PETROLOGY, FLUID INCLUSION THERMOMETRY, AND GEOCHEMISTRY OF TANNURJEH PORPHYRY CU-AU, NORTH EASTERN IRAN

Tannurjeh the first porphyry Cu-Au system discovered in Eastern Iran and is located within volcanic-plutonic of Kashmar- Khaf belt. This belt is eastern extension of the Alpine-Carpathian mountain range and continues east into the Himalaya.

Eocene rhyolite, dacite, rhyodacite and minor andesite are intruded by monzonite, quartz monzonite, diorite and quartz diorite porphyry (Oligo-Miocene). Most of them have small exposure. Hydrothermal breccias (rich in goethite & Au) with circular exposure are being recognized in some portion of the system. Intrusive rocks are meta-aluminous, medium to high-K series, I-type, Na2O > K2O and indicate a continental arc setting. Unaltered intrusive rocks have magnetic susceptibility > 200 ×10-5 SI. Both ASTER and ground checking revealed very broad altered zones characteristic of Cu-Au porphyry systems. Such as propylitic, advanced argillic with kaolinite, alunite and vuggy silica are well developed in the area. The silicified zone covers a large area. Pyrite and minor chalcopyrite occur both disseminated and as fracture filling, but no stockwork.

Au, Cu, Zn, Pb, As, and Mo show anomaly in stream sediments and in rocks. The Au content of surface rock samples are between 0.1 – 11 ppm (average 0.25 ppm). Cu content of the rocks is less than 200 ppm. Due to strong oxidation, most of sulfides are being oxidized and copper is being leached and secondary argillic zone is formed. Secondary iron oxides (mainly goethite) vary between 1 to %10.

Temperatures of homogenization of primary three & two phase fluid inclusions in quartz are between 320-490°C. The salinity of ore fluid was between 15 and 60 wt% equiv. NaCl. Morphology of the intrusive, alteration types and geochemical anomalies indicate that present exposure is high level of porphyry system. High pyrite content, broad zone of silicification, confining the copper with potassic zone at depth, and high and very broad zone of Au anomaly make Tannurjeh to be new type of porphyry Cu-Au deposit.

Keywords: Tannurjeh, porphyry Cu-Au, Iran, breccias