Unveiling Nb–Ta mineralization processes: Insight from quartz textural and chemical characteristics in the Songshugang deposit, Jiangxi Province, South China

The Songshugang deposit is a large Ta–Nb deposit in South China, with Ta–Nb mineralization associated genetically with the granite and pegmatite. A diversity of quartz from topaz–albite granite, quartz–mica pegmatite,quartz–feldspar pegmatite, and quartz–fl uorite pegmatite at Songshugang was studied by CL and LA–ICP–MS in order to constrain enrichment mechanisms of Nb and Ta and to fi nd geochemical indicators of quartz for rare metal deposits.Cathodoluminescence image illuminates a canvas of complexity, the quartz from topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, and quartz–fl uorite pegmatite, exhibits numerous dark CL streaks, patches, and a series of healed fractures. These textures suggest that the rocks were fractured because of deep crustal pressure, and underwent later hydrothermal metasomatism and quartz fi lling. The quartz from quartz–fl uorite pegmatite present limited patches or fractures but distinct growth bands, indicating that the melt fl uid composition during the formation of quartz at this stage varies greatly and is less aff ected by mechanical fragmentation. The LA–ICP–MS analysis of quartz shows that there is a positive correlation between Al and Li in the quartz from topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, to quartz–fl uorite pegmatite, indicating that Al mainly enters the quartz lattice through charge compensation substitution mechanism with Li. However, our data deviate from the theoretical Li:Al mass ratio of ～ 1:3.89 in quartz, indicating that there may be competition between H + and Li in a water-rich magmatic environment. The quartz from topaz–albite granite is enriched in K and Na elements, and the quartz from quartz–fl uorite pegmatite is enriched in fl uorite with a low Ca content in quartz, further elucidating that these rocks were subjected to hydrothermal metasomatism. From topaz–albitite granite to quartz–fl uorite pegmatite, Al, Li and Ge content and Al/Ti, Ge/Ti, Sb/Ti ratios in quartz gradually increased, but Ti content gradually decreased, refl ecting the high evolution of magma, which can enrich rare metal elements. Based on the characteristics of quartz CL textures and trace elements in topaz–albite granite, quartz–mica pegmatite, quartz–feldspar pegmatite, and quartz–fl uorite pegmatite, combined with the albitization and K-feldspathization of rocks, it is suggested that the Nb–Ta mineralization in Songshugang may be infl uenced by the combined action of magmatic crystallization diff erentiation and fl uid metasomatism. By comparing the quartz in the Songshugang pluton with the quartz in the granite type and pegmatite type rare metal deposits recognized in the world, the Songshugang pegmatite share similarities with the LCT-type pegmatite. Combined with previous studies, the Ge/Ti > 0.1 and Ti < 10 ppm, as well as Al, Li, Ge, Sb, K, Na contents and Al/Ti, Sb/Ti ratios in quartz have the potential to be a powerful exploration marker for identifying granite-like pegmatitic Nb–Ta deposits in other places.