The Tuomoerte Fe-(Mn) deposit occurs in metavolcanic-sedimentary sequence within the upper subformation of Upper Silurian-Lower Devonian Kangbutiebao Formation. The vapor and liquid composition of fluid inclusions in this period show that the ore-forming fluid was rich in Na⁺, Cl^- and H₂O, indicating that the ore-forming fluid was of moderate-low temperature, moderate-low salinity and moderate-low density, belonging to the H₂O-NaCl system. The oxygen and hydrogen isotopic characteristics of quartz imply that the ore-forming fluid in the volcano-sedimentation period was derived from mixed magmatic water and seawater, whereas the ore-forming fluid in the regional metamorphism period was derived from mixed metamorphic water and meteoric water.