Mineralogy and geochemistry of the Aushkul, Kamatal and Shartym granite massifs (Balbuk comlex, Southern Urals)

Abstract

The article discusses the petrographic, mineralogical and petrogeochemical features of alkaline granites of the Balbuk complex in three massifs - Aushkul, Kamatal and Shartym. The rocks of the massifs are similar in structural and textural features and mineral composition: they are composed of acidic plagioclase, potassium feldspar, quartz and muscovite. In the Aushkul massif, phenocrysts of potassium feldspar, plagioclase, quartz and primary oligoclase are found in the groundmass, while in the Kamatal and Shartym massifs only phenocrysts of altered plagioclase and quartz are developed, and secondary albite is present in the groundmass. The existing differences in the geochemistry of the rocks of the Aushkul massif in comparison with Kamatal and Shartym (depleted in barium and enriched in niobium) may be associated with minor differences in the composition of magmas and with the peculiarities of their fractionation in intermediate chambers (fractionation of alkali feldspar and Nb-containing phases).