Geology, mineralogy, and isotope (Sr, S) geochemistry of the Likak celestite deposit, SW Iran

摘要

Celestite mineralization in the Likak deposit is hosted by Early to Middle Miocene Gachsaran evaporitic formation. The celestite-bearing layers are composed of medium- to coarse-grained celestite crystals with different morphologies in a carbonate groundmass. The presence of carbonate and gypsum inclusions within celestite crystals as well as the pseudomorphic habits of some crystals suggests that celestite replaced preexisting carbonate and gypsum. The lithofacies features and faunal assemblage of the host rocks indicate subtidal-supratidal environments of deposition for country rocks. Strontium isotope analyses indicate that Sr originated from Middle Miocene seawater. Sulfur isotopic ratios indicate higher δ~(34)S values in analyzed samples than those of Middle Miocene seawater. These higher values were probably resulted by bacterial reduction of sulfate. Based on petrographic evidences and Sr-isotope ages, it is revealed that mineralization occurred as a late-diagenetic process during deposition of Gachsaran Formation. Taking into account the available data, it can be suggested that precursors of the mineralizing fluids were probably produced by evaporation of seawater in a coastal sabkha setting. As these brines entered into underlying sediments, they leached considerable amounts of Sr from host sediments. Once these Sr-enriched fluids discharged back up into overlying beds containing gypsum and carbonate materials, celestite precipitation took place by replacement of the preexisting minerals as well as by mixing of the mineralizing fluids with sulfate-enriched brines entrapped within the beds.