Mineralization processes in the Yaotoushan rare metal deposit in northern Mufushan batholith, central China: Constraints from geochronology and mineralogy

Abstract

The Mufushan area in central China represents a major concentration zone for rare metal ores. It has undergone a complete magmatic-hydrothermal evolutionary process, leading to the widespread distribution of pegmatite deposits. However, the genetic link between large batholith magmatism and rare metal mineralization remains unexplored, limiting the establishment of ore-forming models for such batholiths. The newly identified Yaotoushan rare metal deposit occurs at the contact between two-mica granite and the Lengjiaxi Group on the northern margin of the Mufushan batholith. The mineralized pegmatites in this deposit are classified as microcline-albite pegmatite, amazonite-albite pegmatite, and albite pegmatite. This study investigated the mineralogical features of these pegmatite types to constrain their metallogenic ages and elucidate the magmatic-hydrothermal evolution of the Yaotoushan system. Chronological and mineralogical evidence indicated two distinct metallogenic stages. The magmatic stage (127.6 ± 0.6 Ma) was characterized by Be–Nb–Ta mineralization. Fractional crystallization concentrated Be, Nb, and volatiles in the residual melt, producing Ta-poor columbite-(Mn) and beryl. This metallogenic age was defined by the U–Pb dating of columbite-(Mn). The subsequent hydrothermal stage (123.0 ± 1.1 Ma) involved Li mineralization combined with the secondary enrichment of Be, Nb, and Ta, as determined by the U–Th-Pb_total chemical age of uraninite. The interaction between hydrothermal fluids and primary minerals markedly increased Li and F in micas and Cs in beryl, resulting in the crystallization of Ta-rich columbite-(Mn), trilithionite, lepidolite, and bertrandite. Quantitative analysis demonstrated that the transformation of beryl into bertrandite-enriched BeO was nearly threefold, confirming the critical role of hydrothermal activity in secondary rare metal enrichment. The hydrothermal fluid composition (Li, F, Cs, Ta) was consistent with the evolutionary trend of pegmatite melts, indicating derivation from late-stage magmatic fluid exsolution. Metasomatic processes facilitated the Be–Nb–Ta–Li mineralization. Additionally, a comparison with global LCT-type pegmatites suggests that the Yaotoushan deposit exhibited a similar degree of evolution and therefore possessed significant metallogenic potential for rare metals.