Copper-containing magnesioferrite in vesicular trachyandesite in a lava tube from the 2012-2013 eruption of the Tolbachik Volcano, Kamchatka, Russia

• Published in: Minerals
• Main Authors: Sharygin, VV, Kamenetsky, VS, Zhitova, LM, Belousov, AB, Abersteiner, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPIAG 2018
• Subjects: Earth Sciences; Geology; Mineralogy and Crystallography; Tolbachik; Kamchatka
• Online Access: https://doi.org/10.3390/min8110514; http://ecite.utas.edu.au/129123

Cu-rich magnesioferrite was found in vesicular basaltic trachyandesite in one of lava tubes (Duplex) that formed during the 20122013 eruption of the Tolbachik volcano, Kamchatka. This mineral is commonly associated with hematite, tenorite, halite, sylvite, and Ca-rich silicates (mainly, esseneite and Na-rich melilite) in high-temperature (8001000 C) reactionary zones (up to 100 m) covering vesicular rocks and lava stalactites in the Duplex tube. The mineral relationships of this assemblage indicate the following crystallization sequence: Ca-rich silicates + hematite → Cu-rich magnesioferrite → tenorite → chlorides. This formed due to the reaction of hot gases containing Cu, alkalis, and Cl with solidified lava rock. The composition of magnesioferrite varies strongly in CuO (5.817.3 wt %; cuprospinel end-member1547 mol %), whereas the contents of other oxides are minor, indicating the main isomorphic substitution is Mg 2+ ↔ Cu 2+ . Compositions with maximal CuO content nominally belong to Mg-rich cuprospinel: (Cu 0.48 Mg 0.41 Mn 0.09 Zn 0.02 Ca 0.02 ) (Fe 3+ 1.94 Al 0.03 Ti 0.02 )O 4 . Increasing CuO content of the Duplex Cu-rich magnesioferrite is reflected in Raman spectra by moderate right shifting bands at ≈700710 and 200210 cm −1 and the appearance of an additional band at 596 cm −1 . This supports the main isomorphic scheme and may indicate a degree of inversion in the spinel structure.