SWIR spectroscopy and mineral chemistry of Li-bearing micas in NW Jiangxi: Implications for the genesis and exploration of granite-related Li deposits

• Composition, texture, and SWIR spectral features of Li-bearing micas were studied. • Zoning textures with compositional variations are commonly developed in white mica. • Magmatic high fractionation is critical for supernormal Li enrichment. • Feature SWIR parameters of Li-rich micas hold the potential for Li exploration. The granite-related Li deposit has emerged as a significant source of lithium metal globally, thanks to advancements in the metallurgical process of Li-bearing micas. The total proven Li 2 O reserve of granite-type in the Northwest Jiangxi of China is over 9.2 Mt. To gain deeper insights into the evolution, enrichment mechanisms, and exploration indicators of Li-rich micas, short wavelength infrared (SWIR) spectroscopy, EPMA, and LA-ICP-MS analyses were conducted at the Dagang Li deposit, the Yashan Li-Nb-Ta deposit, and the Ganfang prospecting area. Obvious zoning textures were observed in the white mica of Dagang and Ganfang, with a compositional shift from magmatic Li-Fe mica and zinnwaldite in the core to post-magmatic hydrothermal Li-Fe mica at the edge. Meanwhile, Yashan’s white micas show core-rim textures, with the core dominated by magmatic lepidolite with minor altered Li-Fe mica on the rim. The Li, Si, Rb, and F contents of all white micas show similar varied trends, indicating comparable geochemical behaviors, with Li showing a positive linear relationship with Si. The substitution of Li for Al and Fe in the octahedral site played a crucial role in the Li supernormal enrichment during the granitic fractionation and evolution. However, post-magmatic hydrothermal alteration can potentially decrease the Li grade. Notably, the Yashan granite exhibits a higher degree of evolution compared to the Dagang and Ganfang granites. The coupling of the SWIR parameters with the chemical composition of Li-rich micas holds the potential for establishing exploration indicators for Li. Specifically, the Li-rich mica exhibits distinctive absorption at 550 and 960 nm, along with a lower Al-OH absorption peak position (Pos2200) than common muscovite. The absorption depth at 960 nm can be used to assess Li enrichment and identify lepidolite, while the Pos2200 value can reflect the substitution relationship between Li and Al.