Mineralization of Iron Deposits from Dehbid Area, Fars Province, South Iran: Geochemical and Mineralogical Data

The Dehbid iron deposit is located at about 176 km northeast of Shiraz (the Capital of Fars province) in Sanandaj-Sirjan metamorphic zone along the northeast Zagros orogenic belt. Polyphase deformation structures of the metamorphic zone are consistent with dextral transpressional deformation, which is related to the oblique convergence between the African–Arabian continent and the Iranian microcontinent. The ores are hosted by metasedimentary rocks of late Paleozoic (Permian) and silicified Trias dolomite. The field relationships and microstructures indicate that precipitation of the iron-oxide minerals was related to fluid flow focused along the detachment faults and brecciated zones that were possible feeder channels for aqueous fluids driven by differential stress along the fault. The mineralized zones appear as veins of maximum 15 × 200 m within silicified brown dolomite. Ore veins crosscut dolomite, suggesting that at least one deformation phase predated introduction of Fe-bearing fluids. Mineralogical studies show that the iron ores are dominated by magnetite. Hematite, goethite, specularite and martite occurred as minor phases. Gangue minerals include quartz, dolomite and minor K-feldspar. Primary magnetite ranges in size from fine to coarse-grained crystals. Quartz and minor dolomite occur throughout the orebody as cementing material of magnetite. Locally, hematite has replaced magnetite. Most of hematite resulted from the oxidation magnetite under surface or near-surface conditions. Martitization commonly replaces magnetite along grain boundaries and cleavage planes. The martite/hematite replacement could be product of relatively late-stage intrusion of oxidizing fluids. Goethite is the principal secondary mineral, probably the result of total transformation of the earlier formed oxide iron. Fe

2

O

3

content in mineralized rocks varies between 38 and 73 wt% and mineralogical analyses indicate that Mn, Co and Ni substitute for Fe

2+

in magnetite lattice. Co/Ni ratio in the study area (average 3.6) characterizes hydrothermal origin of magnetite. The P

2

O

5

content is also typically low that supports the hydrothermal origin of mineralization. The Cu content in ores varies from 17–59 ppm and indicates that this deposit could not interpret to be a member of the iron oxide-copper–gold (IOCG) class of deposit. The high K

2

O content (3–3.7 wt%) in the samples just near the ores- host rocks contacts shows an immature potassic alteration which indicated by formation minor K-feldspar in the altered zones. The proposed genetic model involves early sedimentation of dolomitic formation and introduction of silicic fluids, followed by silicification of dolomites, deformation and metamorphism and finally formation of magnetite ores. Temperature and pressure diminutions have a significant role in precipitation of magnetite in these veins as open space fillings.