Unusual silicate mineralization in fumarolic sublimates of the Tolbachik volcano, Kamchatka, Russia – Part 2: Tectosilicates

Shchipalkina, Nadezhda V.; Pekov, Igor V.; Koshlyakova, Natalia N.; Britvin, Sergey N.; Zubkova, Natalia V.; Varlamov, Dmitry A.; Sidorov, Eugeny G.

This second of two companion articles devoted to silicate mineralization in fumaroles of the Tolbachik volcano (Kamchatka, Russia) reports data on chemistry, crystal chemistry and occurrence of tectosilicates: sanidine, anorthoclase, ferrisanidine, albite, anorthite, barium feldspar, leucite, nepheline, kalsilite, sodalite and hauyne. Chemical and genetic features of fumarolic silicates are also summarized and discussed. These minerals are typically enriched with “ore” elements (As, Cu, Zn, Sn, Mo, W). Significant admixture of inline-formulaAs5+ (up to 36 wt % inline-formulaAs2O5 in sanidine) substituting Si is the most characteristic. Hauyne contains up to 4.2 wt % inline-formulaMoO3 and up to 1.7 wt % inline-formulaWO3. All studied silicates are hydrogen-free, including mica and amphiboles which are F-rich. Iron-bearing minerals contain only inline-formulaFe3+ due to strongly oxidizing formation conditions. In Tolbachik fumaroles, silicates were formed in the temperature range 500–800 inline-formulaC as a result of direct deposition from the gas phase (as volcanic sublimates) or gas–rock interactions. The zonation in distribution of major silicate minerals observed in a vertical section of the Arsenatnaya fumarole, from deep (the hottest) to upper parts is diopside inline-formula+ forsterite inline-formula+ enstatite inline-formula+ andradite inline-formula→ diopside inline-formula→ fluorophlogopite inline-formula+ diopside inline-formula→ sanidine inline-formula+ fluorophlogopite inline-formula→ sanidine. This is in agreement with volatilities of major species-defining metals in volcanic gases. From a crystal-chemical viewpoint, this series corresponds to the following sequence of crystallization of minerals with temperature decrease: nesosilicates inline-formula→ inosilicates inline-formula→ phyllosilicates inline-formula→ tectosilicates.



Shchipalkina, Nadezhda V. / Pekov, Igor V. / Koshlyakova, Natalia N. / et al: Unusual silicate mineralization in fumarolic sublimates of the Tolbachik volcano, Kamchatka, Russia – Part 2: Tectosilicates. 2020. Copernicus Publications.


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