بررسي دگرسانيهاي اسيد- سولفات در سنگهاي آتشفشاني انديس معدني شهرزاد (جنوب غرب نائين)

The study of Acid- Sulfate AlteMtiblitJn the Volcanic Ro^feP r in the Shahrzad Ore Deposits (South West of Nain)

The study area is situated in the Cenozoic central Iranian magmatism belt, in Southwest of Nain. The Eocene country rocks covering a vast area are predominantly volcanic and pyroclasitc. These rocks are acid to intermediate in composition and range from pyroxene- andesite through trachy-andesite to trachy- dacite. The country rocks have been subsected to trachy- alterations including silicification, sericitization, chloritiation, kaolinitization and particularly alunitization. The latter alteration is widespread and due to its importance for mercury, silver and gold mineralization a major part of the study has been focused on it. The altered volcanic rocks consist mainly of alunite, natro- alunite, jarosite a well as barite, pyrite, hematite and microcrystalline quartz. The geochemical study of altered rocks was carried out by using NAA and XRD methods. The obtained data indicated that the studied rocks are enriched in silver, mercury and gold and an epithermal model may be proposed for the hydrothermal alteration of the study area.