Mineralogical studies of metasomatic minerals within volcanic rocks of High Zagros salt domes

Kaj-Rostam Abad, Dashtak and Do Ab salt domes are located around Ardal and Farsoun village. This area is situated in High Zagros range (Chaharmahal and Bakhtiary Province). The study area is composed of Lower Cambrian volcano sedimentary complex including basalt, basaltic andesite, andesite, trachyte, pyroclastics, evaporite rocks and Precambrian sedimentary units. According to the mineralogical and petrographic studies of High Zagros igneous rocks and related salt domes, they have complex mineralogical composition. The mineral assemblages in these rocks are formed during three stages, 1- Magmatic stage (plagioclase, clinopyroxcene, and apatite), 2- Late magmatic stage (amphibole, biotite, quartz, albite, calcite and sphene) and 3- Vein mineralization stage (quartz, albite, epidote, amphibole, calcite and garnet). Based on amphibole crystal chemistry, actinolite (Si = 7.87-7.93, CaB>1.5, CaA<0.5, (Na + K)A<0.5) have been distinguished, which is stable in wide range of temperature (320-520ºC) and total pressure 2 k bar. Studies of fluid inclusions in quartz veinlet, from altered volcanic rocks, were shown the high salinity of hydrothermal fluids. Fluid inclusions studies show three phases included liquid, vapour and solid. Also quartz crystals have a lot of inclusion of actinolite needles. The thermal range, 310 to 330 ºC in 42.93% salinity is distinguished for the formation of these quartz veins. The composition of chlorite, epidote and garnet are determined picnochlorite; pistazit and grossular-andradite respected and also the composition of plagioclases are mainly albite. On the base of thermometric studies, those metasomatic mineral are stable in thermal range of 300-500ºC.