雪球石英的形成机制及其与成矿的关系

Snowball quartz describes quartz crystals that enclose concentrically zoned albite inclusions. It occurs in most granite-hosted rare-metal deposits, where the abundant occurrence of snowball quartz is usually associated with well-mineralized ore bodies. The genesis of snowball quartz and the relationship between snowball quartz and ore formation, however, still remain enigmatic..Our project will focus on the No. 414 deposit, the Songshugang deposit, the Dajishan deposit, and the Baerzhe deposit. Rock-forming and ore-forming minerals will be examined using a polarizing microscope and a scanning electron microscope; both microscopes will be couple with cathodoluminescence (CL), specifically for observation of quartz. Furthermore, homogenization of melt inclusions, microthermometry of fluid inclusions, and chemical analyses of both melt and fluid inclusions in different generations of quartz will be carried out. In addition, in-situ oxygen isotope analyses and in-situ trace element chemical analyses of different generations of quartz will be examined using an SIMS and a femtosecond laser-ICP-MS, respectively. We aim to quantify the physico-chemical properties of the magmatic-hydrothermal system, as well as the genesis of snowball quartz. We will also explore the relationship between snowball quartz and rare-metal mineralization, discuss the ore-forming mechanism during magmatic-hydrothermal evolution, and further the recognition of magmatic-hydrothermal processes. The significance of snowball quartz as a prospecting mark for rare-metal deposits will be addressed.

雪球石英是指钠长石等矿物被石英包裹、并出现平行于石英晶面的、旋涡状的定向排列。雪球石英在花岗岩型稀有、稀土金属矿床中广泛发育，其大量产出的部位通常是矿化程度高的矿体。然而，雪球石英的成因尚存争议，其与成矿的关系亦有待深入探索。.本次研究以四一四、松树岗、大吉山和巴尔哲四个矿床为对象，运用光学显微镜和扫描电镜对造岩矿物和矿石矿物开展形貌学研究，并对花岗岩中的各世代石英进行阴极发光成像；对各世代石英中的熔体—流体包裹体进行分类、均一实验、显微测温和成分研究；分别运用离子探针和飞秒激光剥蚀电感耦合等离子质谱仪，对石英进行原位氧同位素测试和原位微量元素含量测定。研究旨在量化雪球石英形成时岩浆—热液体系的物理—化学条件，探索雪球石英的成因；讨论雪球石英与稀有、稀土金属成矿的关系，探究岩浆—热液演化过程中矿质的富集机理，深化对岩浆—热液过程的认识；最后，探讨雪球石英的找矿指示意义。

关键金属是国防军工、航空航天以及电子通讯等产业的核心原料。近年来，关键金属矿床的开采和开发影响着国际局势，相关研究也跃升为国际热点。关键金属储备是国家实力的绝对彰显，更是我国战略布局的王牌砝码。因此，加强理论研究和找矿勘查、保障我国关键金属资源供应的工作迫在眉睫。雪球石英是关键金属成矿花岗岩中普遍发育的一种特殊的嵌晶结构：钠长石等矿物被石英包裹、并出现平行于石英晶面的旋涡状定向排列。这种特殊的结构在其它类型的花岗岩中至今尚未发现。申请人以我国和加拿大几处花岗岩型关键金属矿床为研究对象，基于野外工作认识，利用先进的岩石、矿物观察手段和原位微区分析技术，探究雪球石英的成因及其与成矿的关系。研究认为雪球石英是蚀变矿物组合，表征硅质交代事件，该事件与关键金属矿床中部分成矿元素的超常富集在时空上重合；充实了传统蚀变岩成矿理论的矿物学证据，串联了矿物形貌和成矿事件。因为雪球石英可以在野外被快速、准确识别，深入理解雪球石英与成矿的关系，有望建立以雪球石英为野外标志的找矿模式，改进找矿思路。