The Use of Surface Analysis Techniques and Isotope Mass Spectrometry for the Study of Water-Rock Interactions of Interest in Hot

Abstract

The surface composition of a sanidine feldspar has been analyzed using mass spectrometry after its interaction with a dilute HCI solution, containing isotopically enriched powder. Relatively thick K, Na and AI-depleted surface layers are observed in sanidine after laboratory dissolution experiments in dilute acid solutions. The molar ratios of the elements released to the solution, however, do not correspond to the theoretical formula of the solid. This incongruent dissolution can either be explained by the preferential leaching of the above-mentioned elements from the solid, or by assuming a congruent dissolution followed by the preferential precipitation of certain elements Si) from the solution. Using enriched silicon isotopes in the experiment, isotopic measurements of both mineral and solution indicate that both processes occur.