Holocene salt crust mineralogy and geochemical evolution of the Hoz-e-Soltan Playa Lake, Iran

Ephemeral saline Lake with 25-50 cm depth during wet seasons. It s situated between 34°56 and 35°31 north and 50°53 and 51°20 east and located at 85 km of southwest of Tehran, in the Central Iran zone. It is surrounded by mountains which are composed of Eocene volcanic rocks in the north; west and south, Oligo-Miocene sediments (Qom Formation) are partially exposed to the southeast of the Lake. HZPL is normally 15km long and 13km wide at an elevation of 806m above sea level. It s like many other saline Lake basins (e.g. Death Valley, California, USA) was formed as a graben as the result of blocks faulting. In this research, a detailed mineralogical investigation were carried out with salt crust samples and unconsolidated muddy sediments, below the salt crust of the Lake. The annual halite surface reserve of the Lake is approximately 42×103 ton. The thickness of the salt crust is about 5cm. The salt crust and below the salt crust (1-15cm) evaporate mineralogy were determined by X-ray diffraction method. The analysis were performed with a Phillips model (Cu X-ray tube: λ = 1.54 Å; 2θ = 4°-70°). The microscopic observations were carried out to determine the salt crystals by means of scanning electron microscope (SEM). All of analyses were done in the laboratory of Applied Geological Research center of Iran. The analysis results show that the main zone evaporates mineralogy in the salt crust of the western and slightly eastern part of the Lake consists of halite, gypsum and calcite. The mineralogy of the unconsolidated muddy sediments and below the salt crust which was in the composition of gypsum, halite, bassanite, polyhalite, karnalite, thenardite, hexahydrite and clay minerals including kaolinite (11-78%) and illite (10-90%). The cubic halite crystals were given to dominate all the salt samples. The interior drainage of the HZPL is typical of a closed arid basin. There are no permanent rivers entering the Lake, but two rivers, the Qara-Chi and Rud-Shur Rivers, to the south and northeast of the Lake, sometimes flooded and inundate the western part of the Lake. The chemical analysis of input waters including runoff and groundwater indicated that the chemical composition of brines is root II, on the Eugster and Hardie flow diagram, and after separation of different minerals, the brine type of the Lake is Na-Ca (Mg)-Cl, which is comparable with Maharlou Lake in Iran, Brystol and Great Salt Lake in USA.