In the massive sulphide deposits of the eastern Black Sea region, there are ore facies and ore-bearing sedimentary facies. The former are subdivided into hydrothernial-metasomatic, seafloor hydrothermal, and biological facies. Hydrothennal-metasomatic facies refer to sub-seafloor processes and include network-disseminated, massive vein, and massive lens facies. The precipitation of sulphide minerals within pre-existing volcano-sedimentary rocks occurs largely beneath the seafloor, and these ores form an important component of some deposits. The term seafloor hydrothermal facies refers to sulphide accumulation on the seafloor and is characterised by hydrothermal chimneys and clastic sulphide ores. Clastic sulphide ores can be subdivided into proximal and distal facies. Ore-bearing sedimentary facies are characterised by relatively thin ferruginous chert (exhalite?) beds that occur along the uppermost part of the ore horizon. The biological facies is represented by fossil vent fauna, which are diagnostic for seafloor sulphide formation.