Alunite-Group Minerals of the Kuril-Kamchatka Suprasubduction Zone

Alunite-group minerals from various post-volcanic occurrences within the Kuril-Kamchatka suprasubduction zone, related to Alaid, Bolshoy Semiachik, Mutnovsky and Shiveluch volcanoes and Evevpenta and Vasilevo epithermal gold-silver ore occurrences, have been characterized by the combination of analytical techniques: electron-probe microanalysis, powder X-ray diffraction, and Raman spectroscopy. As a result, jarosite, alunite, natrojarosite, natroalunite and hydroniumjarosite have been found, among which natroalunite and jarosite being the most widespread. These minerals show strong genetic relation to K- and Na-feldspar, pyrite, and hematite. By chemical composition, they show a wide range of ratios for monovalent cations K/ƩM+. Regarding trivalent cations or Fe/(Fe + Al) ratio, both Fe3+- and Al-members are observed as well as rare varieties with intermediate Fe/(Fe + Al) ratios as 0.00–0.32 and 0.72–1.00. The alunite-group minerals from Shiveluch volcano contain Mg impurity up to 0.2 apfu, which is associated with the high Mg content of the host volcanic rocks (dacites and tephra). In individual samples Ca and P impurity is observed, substitution occurs according to the scheme SO₄^2 - + A+ ⇔ PO₄^3 - + A2+. For the first time for the alunite-group of the Kuril-Kamchatka zone, an admixture of hydroxonium (H3O)+ in the position of a monovalent cation was determined by Raman spectroscopy.