Metallogenic process of the metasedimentary rock-hosted HREE deposit at Guangshui (Hubei Province, Central China)

Guangshui (Hubei Province, Central China) is an exceptional heavy rare earth element (HREE) deposit that occurred within a series of metasedimentary rock (e.g. leptynite). This study integrates detailed petrography with in situ U-Pb geochronology, Nd isotope systematics, and mineral chemistry of the principal REE phases—gadolinite, fergusonite, monazite and xenotime—to reconstruct the timing, sources and mechanisms of mineralization. Two generations of each mineral are recognized on the basis of crystal habit and paragenesis: Gad-I/II, Fgs-I/II, Mnz-I/II, Xtm-I/II. U-Pb dating of Mnz-I yields an age of 239 ± 13 Ma, while Xtm-I records 210 ± 6 Ma. These ages coincide with prograde and retrograde stages of Triassic high-grade metamorphism in the Dabie orogen, underscoring a direct link between regional metamorphism and HREE mobilization. Petrological observations indicate that the Mnz-I marks the crystallization of the earliest HREE assemblage (Fgs-I + Gad-I), whereas Xtm-I brackets the final stage of HREE mineralization. Geochemical variations between the two mineral generations are evident. Mnz-I and Mnz-II exhibit low Th contents, consistent with a hydrothermal origin. Mnz-II is spatially associated with Xtm-II, and its pronounced HREE enrichment coincides with HREE depletion from Xtm-I to Xtm-II, suggesting that Xtm-II formed via alteration of Xtm-I. Positive Ce anomalies in Fgs-I and Gad-I suggest crystallization under oxidizing conditions. Combined with petrological evidence and geochemical variation, the composition of Gad-II may have affected by coeval hydrothermal zircon crystallization. For Fgs-II, hydrothermal alteration likely facilitated substitution of LREE and Ca for HREE and Y at the A-site. Nd isotope compositions of Mnz-I (ε_Nd(t) = −5.1 to −5.6; T_DM2 = 1.38–1.43 Ga) and Mnz-II (ε_Nd(t) = −4.8 to −5.8; T_DM2 = 1.38–1.45 Ga) indicate a crustal source for the ore-forming materials, most likely derived from Mesoproterozoic rocks. Regionally, the phosphorus-rich Huangmailing Formation and Triassic metamorphism played critical roles in HREE enrichment. Overall, the Guangshui deposit exemplifies HREE mineralization controlled by metamorphism and fluid–rock interaction during continental collision, firmly tying its metallogenesis to the Triassic evolution of the Dabie orogen.