Replacive formation of sulphides in the oceanic lithosphere and the effect on rock porosity evolution

This thesis describes the replacive formation of sulfides in the oceanic lithosphere through the interplay of discharging hydrothermal fluids and seawater. Chemical and 3D analyses on sulfate chimneys showed that anhydrite precipitation and corrosion likely control porosity and sulfide formation in the chimney conduit. Batch experiments using several oceanic lithologies and a synthetic, H2S-bearing vent fluid showed that sulfide root zones were more easily formed in less reducing rock types where sulfur activity was highest. The onset of anhydrite growth in fractured basalt in a flow-through experiment was found to be only possible at temperatures above 120 degrees C and was accompanied by many Fe-bearing phases in the basalt core. The results of this thesis stress the importance of porosity for sulfide formation in hydrothermal processes.