Geochemistry and genesis of APS minerals in advanced argillic alteration zone, northwest of Shir-Kuh, Yazd

Northwest of Shir-Kuh batholith, a number of leucocratic granitic and granodioritic plutons have intruded sedimentary hosts including shale-sandstone (Triassic-Jurassic) and sandstone-conglomerate (Lower Cretaceous). Contact metamorphism and hydrothermal alterations are widespread. Late alteration assemblage mainly occurs in arkosic sandstones of Sangestan Formation and includes propylitic, quartz-sericitic, advanced argillic and silicific zones. Quartz-sericite zone is the most widespread. Advanced argillic alteration is characterized by the following assemblage: jarosite, alunite, turquoise, from the Al-Phosphate-Sulfate group (APS). Considering this mineral assemblage and probable interactions taking place between the minerals, a geochemical environment with high fO2 and low pH is thought to be prevailing at the time of alteration and formation of alunite, jarosite and turquoise.