A radiochemical study was carried out on massive sulfides from Semyenov hydrothermal district at the Mid-Atlantic Ridge. New and published results provide evidence that 230Th/U ages ob-tained for massive sulfides are reliable. The sulfide deposits from the West, North-West, North-East, and East hydrothermal sites at the Semyenov hydrothermal district were formed between ~124 ka and ~37 ka ago. The hydrothermal activity might have started in the eastern part of the district and moved to the west by episodic ore formation.