Abstract:Shifang-type phosphorite deposit is an important type of phosphorite deposit in China, which is characterized by large scale, high phosphorus grade, and enrichment in rare earth elements (REEs). However, the enrichment regularity and resource potential of REEs in this type of deposit are not studied in detail. This study takes the typical Shifang-type phosphorite deposit in Mianzhu, Sichuan Province, as the research object. Based on field geological investigation, the distribution and enrichment characteristics of REEs in the deposit are explored through microscopic petrographic observation, scanning electron microscope/energy disperse spectroscopy imaging, and whole-rock geochemical analysis for the phosphorus-bearing layers (phosphorite layer, dark grey and maroon S-P-Al-Sr-rich layers) and their roof and floor rocks (dolomite) in the mining area. In turn, the potential resource of REEs in Shifang-type phosphorite deposits in Sichuan Province is discussed. The results showed that the total REEs (La-Lu+Y) contents in the roof and floor dolomites of the phosphorus-bearing layers are very low (13.6×10-6 on average), the REEs contents in the phosphorite are medium (280.0×10-6 on average), while the REEs contents in the S-P-Al-Sr-rich layers are extremely high (2 053.9×10-6 on average), especially the maroon S-P-Al-Sr-rich layer (up to 3 257.2×10-6). Together with previously published REEs content data from adjacent phosphorite deposit, the average REEs content in S-P-Al-Sr-rich layers in the Shifang-type phosphorite deposits in Sichuan Province is 2 259.4×10-6 with the maximum up to 3 286.8×10-6, of which the average concentration of medium and heavy REEs (Sm~Lu+Y) is 1 276.9×10-6 with the maximum up to 2 213.0×10-6, accounting for 55.1% of the total REEs. REEs contents in the Shifang-type phosphorite deposits in Sichuan Province are much higher than those in ion adsorption-type REEs deposits in southern China, Zhijin REEs-bearing phosphorite deposit, and REEs-rich deep-sea sediments. According to preliminary estimates, the total potential REEs resources associated with the Shifang-type phosphorite deposits in Sichuan Province can reach 252 000 tons, 156 000 tons of which are medium and heavy REEs. The potential medium and heavy REEs resources in the S-P-Al-Sr-rich layer alone can reach 96 000 tons. Therefore, the Shifang-type phosphorite deposits in Sichuan Province have important economic and social value, and the development and utilization of REEs in these deposits are expected to alleviate the current shortage of medium and heavy REEs in China.