Employing geochemistry and geochronology to unravel genesis and tectonic setting of iron oxide-apatite deposits of the Bafq-Saghand metallogenic belt, Central Iran

The Bafq-Saghand metallogenic belt is located in the central part of the Kerman–Kashmar tectonic zone and contains 39 individual occurrences of iron oxide-apatite ± REE mineralizations. These mineral concentrations, e.g., Chadormalu, Choghart, Sechahun, and Esfordi, comprise a total of ~ 1500 million tons of iron ore with an average grade of ~ 55% Fe. In terms of origin, time, and geodynamic setting, several modes of formation have been suggested for these ore deposits, including magmatic, hydrothermal, and banded iron formation scenarios. In the present study, the tectonic setting and metallogeny of iron oxide-apatites of the Bafq-Saghand belt are investigated utilizing trace element geochemistry, age dating, and oxygen isotope analyses. The geochemical characteristics of apatite and magnetite and the δ18O values of magnetite (from ? 0.1 to + 2.2 ?) indicate a dominantly magmatic-hydrothermal (δ18O > + 0.9 ?) formation process, although primary magmatic mineralizations were locally leached and hydrothermally redeposited (e.g., samples with δ18O < + 0.9 ?). The Cambrian volcano-sedimentary host rocks to the mineralization is intruded by calc-alkaline tonalite, trondhjemite, granodioritic, dioritic, and granitic rocks that formed in association with subduction of the Proto-Tethys Ocean under the Gondwana supercontinent in the Neoproterozoic to Early Cambrian (525–547?Ma). Additionally, a later geodynamic episode produced intrusions of alkaline syenite and monzosyenite bodies during a continental rifting event. We provide new geochronological constraints for these younger alkaline igneous rocks that document a temporal range from 421 to 447?Ma for their intrusion. In combination with the previously reported overlapping ages of the older calc-alkaline magma bodies (525–547?Ma) with the volcano-sedimentary host rock (528?Ma) and the iron oxide mineralization (510–539?Ma), we can now exclude continental rifting as a geodynamic processes that is linked to ore formation in the region. Our results corroborate that the Bafq iron ore mineralization formed during subduction of the Proto-Tethys Ocean under the Gondwana supercontinent in a near surface continental margin setting. ? 2020, Geologische Vereinigung e.V. (GV).