Petrography, geochemistry and petrogenesis of Abbas Abad volcanic rocks (East Shahroud) with emphasis on associated alteration and copper mineralization

Abbas Abad ore district lies in a volcanic and volcanosedimentary belt in East Shahroud and hosts eight copper deposits. This belt is part of volcanic arc in north of central Iran. Copper mineralization is dominated by chalcocite with minor bornite، digenite and covellite. Mineralization occurs as disseminated، veinlet، and stock works. Four alterations (silicification، carbonatization، epidotization and chloritization) are detectable in the host rocks. Lithologies of the volcanic rocks are trachyandesite، trachyandesit basalt and trachybasalte and they have high potassium calc-alkaline to shoshonitic nature. Fractional crystallization and crustal contamination processes are involved in magma evolution. Plagioclase and pyroxene are main minerals and the most important texture (porphyric and glomeroporphyritic) has been observed in this rocks. Zoning، sieve textures and re-absorption in plagioclases، and sieve textures، the effects of corrosion on the margins of pyroxene، and roundness of mineral implies the existence of non-equilibrium conditions during solidification of magma. LREE and LILE enrichment and depletion of HFSE with negative anomalies of Nb، Ti and Ta elements in studied samples show the alkaline nature associated with arc (active continental margin). Ratio of Ba/La and Th/Ta in rocks confirm subducting continental arc for tectonic environment of this rocks.