Abstract

The Gol-e-Gohar iron ore district in the Sanandaj-Sirjan zone of south-western Iran comprises six major ore bodies. The largest deposit is Gol-e-Gohar No. 3 (Gohar-Zamin) with about 643 Mt @ 53.1% Fe. The host rocks in this district are Late Neoproterozoic meta-sedimentary rocks (para-gneiss, marble), meta-basalt (ortho-amphibolite), and I-type meta-granite (ortho-gneiss). The district is characterized by potassic-sodic (albite-K-feldspar), phyllic (muscovite) and propylitic (chlorite-calcite-dolomite-magnesite with pyrite) hydrothermal alteration, and massive and brecciated Kiruna-type magnetite ± apatite mineralization. There is also boron (B) metasomatism, manifested as tourmaline blastesis. Gol-e-Gohar magnetite contains Mg, Ca and Si up to the percent range, V and Ti in the 100s ppm level, and low Cr, Co, Ni in the tens of ppm range, typical of skarn or IOCG mineralization. The oxygen isotope composition of magnetite is 4.9 ± 0.7‰ δ18O (n = 9) and the iron isotope composition is 0.49 ± 0.05‰ δ56Fe (n = 17). These data suggest that the magnetite ore formed from a magmatic-hydrothermal (high-T) fluid in equilibrium with a granitic source. The hydrothermal carbonate inclusions in late pyrite have δ11B values of 20.3 ± 2.4‰, indicating the imprint of fluids which interacted with the Early Cambrian marine country rocks of the district, such as limestone and/or evaporites. The Gol-e-Gohar iron ore district shows several similarities to the Bafq iron district, located about 400 km to the north, and seems to be a disrupted member of the Kashmar-Kerman arc.

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