Initial Dissolution Behavior of Granite by Hydrothermal Solution in the Temperature Range between 200°C and 350°C

Experiments on hydrothermal dissolution of granite using the batch system autoclave were carried out in order to study water/rock interaction in subcritical water in temperature range from 200°C to 350°C. Two types of pressure conditions for experiments were examined. One is saturated vapor pressure for a given temperature, ant the other is a fixed pressure of 18 MPa at any temperatures for 200°C, 300°C, 330°C and 350°C. Dissolution behavior of major silicate minerals in the granite, such as quartz and feldspar, was estimated on the basis of fluid component of reacted solution. Pressure dependence of dissolution behavior of granite is not so stronger than temperature dependence in the subcritical temperature range from 200°C to 350°C. Dissolution rate of feldspar at 200°C, is faster than that of quartz and feldspar dissolution controls fluid chemistry. However, at higher temperatures, 300, 330 and 350°C, dissolution of quartz controls the concentration of dissolved silica. These results indicate that hydrothermal dissolution of granite was controlled by dissolution of feldspar at relatively low temperature around 200°C, and dissolution of quartz in the granite was predominant reaction under high temperature subcritical conditions above 300°C.