Petrology, geochemistry and petrogenesis of igneous units in the Kuh-Rakhneh district: with respect to mineralization process (Southwest of Birjand, South Khorasan Province)

Kuh-Rakhneh  district is located in the southwest of Qaleh Zari mine in Birjand city and in the central part of Lut block. The geology of the area includes the alternation of volcanic rocks with dacite to andesite composition and subvolcanic units involving granodiorite porphyry, tonalite porphyry, pyroxene diorite porphyry, diorite porphyry, and quartz diorite porphyry that have penetrated them. The alteration zones in the study area include propylitic-chlorite, sericite, argillic, silicification, and carbonate that silicification and argillic alterations are closely related to the mineralization process. Mineralization has occurred in the form of three main veins (A, B, and C) with a southeast-northwest trend within fault zones in andesitic and diorite rocks. Primary ores include pyrite, chalcopyrite, and secondary ores include bornite, chalcocite, covellite, and malachite. Mineralization in these veins is also created in the form of veins, masses, replacement, and breccia.The chemical composition of these I-type subvolcanic intrusions are between predominantly metaaluminous to slightly peraluminous with calc-alkaline characteristics. Also, negative Eu anomalies and a ratio of less than one (Eu/Eu*=0.54-0.96) indicate the presence of plagioclase in the origin of magma. The low amount ​​of Nb and Ti in these units reveals formation at tectonic setting associated with the subduction zone in the active continental margin. Based on geochemical analysis, trace and rare earth elements, the magma source that forms these subvolcanic units had been generated from  1 to 5% partial melting of garnet spinel lherzolite in the enriched mantle and at the depth of about 65 to 67 km.