Occurrence of niobium in biotite-type Fe-REE-Nb ore in the Bayan Obo deposit

The Bayan Obo REE-Nb-Fe deposit, which reserves the current largest REE resources globally, also hosts 63.4% of China's Nb resources. Previous studies mainly focus on the isotopes and petrographic mineralogy of carbonatite dyke, ore-host dolomite and rare earth ore in Bayan Obo deposit, niobium mineralogy is comparatively insufficient. In order to promote the utilization of niobium resources in the Bayan Obo deposit, we focus on the petrological and mineralogical study on the biotite-type Fe-REE-Nb ore of West Mine, by scanning electron microscope (SEM), X-ray energy spectrum (EDX) imaging and micro-XRF scan. From the analysis, we observe that 1) this type of ore shows relative enrichment in niobium, and the size of niobium-bearing minerals up to 1 mm; 2) the niobium mineral composition are extremely complex, with main niobium minerals including aeschynite, fergusonite and columbite and minor niobium minerals ilmenorutile and baotite; 3) REEs are mainly distributed in monazite, bastnaesite and aeschynite and the particle size of the first two is relatively fine; 4) aeschynite occurring as large aggregates maybe the hydrothermal in origin and fluid–rock interaction leads to the aggregation of biotite and the precipitation of niobium-bearing minerals. This study on biotite type Fe-REE-Nb ore has important insights for mineral processing and directive significance on niobium prospecting in the Bayan Obo deposit.