Geochemistry, U-Pb geochronology and Sr-Nd isotopes of the Neogene igneous rocks, at the Iju porphyry copper deposit, NW Shahr-e-Babak, Iran

The Iju porphyry copper deposit is located in the Kerman copper belt in the northwest of Shahr-e-Babak city within the southern extension of the Urumieh-Dokhtar magmatic arc. Based on a cut-off grade of 0.15%, the deposit contains 24 million tonnes (Mt) of ore with an average grade of 0.4 wt% Cu. The igneous rocks at the Iju deposit are primarily made up of Upper Miocene sub-volcanic and volcanic sequences that intruded Eocene volcanic rocks. Sub-volcanic rocks comprise barren quartz-monzonite porphyry and syn-mineralized granodiorite porphyry along with andesitic volcanic rocks. Geochemical evidences show that they are co-genetic, medium- to high-potassium calc-alkaline, and likely part of a subduction zone I-type granitoid magma. These rocks are characterized by enrichment in LREEs relative to HREEs with negative Nb–Ta anomalies similar to subduction zone magmatism. All samples exhibit enriched uniform chondrite-normalized REE patterns without noticeable Eu anomalies similar to magnetite-series granitoids. The igneous rocks of the Iju deposit exhibit geochemical features similar to adakites. The U-Pb zircon dating shows 9.33 ± 0.19 Ma (Tortonian stage) for quartz-monzonite (oldest unit), 9.01 ± 0.20 Ma for granodiorite and 8.83 ± 0.19 Ma for andesite (youngest unit) unit. The initial 87Sr/86Sr and 143Nd/144Nd ratios and eNd(t) values for the quartz-monzonites are 0.704234, 0.512819 and 3.75, respectively, similar to the values for the granodiorite, which are 0.704278, 0.512813 and 3.64, respectively. In most discrimination diagrams, the Iju samples show characteristics of both oceanic slab-derived and delaminated/collisional thickened lower crust-derived adakites. The geochronological, geochemical and isotopic data for the igneous rocks of the Iju deposit indicate that after long term subduction of the Neo-Tethys oceanic crust beneath the central Iranian plate, continental collision between the Arabian and Eurasian plates during the Miocene-Pliocene led to crustal thickening, breaking-off of a subducted slab and development of an asthenospheric window, thereby facilitating partial melting of the subduction-contaminated sub-continental lithospheric mantle and thickened lower crust and generating the Cu-bearing adakites in the Iju region.