Mineralogy, geochemistry, and fluid inclusion studies of the Rayen Fe deposit, Iran: implications for ore genesis

The Rayen Fe deposit is located in the Urumieh-Dokhtar magmatic arc, a major metallogenic belt in Iran. The deposit consists of several hypogene orebodies that occur as high-grade lenticular massive magnetite bodies (up to 50 m long and 3 m wide). Magnetite geochemical compositions, microthermometric analysis of fluid inclusions, and magnetite oxygen isotope data were analyzed to constrain mineralization conditions and the genesis. The Fe mineralization is associated with the intrusion of an Eocene dioritic pluton into Cretaceous carbonate rocks. Magnetite is the most abundant ore mineral, accompanied by minor amounts of pyrite, chalcopyrite, hematite, and goethite. Pyroxene, garnet, quartz, amphibole, epidote, chlorite, and calcite are gangue minerals. The δ¹⁸O values of magnetite, ranging from + 0.15 to + 3.8‰, are consistent with precipitation from magmatic-hydrothermal fluids. The chemical signature of magnetite, including low mean concentrations of Al (0.268 wt.%), Ti (81.85 ppm), V (58.69 ppm), Cr (18.45 ppm), and Ni/Cr (mean = 3), LREE/HREE ratios (mean = 2.41), negative Ce (Ce/Ce* < 1, 0.25–0.65), and positive Eu (Eu/Eu* = 1.08–4.08) anomalies, are consistent with a magmatic-hydrothermal source for the mineralization. Results from microthermometric analyses of fluid inclusions indicate that a magmatic-meteoric mixed fluid was responsible for ore mineralization at the Rayen deposit. The tectonic setting (magmatic arc; Urumieh-Dokhtar magmatic belt), the epigenetic nature of the mineralization, textural evidence, mineral assemblages, adjacent to the dioritic pluton, microthermometric data, oxygen isotope analyses, and geochemical characteristics of magnetite indicate that the mineralization process at the Rayen Fe deposit is similar to that of skarn-type Fe deposits.