Sm–Nd isotopic constraints on rare-earth mineralization in the Bayan Obo ore deposit, Inner Mongolia, China

Sm–Nd isotopic measurements were undertaken to constrain the chronology of REE mineralization events (REE = rare-earth elements) at the Bayan Obo REE–Nb–Fe deposit in northern China. The earliest REE mineralization event was dated precisely using samples of coarse-grained dolomite from the Bayan Obo Orebodies and the carbonatite dikes in their vicinity, which yielded a Sm–Nd isochron age of 1286 ± 27 Ma. The Sm–Nd data indicate that during this early event, the rare-earth elements were sourced from the mantle. A significant thermal event at ca. 0.4 Ga resulted in the formation of late-stage veins with coarse crystals of REE minerals. REE mineralization developed during this event resulted from REE remobilization within the ore-bodies with minimal contribution from external sources. A series of ages between 1.3 and 0.4 Ga reported for Bayan Obo ores in some previous studies resulted from thermal disturbance and do not imply the existence of multiple events.