FLUID INCLUSION THERMOMETRY, S-ISOTOP, PETROLOGY OF KUH-E-ZAR SPECULARITE RICH IRON OXIDE GOLD DEPOSIT, NORTH EASTERN IRAN

Different types of iron oxides deposit have been identified along the east-west trending Sangan-Drouneh Tertiary to Quaternary volcanic and plutonic belt in northern Iran, including Kuh-e-Zar specularite Au deposit, Tannurjeh magnetite Au, Saadat Abad magnetite Cu-Au and Sangan magnetite deposit (>450 million ton).

At Kuh-e-Zar, 75% of the exposed rocks are Paleocene-Eocene rhyolite-rhyodacite-and andesite tuff. Quartz monzonite, granodiorite, monzogranite and syenogranite plutons and related dykes intrude the volcanic rocks. Intrusive rocks are meta-aluminous, medium to high-K series I-type, and show enrichment in LILE = K, Th, Rb and depletion in HFSE = Nb, Sr, Ti.

Fifteen mineralized faults are identified that control the geometry of mineralization associated with both stockwork and hydrothermal breccias. Paragenesis involves specularite-quartz-gold-chlorite ± chalcopyrite ± pyrite ± galena ± barite. Specularite is fine grained and forms 20 to 60 % of the veins. In a few localities, chalcopyrite and minor pyrite and galena are found. SEM studies reveal that gold is fine grained (<40 micron). Propylitic alteration (Repidolite) covers large area. Silicification is found within the fault zones. Albite-chlorite alteration is identified within the intrusive. Argillic was formed due to sulfide oxidation. Gold grades are 0.07 – 36 ppm, Ag average 20 ppm, As and Sb < 30 ppm, Cu is mainly < 50 ppm in some zone up to 8000 ppm, Pb 50-3000 ppm, and Zn 70-2500 ppm. Alanite (REE) and high W 450 ppm is found at deeper zones. Ore reserves are more than 3 million ton at grades of 3.5 ppm. Temperatures of homogenization of primary two phase liquid rich fluid inclusions in quartz associated with specularite-chalcopyrite-gold are 468-430°C, with specularite-chlorite- gold are 335-295°C, and with low gold specularite-siderite are 270-210°C. The δ³⁴S ‰ (CDT) values of chalcopyrite are between -2.4 and -1.1‰. The origin of the sulfur may be direct input from plutonic.