The last three Nautile dives – with Arnaud, Florian and Bleuenn – were located on the west, east and north flank of a massive bulge that corresponds to a lift of rocks from the terrestrial mantle (under the oceanic crust) to the South of the exploration licence.
This type of environment is favorable to the presence of serpentinites, characterized by their greenish color. These serpentinites are the results of mantle rocks alteration, called peridotites, by seawater circulation and hydrothermalism.
Several faults intersect this bulge. A dredge sampled a wall of one of this fault, and over 1.2 tons of rocks came back on board! Numerous blocs were strongly altered volcanic rocks.
Others were composed of quartz with surface mineralization. After a quick cut with the rock saw, bingo! Iron and copper sulfide minerals formed at high temperature (pyrite, chalcopyrite, bornite…) confirmed that along this fault, hot hydrothermal fluids (>300°C) have circulated and formed mineralized quartz veins.
Between diving and dredging operations, Carla tries to locate acoustic echoes in the water column with the multibeam echosounder that could correspond to hydrothermal plumes. Several echoes have been spotted at the summit of the neo-volcanic ridge, in a similar geodynamic context of the Snake Pit site, and could be a hydrothermal plume.