Hydrothermal Mineralization in the Sierra Leone Fracture Zone (Central Atlantic Ocean)

The analysis of data on the location of hydrothermal fields, seismicity, and satellite altimetry evidences that in mid-ocean ridges with low spreading velocity hydrothermal fields tend to be grouped in areas with generally low seismic activity and at intersections of discontinuities and rift zones. Based on this assumption, the Sierra Leone Fracture Zone was studied in 2000 during cruise 22 of the R/V Akademik Nikolaj Strakhov.The study of gabbrodolerite and dolerite showed that sulfide ore minerals in them were formed both by hydrothermal and magmatic processes. The analysis of melt inclusions demonstrated that magmatic complexes formed from a high-temperature (1210–1255°C) low-potassium melt of the N-MORB type. Investigations of fluid inclusions revealed that gabbro and dolerite formed under the influence of an active hydrothermal system at a temperature of 205–226°C. Thus, the Sierra Leone Fracture Zone is considered to be perspective for the discovery of a new hydrothermal field.