三江中段夏塞地区锡与银铅锌成矿作用关联：年代学及微区地球化学制约

Lots of Sn-Ag-Pb-Zn deposits develop in the Xiasai area, central Sanjiang metallogenic belt. They provide an ideal opportunity to study on relationship between Sn and Ag-Pb-Zn mineralization because of the mineralization zoning of Sn and Ag-Pb-Zn ore-bodies. However, ages of Sn and Ag-Pb-Zn mineralization and ore-related granites, relationship with magmatism and mineralization zoning of these deposits are rare studied. The proposed project will focus on zoning of Sn-Ag-Pb-Zn mineralization and alteration, and geochemical analysis of ore and ore-related granites from the Xiasai and Jiaogenma deposits. LA-ICPMS U-Pb dating for zircon and cassiterite grains and sericite 40Ar/39Ar dating (or sphalerite Rb-Sr dating) are used to provide constraints on the formation ages of Sn and Ag-Pb-Zn ore-bodies and ore-related graites. The association and distribution of trace elements in cassiterite and sulfide minerals, as well as compositions for individual fluid inclusions will be analyzed by LA-ICPMS. These geochronological and in-situ geochemical data, in combination with analysis of ore minerals, data of fluid inclusions and S-Pb-H-O isotopes, will provide significant insights into relationship between Sn and Ag-Pb-Zn ore-bodies, and contribution of magmatism to polymetallic mineralization. Furthermore, the evolution process of ore-forming fluids and mechanism of mineralization zoning are will be discussed to build a geologically reasonable metallogenic models for Sn-Ag-Pb-Zn deposits in the Xiasai area. Therefore, results of this proposal will not only significantly promote the understanding of Sn-Ag-Pb-Zn mineralization, but also provide useful guide to mineral exploration in central Sanjiang region.

三江成矿带中段的夏塞地区锡银铅锌矿床具明显的矿化分带，是研究锡与银铅锌成矿作用关联的理想对象。但相关矿床成岩成矿时代、与岩浆作用联系及分带机制等方面研究薄弱。立项选取夏塞和脚根玛两个典型矿床，在详细的野外地质调查和岩相学/矿相学观察基础上，综合利用锆石和锡石LA-ICPMS U-Pb、绢云母Ar-Ar或闪锌矿分相Rb-Sr定年法、锡石和硫化物LA-ICPMS微量元素测试、单个包裹体LA-ICPMS成分分析等先进测试技术，深入研究锡矿体和银铅锌矿体的矿化蚀变特征及分带、成矿时代、锡石和硫化物微量元素组成以及成矿流体性质及成分。结合流体包裹体及S-Pb-H-O多元同位素数据揭示锡矿体与银铅锌矿体间的关联，从根源上探讨岩浆作用对锡及银铅锌成矿的贡献，并精细反演成矿流体演化过程及矿化分带机制，建立合理的成矿模式，为找矿勘查工作提供理论指导。

锡与银铅锌矿床常常相伴生且具明显的分带，其成因联系及分带机制仍存在争论。义敦地体中段的夏塞地区脉状Sn-Ag-Pb-Zn矿床具明显的矿化分带，是研究锡与银铅锌成矿作用关联的理想对象。本项目以夏塞大型Sn-Ag-Pb-Zn矿床为重点研究对象，在详细的野外地质调查和岩相学/矿相学观察基础上，开展了成岩矿物和硫化物、石英等矿石矿物和脉石矿物微区结构、微区元素和同位素分析，得出了如下主要结论及认识：（1）锆石和锡石U-Pb及闪锌矿分相Rb-Sr等时线法厘定成岩成矿时代为102-99 Ma，确定锡矿体和银铅锌矿体均与二长花岗岩关系密切，为Sn与Ag-Pb-Zn伴生提供了一个典型实例。（2）花岗岩中斜长石环带微区Sr同位素组成边部较核部低，成岩过程中有基性幔源成分的加入，为壳幔混合作用提供了直接微区证据。（3）S-Pb同位素限定了该矿床成矿物质来源于A型花岗岩，但包裹体激光拉曼成分、H-O同位素和与闪锌矿共生的磷灰石微区Sr同位素却显示有机物质的参与。（4）EPMA面扫描、BSE和EDS分析，发现了以包裹体形式存在于磁黄铁矿或与磁黄铁矿密切伴生的红锑镍矿，与幔源物质的加入有关。（5）成矿岩体中石英斑晶、Sn矿体和Ag-Pb-Zn矿体石英中单个熔体和流体包裹体微区成分从早至晚阶段含量逐渐降低，不同成矿元素不同阶段沉淀形成了Sn与Ag-Pb-Zn的分带，主要受控于流体混合造成的温度降低及伴随的硫逸度和氧逸度变化。（6）建立了花岗岩-（矽卡岩型-）脉状锡矿体-脉状Ag-Pb-Zn矿体“三位一体”成矿模式并总结了成矿规律，为区域乃至同类型矿床找矿勘查工作提供借鉴与参考。本项目丰富并完善了Sn与Ag-Pb-Zn矿化伴生及分带机制并为找矿勘查提供了理论基础。共发表论文11篇和国际国内学术会议论文4篇。