The Hired Gold Mineralization: an Example of Gold Deposits Related to Reduced Granitoid Intrusions in Iran - South of Birjand

The Hired gold mineralization is located 140 km South of Birjand, Southern Khorasan, and north of Lut Block. In the area, the Jurassic and Cretaceous units are covered by Tertiary volcano-sedimentary sequences. Granite, granodiorite-quartzdiorite and gabbronorite bodies have intruded Tertiary sequences, and mineralization occurs within or at periphery of a subvolcanic granodiorite-quartzdiorite stock with porphyry texture. The existence of ilmenite within subvolcanic granodiorite-quartzdiorite bodies which the lack of magnetite and low magnetic susceptibility (1.5×10-4 SI Units) as well as low ratio of Fe2O3/FeO (<0.5), they are classified as ilmenite or reduced (low fO2) granitoid rocks.Mineralization in Hired area is divided into three main zones based on the distance from the stock. The mineralized zones are as follow: intrusion-hosted mineralization, proximal mineralization and distal mineralization. These three zones are different in host rock, mineralogy, alteration, structure, texture and metal assemblage. In the intrusion-hosted mineralization, the ore-bearing unit is subvolcanic granodiorite-quartzdiorite stock. Three types of major vein-veinlets observed within the stock, including vein-veinlets of tourmaline-quartz-sericite and sulfide (TQSS), quartz-calcite and sulfides (QCS) and quartz-calcite with rare sulfide (QC). The vein-veinlets include sheeted and stockwork arrays. The proximal mineralization occurs in volcano-sedimentary sequences. These sequences include tuff, andesite and conglomerate components. The sulfides occur as disseminated, vein-veinlet and massive textures. Stockwork and rarely sheeted vein-veinlets in this type of mineralization contain quartz, calcite and sulfides. Sericitization, silicification and carbonatization are the principal alterations associated with mineralization zone. The distal mineralization occurs in faults with low angle dips, trending NE-SW and NW-SE. These faults are filled with silica and carbonates, with iron oxides and hydroxides at the surface. The comparison of the most important characteristics of Hired mineralization (including tectonic setting, host rock, mineralogy, mineral paragenesis, ore content, structure, texture and alteration) with the characteristics of different types of gold mineralization suggests that the Hired gold mineralization shows most similarity with the gold mineralization related to reduced granitoid intrusion. This type of mineralization is reported for the first time from Iran