Original paper

Mineral chemistry and geothermometry of Fe-Ti oxides in the Khanlogh magnetite-apatite ore, northwest of Neyshabour, NE Iran

Tehrani, Parvin Najafzadeh; Calagari, Ali Asghar; Roldan, Francisco Velasco; Simmonds, Vartan; Siahcheshm, Kamal


The Khanlogh iron deposit is located to the northwest of Neyshabour in NE Iran within the Cenozoic Sabzevar-Quchan magmatic arc. The ores are hosted by a series of subvolcanic bodies of intermediate composition (dioritic porphyries) of Oligocene age. Mineralization in the study area occurs as vein, stockwork, disseminations, and open-space fillings of fault breccias within the host rocks. Microscopic and SEM examinations demonstrate that magnetite, apatite, and diopside are the main constituent minerals of the ores. Magnetite crystals contain exsolved inclusions of ilmenite in trellis and dispersed forms. Mineral chemistry data show that the minor oxide constituents in magnetite are V2 O3 (0.6%), TiO2 (1.8%), MnO (0.2%), and MgO (0.6%), and in ilmenite include MgO (3.3%), V2 O3(1.9%) and MnO (2.6%). The higher amounts of vanadium in ilmenite relative to the host magnetite is due to substitution of V4+ for Ti4+ in the crystal structure of ilmenite. Geothermometry on magnetite and associated exsolved ilmenite indicate that the Khanlogh iron ores developed at temperatures of approximately 550°C and ƒo2 ≈ 10-18 atm. The ore-forming fluids at Khanlogh had high contents of Fe, Ti, and P, and likely originated from calc-alkaline-tholeiitic magmas.