兰坪金顶Pb-Zn矿床逆冲褶皱带中盐底辟构造的控矿模式

Salt diapiric structures (SDSs) is one of the important factors in controlling the large-scale oil-gas fields in the world, their genetic relationship and formation mechanism have been well revealed. There are widely distributed a number of polymetallic base metal deposits closely relating to the SDSs in the fold- thrust- belt(FTB) environment of the main orogenic belt in the world, while the transportation and accumulation of ore-forming fluid, and the coupling relationship with the regional basin fluid are still remain unclear. Recently, In Jinding Pb-Zn deposit We have found many SDSs controlled by FTB, which is formed in the India-Asia plate collision of Cenozoic. Salt diapiric structures is accompanied with veined breccia type orebody in the inner part and developed stratiform-like sandstone type orebody in outside part, which showing complex alteration-mineralization zoning characteristic and indicating that the SDSs play a key role in controlling the Pb-Zn mineralization. Therefore, this project will take the typical SDSs and Pb-Zn polymetallic ore body as the object of research, systematically analyze the space-time structures, deformation features of the SDSs and the transportation and accumulation of ore-forming fluid adopting the methods including structural lithofacies mapping, microstructural analysis, Geochemistry tracing and 3DMine software, to reveal the coupling relationship between the SDSs and Pb-Zn mineralization, establish its ore-controlling model. This research will help to understand the formation mechanism of the SDSs in FTB and its controlling function on Pb-Zn mineralization, and also offer convincing evidence for the genesis of this ultra-scale deposit.

在全球重要造山带逆冲褶皱带(FTB)环境下，大量发育与SDSs密切相关的贱多金属矿床，但对其与区域盆地流体和局部成矿流体的迁移、汇聚的耦合关系尚不清楚。最近，在印-亚碰撞形成的兰坪新生代走滑/逆冲带内的金顶Pb-Zn矿床发现大量受TFB控制的SDSs，其内部伴生脉状角砾岩型矿体，外部发育似层状砂岩型矿体，并显示复杂的矿化-蚀变分带特征，反映其对铅锌成矿具有关键的控制作用。为此，本申请以区内典型的SDSs及相关Pb-Zn多金属矿体为对象，采用构造-岩相填图、显微构造分析、地球化学示踪及3DMine三维可视化等手段，开展TFB背景下SDSs的时空结构、变形特征及对成矿流体的迁移、汇聚过程控制作用的解剖研究，试图揭示FTB内SDSs与Pb-Zn成矿的耦合关系，建立其控矿模型。研究对理解造山环境下SDSs的发育机制及其对Pb-Zn成矿的控制机制有重要意义，也为深入理解这一超大型矿床成因提供实证。

项目组按照该项目计划，开展了为期3年的室、内外调查与综合研究工作，完成了预期目标。本次研究详细采集获取各矿区的岩性资料、构造要素数据、矿体形态、矿体分布等，系统梳理了兰坪金顶Pb-Zn矿床地质，查明矿区构造变形及控矿特征，查明了金顶矿区盐底辟构造的发育特征和主要类型及其与成矿的关系。（1）矿区盐底辟构造可分为近原地型、逆冲断层型和外源型三种，因赋存围岩层位、岩性及相关构造的差异而呈现明显不同的发育特征。其中，前两种赋存在云龙组（E1y）泥岩中，近原地型盐底辟构造多呈枕状、蘑菇状，结构较为简单，内部流动构造较为明显，角砾主要为砖红色泥岩砾，呈次棱角状，盐丘体与围岩接触关系明显；而逆冲断层型盐丘则表现为穿刺构造和膏岩脉形式。这两种盐底辟构造与成矿均无较大联系。外源型盐丘与成矿密切有关，又可分为砂岩中盐丘和灰岩中盐丘。（2）盐底辟构造可为流体运移提供动力和通道，同时是金属矿床形成的有利空间场所。底辟作用初期或盐枕阶段，流经的流体使底辟构造边缘或顶部的盐岩溶解，促使矿物溶解，从而产生次生孔隙和裂隙，底辟构造顶部、边缘岩石多角砾化，使盐底辟构造边缘成为流体运移通道。盆地沉积地层中被粘土颗粒吸附的分散金属阳离子，被岩层空隙中的流体萃取并向上迁移，富含有机质的地层逐渐成熟，随地层水沿底辟边缘向上迁移，达到浅部底辟构造的上部或附近，流体盐度、温度、压力随之下降，温度较高、高盐度含饱和金属的地层卤水与低温、氧化性质的地表水的混合，由于溶液中含有大量硫酸盐，在温度适宜、大气水充足的条件下，细菌还原硫酸盐反应释放出HCO3-、H2S、CO2或CH4，导致了金属硫化物的沉淀。. 项目完成了预期目标任务，为从本质上认识盐底辟构造成因及对金属成矿的控制作用，建立具有普遍意义的盐底辟构造控矿模型奠定了研究基础。