摘要
金顶铅锌矿床是一个以沉积岩(灰岩与砂岩)为寄主岩石的超大型铅锌矿床。本文在对矿区构造和矿床基本特点研究的基础上,重点阐述了两种不同类型矿体(砂岩型和灰岩型)的构造类型、矿石显微构造及矿石组构的特点。本文研究表明,极其发育的断裂构造系统是兰坪盆地地质构造发育的基本特点,在盆地边缘、盆地内部普遍发育了具有薄皮式逆冲断层和推覆构造组合特点的成矿前断裂,它们造成矿区内大规模地层倒转与堆叠现象;盆地中发育了由构造角砾岩与透镜体带构成、宽度达近3km的NE-NNE向成矿期中轴断裂,它控制着矿体或矿床的发育与分布;近SN方向的成矿后地堑构造对于矿床具有破坏作用,并使之剥露于地表。金顶铅锌矿床主要有两种重要的矿床类型,即板状或层状砂岩型矿床和角砾状灰岩型矿床,它们分别位于白垩系钙质长石石英砂岩与三叠系沥青质灰岩构成的两个逆冲席体内。以凤凰山矿区为典型,金顶铅锌矿床具有3层结构:上部的三叠系白云质灰岩岩盖,中部的砂岩型矿体和下部的灰岩型矿体,三者之间被两条作为圈闭存在的重要逆冲断层带间隔。砂岩型矿体与灰岩型矿体之间由几个角砾岩筒连接,作为成矿时期的矿液运移通道存在。破裂与微破裂构造、块状构造、对生脉状构造及假晶构造等是最常见的显微构造型式,它们的存在揭示出破裂与碎裂、充填和交代作用过程在铅锌矿化过程中均起着重要的作用。金顶铅锌矿床的形成与就位,直接受构造作用控制。成矿前的逆冲推覆作用为高压成矿流体的形成以及成矿圈闭的发育创造了条件,成矿期中轴断裂的活动性促使成矿流体向上运移,而灰岩与砂岩的物理性质(包括孔隙度/渗透率以及力学属性)则制约了两种不同类型矿体的出现。致密的灰岩渗透率较低,含矿流体加热了灰岩并使之软化,同时高流体压力使得围岩易碎,形成由早期到晚期的细角砾岩、粗角砾岩和破裂,成矿物质同时沉淀结晶,胶结围岩角砾形成角砾型灰岩矿体。高压流体通过流体通道进入低孔隙度的砂岩后,便迅速弥散于其中,沿着颗粒边界或裂隙充填,并交代岩石中的钾长石碎屑及方解石胶结物,形成块状的砂岩型矿体。
Jinding Pb-Zn ore deposit is a superlarge deposit hosted by sedimentary rocks （limestone and sandstone）. Based on studies of structures of the mining area and characteristics of the deposit, this paper discusses emphatically the ore structures and microstructures of two types of ore bodies （sandstone type and limestone type）. It is shown that well-developed fault systems are the basic structural characteristics of Lanping Basin. Along the boundaries and in the basin, pre-mineralization faults in thin-skinned thrust and nappe systems are developed, which results in large scale invesion and stacking of the stratigraphie column. A syn-mineralization central axis fault zone in NE-NNE direction and with a width of near 3 km consists of zones of structural breccias and lensoids in the basin. It controls the emplacement and distribution of ore bodies or deposits. Post-mineralization normal faulting in NS direction results in the formation of Lanping graben that destroys the ore deposits and denudes them to the surface. Two types of deposits, tabular or layered sandstone type and brecciaed limestone type, are situated respectively in two thrust sheets which are made up of Cretaceous calc-feldspar-quartz sandstones and Triassic asphalt limestone respectively. Exemplified by Fenghuangshan mining area, Jinding Pb-Zn deposit is of three layers： at the top is the Triassic dolomitic limestone cover, at the bottom is the limestone type ore body, and the sandstone type ore body lies between them. Those layers are separated and trapped by two major thrust faults. As the channels where ore fluid migrates upwards during mineralization, several breccia pipes connect ore bodies of the sandstone and limestone types. Fractures and microcracks, massive structure, syntaxial veins and pseudomorphic crystals are the most popular microstructures, which reveal that the processes of fracturing and fragmentation, open space filling and metasomatism play an important role in Pb-Zn mineralization. The formation and emplacement of Jinding Pb-Zn deposit are directly controlled by structural processes. Pre-mineralization thrusting leads to the formation of high pressure mineralizing fluids and gives rise to traps for mineralization. The activity of the syn-mineralization fault zone enhances the upward migration of ore fluid. The physical properties of limestone and sandstone （e. g. porosity, permeability and mechanical properties）, however, contribute to the differences in mineralization in the two types of rocks and formation of two types of ore bodies. The low permeability and compact limestone is heated and softened by ore fluid. Meanwhile, the high pressure fluid with decreasing temperature results in the cracking of the wall rocks into fine breccia, coarse breccia and fractures. During cracking, mineralizing materials precipitate to cement the breccias to form limestone type ore bodies. After migrating into the high porosity sandstone through fluid channels, the high pressure fluid disperses in the sandstone and fills the grain boundaries and cracks, and meanwhile replaces the clastic K-feldspar and calcite cement, forming massive sandstone type ore bodies.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2009年第10期1376-1387,共12页
Acta Geologica Sinica
基金
国家"973"项目(编号2002CB412607
2009CB421001)
国土资源部公益性行业科研专项经费项目(编号200811008)
教育部111计划(编号B07011)联合资助成果
关键词
沉积岩中的铅锌矿床
构造分析
岩石物理性质
矿床就位
云南金顶
sedimentary hosted lead-zinc deposit
structural analysis
physical properties of rocks
emplacement of ores
Jinding
Yunnan
