北衙金多金属矿田流体演化及其对成矿的制约:基于单个包裹体LA-ICP-MS成分分析

The elaborate depiction of ore-forming process has been of particular interest in the research of magmatic-hydrothermal deposit. The fluid is the important carrier of metals, and its formation, transportation and precipitation of materials from it are considered to represent the entire ore-forming process. Beiya Au-polymetallic orefield located in the middle segment of Jinshajiang-Ailaoshan ore belt comprises of porphyry-skarn-epithermal mineralization, and is the ideal area to study the ore-forming process. This project intend to analyze the melt inclusion and fluid inclusion trapped by gangue at different stages on the basis of LA-ICP-MS (laser-ablation inductively coupled plasma mass spectrometry), in conjunction with microthermometry and micro-Raman spectra, aiming to describe the characteristics and evolution of the ore fluid, clarify the partition of the ore-forming elements between melt and fluid during the fluid exsolution, find out the transportation of this elements in the ore fluid and its controlling factors, and then construct the path of the fluid evolution and ore-formation. This research is benefit for better understanding the metallogenisis of Beiya orefield. It is also significant for further discussing the deposition mechanics of metals and revealing the origin of the variation and zonation of the metals. Furthermore, it is instructive for the study of other deposits in the Jinshajiang-Ailaoshan ore belt and can provide important information for prospection.

成矿过程的精细刻画是岩浆-热液矿床研究的热点。流体作为成矿的精髓，其形成、运移和物质卸载沉淀反映了整个成矿过程。北衙金多金属矿田位于金沙江-哀牢山斑岩成矿带的中段，其内发育一套较为完整的斑岩-矽卡岩-浅成低温热液型矿化，是研究成矿过程的理想场所。项目拟以熔融包裹体与流体包裹体为分析对象，基于详细的野外踏勘与显微镜观测，以单个流体包裹体LA-ICP-MS成分分析技术为主要手段，辅以包裹体显微测温与显微激光拉曼光谱分析技术，精细刻画成矿流体的性质与演化特征，查明岩浆流体出溶阶段成矿元素在熔/流体相间的分配特征，理清成矿元素的迁移形式与影响因素，建立流体演化轨迹，反演成矿过程。研究的开展不仅可深化对北衙金多金属矿田成矿作用的理解，还可从流体的角度深入探讨成矿元素的沉淀机制，揭示矿床品位变化及矿化空间分带的根本原因，为金沙江-哀牢山成矿带上同类矿床的研究提供借鉴，为找矿勘探提供重要信息。

项目以北衙矿床成矿各阶段脉石矿物中发育的多类型包裹体（熔融包裹体和/或流体包裹体）为分析对象，在查明了矿床地质与成矿阶段的基础上，借助单个流体包裹体的LA-ICP-MS成分分析、包裹体显微测温与单个包裹体的显微激光拉曼光谱分析等技术，开展了不同成矿阶段流体的性质与物质组成及成矿元素在流体中的迁移形式及其控制因素等方面的研究。本项研究查明了岩浆流体出溶阶段成矿元素在熔/流体相间的分配特征，理清了成矿元素的迁移形式及其影响因素，建立流体演化轨迹，反演了成矿过程。研究认为北衙矿床流体的形成和演化可能经历了岩浆流体出溶—相分离—减压沸腾—水岩作用（流体与碳酸盐的接触交代）—流体混合的过程。流体的出溶与水岩作用富集了成矿物质，而流体的相分离、沸腾及混合控制了成矿元素的迁移与沉淀，进而导致了矿化的空间分带。成矿元素在流体出溶阶段易于进入流体相，在初始流体形成后，Au、Cu是以气相的形势进行迁移的，而Ag、Pb与Zn是以液相的形势进行迁移的，这在一定程度上导致了成矿元素的空间分带。研究的开展不仅深化了对北衙金多金属矿田成矿作用的理解，从流体的角度揭示了矿床品位变化及矿化空间分带的根本原因，为金沙江-哀牢山富碱斑岩成矿带上其他同类型岩浆-热液矿床的研究提供借鉴，为找矿勘探部署工作提供重要信息。