The study of fluid inclusion and mineralogy in the hydrothermal alterations of Astaneh granitoids (Sanandaj_Sirjan zone)

The middle-Jurassic Astaneh granitoid body is composed of mainly of granodiorite. From the ancient time, Au mineralization and prospecting site have been known. The Astaneh granitoid have been altered in some parts and phyllic and silicaceous alterations can be recognized in some areas, especially in Shir Mazd Mountain which is vast area. Other alteration zones are: propylitic, chloritic, argillic, tourmalinzation, sodic metasomatism and spinel - phlogopite. The most widespread alteration zones are phyllic (quartz- sericite) and propylitic. There are two types of fluid inclusions in the quartz veins. On the bases of hydrothermometry study, the thermal phase of hydrothermal is from 337-341°C to 350-355°C. The density of fluid inclusions is low to intermediate (10-17 percent NaCl) while there is no daughter crystal. Temperature decrease and density of fluid inclusions are the result from mixing of magmatic with meteoric waters. The necking down of fluid inclusion is in consequence of temperature lower than 220°C. The depth of vein was controlled by dense fluid, temperature and pressure, also mineralization occurs in the depth 400-900 meter. The spider diagram show enrichment of LREEs in contrast to HREEs in unaltered samples with lack of HREEs differentiation. Tourmaline alteration displays a flat REE pattern and does not show enrichment but silicaceous alteration shows depletion of LREEs and enrichment of HREEs.