Around 60 % of molybdenum worldwide comes from porphyry copper deposits in which the concentration of molybdenum as a secondary mineral varies from 0,01% to 0,50%. The obtained molybdenum is relevant for the metallurgical industry as it is used as metal alloy in stainless steels due to its resistance to high temperatures and corrosion.In porphyry copper deposits mining, copper and molybdenum bearing ores are jointly floated in a bulk concentrate using mainly sulfidic collectors. Sodium hydro sulphide (NaSH) is then preferably used as a depressing agent for the differential flotation separation of copper and molybdenum carrying minerals. NaSH produces a partial desorption of the initial collector from the surface of the copper-bearing minerals and an apolar collector is added to selectively collect the molybdenite. The separation of these two minerals, mainly chalcopyrite and molybdenite, is carried out under conditions that make this process dangerous due to the risk of creating HS gases, requiring the use of HS sensors and breathing apparatus. Because of these gases' high toxicity, alternative reagents are being assessed in order to make this process safer. In this study, thiourea's (TU) effect is evaluated as a chalcopyrite depressant. The depression mechanism is evaluated through zeta potential measurements in pure chalcopyrite and molybdenite minerals; contact angle measurements depending on the pH in pure surfaces and modified by the reagent (TU) were performed using the captive bubble technique. Flotation efficiency was evaluated through depressant selectivity, reflected in the values of concentrates produced and recoveries of ores of interest in concentrates and tailings through Partridge Smith micro-flotation cell tests.