Abstract

We have measured the pH and aqueous concentrations of F, K, Al, and Si in quenched solutions that were buffered by the following topaz-bearing assemblages at 400 degrees to 700 degrees C and 1 kbar: (1) andalusite-topaz-quartz, (2) andalusite-muscovite-topaz-quartz, (3) sanidine-muscovite-topaz-quartz, and (4) andalusite-sanidine-topaz-quartz. Total fluoride concentrations range from about 0.0035 molal for the andalusite-topaz-quartz assemblage at 400 degrees C to about 0.20 molal for the muscovite-absent assemblages at 700 degrees C. At high pressures and temperatures, much of the fluoride is complexed by silicon; concentrations of HF and KF are relatively low. Aluminum appears to form a fluoro complex, but the evidence is somewhat ambiguous due to a lack of data from less complex systems and to possible competing reactions.Additional experiments were carried out to determine the effect of fluoride on the stability of muscovite in 1 molal chloride solutions. Our results indicate that the stability of muscovite in terms of (K/H) ratios is not expanded significantly by the fluoride concentrations fixed by the above topaz-bearing assemblages.

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