Nanfen BIF（Banded iron formation） is one of the important iron deposits in the Anshan—Benxi area, which is distributed in a laminate or quasi laminate manner in the ore- bearing rock series of the Cigou Formation of the Neoarchean Anshan Group. It is composed of three iron ore bodies, Fe1, Fe2, and Fe3, from bottom to top. Based on mineral assemblage and paragenesis, the evolutionary phases of mineralisation can be divided into five phases: ① primary depositional, ② diagenetic, ③ regional metamorphism and deformation, ④ hydrothermal transformation and ⑤ supergene oxidation stages. The natural types of ore are mainly magnetite quartzite, tremolite magnetite quartzite, hematite magnetite quartzite and hematite quartzite. This study devotes to ascertain the characteristics of oreforming fluids and further understand the ore genesis of the Nanfen iron deposit.Methods: Based on field investigation and indoor microscopic study, the petrographic observation, microthermometric measurements on the fluid inclusions hosted in different stage quartz from the Nanfen BIF, were systematically carried out in this study.Results:The petrographic results of fluid inclusions show that there are mainly three types of inclusions developed in Nanfen iron ores: type- Ⅰ secondary fluid inclusion, type- Ⅱ primary fluid inclusion (including type- Ⅱa liquid- rich two- phase inclusion and type- Ⅱb vapor- rich two- phase inclusion), type- Ⅲ CO2- rich three- phase fluid inclusion. The results show that two kinds of fluid inclusions formed in the peak stage of epidote—amphibolite facies metamorphism: type- Ⅱb vapor- rich inclusion and Ⅲ- type three- phase inclusion containing liquid CO2. The homogenization temperatures of these inclusions range from 283.2 ~ 423.5 ℃ and salinity values vary in the range of 3.39% ~ 9.47% NaCleqv, indicating that the metamorphic fluid is characterized by high temperature and low salinity. Two kinds of fluid inclusions formed after the peak stage of epidote—amphibolite facies metamorphism: type- Ⅱa liquid inclusion and type- Ⅰ secondary fluid inclusion.The homogenization temperatures of these inclusions range from 191.3 ~ 308.8 ℃ and salinity values vary in the range of 2.24% ~ 10.67% NaCleqv, showing broad ranges. Conclusions:The characteristics of fluid inclusions combined with other geologic evidence reveal that the Nanfen iron ores were reformed by metamorphism after their formation and probably have afeature of multiple periods.