兰坪盆地西缘脉状铜矿床富CO2流体来源及其与Cu成矿的关系

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China, which has much economic potential and produced numerous economically significant deposits. A series of vein-type Cu deposits occur in the western Lanping basin, mostly including the Jinman Cu deposit, the Liancheng Cu–Mo deposit, and several small vein-type Cu±deposits. The ore-forming fluids responsible for these vein-type Cu deposits are characterized by abundant CO2-rich fluid inclusions, which are significantly uncharacteristic of basinal fluid systems, responsible for these Pb–Zn deposits in other parts of the Lanping basin. Several previous studies have revealed that abundant CO2-rich fluid inclusions are common in syn-ore quartz from these vein-type Cu deposits in the western Lanping basin, but no systematic studies on the CO2-rich fluids have been conducted. Therefore, the sources of the CO2-rich fluids and their significance for the Cu mineralization have not been fully understood. Typical vein-type Cu deposits will be selected to investigate the geochemistry, physical and chemical conditions and the details of wall-rock alteration of the minerals/rocks in these deposits. Fluid-inclusions and isotopic compositions (stable isotopes C, H, O, He-Ar isotopes, non-traditional Cl isotopes) will be combined to constrain the sources of CO2-rich fluids, the conditions of migration and precipitation, and the metallogenic processes of the vein-type Cu deposit in the western Lanping basin. The main scientific objectives of this project are to acquire a better understanding of: (1) the sources of the CO2-rich fluids; (2) the relationship between the Cu mineralization in the western Lanping basin and the CO2-rich fluids responsible. The study will provide a scientific basis for in-depth understanding of the background and process of Cu mineralization in the western Lanping basin. Comparisons will be made between Cu and Pb-Zn deposits in order to better understand the special conditions responsible for forming the vein-type Cu deposits. By recognizing the processes for Cu mineralization, and the relationship between the metallogeny and the CO2-rich fluids, we obtain the theoretical evidence for building up a mineralization model and the exploration tools for the vein-type Cu deposits in the western Lanping basin..

兰坪盆地盆地西缘广泛发育大量沉积岩容矿脉状铜矿床，这些脉状铜矿床的成矿流体以普遍存在大量富CO2流体包裹体为特征，显著区别于盆地流体成矿系统主导成矿的Pb–Zn矿床。有关这种富CO2流体的系统研究尚未很好的开展，富CO2流体的来源及其对Cu成矿的作用尚不清楚。本申请拟以兰坪盆地脉状铜矿床普遍存在的富CO2流体为研究对象，开展流体包裹体地球化学（岩相学、显微测温、激光拉曼、单个包裹体LA-ICP-MS、SRXRF成分分析）、元素-稳定同位素（C、H、O、He-Ar同位素、非传统Cl同位素）的系统研究，重点解决两个关键科学问题：（1）盆地脉状铜矿床中富CO2流体的来源；（2）富CO2流体与Cu矿化的关系。该项目的开展，对深入探讨兰坪盆地脉状铜矿床的成矿演化过程和矿床成因，揭示盆地内Cu和Pb–Zn成矿作用差异的内因，以及指导该区脉状铜矿床的找矿勘查实践，均具有十分重要的意义。

兰坪盆地西部发育大量沉积岩容矿Cu-Ag-Pb-Zn多金属矿床，矿体的分布受逆冲推覆系统控制。逆冲推覆系统根部带主要发育脉状Cu-Ag（Mo）矿床（包括金满Cu-Ag、连城Cu-Mo及一系列脉状Cu矿床）；前锋带主要发育Pb-Zn-Ag（±Cu）矿床（包括白秧坪Pb-Zn-Ag-Cu多金属矿集区及一系列小型的Pb-Zn矿床)。.项目系统分析了盆地西缘Cu-Ag（±Pb-Zn）多金属矿床成矿时代、流体包裹体及C、H、O同位素特征，加强根部带Cu和前锋带Pb-Zn矿床的对比研究，探讨盆地西缘Cu-Ag（±Pb-Zn）多金属矿床成矿流体的性质、来源及演化。研究表明，根部带Cu矿床主成矿阶段为56~48Ma，对应于印度-亚洲大陆碰撞造山主碰撞阶段，后期（47~35Ma）很可能存在一期Cu-Ag（Mo）的叠加或改造成矿作用；前锋带Pb-Zn-Ag（±Cu）多金属矿床的成矿作用主要发生在31~29Ma，对应于印度-亚洲大陆碰撞造山的晚碰撞构造转换期。根部带的Cu-Ag（Mo）多金属矿床成矿流体主要为壳源深部流体，具有富CO2、中高温（集中在280~340°C）、中低盐度w（NaCleq）（1%~4%）的特点；前锋带Pb-Zn-Ag（±Cu）多金属矿床成矿流体则主要为源于大气降水的盆地卤水，具有贫CO2、中低温（集中在160~240°C）、中高盐度w（NaCleq）（集中于22.0%~24.0%）的特点。