PETROLOGICAL INVESTIGATIONS IN A CU PORPHYRY DEPOSIT IN URUMIEH DOKHTAR VOLCANIC ARC (IRAN)

Study area is located in Central province of Iran about 120 km SW of Tehran. The Neogene igneous rocks in this area are situated in Urumieh Dokhtar volcanic arc wich is part of Zagros orogenic belt and part of Alpian Himalyan orogenic metallogenic belt that extends in a NW-SE direction from the East Anatolian Fault of eastern Turkey to the Oman line in southern Iran The most igneous rocks associated with Cu mineralization are found in the Zagros orogenic belt Early studies showed that Urumieh Dokhtar represents an Andean type magmatism formed by subduction along the active continental margines of central Iranian block during the Alpian orogeny. Surface sampling in study area recognised a porphyry Cu Au mineralization with an alteration system covering an area of 3 *6.5 km Some characteristics of the mineralizing area is: hydrothermal alterations of potassic phyllicand propylitic Au rich porphyry cu deposit associated with porphyritic felsic intrusives and widespread quartz magnetite stockworks associated with Cu-Au mineralization. Average surface rock samples at two porphyry centers returned ~0.7% Cu and 1g/t Au. Potassic zone in this area recognized by secondary biotites associated with quartz chalcopyrite pyrite and magnetite. This zone is overprinted by Phyllic zone and characterized by replacement of rock forming silicates by sericite and quartz Propylitic alteration is recognized by epidote chlorite and calcite. The chemical composition of rocks range from andesite to dacite. Geochemical studies show that these rocks are calcalkaline in origin and composed mainly of plagioclase amphibole biotite with variable amount of opaque minerals such as pyrite chalcopyrite magnetite and hematite.These rocks are moderate to strongly enrich in highly incompatible elements whereas depleted in compatible elements. On the primitive mantle normalized diagram they are enriched in LILE with respect to LREE and HFSE and depletion in HFSE with respect to LILE and LREE. All these evidences with strong negative anomalies of Nb and Ti and positive anomalies for Pb are characteristics of an orogenic magmatism and convergent margin magmas The behavior of trace element suggest that rocks were probably derived from magmas which are generated in a subduction enriched subcontinental lithospheric and is contaminated from the continental crust.