内蒙古二道河子铅锌（银）矿床硫化物原位微量元素和流体包裹体对矿床成因的制约

The Erdaohezi Pb-Zn (-Ag) deposit is typical in the Derbugan polymetallic metallogenic belt，whereas the ore genesis is still in debate and the detailed study of ore-forming process is lack. The sphalerite which is the main ore mineral in the Erdaohezi Pb-Zn (-Ag) deposit exhibits four generations and show two different structures (core-rim zonal structure and non-core-rim zonal structure).The pyrite also exhibits two generations. The fluid inclusions trapped in transparent minerals do not necessarily provide reasonable estimates of the depositional conditions of the ore minerals even though they intimately coexit. For the mineral with complex structures and/or different generations, the traditional wet chemical methods may get the mixed information without genesis significance.Therefore, in this proposal, We will analyze the in-situ trace element compositions of pyrite and sphalerite with different generations and structures by LA-ICP-MS to reveal the genesis of pyrite and sphalerite, and constraint elements enrichment regularity，and furthermore provide new evidences for the ore genesis.The Infrared microthermometric analysis will be carried out to obtain the characteristics of the fluid inclusions in different generations of sphalerite to constrain the physicochemical properties of the ore-forming fluid, study the evolutions of ore-forming fluid and the ore-forming process. This research will not only deepen the understanding of the genesis of the Erdaohezi Pb-Zn (-Ag) deposit, but also have valuable reference to the study on the regional same kind of deposits.

二道河子矿床是得耳布干成矿带最具代表性的铅锌矿床，目前缺乏对成矿过程的精细刻画，在矿床成因上还存在较大争议。该矿床的主要矿石矿物闪锌矿具有不同世代和颗粒类型(具环带结构和不具环带结构)，与之共生的黄铁矿也具有不同世代。与矿石矿物共生的透明矿物流体包裹体不一定代表成矿时的实际流体和成矿条件；采用传统的湿化学法对这种具复杂结构及不同世代的矿物进行微量元素测试，获得的多是混合信息，不具成因指示意义。因此，本项目拟采用LA-ICP-MS 技术对不同颗粒类型、不同世代的黄铁矿和闪锌矿进行原位微量元素测试，研究硫化物的沉淀过程，约束元素的迁移富集规律，为判别矿床成因提供新证据；采用红外显微测温技术对各世代闪锌矿的流体包裹体进行观察测试，更直观地研究该矿床成矿流体的物理化学性质，追溯流体演化，精细刻画成矿过程。本项目的研究不仅深化了对二道河子矿床成因的认识，而且对区域其它同类矿床研究具有重要借鉴意义。

二道河子铅锌银多金属矿床位于得耳布干成矿带的中段。野外地质调查、室内岩相学观察及矿物共生组合特征显示该矿床共经历了三个热液成矿阶段：成矿早阶段（石英-黄铁矿）、主成矿阶段（石英-多金属硫化物）和成矿晚阶段（石英-方解石-黄铁矿）。硫化物具有多世代特征，其中黄铁矿具有5个世代，闪锌矿具有3个世代。采用LA-ICP-MS和红外显微镜技术，对不同世代黄铁矿和闪锌矿的微量元素和流体包裹体进行详细研究，初步得出以下结论：①成矿流体早期为中温、中低盐度、CO2-H2O-NaCl体系，晚期变为中低温、低盐度、H2O-NaCl体系；②成矿物质可能与围岩火山岩同源的后期岩浆热液相关，成矿过程中流体发生过多次脉冲，中晚期有大量大气水的加入；③二道河子矿床发生过两次成矿作用，第一次成矿作用发生在主成矿阶段，主要为Zn 、Pb、Cu和微量Ag富集，第二次成矿作用发生在成矿晚阶段，主要为Ag和微量Au富集；④二道河子矿床属中、低硫型浅成低温热液矿床。