Abstract: Iron is the main valuable element of Bolivia Mutum iron ore， iron grade in the ore is 57.84%. More than 99% of the iron exists in the magnetite， hematite and limonite. The harmful impurity Si and Al in the ore is slightly higher， and it is distributed in minerals such as quartz， silicate minerals and gibbsite. Ore structure has massive structure， porphyritic structure and disseminated structure. Ore texture mainly includes porphyric structure， inclusion structure， granular structure， residual-skeletal structure， pseudomorphic structure. Hematite is usually irregularly in granular form and sparsely disseminated in gangue minerals. Martite is porphyritic and contains a lot of gangue inclusions in the phenocryst， and it is coexisted with locally untransformed magnetite. Magnetite is mostly idiomorphism and subhedral shaped grain， and it is often metasomatized by hematite to form residual-skeletal structure. Limonite is porphyritic closely intergrowth with ferric clay. The disseminated grain size of iron minerals is inhomogeneous. Part of iron minerals contain fine quartz and sericite， which are difficult to dissociate even through fine grinding. So the gangue minerals associated with iron minerals enter iron concentrate and affect concentrate grade. More than 77% of the magnetite， hematite and limonite in the ore can be liberated when the grinding fineness is -0.074 mm accounting for 85%. However， the liberation degree of iron mineral is not significantly increased when grinding fineness is increased. As a result， the grinding fineness with -0.074 mm accounting for 85% should be selected for separation.

Key words: Iron ore, Process mineralogy, Dissemination characteristics, Liberation degree