| Summary: | Sorkheh-Dizaj apatite-iron oxide deposit is located 32 km southeast of Zanjan. The area is situated within the Tarom subzone of Western Alborz-Azarbaijan structural zone. The oldest units at the Sorkheh-Dizaj area are Eocene trachyte, trachyandesite, olivine basalt and volcanoclastic brecciate tuff and lapilli tuff which intruded by a quartz-monzonite, monzonite and granite subvolcanic pluton of Upper Eocene- Early Oligocene age. Subvolcanic plutonic rocks in the area show characteristics of the I-type granites. Magmatism of the area is of synorogenic to postorogenic related to magmatic arc environments. Mineralization at the area is divided into three main zones (A, B and C) that all of which are located in the host subvolcanic pluton. These three zones are similar in terms of host rock, mineralogy, alteration, structure, texture and metal content. Mineralization in the volcanic rocks occurs as veins similar to those in three main zones, but less abundant. Geometry of the ore bodies is of vein type and their textures are stockwork, massive, banded, brecciate and vein-veinlet. The most important minerals at Sorkheh-Dizaj deposit are magnetite (low Ti) and apatite that associated with them minor sulfide minerals such as chalcopyrite, bornite and pyrite. Minerals such as ilmenite, spinel (titanium magnetite), galena and sphalerite occur in low contents. The supergene minerals like chalcocite, malachite, azurite, covellite, hematite and goethite have been formed due to weathering and supergene processes. The main alterations at the deposit are K-feldspar metasomatism, actinolitization, argillic, sericitization, silicification, tourmalinization, and chlorite-epidotic. Rare earth elements (REE) studies demonstrate that the deposit is more enriched in LREE than in HREE. The REE patterns in the apatite, magnetite and host rocks are similar suggesting a magmatic relationship. The REE contents of the apatites are higher than those of the host rocks and magnetites. Fluid inclusion studies were conducted on two generations of apatite in the deposit. Based on the studies, the temperature and salinity of the first generation apatites are higher than those for the second generation apatites. The most important characteristics of the Sorkheh-Dizaj iron-oxide apatite deposit indicated magmatic Fe-P-REE-rich fluids source for the mineralization. Comparison of the most important characteristics of the Sorkheh-Dizaj iron-oxide apatite deposit (including tectonic setting, host rock, mineralogy, alteration, structure and texture and geochemistry) with those of various types of iron mineralization in the world suggest that Sorkheh-Dizaj iron-oxide apatite deposit shows the most similarity with the Kiruna type iron-oxide apatite deposits classified as a subgroup of hydrothermal Iron Oxide Copper Gold (IOCG) deposits.
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