西南三江碰撞造山带沉积岩容矿Pb-Zn-Ag-Cu贱金属复合成矿与深部过程

西南三江特提斯造山带中新生代沉积盆地中(沱沱河、玉树、昌都和兰坪-思茅地区)发育包括金顶超大型铅锌矿床在内的一系列以沉积岩容矿的Pb-Zn-Ag-Cu贱金属矿床,构成长达千余千米的青藏高原东缘贱金属成矿带。作为大陆碰撞环境成矿谱系的重要矿床类型,加强这些矿床的理论研究对提高和完善大陆碰撞造山成矿理论和指导找矿勘查等具有重要意义。已有研究表明这些Pb-Zn-Ag-Cu矿床的分布受盆地形成后新生代大型逆冲推覆-走滑构造控制,其容矿岩石和成矿作用特征与SEDEX和MVT矿床存在明显的差异,矿床成矿流体表现出多来源混合的特征,成矿与深部过程密切相关。尽管取得重要进展,但由于缺乏高精度年代学数据制约,成矿动力学背景及其与碰撞造山的时空联系存在较大争议。一些矿床的研究显示复合成矿迹象,但是复合成矿过程与深部驱动等问题仍不清楚。近年来我们以兰坪和昌都盆地的Pb-Zn-Ag多金属矿床和Cu多金属矿床为重点研究对象,系统开展了成矿年代学、成矿流体源-运-储系统和复合成矿机制以及深部过程对成矿制约等方面研究。结果表明,兰坪盆地西缘Cu(Mo)多金属矿床主要形成于48～58Ma,兰坪和昌都盆地Pb-Zn-Ag多金属矿床主要形成于27～33Ma。成矿流体表现出明显的多来源混合的特征,主要存在三种类型:1)变质流体与盆地卤水或大气降水复合成矿,以金满-连城Cu矿床为代表; 2)盆地卤水与大气降水复合成矿,以金顶Pb-Zn矿床为代表; 3)盆地卤水和岩浆流体复合成矿,以拉诺玛Pb-Zn-Sb矿床为代表。兰坪盆地西缘Cu矿床主要形成于新生代印度-欧亚大陆主碰撞挤压阶段,与成矿密切相关的变质流体可能来源于陆-陆碰撞俯冲引起的高压变质。Pb-Zn矿床主要形成于印度-欧亚大陆晚碰撞构造转换环境,构造挤压和造山隆起驱动盆地流体迁移,同期的岩浆活动主要为成矿提供热驱动力或成矿物质。

Composite metallogenesis of sediment-hosted Pb-Zn-Ag-Cu base metal deposits in the Sanjiang Collisional Orogen, SW China, and its deep driving mechanisms

A great number of sediment-hosted Pb-Zn-Ag-Cu deposits occur in the Meso-Cenozoic sedimentary basins within the Sanjiang Tethyan orogeny, SW China, which compose a significant base metal metallogenic belt with an extension over 1000km along the northeastern margin of the Tibetan Plateau. For it is an important type in the continental collision-related deposit spectrum, further study upon these deposits is greatly helpful to understand and improve the theories of the continental collision metallogenesis and guide the exploration. Many studies suggest that these deposits are distinct from the SEDEX and MVT model in terms of ore controls, host rocks and other features, and that multiple sourced fluids associated with mineralization should have been driven by deep processes. However, it is intensively debated on the geotectonic settings of ore formation and spatial-temporal association with the collisional orogeny due to lack of highly resolved chronological data. Some studies indicate that they were resulted from composite mineralization, but these studies did not well document its mechanisms. A comprehensive study has thus been carried out on the geochronology, ore-forming fluids and metal sources, composite metallogenesis and mechanisms for the Pb-Zn-Ag and Cu polymetallic deposits in the Lanping and Changdu basins. The results show that the Cu deposits were mainly formed in 48~58Ma and the Pb-Zn deposits were formed in 28~33Ma. Also, three types of composite mineralization have been recognized:1) metamorphic fluids and basinal brines or meteoric water, represented by the Jinman-Liancheng Cu deposits; 2) basinal brine and meteoric water, represented by the Jinding deposit; and 3) basinal brine and magmatic fluid with an example of the Lanuoma Pb-Zn-Sb deposit. The Cu deposits happened synchronously with the main collisional compression of the India-Asian continental collision and metamorphic fluids were probably generated by subduction-caused high-pressure metamorphism. The Pb-Zn deposits were formed by basinal brine-dominated fluids driven by orogenic uplift as well as tectonic compression in the stage of the late collisional tectonic transform. Contemporaneous magmatism may have mainly played as heat sources or provided ore materials.