The occurrence and geochemistry of huntite from Neogene lacustrine sediments of the Yalvaç-Yarikkaya Basin, Isparta, Turkey

Huntite-magnesite assemblages were formed as a result of Neogene tectonic activity in a shallow lacustrine Yalvaç-Yarιkkaya basin in the Isparta Bend, southwestern Turkey. The study area hosts two sediment-hosted magnesite occurrences where extremely white huntite levels up to 2 meter-thick were formed intercalated with dolomite. The basement comprises dolomitic and ultrabasic rocks that were thought the primary source of magnesium-rich formations. The huntite occurs both as massive form and void-fillings in dolomite. SEM studies show that the Yalvaç huntite is composed of randomly oriented fine-grained platy crystals (<6 μm), which were seen in the form of face-to-face aggregates. The ICP-ES analyses indicate that the MgO contents of huntite range between 30.29 to 36.05 wt.% with an average of 32.70 wt.%. On the other hand, the CaO contents of huntites vary relatively in a wide range (9.57 to 18.82 wt.%) with an average of 13.84 wt.%. The Yalvaç huntites are characterized by relatively high As (9.20-118.00 ppm), Sr (363.30-654.40 ppm), B (130-223 ppm), Li (16.30-33.50 ppm), Ba (71.15-148.00 ppm), and Zr (2.00-17.40 ppm) contents. It was designated that in a measured vertical lithological unit consisting of entirely dolomite, magnesite, huntite, and to a lesser extent calcite, the trace elements such as As, B, Li, Zr, Sb, and Co were preferentially concentrated within the huntite zones. The ICP-MS analyses point out that the amount of rare-earth elements in huntite is significantly low (∑ REE = 0.34 to 4.19 ppm) and, in most cases, close to the detection limits. Huntites show marked negative Ce and Eu anomalies in chondrite-normalized REE patterns. Combined DTA and TGA curves of the Yalvaç huntite show two characteristic endothermic peaks at 618.6 and 811.1 °C that resulted from the decompositions of MgCO₃ and CaCO₃ components, respectively with a 40 % weight loss on heating 1200 °C. The Mg/Ca mole ratios of huntite range between 2.04 and 3.85 with an average of 2.77.