Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Peter Koděra, Juraj Majzlan, Kilian Pollok, František Šimko

Vegrandisite (BaCl₂) a new mineral from salt melt inclusions from the Biely Vrch porphyry gold deposit, Slovakia

Journal of Geosciences, volume 70 (2025), issue 3, 189 - 197

DOI: http://doi.org/10.3190/jgeosci.0035.25

The new mineral vegrandisite (BaCl₂) was discovered at the porphyry gold deposit Biely Vrch, 3.5 km southeast of the town Detva, in the Central Slovak Volcanic Field. It occurs as a minor phase in salt melt inclusions hosted by vein quartz, where it forms small anhedral and transparent crystals up to 4 μm long, accompanied by halite and several other daughter minerals, mainly javorieite, rinneite, chlorocalcite and hibbingite. Vegrandisite was identified by techniques embedded in transmission electron microscopy but many mineral properties, including optical and structural ones, are known from the synthetic BaCl₂ analogue. Strongest bands in the Raman spectra include 114, 125, 187 cm^-1 and in the IR spectra in the region between 2852 and 2944 cm^-1. Vegrandisite in inclusions approaches the composition of BaCl₂, but Sr (up to ~4.5 wt. %) and Br (up to ~2.1 wt. %) are also incorporated. It is orthorhombic, belongs to the space group Pnma. Obtained unit-cell parameters a = 7.80(3) Å; b = 4.71(2) Å; c = 9.60(9) Å, V = 352.68 (54) ų are consistent with the published parameters of α-BaCl₂ that exhibits a PbCl₂-type (cotunnite) structure. Solid phases in salt melt inclusions, including vegrandisite, have crystallized from the salt melt on cooling of the inclusions. Late crystallization of BaCl₂ is related to accumulation of the incompatible element barium in the residual salt melt. Parental salt melt evolved from a hypersaline liquid, accompanied by a magmatic vapor, that were exsolved from a shallow dioritic magma.