A study of mineralogy and mineral chemistry of ore-bearing pegmatites in the Daqianggou lithium-beryllium deposit, western Sichuan

The Daqianggou pegmatite type lithium-beryllium deposit is a typical medium-sized lithium-beryllium deposit in Jiulong area.Its geotectonic location is located in the Yajiang residual basin on the southern margin of the Songpan-Garze fold belt, and the deposit is an important part of the Songpan-Garze lithium metallogenic belt.The main types of ore-bearing pegmatites in the Daqianggou deposit can be divided into albite type and albite-spodumene type, and the main ore minerals are spodumene and beryl.In this paper, based on the field geological survey work, the authors chose typical veins (Ⅰ_{Li, Be} and Ⅱ_Be) in the Daqianggou lithium beryllium deposit to conduct studies of facieology, mineralogy and mineral chemistry in order to reveal the sequence order of mineral formation and ore-forming stages.The results of electron microprobe analysis show that the lithium-containing mineral is mainly spodumene.The content of Li₂O in spodumene is 7.94%~8.29%, averaging 8.12%.Mica minerals are muscovite and lithium-rich phengite.The content of Li₂O in muscovite is 0.08%~0.35%, averaging 0.21%, and the content of Rb₂O is 0.13%~0.35%, averaging 0.24%.The Li₂O content in lithium-rich phengite is 1.11%~1.43%, averaging 1.28%, and the Rb₂O content is 0.79%~0.94%, averaging 0.87%.Tourmaline belongs to an iron tourmaline-lithium tourmaline series, with Li₂O content of 0.48%~0.85%, averaging 0.64%.Based on the detailed study of the microscopic characteristics of minerals combined with electron microprobe analysis, the authors hold that the rare metal mineral changes in pegmatite are in order of beryl → beryl + spodumene → spodumene → spodumene + lithium-rich phengite, mica changes from muscovite to lithium-rich phengite, tourmaline transition from iron tourmaline to lithium tourmaline, feldspar mineral is composed of micro-plagioclase + albite → albite → metasodium albite, and quartz changes from primary quartz to late hydrothermal quartz.Finally, a comprehensive analysis suggests that the metallogenic stages of the Daqianggou lithium-beryllium deposit underwent a multi-stage evolution process, which could be mainly divided into crystallization stage, metasomatic stage and hydrothermal stage.The formation of rare metal minerals such as lithium and beryllium minerals mainly occurred in the crystallization stage and metasomatic stage.