Experimental simulations of basalt-fluid interaction at supercritical hydrothermal condition (400 °C-500 bar)

Two experimental simulations of basalt-fluid interaction under supercritical hydrothermal conditions have been carried out to examine the relationship between fluid and secondary mineral compositions with respect to pressure-temperature conditions and time. Fresh basalt was reacted with distilled water and geothermal brine at 400 degrees C, 500 bar using a flow-through high P-T hydrothermal apparatus. Results indicate that high silica concentrations, which reached quartz saturation, early in the experiments are due to the dissolution/devitrification of volcanic glass. Low pH is attributed to the release of sulfur from the glass. In the basalt-distilled water experiment, an assemblage of grossular - amphibole (possibly actinolite) - diopside was identified while in the brine experiment hornblende - biotite appeared as secondary phases. Fluid compositions are reasonably consistent with known mineral equilibria implying that reaction rates are extremely rapid at these conditions. (C) 2017 Published by Elsevier B.V.