An approach to the genesis of Mahoor copper deposit, southwest of Nehbandan, based on mineralogy, fluid inclusions and sulfur isotopes studies

The Mahoor area is located about 135 km southwest of Nehbandan city, Khorasan Jonoobi Province, and in the central Lut block volcano-plutonic belt.  The intrusion of an Oligocene granitoid pluton with diorite, quartz diorite, quartz monzodiorite, and quartz monzonite into Paleocene-Eocene volcanic rocks that led to alteration and mineralization. Hydrothermal alteration zones consist of argillic (clay minerals), propylitic (chlorite, sericite, calcite, epidote), phyllic (quartz, sericite, pyrite), and silicification. The main ore minerals include sphalerite, chalcopyrite, magnetite, pyrite, stibnite, tetrahedrite, jamesonite, covellite, cubanite, arsenopyrite and galena, occurring as veinlets and disseminations. According to crosscutting relationships, two type of veinlet have been identified at deep levels of Mahoor deposit. Type (1) Quartz + sphalerite+ pyrite ± chalcopyrite, and type (2) Quartz +pyrite +chalcopyrite± sphalerite. The homogenization temperature and salinity of fluid inclusions in type 1 of veinlets range from 315 to 575°C and 6.8 to 21.2 wt. % equivalent NaCl, respectively. Fluid inclusions in type 2 of veinlets show homogenization temperature and salinity from 177 to 454°C and 7.9 to 20.2 wt. % equivalents NaCl, respectively. The microthermometric data indicate that the ore forming hydrothermal solution evolved through boiling events and mixing of magmatic fluids with meteoric waters. Sulfur isotopic values of pyrite and chalcopyrite vary from 1.8‰ to 3.15‰, suggesting that S was derived from a magmatic source. Geology, alteration, mineralization, fluid inclusion, and stable isotope studies indicate that mineralization in Mahoor area occurred as porphyry system.