Acta Musei Moraviae

Chromium rich spinels of Upper Carboniferous Balinka conglomerates from south part of Boskovice Graben

Balinka conglomerates formed the basal Upper Carboniferous sedimentation of Boskovice Graben and locally contain light-green fine-grained aggregates of Cr-mica and clay minerals. During the study of these phyllosilicates, relicts of Cr-rich spinel were found. Cr-rich spinel is a common minor to accessory mineral in the Moldanubian peridotites. Two principal compositional types of spinel from Balinka conglomerates were identified: a) low Cr# (0.1–0.3) and high Mg# (0.71–0.76), which correspond to spinels from Hrubšice peridotite (Fo-Spl-Opx±Prp) analysis and b) high Cr# (0.72–0.77) and middle Mg# (0.43–0.51), which correspond to spinel analysis from Hrubšice serpentinite (Srp-Spl). Studied Cr-spinels from Hrubšice peridotite to serpentinite consist of variable amount of TiO₂ what shows limited using of this plot for distinguish between origin of spinel, which is common use in literature. Grains of partially corroded garnets were found in heavy fraction.