The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure car-bonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene). The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H 2 S and CO 2 were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the an-hydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite. The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and O 2 conditions of 430–550 • C and 10 −26 –10 −23 , respectively .

The Astamal Fe-LREE skarn deposit is the largest iron skarn in NW Iran. It is a unique case, as a distal skarn deposit which crops out approximately 600 m from the associated Oligo-Miocene granodioritic pluton. This deposit formed in the south-southwest of the pluton where fractures and faults within the Upper Cretaceous volcano-sedimentary host rocks acted as conduits for the mineralizing fluids. The deposit contains three iron ore bodies: southern, northern and eastern. The main mineral assemblage within the ore zones is characterized by magnetite, pyrrhotite and pyrite, with lesser quantities of chalcopyrite, hematite, goethite and limonite. The skarn minerals predominantly comprise garnet, epidote, actinolite, calcite, quartz, clinopyroxene and chlorite (in order of abundance). Retrograde alteration is strongly developed in the skarn zone where most of the garnet has been pervasively altered to secondary minerals (e.g. epidote, calcite and quartz) both in the rims and the cores whereas the majority of the clinopyroxene has been replaced by a hydrous retrograde mineral assemblage (e.g. tremolite, actinolite and chlo-rite). Garnets with andradite–grossular compositions are the dominant mineral in the skarn zone, which are generally isotropic with a narrow compositional range along the growth lines (Adr 94.3–64.5 Grs 21.9–2.7 Alm 11.1–0.2). These garnets are Fe-rich and have high Fe/(Fe + Al) ratios (between 0.96 and 0.78). Cu and Ni are enriched in the garnets. This suggests that these elements were enriched in the hydrothermal fluids from which the garnet precipitated. This is supported by the presence of chalcopyrite and Ni-bearing massive magnetite in the study area, which also suggests that Cu and Ni were enriched in the late stage ore-bearing hydrothermal fluids. Clinopyroxene with a hedenbergitic composition is generally homogenous and has particularly high Fe/Fe + Mg ratios (between 0.99 and 0.86) and is poor in TiO 2 , MnO and Cr 2 O 3. High Zn concentrations were also detected in the clinopyroxenes (up to 1044 ppm), despite an absence of significant Zn mineralization (such as sphalerite) in the district. Therefore, it is believed that the proportion of Zn in the hydrothermal fluids decreased significantly from the time of clinopyroxene formation to the period of the sulfide deposition phase. Allanite and LREE-bearing epidotes are the main LREE bearing minerals in this deposit. The epidote is also Fe-rich with high Fe/(Fe + Al) ratios (between 0.32 and 0.44). Due to a lack of replacement texture between both garnet and clinopyroxene and garnet and actin-olite (which is formed by alteration of clinopyroxene), it is believed that these two minerals have grown simultaneously and are coexisting minerals. In the Astamal skarn, these minerals can be stable and coexisting at temperatures between 490 and 560 °C and LogƒO 2 = −16 to −31.

The Qozlou Fe skarn deposit is located at the Abhar–Mahneshan belt of the Central Iranian Zone. It is associated with Upper Eocene porphyritic granite that intruded into the Upper Cretaceous impure carbonaceous rocks. The Qozlou granite has high-K calc-alkaline affinity and is classified as subduction-related metaluminous I-type granitoids. Skarn aureole in the Qozlou is composed of endoskarn and exoskarn zones, with the exoskarn zone being the main skarn and mineralized zone. It includes garnet skarn, garnet-pyroxene skarn, pyroxene skarn, epidote skarn, and pyroxene-bearing marble sub-zones. The Qozlou Fe deposit is 300 m long and 5–30 m wide. Magnetite is the main ore mineral associated to pyrite, chalcopyrite, and pyrrhotite. Garnet, clinopyroxene, actinolite, epidote, calcite, and quartz occur as gangue minerals. Covellite, hematite, and goethite were formed during the supergene processes. The ore and gangue minerals have massive, banded, disseminated, brecciated, vein–veinlets...

Field and laboratory studies show that there are two types of skarn deposits in NW Iran: granite-associated (type I) and gabbrodiorite-associated (type II). Granite-associated deposits are accompanied by Cu and Fe mineralisation, whereas Mn and Fe are the main ore metals in gabbrodiorite-associated skarn deposits. There are some differences in the mineralogy of these skarn deposits. Bixbyite, piemontite and Cr-bearing

The Kuhshah ultramafic complex is located in the south-east of Sanandaj-Sirjan metamorphic zone, near the probable remnants of Neotethys plate in Iran. It consists of highly depleted harzburgites, dunites, chromitite bands and altered gabbros. The ultramafic parts have been intruded by numerous clinopyroxenite dykes and veins. In the harzburgites, there are different generations of olivine, orthopyroxene and spinel. The chemical composition of the first generation minerals indicates that the harzburgites are depleted in incompatible elements, but the other generations show melt/rock interaction features which can be found in a suprasubduction zone setting. During subduction of the Neotethys plate beneath the Sanandaj-Sirjan zone, a back arc basin developed between the Sanandaj-Sirjan arc and the central Iranian microcontinent. Whole rock and mineral chemistry, specially, cromespinels, show that the harzburgites formed underneath this basin. After depletion, ascending melts with boni...