Petrography, Geochemistry, Magmatic Evolution and Tectenomagmatic setting of Igneous Rocks Associated with Nikuyeh Epithermal Mineralization (west of Qazvin)

The Nikuyeh district is located south of the Tarom-Hashtjin metallogenic province in Western Alborz. Oligo-Miocene subvolcanic intrusion and Mid-Eocene volcanic rocks with composition of dacite (hybrid dacite) to andesite are main igneous units associated with Nikuyeh polymetallic epithermal ore mineralization. Subvolcanic igneous phase consists of I type porphyritic monzodiorite to quartz monzonite and quartz syenite (quartz syenite), and have an average alkali (Na2O+K2O) content of 4.62- 9.9 wt%, and K2O/Na2O content of 0.45- 1.66. The chemical compositions of igneous rocks show that belong to meta- alumina series, high–K calc-alkaline to shoshonitic rocks. Sieve-textured and zoning in plagioclase, corrosion and rounded of phenocrysts, presence of quartz xenocrysts, zoning and bimodal composition of clinopyroxene phenocrysts and presence of hybrid dacite and its three different glass compositions show physicochemical disequilibrium and probably magmatic mixing. Spider diagrams show that igneous rocks are enriched in in large ion lithophile elements (LILE) and depleted in Ta, Nb and Ti which these features are typical of the subduction-related magmas. On the other hand, highly LILE/HFSE and LREE/HREE ratios, low content of TiO2 (<1 percent), and high Ba/Ta ratio are subduction magma features. Tectonic setting diagrams show that district volcanic rocks have high–K calc-alkaline, and subvolcanic rocks located in volcanic arc granitoid (VAG).