ore geology, fluid inclusions and o-s stable isotope characteristics of zajkan epithermal base metal deposit, tarom-hashtjin metallogenic belt, nw iran

Zajkan is a small (0.2 mt) epithermal base metal deposit in the tarom–hashtjin metallogenic belt (thmb), northwestern iran. it occurs as quartz-base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation. four stages of ore formation are identified at zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273°c from fluids with salinities between 1.7 and 6.4 wt.% nacl equiv. the oxygen isotopic compositions (δ18owater of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. sulfur isotopic values of sulfide minerals vary over a narrow range from –5.0 to –0.9‰ (averaging −2.2‰), suggesting that sulfur was derived from a homogeneous magmatic source. the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan. our data suggest that the zajkan deposit is an intermediate-sulfidation style epithermal mineralization.