in intergrade between highstand systems tract and transgressive systems tract. Main ore bodies of Changba style lead-zinc-(silver) deposit lie in transitional position from carbonate plateform fades to basin argillic and fine clastic fades, while Bijiashan style lead-zinc-(silver) deposit in the position from plateform margin shoal facies to basin argillic facies. In the interim from highstand systems tract to transgressive systems tract, faulting is violent in the basin, different kind of fluids coming from dissimilar position of lithosphere enter into synsedimentary faults served as a place fluids mixed to form ore-bearing Hydrocarbon Alkali-Fluids. The fluids upwelled to seafloor along fault thus ore-forming metals accumulated.2.This paper indicated the definition the hydrothermal sedimentary rocks.The definition is a group of especial sedimentary rocks forming at the temperature ranging from 70?to 350癈(or more high) through sedimentation and synsedimentary metasomatism in the seafloor. Many kinds of seafloor hydrothermal sedimentary rocks, such as silica rock, albitite, potassium feldspar rock,baritite, chloritite,dolomitite, tremolitite, and ankerite speckle phyllite. have been found in the sedimentary pile of Devonian in the area associated with hydrothermal sedimentary mineralization. The compositional minerals and elements are much complex and poorly differentiated, on the plot of Si-Mg and (SiO2/Al2O3)-[(CaO+-Na2O)/K2O],hydrothermal sedimentary rocks lie in intergrade place among natural sedimentary rocks or between magmatite and sedimentary rocks.Silicon isotope composition 8 30SiNBS-28 of silica rocks ranges from -0.1 to-0.6%o,indicating silicon coming from sedimentary rocks of deeplying sedimentary pile, which is consistent with research result of strontium isotope and carbon isotope. The result of study of geology and geochemistry indicates that forming manner is exogenous, but compositions mainly comes from deep part of lithosphere.3.Acceding to geological characteristics of ore deposits and the mode of mineralization, deposits of lead更多还原