Fluid inclusion and stable isotope geochemistry of the orogenic-type Zinvinjian Cu-Pb-Zn-Au deposit in the Sanandaj-Sirjan metamorphic belt, Northwest Iran

The Zinvinjian polymetallic deposit occurs as veins controlled by a NW-SE trending-structure within the Cretaceous metamorphosed limestone and dolomite, schist, and metavolcanic rocks, northwest of Iran. The retrograde greenschist facies metamorphism was accompanied by large-scale transpressional faulting, crack-seal veins, infiltration of large volumes of hydrous fluid with high XCO2, and is largely overlapped by the main hydrothermal events. The metamorphism has resulted in two stages of mineralization in the Zinvinjian deposit. These are early-stage polymetallic sulfides-quartz and late-stage pyrite-quartz veins. The early-stage veins filled fractures and are undeformed, suggesting a tensional shear setting. The late-stage veins are also mainly open-space fissure-fillings that cut or replace earlier veins. Three types of fluid inclusions (FIs), including aqueous (type-I), mixed carbonic-aqueous (type-II), and carbonic (type-III), were identified in ore-related quartz veins. The early-stage quartz contained all three types of primary FIs homogenized at temperatures of range 197-300 °C and salinities of 2.5-15.2 wt% NaCl equivalent. In contrast, the late-stage quartz veins contained only type-I FIs with homogenization temperatures ranging between 192 and 210 °C, and salinities of 0.2-2.7 wt% NaCl equivalent. This indicates that the metallogenic system evolved from a carbonic-rich, metamorphic fluid to a carbonic-poor, one through input of meteoric fluids. All three types of FIs in the early-stage minerals displayed evidence of vein formation during an episode of fluid immiscibility. Quartz δ18O (+ 15.3 to + 19.0‰) and sulfide δ34S (− 9.4 to + 11.6‰) indicate isotopic equilibrium with host metasediments (rock buffering) and a metasedimentary source of sulfur during early-stage. It is believed that ore mineralization is the result of a decrease in base-metal solubility during an episode of the fluid immiscibility. This study suggests that mineralization at the Zinvinjian deposit is metamorphogenic in style, probably related to a deep-seated orogenic system.