Stable isotope evidences of jarosite–barite mineralization in the Rangan rhyolitic dome NE Isfahan, Iran

The Rangan area is part of Cenozoic magmatic belt of central Iran. Eocene volcanic flows and pyroclastic rocks are intruded by a Neogene rhyolitic dome along the major Qom–Zefreh fault. The dome is pervasively hydrothermally altered. The main mineral assemblage is jarosite+barite+pyrite+quartz+sericite. This assemblage indicates acid sulphate or advanced argillic alteration. Sulfur and oxygen isotope data (δ34S & δ18O (SO4)) obtained from jarosite and barite indicate a mixing episode during the evolution of hydrothermal system and reflect the overlapping of two distinct sources of acid sulphate alteration in Rangan, i.e., a magmatic–hydrothermal fluid reacting with steam-heated meteoric water. Considering the position of brittle–ductile transition and major fault movements, jarosite and barite seemingly precipitated from rapid injection of magmatic–hydrothermal fluids into the upper portions of a steam-heated environment.