Compositional characteristics of garnets in the granite-pegmatite system in the Mufushan area and their implications for magma evolution and rare metal mineralization

Mufushan area is an important pegmatite type rare metal concentration area in China, where large-scale magmatism formed many rare metal deposits. In order to study the magnetic evolution process of granules-pegmatites in this area and acquire the mineralological indicators of mag matic evolution and rare metal mineralization, the garnets in various granules and pegmatites have been studied by EPMA and LA-ICP-MS. The results show that the garnets studied in the granite-pegmatite system belong to the solid solution series of almandine-spessartine, and they all belong to magmatic type. The magma of granite and pegmatite shows characteristics of a continuous evolution. The granitic magma has begun to enrich rare metal elements in the early stage, and in the process of multi-stage magmatic evolution,rare metal elements gradually enriched in magma and the intensity of mineralization gradually increased, showing that the Mufushan area has a great potential for rare metal mineralization. In the process of magmatic evolution, garnets are gradually rich in Mn and HREE. The evolution trend of Mn content of garnet in the granular stage, influenced by the crystallization of biotite, is opposite to the degree of magnetic evolution. The "cliff-like" decrease of HREE content of garnet in the late pegmatite stage indicates the metallogenic system has changed from magnetic stage to fluid-rich stage. The Mn content of garnet in pegmatite stage are positively related to the magnetic evolution, garnet with high Mn content (MnO > 27.1%) is a sign of highly fractionated and mineralized pegmatite. At the same time,it is also a mineralological sign of Li mineralization. In addition, garnet with low HREE content (< 66.3x10(-6) ) and high dilute alkaline content (>572x10(-6) ) can also be used as a sign of highly fractionated and mineralized pegmatite.