榍石原位分析对热液成矿过程的约束：以金沙江-哀牢山富碱斑岩成矿带为例

Titanite is a common accessory mineral in hydrothermal deposit. The geochemical characteristics of titanite can record the ore-forming process of hydrothermal deposits and the physicochemical condition of their formation, which serves as mineralization process tracer and is significant for the hydrothermal deposit study. The Jinshajiang-Ailaoshan alkaline porphyry metallogenic belt in “Sanjiang area” is the most typical example of Cenozoic alkaline porphyry related deposit in China. Further studies need to be done to reveal the physicochemical condition and material source of different deposits in this belt as well as their influence on the ore-forming elements and deposit scale. In this study, four typical deposits (Beiya, Machangqing, Habo and Changanchong) belonging to the porphyry-skarn hydrothermal ore-forming system in the metallogenic belt are selected. Magmatic and hydrothermal titanites from these deposits will be examined by systematic in-situ geochemical analysis to study the physicochemical condition, material source and geochronology, which not only constrain the ore-forming process, but also indicate the metallogenic regularity of the belt and establish the geochemical indicator of titanite for discriminating different deposits (copper-molybdenum or gold deposit). The solution of these scientific issues will provide theoretical support for metallogenic mechanism study in Jinshajiang-Ailaoshan alkaline porphyry metallogenic belt and porphyry-skarn hydrothermal deposits exploration.

榍石是热液矿床中的常见副矿物，其地球化学特征记录了热液矿床的形成过程和相关的物理化学条件，是热液成矿过程的示踪剂，对热液矿床的研究有着重要的指示意义。“三江”地区金沙江-哀牢山富碱斑岩成矿带是我国新生代最重要的富碱斑岩矿床典例，其中不同矿床形成时的物理化学条件和物质来源及其对成矿元素和矿床规模的影响仍有待深入的研究和探讨。本项目拟选取该成矿带上同为斑岩-矽卡岩热液成矿系统的四个典型矿床（北衙、马厂箐、哈播和长安冲）为研究对象，通过对岩浆和热液成因榍石原位主微量元素及同位素组成的系统研究，提取矿床形成时的物理化学条件、形成年代及物质来源等关键信息来约束成矿过程，总结成矿带上的成矿规律并建立判断不同种类矿床（铜钼矿或金矿）的榍石地球化学指标，进而为金沙江-哀牢山富碱斑岩成矿带形成机制的探讨及斑岩-矽卡岩型热液矿床的找矿勘察提供重要科学依据。

“三江”地区金沙江-哀牢山富碱斑岩成矿带是我国新生代最重要的富碱斑岩矿床典例，其中不同矿床形成时的物理化学条件和物质来源及其对成矿元素和矿床规模的影响仍有待深入的研究和探讨。本项目选取该成矿带上同为斑岩-矽卡岩热液成矿系统的四个典型矿床（北衙、马厂箐、哈播和长安冲）为研究对象，以榍石原位地球化学组成和制约因素为研究主线，采用EPMA和LA-ICP-MS等原位分析手段，探讨了榍石的微量元素如何对成矿条件进行制约，并且通过榍石U-Pb年代学分析，揭示成岩成矿时代。其中重点以北衙和马厂箐为例，对比了不同矿床间的榍石化学成分差异并探讨其对成矿带成矿规律的指示作用。此外，对目标矿床中的石榴子石和褐帘石等热液矿物系统的开展了原位微量元素和U-Pb同位素分析，精确限定矿床成矿时代，探讨成矿条件，与榍石的研究结果相互验证和制约。结果显示，马厂箐热液榍石形成于34.3±1.2Ma，相比于北衙，马厂箐矿床具有相对较低的氧逸度和F含量。北衙和马厂箐褐帘石U-Pb同位素年龄分别为33.4±4.6 Ma和35.4±9.8 Ma，代表了两个矿床的退变质蚀变年龄，北衙褐帘石具有更高的Fe3+/(Fe3++Fe2+)比值和Th、U含量，指示北衙的成矿流体相对于马厂箐具有更高的氧逸度和F含量，与榍石结果相同，这种成矿流体的差异性可能是导致两个矿床不同成矿规模和成矿金属种类的重要原因之一。