Results of the chemical analyses made on the post-experiment fluids are shown in Table 1. Only the four relevant major elements are shown since all other elements such as Fe, Ni and K were below detection limits. Si concentration is clearly temperature dependent, varying from 5 ppm at room temperature to nearly 300 ppm at 275°C. When ln(Si) is plotted against the inverse of temperature (in Kelvin), it is clear that Si solubility is controlled by an Arrhenius function (Figure 7a). Furthermore, these measured silica concentrations are very similar to those determined experimentally for de-ionized water in equilibrium with quartz [Dove, 1995]. Al concentration shows a less well defined temperature dependence relative to silica (see Table 1), with concentrations that are much lower, only reaching about 9 ppm at high temperature. The Ca and Na concentrations do not show any systematic change with temperature (Table 1). Si and Al concentration also appear to be stress dependent. Concentrations are positively correlated at low deviatoric stresses before leveling off at a deviatoric stress of about 50-60 MPa (Figure 7b, Table 1). Such stress dependent changes to fluid composition have been observed in other similar flow-through experiments [Elias & Hajash, 1992]. Ca and Na concentrations do not exceed 4 ppm and 12 ppm, respectively, and are not stress dependent.

When the chemical data presented above are compared to the permeability data, a distinct correlation between the two is revealed. On figures 7c and 7d are the cumulative permeability reduction at the end of each experiment plotted against the inverse of temperature and maximum effective stress, respectively. As with the variable temperature Si data, total permeability reduction exhibits an Arrhenius relationship when plotted against temperature (Figure 7c). Permeability reduction also shows a dependence on stress up to 50 MPa after which little change is observed (Figure 7d). This stress and temperature dependence is remarkably similar to that for the Si concentration data. The fact that fluid chemistry and permeability data follow near identical trends when plotted against temperature and stress suggests that the permeability reduction process is closely linked to the system's chemical evolution.

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