Geology and Genesis of the Baba-Mohammad Celestite Deposit in boundary of Gachsaran and Mishan Formations, Kohgiluyeh and Boveirahmad province

The Baba-Mohammad celestite deposit is located in southwest Iran and 18km south of Gachsaran city. In these area celestite horizons is located at the contact zone of Gachsaran and Mishan formations. Based on the shape and arrangement of celestite in the evaporitic sequence, the genesis of major part is believed to be diagenetic; while a small part has been probably formed synsedimentarily by saturation of strontium ions in solutions of evaporitic environment. According to the abundance of gypsum in evaporitic environment and abundance of sulfate ions in water and low rates of strontium sulfate solubility in comparison with calcium sulfate, strontium sulphate (celestite) was formed due to the presence of strontium ions in the environment. The source of strontium is seawater or brines originated from sea water. In this way the initially mineralizing fluid is created in sabkha through the evaporation of sea water and as the brines enters into the underlying sediments, then leached significant amounts of strontium from the host sediments. When these strontium rich fluids are evacuated into the surface layer that includes carbonate and gypsum. Celestite sedimentation is occurred by the replacement of existing minerals and also through the incorporation of mineralizing fluid with sulphate-rich brines, which have been trapped inside the layers. Existence of celestite crystals along with the typical crystal habit (figure/shape) of anhydrite and gypsum indicates the replacement of these minerals by celestite. According to field observations, geological, mineralization, geochemical studies and analysis of sediment facies the Baba-Mohammad celestite deposit is a sedimentary-diagenetic deposit.