Abstract: This study selected typical fluorite−rich Bayan Obo tailings and conducted systematic process mineralogy investigations. By comprehensively employing various characterization techniques, including chemical composition analysis, X−ray diffraction, Advanced Mineral Identification and Characterization System, electron probe scanning electron microscopy, mineral liberation analysis, and laser particle size testing, the mineral composition, elemental distribution, and dissemination characteristics of this ultrafine−grained tailings system were precisely revealed for the first time. The results indicate that the valuable elements in the tailings sample are mainly CaF₂, followed by REO, with contents of 45.24% and 1.23%, respectively; The useful minerals are mainly fluorite, with bastnaesite and monazite as secondary components, with mass fractions of 37.55%, 3.66%, and 2.70%, respectively. The ore sample exhibits significant fine particle characteristics, with the −74 μm fraction accounting for 99.70% of the total, and the −25 μm fraction making up 79.20%. The distribution rates of CaF₂ and REO are 78.92% and 83.71%, respectively. The fluorite shows a relatively high single dissociation degree of 87.96%, primarily occurring in semi−automorphic to euhedral granular structures. However, it often forms dense associations with gangue minerals such as barite, apatite, and dolomite, and is frequently enveloped by rare earth minerals, resulting in complex spatial configurations. The rare earth minerals, bastnaesite and monazite, have slightly lower single dissociation degrees compared to fluorite, at 69.89% and 79.43%, respectively. These minerals mainly occur in association with fluorite and, in some cases, form complex intergrowths with gangue minerals. The aforementioned fine particle characteristics and intricate dissemination relationships make conventional flotation separation challenging. This study provides critical mineralogical evidence for the comprehensive recovery and utilization of fluorite resources from the Bayan Obo fine−grained tailings in subsequent stages.