Tracing lithium enrichment processes in the Yifeng granite-type Li ore field, Jiangnan Orogen Belt, South China: constraints from mica geochemistry

The Yifeng granite-type lithium ore field in northwestern Jiangxi, South China, represents one of the most significant granite-hosted lithium discoveries globally. Despite its economic importance, the magmatic-hydrothermal processes responsible for such extreme lithium enrichment remains poorly constrained. This study presents a comprehensive investigation of mica geochemistry across the Ganfang, Guyangzhai, and Baishuidong granites to elucidate the lithium enrichment mechanisms in this world-class deposit. Mica compositions document a continuous evolutionary trend from muscovite through Li-phengite to lepidolite, controlled by Al 4 Si 3 □ and Si 2 LiAl 3 substitution mechanisms. Trace element systematics, including progressive enrichment of Li, F, Rb, Cs, Ta, and Nb, alongside decreasing K/Rb and K/Cs ratios, demonstrate that fractional crystallization was the dominant process governing lithium enrichment in the Baishuidong granite. However, the extreme enrichment of Li (28,027 ppm), F (6.90 wt%), Cs (10,338 ppm), and Rb (13,147 ppm) in the bright rims of mica in Baishuidong granite, together with the decoupling of Nb-Sn depletion and Ta enrichment, points to a transition from magmatic crystallization to aqueous-dominated crystallization. This transition represents the key process that upgraded lithium mineralization to economic grades. In addition, during this magmatic-hydrothermal process, volatiles not only sustained prolonged fractional crystallization but also effectively extracted and transported lithium, ultimately facilitating the attainment of economic grades. These findings have direct implications for the exploration of similar granite-hosted lithium systems worldwide.