白云母成分对富锂铍伟晶岩成因的指示：以卡鲁安稀有金属矿田为例

新疆阿尔泰造山带是我国重要的稀有金属矿床矿产资源基地，尤以富Li和富Be伟晶岩型矿床广泛发育为特色。本研究选择阿尔泰造山带卡鲁安-阿祖拜矿田富Li和富Be伟晶岩型矿床开展典型解剖，以贯穿岩浆阶段-伟晶岩阶段的白云母矿物为研究主线，探讨不同矿化类型伟晶岩中云母的成分演化规律、花岗岩与伟晶岩的成因联系。矿物学特征显示富Be伟晶岩中发育大量磷酸盐矿物，而富Li伟晶岩含较多橙色锰铝榴石、锂云母而缺乏典型的Fe-Mn磷酸盐。白云母成分分析显示，从白云母花岗岩→富Be伟晶岩→富Li伟晶岩，白云母总体呈Nb含量和Nb/Ta值降低，指示白云母花岗岩、富Be伟晶岩经历了不同程度的分离结晶作用，也代表了富Li伟晶岩的岩浆分异演化程度更高。尽管利用云母成分变化(尤其是K、Rb、Cs等大离子亲石元素)模拟岩浆结晶演化过程，显示可由初始花岗质岩浆经瑞利分离结晶作用依次形成白云母花岗岩→富Be伟晶岩→富Li伟晶岩的假设。但研究区年代学、矿物学、同位素证据指示富Li伟晶岩和富Be伟晶岩具有不同的熔体性质和形成时代。因此，应用云母成分探讨伟晶岩的成因联系应当建立在花岗岩-伟晶岩系统具有合理的时空分布和其它支持源自同一...

Implications of muscovite composition on the genesis of Li-rich and Be-rich pegmatites: A case study of the Kalu'an rare-metal pegmatite ore-field

The Altay orogenic belt in Xinjiang is a significant rare-metals resource base in China, hosting a large number of pegmatite-type lithium and beryllium deposits. In this study, we investigated the chemical compositions of muscovite that is a ubiquitous mineral phase in the Li-rich pegmatites and Be-rich pegmatites in the Kalu''an-Azubai ore field. The purpose is to explore the compositional evolution of muscovite in different mineralized pegmatites and its implications for the genetic relationship between the granite and pegmatites. Field and petrographic observations show that there are a variety of phosphate minerals in Be-rich pegmatites, whereas the Li-rich pegmatites contain abundant orange spessartine and lepidolite but lack typical Fe-Mn phosphates. The Nb contents and Nb/Ta values of muscovite decrease from the muscovite granite to Be-rich pegmatite to Li-rich pegmatite, likely indicating an increasing differentiation degree of the granite/pegmatite-forming melts. The magmatic evolution of the granite-pegmatite system was modeled using the mica chemistry (particularly LILE including K, Rb, and Cs). According to the modelling, the evolutionary trend of mica compositions is consistent with the assumption that the muscovite granites, Be-rich and Li-rich pegmatites successively formed via Rayleigh fractionation of a parental magma. Nevertheless, the chronological, mineralogical, and isotopic evidence suggest that the melts forming the Li and Be pegmatites might have different geochemical characteristic and that the studied Li and Be pegmatites exhibit distinct age difference. Therefore, using the evolutionary trend of mica compositions to address the genetic relationships of different rare-element mineralized pegmatites in the same regions should be under the precondition that the granite-pegmatite system has a reasonable spatio-temporal distribution and other evidence supporting the successive evolution of a common parental magma is also needed.