内蒙古维拉斯托锂锡多金属矿床稀有金属的富集机制研究：来自（锂）云母等矿物微观结构和组分的约束

The mechanism for enrichment of rare metals in magmatic-hydrothermal process is the key to understand the genesis of granite-type rare metal deposits. Previous studies have mostly focused on the fractional crystallization in the early stage of magmatic process. However, little is constrained regarding to the mechanism and efficiency of rare metal enrichment during the magmatic-hydrothermal transitional process. Our plan is to use Weilasituo deposit as our research subject. The reasons for this are twofold: 1)Microscopic geode structure which represented magma-hydrothermal transition stage was found in ore-bearing granite rock; 2)Lithium-bearing micas were continuously precipitated throughout the whole magma-hydrothermal stage. the evolution of lithium, rubidium, niobium, tantalum, cesium and other elements in magma-hydrothermal processes is potentially amplified. Based on above description, we will focus on the systematics of the microstructures and compositions, using lithium-bearing mica as the main tracer carrier, which developed in microscopic geode structure and different hydrothermal stage. This project will use recently-emerged in situ analysis techniques (e.g., LA-ICP-MS) to reveal the compositional evolution of rare metals in lithium-bearing mica from the early magmatic stage to the late hydrothermal stage. Combining the analyses of Li and Sn isotopes from different stages, we seek to shed some light on the genesis of the rare metals and figure out the enrichment processes of different rare metals.

岩浆-热液过程中稀有金属富集机制是认识花岗岩型稀有金属矿床成因的关键。已有研究主要针对岩浆早期的分异演化过程，而岩浆-热液过渡过程中稀有金属的富集方式、效率等问题并未得到较好限制。新近发现的维拉斯托稀有金属矿化花岗岩，存在代表岩浆-热液过渡阶段的显微晶洞构造，而且（锂）云母类矿物连续发育于显微晶洞构造、似伟晶岩壳乃至矿床的不同蚀变-矿化阶段，锂铷铌钽铯等元素在岩浆-热液各过程的变化可能被有效放大。为此，本课题探索以（锂）云母为主要示踪载体，采用先进的LA-ICPMS微区测试技术，对显微晶洞构造及不同成矿阶段的各类（锂）云母开展系统的微观结构和组分研究，将调查扩展到岩浆-热液演化的全过程。通过对比不同阶段云母中稀有金属含量变化，结合各阶段Li，Sn同位素特征，示踪稀有金属来源及其富集过程。

岩浆-热液过程中稀有金属富集机制是认识花岗岩型稀有金属矿床成因的关键。已有研究主要针对岩浆早期的分异演化过程，而岩浆-热液过渡过程中稀有金属的富集方式、效率等问题并未得到较好限制。本项目选择维拉斯托、石灰窑及加不斯稀有金属矿化花岗岩以及新近发现的代表岩浆-热液过渡阶段的显微晶洞构造为研究对象，基于云母、锡石等矿物连续发育于显微晶洞构造、似伟晶岩壳乃至矿床的不同蚀变-矿化阶段，锂铷铌钽铯等元素在岩浆-热液各过程的变化可能被有效放大。项目采用EPMA和先进的LA-ICPMS微区测试技术，对不同成矿阶段的各类（锂）云母、锡石及铌钽氧化物开展系统的微观结构和组分研究，将调查扩展到岩浆-热液演化的全过程。通过对比不同阶段云母中稀有金属含量变化，发现岩浆及岩浆-热液过渡阶段的云母W、Sn、Nb和Ta含量均明显高于热液脉体及隐爆角砾岩筒，证实云母组分时空变化可以作为示踪成矿流体演化过程的潜在指标。同时，岩浆-热液过渡阶段，W开始从岩浆从抽离而进入到流体相，同时，该阶段形成的富Si、F、Li、高场强元素以及大离子亲石元素的过渡性流体中可有效萃取熔体中的Ta、Nb进入水硅流体之中。