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Thermodynamic model of the hydrolysis of microcline in acid-sulfate solutions

Description: A theoretical model of the hydrolysis of microcline by a hydrothermal solution has been determined for a closed system at constant temperature. Hypothetical solution compositions and temperatures were chosen to match the known geothermal system at Roosevelt Hot Springs, Utah. The calculated reaction paths indicate that the overall reaction process is an exchange of potassium from the reactant mineral, microcline, for hydrogen from the solution. Aluminum is nearly conserved among solid phases. The amount of microcline reacted per kilogram of solution before overall equilibrium is reached is a function of temperature and inituial solution pH. Since the system is closed and at constant temperature natural conditions are not reproduced well enough to apply the model as a geothermometer. The reaction paths suggest qualitative models of alteration mineral zoning patterns that are similar to zoning at Roosevelt Hot Springs, Utah; Steamboat Springs, Nevada, and Butte, Montana. The models presented view alteration zoning as a function of temperature and pH gradients within homogeneous host rocks where microcline and quartz are abundant.
Date: December 1, 1976
Creator: Dedolph, R.E. & Parry, W.T.
Partner: UNT Libraries Government Documents Department

Physicochemical basis of the Na-K-Ca geothermometer

Description: Regular changes in solution composition were observed experimentally during granite reaction with dilute NaCl (+CaCl/sub 2/) solutions; these changes closely follow the empirical Na-K-Ca geothermometer relationship. Initial minerals forming the granite (quartz, plagioclase, K-feldspar, and biotite) were etched by the reactions. Alteration phases formed include calcium-zeolite at <300/sup 0/C, feldspar overgrowths at >300/sup 0/C, and minor amounts of clay and calcsilicate at all temperatures. Amphibole overgrowths were also found at 340/sup 0/C. Quartz is near saturation in all experiments, and preliminary calculations of aqueous species distributions and mineral affinities indicate that the solutions achieve super-saturation with feldspars as the temperature increase. A consistent variation attributable to pH differences was observed in the empirical geothermometer relationship for all experimental data. At 340/sup 0/C, the experimental solutions appear to have deviated slightly from the empirical Na-K-Ca relationship. Such deviations may also be found in natural systems that attain such temperatures.
Date: August 1, 1986
Creator: Janecky, D.R.; Charles, R.W.; Bayhurst, G.K. & Benjamin, T.M.
Partner: UNT Libraries Government Documents Department