The Hired gold deposit, Lut Block, East Iran: example of a gold deposit related to reduced I-type intrusive bodies

The Hired gold deposit in the Lut block, East Iran, is closely associated with an intermediate-mafic intrusive complex consisting of granodiorite to diorite, hornblende quartz-monzonite, and gabbro-diorite intruded into Eocene volcanic rocks. The intrusions are distinguished by high contents of CaO, FeOt, and MgO, and rather low K2O+Na2O implying they crystallized from weakly differentiated magmas. This subject, and the relatively high Mg# (36.36 to 52.32) imply the involvement of a mantle source in the production of the parent magma. The intrusions are metaluminous, calc-alkaline to high-K calc-alkaline, and distinguished by the occurrence of ilmenite as an accessory mineral. Mineralization occurs in veins and veinlets disseminations in the granodiorite intrusion and the volcanic rocks, closely associated with tourmaline, silicic, and carbonate alterations, and is distinguished by abundant pyrrhotite, arsenopyrite, pyrite, and minor chalcopyrite, galena and sphalerite. Gold occurs mostly as submicroscopic grains in the pyrite and arsenopyrite. The mineralogical and geochemical attributes of the intrusive complex, and the ore mineralogy, allow the Hired to be classified as a gold deposit related to reduced I-type granitoids. The reducing nature of the parent magma can be explained by introduction of reduced crustal materials into the source area, and/or assimilation of carbonaceous metasedimentary rocks.