多宝山弧形构造带变形特征、形成机制及其对古老斑岩型铜矿床的改造

The emplacement of porphyry deposits is often controlled by lineament structures in ore field scale. Multistage deformations are common in these lineament structures due to tectonic evolution. They record the information of metallogenic kinetics background of the porphyry deposits and regional tectonic evolution . It's significant to study the deformation features, mechanism and relationship between regional tectonic evolution and deformation sequences, for they contribute to comprehensively understand the formation, distribution, transformation and preservation processes of porphyry deposits and also are useful to recognize information of tectonic evolution and dynamic background changes. So studying lineament structures can contribute to new deposits exploration and enrich the theory of porphyry deposit deformation...This project will study the Duobaoshan curve structural belt, which hosts the Ordovician Duobaoshan gold-rich porphyry copper deposit and the Tongshan porphyry copper deposit and experienced long-term tectonic evolution. In order to systematically study the deformation characteristics, mechanism and their transformation effects on ancient porphyry deposits, multiple methods will be applied, including structural analysis, magnetic fabric analysis, mineral geochemical micro-analysis, geochronology and fluid inclusion planes analysis.These work will reveal the coupling relationship between the evolution of the Duobaoshan curve structural belt and the transformation and remobilization of ancient porphyry copper deposits. At the same time, the deformation process and remobilization mechanism of the ancient porphyry deposits will be discussed.

斑岩型矿床的就位常受矿田尺度的线性构造带的控制，这种线性构造带受构造演化控制常具有多期构造变形特征，记录着斑岩型矿床成矿动力学背景及区域构造演化信息。研究这类线性构造带的变形特征、形成机制、变形序列与区域构造演化的对应关系等，有助于完整掌握斑岩型矿床形成、分布、改造、保存过程，提取构造演化和动力学背景转变等信息，在寻找新矿床、丰富构造与斑岩成矿理论等方面有重要意义。. 本项目选取赋存奥陶纪斑岩型铜矿床（多宝山富金斑岩型铜矿床和铜山斑岩型铜矿床）且经历长期构造演化的多宝山弧形构造带为研究对象，综合运用构造解析、磁组构分析、矿物地球化学微区分析、构造年代学、流体包裹体面分析等多种方法，系统研究多宝山弧形构造带变形特征、形成机制及其对古老斑岩型矿床的改造作用，揭示多宝山弧形构造带演化与古老斑岩铜矿床改造-再活化的耦合关系，探讨古老斑岩型矿床变形过程和成矿组分活化机制。

本项目研究中亚造山带东段多宝山弧形构造带的构造变形特征、形成机制及其对斑岩铜矿床的改造。识别出三期主要构造变形。第一期典型构造为北西-北西西轴向的复式紧闭褶皱、北西-北西西走向的片理和劈理、北东至北北东走向的拉伸线理、北西-北西西走向逆冲断层，构造解析和磁组构分析揭示该期构造变形的形成机制为褶皱和与褶皱同期或稍晚的逆冲作用，非前人所认为的走滑作用，形成时代约为270Ma（绢云母Ar-Ar），构造面理与附近古亚洲洋体系窝里河蛇绿混杂岩基质的主体构造面理一致，判断该期构造变形的动力学背景为兴安地块和松嫩地块间古亚洲洋的闭合和碰撞造山。第二期为北东轴向的开阔褶皱、北东走向的劈理，形成时代区间为270Ma-240Ma。第三期为近东西走向的逆冲断层，以铜山断层为代表，形成时代区间为230Ma-207Ma（锆石和磷灰石U-Th-He等），由时代和区域背景判断第二、三期构造变形与鄂霍茨克洋向南俯冲有关。.三期构造对斑岩矿床的改造作用体现在：第一期构造变形造成研究区多宝山和铜山斑岩铜矿床和矿体北东-南西方向被缩短、北西-南东方向被拉长形成纺锤形态，并导致矿体在倾向方向的褶曲和起伏；第二期构造变形造成矿体在走向方向的褶曲和起伏；第三期构造截切铜山斑岩铜矿，导致矿床被肢解。.第一期构造变形导致多宝山和铜山斑岩铜矿局部发生矿质活化和再沉淀，形成与细脉浸染状矿化不同的富黄铜矿脉系，这种脉系常见方解石、绿泥石和金属硫化物共生。构造变形岩石中黄铁矿内部结构和成分复杂，微区应力体系指示同构造变形过程中黄铁矿被溶蚀和交代，内部含磁黄铁矿，指示黄铁矿发生了向磁黄铁矿的相变。由脉系矿物组合以及流体包裹体分析判断活化迁移矿质的流体主体为富钙、富CO2、偏还原性、较低温的流体。.综合构造解析、蚀变分带、矿物地球化学分析对第三期构造的典型代表—铜山断裂进行复位，并据此预测下盘3号矿体南侧有隐伏热液中心和厚大矿体。