Geology, geochemistry and fluid inclusion of Qarachilar Cu-Mo-Au quartz veins, northeast of Kharvana, East Azerbaijan

The Qarachilar Cu-Mo-Au occurrence is located in the Arasbaran ore zone (AZ), NW Iran, some 70 km north of Tabriz. The AZ is characterized by occurrence of different types of mineralization and hosts many Cu-Mo porphyry (PCD), Cu skarn, and epithermal Au deposits (Jamali et al., 2010; Jamali and Mehrabi, 2015). The main rock unit exposed in the area is Qaradagh batholith (QDB). A variety of porphyry and vein-type Cu–Mo–Au mineralization are associated with QDB. The most pronounced occurrences are in Qarachilar, Qara-Dareh, Zarli-Dareh, Aniq and Pirbolagh. This type of mineralization can be followed in other parts of northwest Iran, such as Masjed-Daghi porphyry Cu–Au deposit and Mivehrood vein-type Au mineralization in the southwest of the QDB, the Sungun PCD and the related skarn in its southeast, and Astamal Fe skarn deposit in the south of the QDB. To date, no detailed study has been undertaken to understand the characteristics of the Qarachilar occurrence and its mineralization type is controversial. The recent work by Simmonds and Moazzen (2015) also did not present relevant information for an understanding of the Qarachilar occurrence. The Re–Os age data obtained in their work were compared with similar events along the Urumieh-Dokhtar magmatic arc (UDMA) and southern Lesser Caucasus in order to elucidate the temporal pattern of mineralization across the whole QDB and the UDMA. The present paper provides an overview of the geological framework, the mineralization characteristics, and the results of geochemistry and fluid inclusion studies of the Qarachilar Cu-Mo-Au occurrence with an application to the ore genesis.

More than 37 polished thin sections from Qarachilar host rocks and mineralized and altered zones were studied by conventional petrographic and mineralogic methods at the University of Zanjan. In addition, 9 samples from non-altered and altered host rocks and mineralized veins were analyzed by ICP-MS for trace elements and REE at the Zarazma Co., Tehran, Iran. Microthermometric data were performed on primary fluid inclusions using the Linkam THMS600 heating–freezing stage at the Iranian Mineral Processing Research Center (IMPRC), Tehran, Iran.

The rock units exposed in the Qarachilar area are different sets of magmatic phases of QDB including granodiorite-quartz monzodiorite, porphyritic granite, quartz monzonite and acidic-intermediate dikes. Granodiorite-quartz monzodiorite is the dominant phase which hosts the Qarachilar quartz-sulfide veins. Mineralization at Qarachilar occurs as three quartz-sulfide veins. The veins reach up to 700-m in length and average 1-m in width, reaching a maximum of 2-m. They are generally steeply-dipping to the NE at 80°. The reported grades of Mo, Cu and Au range from 20 ppm to 3.6 wt%, 0.7 wt% to 5 wt%, and 0.23 to 37.2 g/t, respectively.
Four stages of mineralization can be distinguished at Qarachilar. Stage-1 is represented by quartz veins (ranging from centimeters up to ≤1-m width) that contain variable amounts of chalcopyrite and pyrite. Stage-2 is marked by Tm-h) and type-2 (Tm-h>Th) inclusions are homogenized in the range of 197-530°C and 203-375°C, respectively. They have a calculated bulk salinity of 29.5 to 55.1 and 32.4 to 45.6 wt% NaCl equiv., respectively. The variations in salinity and Th could be explained by a combination of mixing and boiling hydrothermal fluids. These processes led to the deposition of Cu, Mo and Au in the veins. Geology, ore mineralogy, textures, geochemistry and microthermometric data of Qarachilar occurrence are comparable with vein-type Cu-Mo-Au mineralization related to Cu-Mo porphyry and intrusion related gold deposits.