Geochemistry on pryite concretions from the Romanche Trench

Unconsolidated sediments are scarce or absent in this area of the Romanche Valley. Some of the sulfide concretions were transformed into Fe hydroxides by the action of seawater.

The major element, trace metal, rare earth element and sulfur isotopic chemistry of these concretions suggest that they were deposited from Fe- and S-bearing hydrothermal solutions at or beneath the seafloor. These findings support the hypothesis that oceanic fracture zones are the locus of metallogenesis. Heat flow patterns suggest deep sub-seafloor hydrothermal circulation in the highly fractured offset zones.