An Experimental Study of the Stability Relations, Na-K Exchange, and Isotope Exchange Properties of Jarosite at 200oC and Above

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In this study, experiments will be conducted to determine the position of the jarosite and natrojarosite stability fields as functions of the H2SO4-K2SO4 and H2SO4-Na2SO4 Concentration in the coexisting aqueous phase. Experimental Temperatures will range from 200oC to the upper stability limit of jarosite and natrojarosite, which is expected to be below 450oC. In addition, the partitioning of sodium and potassium between jarosite and aqueous sulfate solutions, the D fractionation between the hydroxyl sites of jarosite and water, and 18O fractionation between the jarosite hydroxyl and sulfate sites and water will be measured. These experiments, which will be conducted in standard cold-seal hydrothermal vessels at a pressure of 500 bars, are an extension of work in progress on alunite to a ferric-iron bearing system. They should improve our ability to interpret isotope data on acid-sulfate alteration, which frequently includes both alunite and jarosite. In addition, they will help to constrain the chemical and isotope systematics of jarosite at lower temperatures, and thus complement ongoing studies of jarosite at 25oC. A better understanding of the properties of jarosite at surficial conditions will be important in the study of acid-mine drainage, and also in the interpretation of natural weathering and oxidation of pyritic ore deposits.