Economic Geology
nasrin khajehmohammadlou; Ali Asghar Calagari; Kamal Siahcheshm; Ali Abedini
Abstract
The Aghbolagh iron-copper skarn is located in ~21 km north of Oshnavieh, southwest of West-Azarbaidjan province. The intrusion of Cretaceous granitic body into the Cambrian Barut, Zagun, and Lalun Formations (carbonate, shale, and sandstone) was accompanied by development of calcic-type skarn, hornfels, ...
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The Aghbolagh iron-copper skarn is located in ~21 km north of Oshnavieh, southwest of West-Azarbaidjan province. The intrusion of Cretaceous granitic body into the Cambrian Barut, Zagun, and Lalun Formations (carbonate, shale, and sandstone) was accompanied by development of calcic-type skarn, hornfels, and marble in the study area. The garnets of the Aghbolagh skarn belong to solid solution series of grossularite-andradite in which andradite is the dominant phase (>80%). These garnets are isotropic and lack zonation. The pattern of REE distribution in these garnets shows the enrichment of LREE relative to HREE and also the occurrence of negative anomalies of Eu/Eu* and Ce/Ce*. The comparison of the distribution pattern of REE in garnets with those in igneous (granite and monzonite) and sedimentary (carbonates and sandstones) rocks demonstrates that the REE in garnets were derived mainly from the igneous rocks rather than the sedimentary units. The increase in Pr/Yb ratios in parallel with increase in the ƩREE is indicative of the magmatic origin of the ore-forming fluids in the Aghbolagh skarn. However, the lack of sensible variations between Ce/CE* and ƩREE values indicate that the meteoric waters might have also played a part in skarn-forming fluids at Aghbolagh.
Petrology
Zahra Alaminia; Zahra Rahmati; Hossein Azizi
Abstract
The Dorojin granitoid at the northeastern Isfahan is located in the central Urumieh-Dokhtar zone and within the volcano-sedimentary complex. The Dorojin iron deposit is the one of the several ore deposits that Dorojin granitoid body is caused in its surrounding rocks. According to microscopic evidences, ...
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The Dorojin granitoid at the northeastern Isfahan is located in the central Urumieh-Dokhtar zone and within the volcano-sedimentary complex. The Dorojin iron deposit is the one of the several ore deposits that Dorojin granitoid body is caused in its surrounding rocks. According to microscopic evidences, mineral assemblage of wollastonite, garnet, pyroxene (diopside), amphibole, epidote, feldspar, calcite and quartz, Dorojin deposit attributed to the class of calcic skarns that occur during two stages progressive and regressive. Based on electron microprobe analysis, some garnets are andradite (An92-97Gr1-5) in core and andradite-grossular (An53-66Gr30-41Sp2-4) in rim. In the beginning, andradite fluid inclusions with temperature range from 369˚ to 444˚C and salinity range from 11.22 to 12.96 wt.% NaCl eqv., originate from magmatic fluids, while with change in the acidity condition of environment and the opening of system, grandite, epidote and calcite fluids with a temperature between 221˚ and 305˚C and salinity between 0.4 and 10.11 wt.% NaCl eqv., are dominated by mixing and dilution of early magmatic fluids with meteorite waters. Sr isotopic ratio of garnet vary between 0.70760 and 0.70805, suggesting that prominent role of the magmatic fluids for the formation of andraditic garnet.
Petrology
Seyyed Navid Seyyed Mardani; M. Moazzen; Ahmad Jahangiri
Abstract
The Muth-Golpayegan metamorphic complex is situated at north of Golpayegan city in the Isfahan province. This complex is constituted from different metamorphic rocks including variety of pelitic schists, amphibolite, gneiss, quartzite and marble. Garnet schists are dominant lithology in the area and ...
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The Muth-Golpayegan metamorphic complex is situated at north of Golpayegan city in the Isfahan province. This complex is constituted from different metamorphic rocks including variety of pelitic schists, amphibolite, gneiss, quartzite and marble. Garnet schists are dominant lithology in the area and contain different minerals, such as garnet, quartz, chlorite, muscovite, biotite, staurolite, andalusite, kyanite and sillimanite. Lepidoblastic, porphyroblastic, poikiloblastic, augen and millipede are the main textures in these rocks. The degree of metamorphism increases from SW to NE in a way that slate and phyllite at SW change gradually to chlorite schist, biotite schist, garnet schist, staurolite schist, sillimanite schist and kyanite schist. The occurrence of these schists is accompanied by appearance of chlorite, biotite, garnet, staurolite, sillimanite and kyanite mineralogical zones in the field. The succession of these zones is compatible with Barrovian regional metamorphic gradient. Chlorite, biotite and garnet zones belong to the greenschist facies and staurolite, sillimanite and kyanite zones belong to the amphibolite facies. Temperature range calculated for these rocks by garnet-biotite thermometry is 471-581 C. This metamorphic gradient is a result of continental collision.
M Norouzi; M. Lotfi; M. H. Emami; H. Jamali; A. Abedini
Abstract
Mesgarabad area is located in ~10 km southeast of Tehran, the Central- Alborz structural zone (CASZ) of Iran. The rock units exposed in the area consist of Eocene volcanics, volcano-sedimentary and sedimentary rocks intruded by post upper Eocene granodiorite to quartz monzo-diorite. These subvolcanic ...
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Mesgarabad area is located in ~10 km southeast of Tehran, the Central- Alborz structural zone (CASZ) of Iran. The rock units exposed in the area consist of Eocene volcanics, volcano-sedimentary and sedimentary rocks intruded by post upper Eocene granodiorite to quartz monzo-diorite. These subvolcanic intrusive bodies show porphyroid to microgranular textures and have calc-alkaline magmatic nature. These bodies produced hydrothermal fluids causing extensive alteration zones developed along the Se-Darreh-e-Bozorg strike-slip fault. The effects of hydrothermal fluids on the entire Eocene rock units and subvolcanic intrusive bodies are remarkable. The main alterations are silicification, sericitization, chloritization, epidotizaton, actinolitization, argillization, carbonatization, and alunitization-jarositization, which provided suitable physico-chemical conditions for ore-mineralization. The penetration of subvolcanic intrusive bodies into the Eocene volcanics, volcano-sedimentary and sedimentary rocks brought about skarn mineralization and epithermal barite veins. Microscopic studies and advanced analysis showed that the principal mineral phases in the epithermal zones are magnetite, pyrite, chalcopyrite, bornite, chalcocite, barite, Cu+Sn+Fe alloy, hematite, psilomelane, jacobsite, martite, geothite, and lepidochrosite. The skarnification processes occurred at two distinct stages, (1) progressive and (2) retrogressive. The pyrometasomatic anhydrous minerals such as andradite-grossularite formed during progressive stage and the hydrous minerals like epidote, chlorite, tremolite- actinolite, calcite, quartz, pyrite, chalcopyrite and chalcocite were developed during retrogressive stage. Fluid inclusion studies on primary aqueous inclusions trapped in barite crystals revealed fluid that mixing of two fluids having different physico-chemical conditions played an important role for ore deposition.
S Ranjbar; S.M Tabatabaei manesh; M.A Mackizadeh
Abstract
The Khuni skarn has been developed in the contact between small tongues of the Late Eocene-Oligocene I-type Kal-e kafi granitoidic intrusive body and the Precambrian Lakh marble-dolomite unit, Located 220 km northeast of Esfahan in the Central Iran structural zone. Skarnification could be divided into ...
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The Khuni skarn has been developed in the contact between small tongues of the Late Eocene-Oligocene I-type Kal-e kafi granitoidic intrusive body and the Precambrian Lakh marble-dolomite unit, Located 220 km northeast of Esfahan in the Central Iran structural zone. Skarnification could be divided into two subzones: endoskarn and exoskarn. There is no significant mineralization in relation to this skarn system. The extent of the endoskarn subzone is very limited (often from 2 mm to 2 cm), but the exoskarn has the most extension across the contact. The endoskarn subzone can be recognized by formation of euhedral garnets adjacent to the carbonate part. In the immediate vicinity of the endoskarn, the exoskarn subzone initiates with formation of garnet and clinopyroxene in the carbonates and is extended far away from the contact as represented by vesuvianite and phlogopite minerals. Garnet is one of the most abundant minerals in this skarn system and is found in different sizes and forms. In this paper, the zonation pattern of garnet crystals in the exoskarn subzone in the immediate vicinity of intrusive body is investigated. These garnets are mainly euhedral and isotropic and in some cases anhedral and anisotropic. They are commonly cored by a grossular-rich inner part, and a sharp considerable increase in their andradite content is found toward the rim in most cases. Most studies on skarn systems consider boiling to be the most important cause for this phenomenon. This means that boiling increases the Fe content and oxygen fugacity in the final stages of the system evolution, which consequently increases the andradite content of garnet in its solid solution
S Alipour; P Shirmohammadi; Y Rahimsouri; H Bagheri
Abstract
Baba-Nazar garnet occurrence is located in northwest part of Sanandaj-Sirjan geological zone. Rock units in the area, including hornfels, garnetite and extensively weathered host rocks in contact with granite indicate garnet may have formed by metamorphism of clay-argillite, sandstone and calcareous ...
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Baba-Nazar garnet occurrence is located in northwest part of Sanandaj-Sirjan geological zone. Rock units in the area, including hornfels, garnetite and extensively weathered host rocks in contact with granite indicate garnet may have formed by metamorphism of clay-argillite, sandstone and calcareous rocks. The mineralogical and petrographical studies revealed that the evolution of mineralization has occurred during several progressive, retrograde and supergene alteration, while garnet has formed during progressive alteration. The results of the petrographical study of fluid inclusions show that most of the fluid inclusions in the garnet crystals fall in two groups: (1) Primary inclusions distributed randomly on the crystal faces and (2) secondary inclusions oriented along fractures and cleavage surfaces. Based on the inclusion diversity, four groups of these inclusions were differentiated: (1) single-phase liquid, (2) two-phase liquid-vapor, (3) solid multi-phase and (4) two-phase liquid–liquid. Micro thermometry of fluid inclusions in the garnet and quartz crystals show homogenization temperatures and salinities from 318 to 438 °C and 18.63 to 22.71 weight percent NaCl equivalent for garnet, and from 209 to 219 °C and 239 to 254 C° with 4.18 to 10.61 weight percent NaCl equivalent for quartz crystals.
N. Askari; M. H. Emami; M. Kheirkhah
Abstract
The post Eocene rhyolitic rocks of the Kahak area are located in SE of the Qom quadrangle map in scale of 1:250,000 and in the Kahak sheet in scale of 1:100,000. This area is situated at the marginal part of SW Central Iran, in the Urmia- Dokhtar magmatic belt. The rhyolitic rocks outcrop as endogenous ...
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The post Eocene rhyolitic rocks of the Kahak area are located in SE of the Qom quadrangle map in scale of 1:250,000 and in the Kahak sheet in scale of 1:100,000. This area is situated at the marginal part of SW Central Iran, in the Urmia- Dokhtar magmatic belt. The rhyolitic rocks outcrop as endogenous domes and due to the presence of these rhyolitic masses along the Meyem strike-slip fault, it can be resulted that this fault has probably played an effective role in emplacement of magma ascending. The rhyolitic rocks are calc-alkaline and on the base of chemical composition of them and the chemistry of the present garnet and mica, the rhyolitic magma is S-type and peraluminus, which, belongs to the collision geotectonic environment and suggesting the role of continental crust in generation of these rocks. Since garnet is phenocrystal and seen individually in rhyolitic rocks and it could not be crystallized in most of the basic magmas, therefore the rhyolitic rocks could not derived from the fractional crystallization of basic magma.
R. Samadi; M. V. Valizadeh; H. Mirnejad; A. A. Baharifar; S. J. Sheikh Zakariaee
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.
S. Zandifar; M.V. Valizadeh; M. A. Barghi; M. R. Foroodijahromi
Abstract
The crystallization history of a rock is recorded by the size and the distribution of its minerals. The porphyroblast crystal size in metamorphic rocks can give notable information about its growing medium. Considering the varieties of mineralogy in the Hassan-Abad's skarn and high frequency of garnet ...
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The crystallization history of a rock is recorded by the size and the distribution of its minerals. The porphyroblast crystal size in metamorphic rocks can give notable information about its growing medium. Considering the varieties of mineralogy in the Hassan-Abad's skarn and high frequency of garnet porphyroblasts in different metamorphic zones and special different sizes in the first metamorphic zone of the NE skarn, the crystal size distributions of this mineral is studied. With regard to this, digital photos of cutting surface were provided and analyzed by JMicrovision software. It has been expected, two different slopes can show three suspections: 1- parent rock composition effect; 2- crystal growing time; 3- fluid flow around plutonic rock. According to the presence of clintonite, vesuvianite and garnet and as many as joints in the region, the role of fluid in growing the size of garnet porphyroblast in part of the first metamorphic zone seem to be noticeable.
