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Hormuz Island is a salt diapir in southern Iran, which also comprises transported blocks of rhyolitic and rhyodacitic rocks, which were brought to the surface during the island's diapiric emergence from the Persian Gulf. The rhyolites (558 ± 7 Ma) and rhyodacites, have both formed from the same peraluminous calc-alkaline I-type magma, in a volcanic arc settings at an active continental margin. The volcanic rocks contain significant quantities of accessory apatite. The majority of the small crystals of apatites (type-I) have crystallized during an early magmatic phase. Additionally, large single crystals of apatite (type-II) occur together with magnetite in veins within the rhyodacite rocks. The geochemical investigation of the two types of apatite revealed they both formed from the same magma source. Based on the microthermometric characteristics of primary fluid inclusions, two different events during the formation of apatite type-II crystals were distinguished. Our study revealed that in addition to the igneous fluids, a second set of fluid inclusions was trapped in the core of the crystals, indicating a post magmatic interaction with external basinal fluids during the growth of apatite type-II. On Hormuz Island, iron oxides occur as well in different styles from massive iron oxide bodies, magnetite-apatite veins, to red magnetic-hematitic soils. Based on the volcanic structures and textures of the massive iron oxide bodies as well as geochemical results from the magnetite, it is proposed that a source potential for both Fe and P could have been an immiscible iron-rich volatile phase which evolved from the parental felsic magma. Results from fieldwork, microscopy, and geochemistry revealed that mega-crystals of hematite and specularite in the magnetite-apatite veins were formed from magmatic-hydrothermal fluids released from the crystallizing magmas. The occurrence of exotic banded iron ores, red soils and alternating bands of hematite with evaporite minerals could be the result of seawater-rhyolite interactions by circulating exhalative hydrothermal fluids. • The Hormuz Island (Iran) apatites and iron oxides are described. • Apatite and iron oxides recorded the petrogenetic information of the parental magma. • The two types of apatite are formed from the same calc-alkaline and I-type magma source. • We provided a magmatic model involving immiscibility in silicate and iron oxide-rich melts. • Seawater-rhyolite interactions by circulating hydrothermal fluids made different iron oxide's styles. [ABSTRACT FROM AUTHOR]

The Panj-Kuh iron deposit, hosted by Late Eocene igneous rocks in north of central Iran, is associated with a syenitic intrusive body. Magnetic fabric investigations indicate that the Panj-Kuh pluton was emplaced within a sinistral shear zone. Corridors of sheared and metasomatized rocks show that the shear zone was active after emplacement of the pluton and in the final steps of crystallization. The sheared rocks allowed for circulation of hydrothermal fluids during cooling of the magma and caused the pervasive Na–Ca alteration. The ferrimagnetic phase in fresh syenite is mostly euhedral or subhedral magnetite, and is observed adjacent to, or as inclusion in biotite and pyroxene. Anisotropy of magnetic susceptibility (AMS) in the fresh syenite is due to preferred shape orientation of magnetite grains. In Na–Ca altered syenites, magnetite has reduced or has been totally absorbed. The alteration results in decreased bulk susceptibilities (Km) and higher anisotropy degrees (P%), accompanied by changes in the shape of magnetic susceptibility anisotropy ellipsoid. This study of the Panj-Kuh pluton suggests that AMS can be used for mapping lithology and hydrothermal alteration types. Since various types of hydrothermal alteration create, transform or destroy ferrimagnetic minerals in a mineralized system, susceptibility measurements aid mapping of igneous rock type, alteration zoning and mineralization. Integrating petrography, magnetic mineralogy, bulk magnetic susceptibility and preferred orientations of principal axes of the AMS in fresh and altered rocks can be used to generate predictive magnetic exploration models for metasomatic iron oxide deposits. [ABSTRACT FROM AUTHOR]