Mineralogical and geochemical significance of secondary burial-related barite and celestine: Evidence from Late Paleozoic evaporites in the Karawanke Mountains (Slovenia)

The evaporites in the Karawanke Mountains (northwestern Slovenia) are hosted in a structurally complex lithological sequence, intercalated between Carboniferous-Permian and Permo-Triassic rocks. These evaporites are primarily composed of gypsum, with minor amounts of anhydrite, dolomite, and barite-celestine. Geochemically, the evaporites are characterized by elevated Sr (2000–2700 mg kg −1 ) and low Ba (210–400 mg kg −1 ) contents, reflecting the contrasting solubility behaviors of these elements in low-temperature syngenetic environments. Thermal dehydration, induced by peak burial temperatures ranging from 190 to 260 °C facilitated the transformation of gypsum to anhydrite. Subsequent cooling below the anhydrite stability threshold enabled gradual rehydration, accounting for the coexistence of both minerals. Thermal alteration also mobilized trace elements from the evaporites, which precipitated as secondary celestine and barite through dissolution-reprecipitation mechanisms, producing compositionally zoned fracture infills. The observed zoning, transitioning from Ba-rich to Sr-rich endmembers, likely reflects shifts in temperature, solubility and the chemical reactivity of evaporite-derived brine. Sulfur isotope analyses reveal δ 34 S values of +11.8 to +13.7 ‰ for the evaporitic sulfates, showing minimal variation and only a small difference relative to coexisting sulfides. This small isotopic offset indicates nearly complete sulfate reduction under high-temperature conditions, consistent with thermal alteration inferred from burial temperatures. These geochemical and isotopic results put forward not only the thermal and diagenetic evolution of the Karawanke evaporites but also their broader significance as minor reservoirs of strontium, a critical element with growing industrial and technological importance. • Burial-induced alteration of gypsum resulted in secondary Ba- and Sr-sulfates. • Barite prevalence in evaporite-derived ore deposits reflects solubility control. • Ba loss raised Sr/Ba, driving precipitation of Sr-barite and celestine.