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 to andesite are main igneous settings associated with Nikuyeh polymetallic epithermal ore mineralization. Igneous phase in the Nikuyeh district are porphyritic granodiorite, monzodiorite, quartz monsonite and quartz syenite, which classified as I type granite, with 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 the igneous rocks 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 three different glass compositions in the volcanic rocks 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 (similar to volcanic arc). Also, 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). Harker diagrams of volcanic and subvolcanic rocks have same trend, and don’t show any separation which can related to same genetic and source of parent magma of all of igneous rocks.