Abstract: Abstract:The REE content in fluid inclusions of minerals in the Koktag lead-zinc deposit was determined by the ICP-MS. The results indicate that the ore fluids are LREE-enriched and have pronounced positive Eu anomalies. Ore sulfide fluid inclusions have three REE distribution patterns, i.e. gently right-inclined type, flat type and inverted “V” type. The total REE content of the footwall rocks of the orebody is notably higher than that of the hanging wall rocks, and they have pronounced negative Eu anomalies. The ore-forming fluids have the features of multiple sources and multi-stage overlapping and show the feature of the double leaching model.