Mineralization of the Bayan Obo Rare Earth Element Deposit by Recrystallization and Decarbonation

Abstract The genesis of the Bayan Obo giant rare earth element (REE) deposit has been debated for several decades. Here, we report isotopic effects dynamic recrystallization in H8 carbonatite, which is principal ore carrier deposit. We studied fresh drill core to a depth 1.78 km and documented elemental C-O-Sr isotope evolution rock-forming dolomite during its deformation reaction with fluids. precursor products differ δ13CVienna-PeeDee Belemnite (V-PDB) (–1.09 2.37 vs. –3.59 0.79‰, respectively) 87Sr/86Sr (0.70241–0.70394 0.70288–0.71409, respectively), show similar δ18Ovienna-standard mean ocean water (V-SMOW) range (10.3–16.9‰). strong negative shift δ13CV-PDB indicates that, locally, there was as much 40% loss CO2 from dolomite, although most recrystallized experienced decarbonation on smaller scale. Clumped monazite grains associated apatite paragenetically samples yielded variable situ Th-Pb dates (980–340 Ma), whereas those monomineralic veinlets give consistent age ~400 Ma initial Nd ratios. This that wide may not represent real REE depositional events primary minerals deposited Mesoproterozoic underwent reequilibration remobilization mid-Paleozoic. Recrystallization unit were facilitated by subduction-derived silica- halogen-rich fluid, genetically linked plate-convergence processes along northern margin North China craton, did require an influx REEs external source.