A radiochemical study was carried out on massive sulfides from three hydrothermal fields in the Mid-Atlantic Ridge. The main objective was to check whether ²³⁰Th/U dating yields reliable results. The absolute ²³⁰Th/U ages of massive sulfide samples of three hydrothermal fields at the Mid Atlantic Ridge were determined 58.2±4.2 ka and 16.8±1.0 ka for the "Logatchev-1" site, 3.9±0.4 ka for the "Logatchev-2" site and 23.0±1.5 ka, 3.9±0.6 ka and 2.2±0.3 ka for the "Rainbow" site. The dates correspond to the activation periods of hydrothermal ore formation systems.