Fluid and solid inclusions in large halite veins in the Kłodawa Salt Dome (Central Poland) – insights into its development

Secondary rocks are often found in salt domes. Among these, large halite crystal (LHC) veins and nests are common, as in the Kłodawa Salt Dome of Poland. Mineralogical tests carried out on LHC here showed the presence of fluid and solid inclusions in the halite crystals. The halite itself commonly exhibits birefringence, suggesting lattice stresses. Among the solid inclusions, anhydrite is the most common. Three types of anhydrite crystals have been distinguished as regards their size and occurrence, while small, rounded inclusions of sylvite appear much less frequently. Fluid inclusions are generally rare and mostly of the secondary type. This type of fluid inclusion assemblage (FIA) comprises various kinds as regards their size and shape, as well as in their liquid-to-gas phase ratio. Primary FIAs are of two types: small, chevron-like inclusions containing sylvite daughter minerals, and large liquid-gas inclusions with carnallite and other daughter minerals. The melting temperature of sylvite ranged from 90 to 278°C, and for carnallite from 68 to 142°C. Complete homogenization of the inclusions took place at temperatures between 260 and 471.2°C. This indicates the high-temperature origin of the LHC and the presence of significant amounts of K⁺, Mg⁺², Ca⁺², and SO₄^-2 ions in the solutions.