小秦岭金矿区剪切变形特征与成矿关系研究

Xiaoqinling gold district is located at the southern margin of the North China plate, and is the second largest gold deposit in China. The current study revealed that the Xiaoqinling gold district is the typical quartz vein gold deposit, and there are multiple trends ore bearing vein in the gold deposit, such as nearly east-west, northeast, northwest and nearly north-south. This gold district developed 2 periods mineralization of Indosinian orogenic type and Yanshanian craton destruction type. The quartz veins with different trends are obviously controlled by the shear deformation belts, and there are some disputes on the tectonic mechanism, deformation time and tectonic background of the ore controlling by shear deformation. The fundamental cause for this dispute is the lack of the structural deformation study in Xiaoqinling, especially for the anatomization on the shear deformation process which related to the mineralization process. Based on the tectonic deformation research, this project will study the geometry, kinematics, superimposed relationship, deformation sequence and age for the shear deformation belts, and find out the structural location of ore bodies, tectonic intrusive foliation of minerals and metallogenic time. And then, we will recovery the ore-forming fluid emplacement-migration process related to the shear deformation, and construct the tectonic relationship between the deformation characteristics of the shear deformation belts with different trends and two period mineralization events. Discuss the tectonic ore controlling process in the Xiaoqinling area, and the Mesozoic tectonic evolution at the south margin of the North China plate.

小秦岭金矿区位于华北板块南缘，是我国第二大金矿区。现有研究表明，小秦岭金矿区属于典型的石英脉型金矿，发育有近东西向、北东向、近南北向以及北西向等多组方向的含矿脉体，经历了印支期造山型和燕山期克拉通破坏型两期成矿作用过程的叠加。这些不同方向的矿脉明显受剪切变形带控制，但是目前对于剪切变形带控矿的构造机制、时代和背景等方面认识上存在争议。其根本原因在于缺乏对小秦岭金矿区构造变形，尤其是与成矿过程密切相关的剪切变形过程的解剖。本项目以构造变形研究为基础，通过研究剪切变形带的几何学、运动学特征，以及它们的叠加关系、变形序列和时代，同时查明矿体的构造位置、含矿物质侵入的构造面和成矿时代等特征，恢复剪切变形过程中成矿流体侵位和迁移的过程，从而构建小秦岭金矿区不同方向剪切变形带的变形特征与两期成矿事件之间的构造关系，探讨小秦岭金矿区构造控矿作用过程，以及华北板块南缘中生代构造演化过程。

小秦岭金矿区位于华北克拉通南缘，矿区内发育有产出于不同走向剪切变形带内的金矿脉。但是目前研究和认识对矿脉和剪切变形带、以及不同方向矿脉之间的构造关系并不清晰。本项目选择小秦岭地区不同构造带与矿脉的构造解析、年代学、地球化学、包裹体等方面的综合研究，系统分析了小秦岭金矿区内发育的四组方向剪切变形带的几何学、运动学、动力学特征及变形时代，其中近东西向与北东东向剪切变形带具有脆韧性变形特征，时代为晚三叠世，而北北东与近南北向剪切变形带则以韧脆性为主，时代为早白垩世，总体经历了NW-SE向挤压向近东西向伸展应力场的构造转换。通过典型矿脉的构造解析，确定了Q507、Q8、F5、Q185等不同方向重要矿脉产出的构造位置、成矿物质组成及流体特征、成矿时代等方面的特征，并以近东西向和北北东向矿脉为主。其中，近东西向矿脉走向总体与剪切带近平行，舒缓波状延伸，总体倾角约30~60，矿脉一般叠加于早期厚大无矿石英脉中，并与右行逆冲变形相关；北北东走向金矿脉以右阶排列的石英脉透镜体为特征，主体产状为120°∠70°，矿脉产出于与之近平行的左行逆冲剪切变形带内，并改造了早期近东西向剪切变形带和矿脉。结合小秦岭地区中-新生代的变形过程与成矿作用的关系，总结出小秦岭金矿区经历了三叠纪和白垩纪两期构造变形与成矿的叠加，并经历了新生代伸展变形的强烈改造，上述构造-成矿过程与华北地块南缘由碰撞造山挤压变形到克拉通破坏伸展变形的转换过程密切相关。