滇西芦子园矽卡岩型Fe-Pb-Zn矿床成矿流体来源和演化：来自流体包裹体及其寄主矿物微区原位成分研究的制约

Conventional research methods employed for ore-forming fluid including microthermometry, Laser Raman analysis, stable isotopes and bulk quantification couldn't achieve accurate fluid properties in different evolution stages, which limit the understanding of ore-forming fluid evolution and factors controlling ore deposition in skarn deposits. The in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of fluid inclusions and host minerals could obtain the compositions of fluid in different stages, which has offered direct approaches to ore-forming fluid compositions. Garnet at the early stage and quartz from different paragenetic stages have complex growth zones. Furthermore, these growth zones have abundant fluid inclusions, which directly record the information of the ore-forming fluids through the whole mineralization process. In this study, based on the observation of petrology and micro thermometry, we plan to select typical fluid inclusions and the host minerals from different growth zones in garnet and quartz for microthermometric and LA-ICP-MS compositional analyses, to trace the source of ore-forming fluid, reconstruct the evolution processes of ore-forming fluid, and reveal the mechanism of ore precipitation.

传统的成矿流体研究方法（如包裹体显微测温、激光拉曼、C-H-O-S稳定同位素和群体包裹体成分分析等）难以精确获取成矿过程中各阶段流体的特征，制约了对矽卡岩型矿床成矿流体演化和矿质沉淀机制的深入理解。流体包裹体及其寄主矿物LA-ICP-MS原位成分分析技术可以精确测定不同阶段流体和矿物的成分，是研究成矿流体最直接的手段。滇西芦子园矽卡岩型Fe-Pb-Zn矿床中石榴子石和各阶段石英不仅生长环带结构发育，而且不同环带内广泛发育流体包裹体，直接记录了从矽卡岩化早期至成矿结束后的流体信息。本申请拟在岩相学观察和显微测温的基础上，利用LA-ICP-MS原位分析技术系统测定石榴子石和石英中不同环带内矿物和流体包裹体物质组成，示踪流体来源，精细刻画流体演化过程，从而揭示控制成矿金属沉淀的机制。

芦子园Fe-Pb-Zn矿床位于我国西南三江造山带保山地块南部，铁矿石量大于300 Mt，Pb+Zn 金属量大于4.2 Mt，是我国西南最大的矽卡岩型矿床之一。然而，其成矿年龄、成矿流体来源以及控制矿质沉淀的关键因素等科学问题尚未解决，严重阻碍了对芦子园矿床成矿作用以及保山地块区域成矿规律的深入理解。本项目通过对芦子园矿床不同成矿阶段代表性矿物（包括成矿前阶段石榴子石和辉石，氧化物成矿阶段石英，硫化物成矿阶段闪锌矿、石英和方解石，以及成矿后阶段的石英和方解石）中流体包裹体显微测温，并利用LA-ICP-MS微区原位分析技术测定不同成矿阶段石英中的流体包裹体元素成分，揭示了成矿流体起源于岩浆热液，演化过程中有明显的低温低盐度的大气降水混入。低温低盐度的大气降水混入导致成矿流体温度和盐度降低，从而降低了金属元素在成矿流体中的溶解度，导致流体中金属元素沉淀成矿。同时，水-岩反应降低了成矿流体的氧逸度和pH值，也可能对成矿有一定的贡献。此外，石榴子石U-Pb年龄揭示芦子园矽卡岩型Fe-Pb-Zn矿床的成矿年龄约为463 Ma，系早古生代奥陶系原特提斯洋闭合后陆陆碰撞所引发的花岗质岩浆活动的产物。