Magmatic and hydrothermal superimposition in Nb-Ta-Li mineralization at the Hailuoling deposit, South China: Records from columbite-tantalite chronology and mica chemistry

The Hailuoling Nb–Ta deposit in the Wuyi metallogenic belt of South China represents a typical granite-related rare-metal system that has recently been recognized to host associated Li mineralization. To constrain its metallogenic evolution, we integrate petrological, geochronological, and geochemical data. LA–ICP–MS U–Pb dating of monazite and columbite–tantalite indicates that the porphyritic biotite monzogranite crystallized at 147.2 ± 1.9 Ma, whereas Nb–Ta mineralization occurred at 144.4 ± 2.1 Ma, both during the Late Jurassic–Early Cretaceous transition. Li-bearing micas including protolithionite, zinnwaldite, lithium phengite, and lithium muscovite, in mineralized granite replace primary biotite, feldspar, and quartz and display irregular grain boundaries and well-developed compositional zoning, providing textural evidence for hydrothermal metasomatism. Mica compositions define a systematic evolutionary trend characterized by increasing SiO 2 and decreasing FeO contents, while trace element data reveal an initial enrichment followed by depletion of Li, Nb, and Ta. These features support a two-stage model involving an early post-magmatic hydrothermalism stage followed by a later hydrothermal metasomatism stage. Hydrothermal micas are characterized by Nb/Ta ratios of 0.5–2.5 and K/Rb ratios of 8–12. Comparative analyses with micas from unmineralized granites and from the Maoping and Xianghualing deposits highlights the necessity of overprinting by late-stage magmatic–hydrothermal fluids, in combination with external fluid input, to achieve economically significant rare-metal enrichment in early intrusions that did not independently reach ore-forming thresholds. We conclude that the interplay between magmatic differentiation and hydrothermal overprinting is critical for the mobilization and concentration of rare metals in certain granitic systems.