Synthesis on productive, sub-productive and barren intrusions in the Urumieh-Dokhtar magmatic arc, Iran, constraints on geochronology and geochemistry

Abstract The Cenozoic Urumieh-Dokhtar magmatic arc (UDMA) is considered as one of the major Cu-bearing regions in the world with high potential for the occurrence of porphyry Cu ± Mo ± Au systems. This study conducts a comprehensive synthesis of geological, geochronological, and geochemical data of intrusion rocks in some productive, sub-productive deposits and barren intrusions in the UDMA to find out discrimination criteria. U-Pb dating of zircon grains provides emplacement ages of 19.3 ± 0.4 to 21.1 ± 0.2 Ma for the Ghahan diorite, and tightly clustered ages of 14.5 ± 0.2 to 14.9 ± 0.1 Ma, 12.2 ± 0.1 Ma, and 27.3 ± 0.4 to 29.2 ± 0.3 Ma for Kahang monzonite, Meiduk diorite and Zaftak granodiorite porphyry copper deposit systems (PCDs), respectively. According to geochemical characteristics the Zaftak and Ghahan samples display the sub-productive signatures, whereas the Kahang and Meiduk samples are charachterized by the adakitic and productive signatures. Lowest average Sr/Y ratios are observed in Zaftak and Ghahan barren and sub-productive intrusive rocks (15.86, 13.46 and 20.19 for Eocene, Oligocene and Miocene, respectively), while the productive bodies of Kahang and Meiduk show 70.67 and 63.93 respectively. This study suggests two major mineralization episodes for UDMA porphyry copper deposits: 1) non-adakitic deposits generated during Oligocene to Early Miocene, and 2) Early Miocene to Late Miocene adakite-like deposits. The former mainly developed during pre-plate final closure Neo-Tethys Ocean, and latter reveals a post-collisional setting. In comparison with the barren and sub-productive intrusions, the productive PCDs suites, especially during Middle to Late Miocene times, are characterized by the enrichment of LREE. This transfer is the result of compressional stress along with tectonic shortening during Eocene-Oligocene (~30–35 km crustal thickness) to mid-late Miocene (~45–55 km thick or 12–15 kbar). In general, our data have nullified the previous mentioned progressive decrease of PCDs mineralization in UDMA. The ca. 19 to 21 Ma mineralization ages of central UDMA (Ghahan region) are obviously in contrary with a single stage of Early Miocene. Obviously, the formation of porphyry deposits with high grade-tonnage in UDMA is limited to the time interval after collision, with adakite evidence, and before the collision, other ore deposits such as Zaftak and Ghahan have been formed with sub-productive signature. Geochemical signatures of intrusions in UDMA during the Eocene, Oligocene, and Miocene periods suggest a progression and evolution, and the maturity of the magma arc towards the Miocene and, consequently, an increase in the probability of productive mineralization. It is also noteworthy that the Eocene magmatism seems to lack the necessary parameters for the formation of sub-productive and productive porphyry systems, the Oligocene magmatism is more susceptible and, naturally, towards the Miocene this potential has increased.