Geochemometric modeling and geothermal experiments of Water/Rock Interaction for the study of alkali-feldspars dissolution

Abstract

Listen

Translate article

Water/Rock Interaction (WRI) experiments, Na–K geothermometry and geochemometrics modeling have been used for the study of the kinetic behavior of the volcanic rock dissolution under geothermal conditions. Ionic exchange reactions between Na–K and alkaline-feldspar minerals were monitored at 90 °C and 150 °C for a period of nearly 24 and 3 months, respectively. Na/K ratios (inferred from WRI experiments and Na–K geothermometers) and reaction times were used for estimating the most probable quasi-steady state conditions.A geochemometrics modeling was also performed to predict the reaction times required to achieve quasi-steady state conditions in the WRI experiments. This modeling was validated with WRI experimental data reported in the literature for which quasi-steady state conditions were known with accuracy. New WRI experiments were additionally carried out using batch reactors under controlled pressure and temperature conditions. Volcanic rock (basalt and dacites) crushed samples (500–1000 μm grain size) were reacted with distilled water at 90 °C and 150 °C using a W/R mass ratio of 5. Rock and fluid samples were collected and analyzed for major composition, before and after each experiment. The experimental results were subsequently used to calculate log(Na/K) values for describing the kinetic behavior of the alkaline-feldspar mineral dissolution. Values of log(Na/K) and reaction time at quasi-steady state conditions were reproduced with good accuracy by using the rational polynomial and logarithmic transformation regression models. These results were compared with those values inferred from the Na–K geothermometry, which theoretically assume deep geothermal equilibrium conditions.