Petrography and petrogenesis of Hasht-kuh Khezrabad of Yazd skarns

The Khezr-Abad granitoid intrusive body is located in the north-west of Yazd province within Urumia-Dokhtar magmatic arc. The intrusion of this body into the Cretaceous carbonate rocks (Taft Formation)، gave rise to Hasht-kuh skarn mineralization with the following mineral assemblage: Garnet+ Clinopyroxene+Epidote+Tremolite-Actinolite+Chlorite+Calcite+Quartz Mineral associations studies show that pyroxene- garnet occurrence have most relations and are widespread in skarn. A detailed study of paragenetic relationships of skarn minerals clearly demonstrate that there are two stages in skarn evolution system، so the Hasht-kuh skarn can be considered as a polygenic skarn. On the basis of mineral chemistry data the garnet tends to be grossular and pyroxene is augite in composition. The peak temperature of contact metamorphism episode is accompanied by pyroxene crystallization in the early stage followed by overprinting of garnet formation. Due to presence of Al/Fe+3 periodic changes in fluids during garnet precipitation، zoning structure in some garnets was developed. The prevailing oxidation conditions during crystallization of fluids caused the instability of pyroxene (reducing ƒO2) and the growth of andradite garnet could be occurred at T<550°C in skarn system.