ABSTRACT

To simulate the discharge zone of hydrothermal systems in the laboratory, we developed a flow-type hydrothermal apparatus that can reproduce water-rock reactions at elevated temperatures and pressures under flow-through conditions and also the mixing of hydrothermal fluids with seawater. Using this apparatus, basaltic rocks were reacted with ultra-pure water at 340°C and 40 MPa for 1271 h under flow-through conditions. An increase in Al, Fe, K, Na, P and Si in the reacted water was observed during the experiment, reproducing the process of dissolution from the basaltic rocks. An increase in pH to 9 during the experiment can be attributed to the dissolution of silicate minerals in the basaltic rocks. That the pH in the experiment is higher than the pH observed in natural hydrothermal fluids at mid-ocean ridges is a result of higher Si concentrations observed in the experiment than those of natural hydrothermal fluids.