Re–Os dating of molybdenites from Oligocene Cu–Mo–Au mineralized veins in the Qarachilar area, Qaradagh batholith (northwest Iran): implications for understanding Cenozoic mineralization in South Armenia, Nakhchivan, and Iran

Abstract

Subduction of Neo-Tethyan oceanic crust and the subsequent continental collision has created important geological features along the Alpine-Himalayan orogenic belt, including various magmatic arcs and related mineralizations. In Iran, the Tertiary Urumieh–Dokhtar magmatic arc (UDMA) is formed in this way and hosts most of the porphyry copper deposits (PCDs) and prospects in Iran. The northernmost intrusion along the UDMA is the Qaradagh batholith, which lies in the Ahar–Jolfa metallogenic zone, and contains vein- and stockwork-type Cu–Mo–Au mineralization, while its northern extension in the South Armenian Block (SAB), known as the Meghri–Ordubad pluton, also hosts several large porphyry Cu–Mo deposits. Mineralization in the Qaradagh batholith has occurred within Eocene–Oligocene granitoid rocks, among which the granodioritic component is the dominant rock type.The Re–Os model ages calculated for molybdenite samples from the Qarachilar area in the central part of the Qaradagh batholith range between 25.19 ± 0.19 Ma and 31.22 ± 0.28 Ma, referring to middle–late Oligocene. On a regional scale, the studied mineralization is contemporaneous with the third metallogenic epoch in the Lesser Caucasus, definitely with the Kadjaran and Paragachai PCDs in the SAB. However, it is younger than most of the other events across the Meghri–Ordubad pluton, which occurred during the Eocene. Integration of the data obtained in this study with the other age reports across the Meghri–Ordubad pluton may reflect the protracted and episodic nature of magmatism–mineralization in the whole region. Meanwhile, the obtained ages are older than the few age reports from central Iran (Miduk, Sarkuh, and Iju PCDs), which show middle–late Miocene ages. This age difference may reflect the dischronous and later-stage closure of the Neo-Tethys Ocean in central parts of Iran compared with its northwestern section.