Mineralogical characteristics of Huangshan granites (Anhui, China) and their implications for rare-metal mineralization

Ferberite, rossovskyite, and columbite-(Fe) have been identified within the Huangshan pluton through the crystal structures refinement (a) and Raman spectra characterization (b). • The Huangshan granites exhibit distinctive features of rare-metal mineralization. • Magmatic Nb–Ta mineralization and oxidized hydrothermal W–(Sn)–Be mineralization. • Ta-rich end-member rossovskyite was first discovered. • Raman spectra of Nb-Ta-W-bearing oxide minerals are compared. • A new example within the rare-metal mineralized zone of Jiangnan orogen. The Huangshan pluton in the Huangshan (Yellow Mountains), southern Anhui Province, China, comprises three main lithological units: coarse-grained porphyritic biotite granite (CPG), medium-grained porphyritic biotite granite (MPG), and fine-grained porphyritic biotite granite (FPG). Based on their tectonic setting and geochemistry, these are highly evolved A-type granites. Although rare-metal mineralization remains undocumented in this pluton, we identified significant enrichment of rare-metal elements and minerals in the Huangshan granites. Typical accessory minerals in these granites include Li-bearing micas (specifically Li-siderophyllite), topaz, Nb–Ta–W–Sn oxide minerals, and beryl, all of which are characteristic of rare-metal granites. Zircon U–Pb age data confirm that all three units formed during 131–128 Ma. Integrated with the whole-rock trace-element geochemical trends (i.e., progressive increased Li, Rb, Cs, and Nb, and depleted rare earth element) from CPG through MPG to FPG, the Huangshan granites record continuous magmatic differentiation. Moreover, the FPG exhibits the highest degree of magmatic differentiation, as evidenced by Li-siderophyllite with elevated Li–F contents, columbite-group minerals (CGMs) with high Ta# values (atomic Ta/ [Nb + Ta]), and abundant topaz. A suite of Nb–Ta–W–Sn oxide minerals, including ferberite, rossovskyite, columbite-(Fe), and cassiterite, has been identified within the Huangshan pluton through single-crystal X-ray diffraction, electron probe microanalysis and Raman spectra characterization. Rossovskyite, which has high Fe ox values (atomic Fe 3+ / [Fe 3+ + Fe 2+ ]; up to 0.70) and has only previously been documented in Mongolian Altai pegmatites, was discovered in the studied rare-metal granites; while CGMs have low Fe ox values (<0.2 in the CPG and MPG; <0.31 in the FPG), and ferberite and cassiterite have high Fe ox values (0.33–0.47 and 0.34–1.00, respectively). These oxide minerals formed by magmatic–hydrothermal processes under changing redox conditions. Magmatic CGMs crystallised during the late-stage magmatic evolution. Subsequently, W-rich oxidised hydrothermal fluids induced the transitions from Fe 2+ to Fe 3+ and from Sn 2+ to Sn 4+ , which triggered the precipitation of rossovskyite and cassiterite. Abundant alkali-poor and H 2 O-poor beryl occurring in the ferberite-bearing samples record Be enrichment in the oxidized hydrothermal fluids. These results confirm the presence of magmatic Nb–Ta mineralization and subsequent hydrothermal W–(Sn)–Be mineralization in the Huangshan pluton. Moreover, evidence from this pluton provides crucial support for a potential genetic relationship with the nearby Huangshidang W ore occurrences. Together with the Lingshan and Suzhou plutons, the Huangshan pluton constitutes an additional example within the rare-metal mineralized zone of Jiangnan orogenic belt.