Economic Geology
Z. Zandi; A. R. Jafari rad; A. Gourabjeripour; M. Lotfi
Abstract
The Saheb Fe-Cu skarn deposit is located in the Sanandaj-Sirjan metamorphic belt, SE Saqqez, western Iran and has been formed along the contact between the Oligo-Miocene aged Saheb granitoid and the Permian aged impure calcareous rocks and includes endoskarn and exoskarn. Exoskarn is widely developed ...
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The Saheb Fe-Cu skarn deposit is located in the Sanandaj-Sirjan metamorphic belt, SE Saqqez, western Iran and has been formed along the contact between the Oligo-Miocene aged Saheb granitoid and the Permian aged impure calcareous rocks and includes endoskarn and exoskarn. Exoskarn is widely developed and include garnet and epidote skarn zones. The majority of mineralized zones are concentrated in garnet skarn. The relatively oxidizing mineralogical assemblage of the Saheb skarn includes garnet (andradite-grossular), pyroxene (diopside-hedenbergite), magnetite and hematite. Magnetite is the main and abundant ore mineral throughout the ore deposit. Based on field evidences and microscopic studies of skarn zone samples, two stages of prograde and retrograde alteration are distinguishable. According to the results of sample analysis of Saheb skarn productive intrusive body by XRF and ICP-MS techniques, the combination of this body is chiefly granite to granodiorite-diorite and belong to the I-type granitoids, metaluminous and K-rich calc-alkaline series. The Saheb granitoid is related to the VAG (Volcanic Arc Granite) tectonic setting.
F Yousefi; M Sadeghian; S Samyari; H Ghasemi
Abstract
In Ahmadabad Khartouran region located in 175 Km southeast of Shahrood, A significant number of adakitic domes crop out, which intruded into the Paleocene- Eocene volcanosedimentary rocks. Lithological compositions of these domes include andesite, trachyandesite, trachyandesite and dacite. Pyroxene (augite), ...
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In Ahmadabad Khartouran region located in 175 Km southeast of Shahrood, A significant number of adakitic domes crop out, which intruded into the Paleocene- Eocene volcanosedimentary rocks. Lithological compositions of these domes include andesite, trachyandesite, trachyandesite and dacite. Pyroxene (augite), green hornblende and plagioclase are typical mafic and felsic rock forming minerals. With respect to low HREE and high LREE along with other characteristic such as silica content (58.91- 63.41), Na2O more than 3%, Al2O3 more than16%, Yb less than 1.8 ppm, Y less than 18 ppm and K2O/Na2O ratio between .98- 2.3, these rocks can be classified as the high silica adakite. Enrichment of LREE relative to the HREE and depletion of Nb, Ti, and high concentration of Rb, Ba, K and Th, which imply crustal contamination of the mentioned adakitic domes. Enclaves with different size and composition have been seen in these domes which indicate contamination and magma mixing with continental crust. The evidence of petrographic and geochemical show that the magma forming of these rocks originated from melting of subducted metamorphosed Neotethys oceanic slab (Sabzevar – Darouneh branch) in P-T conditions of amphibolite facies.
M Poosti; M Fadaeian
Abstract
The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. ...
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The study area is located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais formed of Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and occasionally analcimite. They are silica saturated or relatively saturated. According to tectonomagmatic diagrams, the original setting of the parental magma was a volcanic arc and subduction zone. The negative anomalies of Nb, the high ratio of LILE/HFSE, the high mounts of Al2O3& P2O5, the low titanium contents, and the degree of partial melting of the metasomatized upper mantle, strengthens the subduction related processes for the formation of the primary magma (alkali olivine basalt). Petrographic evidences suggest that the primary magma is mixed with crustal materials. The chemical composition of rocks, according to geochemical diagrams, is shoshonitic. These rocks may have been formed by the subduction of the oceanic crust of Neoteties during the Mesozoic and early Cenozoic periods. Releasing fluids exerted from the subducting slab, metasomatism of the lithospheric mantle and subsequently the appropriate conditions for melting of the metasomatized mantle, all led to the formation of potassic magmatism and finally, generation of magma with a shoshonitic nature found its way to the surface under the influence of an extension phase and complex fault systems.
A Zahedi1; M Boomeri; M.A Mackizadeh
Abstract
The garnets from the KhutSkarn in the west of Yazd have been formed as a result of hydrothermal activity ofOligo-Miocene calc-alkaline plutons. The chemical composition of garnets in the Khutskarn are divided into two solid solution of grossularitic-andraditic and almost pure andradite different types. ...
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The garnets from the KhutSkarn in the west of Yazd have been formed as a result of hydrothermal activity ofOligo-Miocene calc-alkaline plutons. The chemical composition of garnets in the Khutskarn are divided into two solid solution of grossularitic-andraditic and almost pure andradite different types. The Fe-rich garnets are isotropic (Adr>96), whereasgrossularitic-andraditic garnets are anisotropic and show compositional zoning and sectorial twinning(Ad74.3Gr24.8-Ad32.1Gr66.6). The compositional zoning of anisotropic garnets may result from hydrothermal overgrowths on contact metamorphic minerals, variations in P, T, XCO2, concentrations of Fe3+ and Al, or kinetic factors. The Laser Ablation ICP-MS results show isotropic garnets exhibit LREE-enriched and HREE-depleted patterns, with a positive Eu anomaly. These garnets grow rapidly under relatively high W/R ratios from the magmatic-derived fluids during infiltration metasomatism process, whereas anisotropic garnets have much lower enrichment in LREE and show a weak negative Eu anomaly. These garnets formed by prolonged interaction of pore fluids with the host rocks during the diffusive metasomatism process.
K. Mohammadiha; M. Sabzehie; M. Ghahraei pour; A. Kosari Torbehbar
Abstract
Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole ...
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Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole and plagioclase are of the most significant minerals occurring in the rocks. Here we represent the chemical variations of those metamorphic minerals in relation to their host rocks and prograde metamorphism. Mineral chemistry analyses of amphibole minerals reveal an increase in Al2O3, TiO2 and a decrease in MgO, MnO during mylonitization of gabbroic rocks. Affected by metasomatism, the Al2O3 and Na2O contents of amphiboles have been also increased. CaO content of plagioclase has declined; in contrast, Al2O3 and Na2O have raised during mylonitization and metasomatism processes. These variations are overally ruled by chemical composition of the intruded pluton, pressure-temperature condition, oxygen fugacity and occurrence of equilibrant phases. Increasing Al and Na brings about tschermakite substitution in the deformed amphiboles and edinite substitution in the metasomatized rocks respectively.
G. Ahmadzadeh; A. Jahangiri; M. Mojtahedi; D. Lentz
Abstract
In this paper the study of Plio-Quaternary post-collisional magmatism in northwest of Iran and northwest of Marand is considered. The studied Potassic and ultrapotassic (UP) alkaline rocks were erupted at northern part of Urumieh-Dokhtar magmatic arc (UDMA). The studied rocks dispaly microlithic porphyritic ...
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In this paper the study of Plio-Quaternary post-collisional magmatism in northwest of Iran and northwest of Marand is considered. The studied Potassic and ultrapotassic (UP) alkaline rocks were erupted at northern part of Urumieh-Dokhtar magmatic arc (UDMA). The studied rocks dispaly microlithic porphyritic texture with phenocrysts of clinopyroxene, leucite, and plagioclase ± biotite ± olivine. The UP volcanic rocks are mostly silica undersatuated with normative nephline, high Mg# and high K2O/Na2O ratios. They characterized with significant enrichment in LILEs and LREEs and depletion in high field strength elements such as Nb, Ta and Ti. Exhibit high Ba/Nb (41-60) and Ba/Ta (682-1139) ratios, which are a typical feature of subduction. With considering end of subduction (upper cretaceouse) and stratigraphic age of studed rocks (plio-quaternary), we can say that these rocks has formed in post collisional environment and metasomatic mantle due to addition of volatiles and incompatible elements lead to enrichment of these magmas. And in fact we can say that the subduction properties of these rocks inherited from an ancient subduction. On the otherhand, high contents of LILE such as Th and Ba and Ba/Nb, Ba/Ta ratios indicate the involvement of crustal components in genesis of these rocks by addition of crustal components to source and contamination through ascent of magma. Rare earth elements modeling indicate that they can be generated from low degree partial melting of lithospheric mantle with garnet-spinel peridotite source.
