Kharazmi Journal of Earth Sciences

Metalliferous basinal brines, as the key factor, are commonly involved in the formation of structural-related F–Ba (±Pb–Zn) deposit, although in many instances, the sources of metals is often thought to be the underlying basement rocks. The Atash Kuh F–Ba±Sulfide vein-type deposit in the southwestern of the Markazi Province is an example of these deposits which is recognized by epigenetic characteristics, open space filling, breccia and vugy textures, occurred in lower to middle Jurassic carbonated-shale host rock. The vein-type mineralization is associated with ESE–WNW and NNE–SSW-oriented local fractures,  dolomitization, silisification and argillic alterations. Minor amount of sulfide minerals such as galena, pyrite and chalcopyrite dispersed in the vein system. Evidences show that fluorite mineralization and accompanied minerals occurred at the three stages with three types of fluid inclusion including, 1) liquid-rich (L+V), 2) solid-bearing (L+V+S), and 3) CO₂-bearing (L₁+L₂+V), in the fluorite, barite and quartz host minerals. The pressure-temperature estimation based on aqueous and CO₂-bearing fluid inclusions isochore intersection, suggest P-T condition entrapment of 150 Mpa and 250°C in the early stage and 100 Mpa and 200°C in final stage of mineralization. Microthermometry and microchemical evidences of fluid inclusions at Atash Kuh area, suggested that the salt-rich basinal brines experienced an extensive fluid-rock interaction between Na-rich to Ca–Na±Mg–K end-members. Mg-metasomatism and dolomitization could be result of Ca/Na increase and fluorite mineralization. Evidences shows that the Atash Kuh F–Ba±sulfide veins probably occurred as heterothermal mixing of two end-member brines includes: primary Na–K±Ca–Mg brines (with Triassic-Jurassic evaporitic source) and secondary Ca-rich brines (due to fluid-rock interaction). Consequently, due to depressurization and wide migration of meteoric dilute recharge fluids in shallow depth occurred at the final stage of mineralization