Hematite from fumaroles of the Tolbachik Volcano (Kamchatka, Russia): Chemistry and associated minerals relationship

[Marco E. Ciriotti]

Referenza:
▪ Sandalov, F.D., Pekov, I.V., Koshlyakova, N.N., Latyshev, A.V., Zhegunov, P.S. (2023): Hematite from Fumaroles of the Tolbachik Volcano (Kamchatka, Russia): Chemistry, Relationship with Associated Minerals, Morphological and Genetic Features. Zapiski RMO, 152(4), 16-46.

Abstract:
Exhalation hematite from the fumaroles of the Tolbachik volcano (Kamchatka) was studied in detail. It contains significant admixtures of chalcophile elements: tin (up to 9.2 wt.% SnO 2 - the maximum content for natural hematite), copper (up to 4.7 wt.% CuO) and, for the first time for this mineral, antimony (up to 2.6 wt.% Sb 2 O5 ). Other significant impurities: Ti, Mg, Mn, Al, Cr. Previously unknown Sn-Cu- and Sn-Cu-Sb-containing varieties of hematite and new isomorphic schemes for this mineral Sn 4+ + Cu 2+ → 2Fe 3+ and Sb 5+ + 2(Cu,Fe) 2+ → 3Fe have been established 3+. It has been shown that in Tolbachik fumaroles of the oxidative type, hematite is the leading concentrator of Sn and Sb. Epitaxy on hematite of minerals of the rutile group (cassiterite, rutile and tripuhyite), spinels (magnesioferrite, ganite and cuprospinel) and corundum was characterized. The formation of exhalative hematite rich in impurities occurred in the temperature range of 500–850 °C. The source of chalcophile elements (Sn, Sb, Cu, Zn) was volcanic gas, and the highly volatile components (Mg, Al, Cr, Ti) were the basalt hosting the fumarole chambers; for Fe, Mn and V a mixed source is assumed. The chalcophilic specificity of the composition of impurities is a typomorphic feature of fumarole hematite. "Martite" was found in Tolbachik fumaroles, which indicates an increase in oxidation potential during exhalation mineral formation.