Geochemistry, geochronology, isotope and fluid inclusion studies of the Kuh-e-Zar deposit, Khaf-Kashmar-Bardaskan magmatic belt, NE Iran: Evidence of gold-rich iron oxide–copper–gold deposit

Abstract

The Kuh-e-Zar deposit is located in the central part of the Khaf-Kashmar-Bardaskan Tertiary magmatic belt, NE Iran. The prevailing stratigraphic unit is composed of Cenozoic volcanic rocks (rhyolitic to andesitic in composition), which are intruded by subvolcanic plutons. Intrusive rocks spatially close to mineralization include metaluminous to peraluminous, calc-alkaline and I-type diorite, granodiorite, quartz monzonite, quartz monzodiorite, and syenogranite. The quartz monzonite and quartz monzodiorite have identical zircon U–Pb ages of ca. 40.7–41.2Ma. The intrusions are characterized by enrichment in large-ion-lithophile elements (LILEs) and light rare-earth-elements (LREEs), depletion in heavy rare-earth-elements (REEs, LaN/YbN≈7 to 9.07) and high-field-strength-elements (HFSEs) and εNd(t) ranging from −0.06 to −2.93 at 86Sr/87Sr(t)=0.7054–0.7064 and 206Pb/204Pbi=18.6–18.71. The intrusive rocks of Kuh-e-Zar are products of crustal assimilation by melts derived from the metasomatized mantle wedge above the subducting Neotethyan Ocean slab beneath SW Eurasia.Field work and mineralogical, petrological studies show that, the hydrothermal alteration produced a zone of silicification, propylitic alteration, and albitization associated with minor sericitic-argillic alteration. The mineralization of Kuh-e-Zar occurs in veins, stockworks, and breccias, which is located near or within NE−SW and NW−SE faults cutting through volcanic rocks and wall rocks. The ore minerals are dominated by specular hematite and gold with small amounts of pyrite, chalcopyrite, and galena. Hematite, goethite, malachite, covellite, and cerussite are secondary minerals. The main gangue minerals include quartz, siderite, chlorite, and albite. Microthermometric study of fluid inclusions shows homogenization temperatures at medium-high temperature of 248 to 491°C. Salinities of ore-forming fluids are medium-low ranged from 4 to 19.2wt% NaCl equivalent. The sulfur isotope composition of chalcopyrite (δ34S=−2.5 to 0.9‰) suggests that sulfur was derived mainly from igneous rocks. The oxygen isotopic data (δ18Owater=7.4–7.9‰) indicate that the ore fluids were in magmatic origin.The mineralogy, alteration, geochemistry, stable isotopes, and petrogenesis of intrusions of the Kuh-e-Zar deposit indicate it is an Eocene gold-rich iron oxide-copper-gold (IOCG) deposit.