Iron ore mineral processing techniques are constantly challenged with the emergence of complex gangue minerals such as amphiboles, pyroxenes and others. Magnetic separation technique that achieves good results for some richer iron ores cannot guarantee the same results for such complex ores. The flotation route allows upgrading the concentrate grade but is also challenged because of the depression of Fe-Mg-Al-bearing silicates due to the presence of metal ions on the mineral surface, which can form strong chemical complexes with starch molecules used as depressant of iron oxides. The adsorption mechanism of the principal depressants used in oxide ore flotation was investigated on chamosite (chlorite group), diopside (pyroxene group) and epidote. Since the adsorption of reagents is related to the mineral surface charge in physical adsorption systems, the electrokinetic properties of these minerals were also investigated to develop a common approach for complex iron ores processing by flotation when the gangue is presented by complex Fe-Mg-Al bearing silicates.