Fluid inclusion and stable isotope constraints on the genesis of the Jian copper deposit, SanandajS']jSirjan metamorphic zone, Iran

The Jian copper deposit, located on the eastern edge of the SanandajSirjan metamorphic zone, southwest of Iran, is contained within the Surian Permo-Triassic volcano-sedimentary complex. Retrograde metamorphism resulted in three stages of mineralization (quartz +/- sulfide veins) during exhumation of the Surian metamorphic complex (Middle Jurassic time; 159167Ma), and after the peak of the metamorphism (Middle to Late Triassic time; approximately 187Ma). The early stage of mineralization (stage 1) is related to a homogeneous H2OCO2 (XCO2>0.1) fluid characterized by moderate salinity (<10wt.% NaCl equivalent) at high temperature and pressure (>370 degrees C, >3kbar). Early quartz was followed by small amounts of disseminated fine-grained pyrite and chalcopyrite. Most of the main-ore-stage (stage 2) minerals, including chalcopyrite, pyrite and minor sphalerite, pyrrhotite, and galena, precipitated from an aqueous-carbonic fluid (818wt.% NaCl equivalent) at temperatures ranging between 241 and 388 degrees C during fluid unmixing process (CO2 effervescence). Fluid unmixing in the primary carbonaceous fluid at pressures of 1.53kbar produced a high XCO2 (>0.05) and a low XCO2 (<0.01) aqueous fluid in ore-bearing quartz veins. Oxygen and hydrogen isotope compositions suggest mineralization by fluids derived from metamorphic dehydration (18Ofluid=+7.6 to +10.7 parts per thousand and D=33.1 to 38.5 parts per thousand) during stage 2. The late stage (stage 3) is related to a distinct low salinity (1.58wt.% NaCl equivalent) and temperatures of (120230 degrees C) aqueous fluid at pressures below 1.5kbar and the deposition of post-ore barren quartz veins. These fluids probably derived from meteoric waters, which circulated through the metamorphic pile at sufficiently high temperatures and acquire the characteristics of metamorphic fluids (18Ofluid=+4.7 to +5.1 parts per thousand and D=52.3 to 53.9 parts per thousand) during waning stages of the postearly Cimmerian orogeny in Surian complex. The sulfide-bearing quartz veins are interpreted as a small-scale example of redistribution of mineral deposits by metamorphic fluids. This study suggests that mineralization at the Jian deposit is metamorphogenic in style, probably related to a deep-seated mesothermal system.