Tetragonal shape of Cu2S in recent hydrothermal deposits

The samples studied through this research were collected from active black smokers located in the mid-oceanic ridge from a depth of 2276m by a sea-born ship “Academician Mstislav Keldysh”(2002), in its 47th research mission. The collected samples were studied by microscopic, microprobe and X-ray analysis (Debye-sherer). These samples were in the form of narrow pipes with zoned structure, which included the following zones from the core to the margin: isocobanite, Chalcopyrite, Bornite and cupper sulfide zones. For the first time, it has been observed that tetragonal phase within the cupper-sulfide zone in recent sulfide, deposits. Tetragonal phase of Cu2S, which is an unstable form of chalcocite, is stable only at high pressures (more than 0.8 Kb) and temperatures higher than 102 oC. The tetragonal form of Cu2S in one of the studied samples was associated with Chalcocite-Djurleite mixture and in another studied sample was associated with chalcocite-Bornite mixture. Its average chemical composition was also determined as Cu2.02S. It is likely that the emergence of this unstable phase in young hydrothermal deposits, which are formed at 250-350 oC, is not odd but after hydrothermal activity and temperature reduction it is changed to more stable phases. Evaluation of older black smokers showed no trace of tetragonal phase.