Economic Geology
Zahra Kaboodi; Majid Ghaderi; Ebrahim Rastad
Abstract
The Kahak copper deposit occurs in the Eocene volcano-sedimentary sequence of Qom region, Urumieh-Dokhtar magmatic arc. The oldest rock unit in this sequence is a crystal tuff, overlain by tuff, andesite, sandstone, conglomerate, and limestone. Host rocks to the Kahak deposit include andesite and tuff, ...
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The Kahak copper deposit occurs in the Eocene volcano-sedimentary sequence of Qom region, Urumieh-Dokhtar magmatic arc. The oldest rock unit in this sequence is a crystal tuff, overlain by tuff, andesite, sandstone, conglomerate, and limestone. Host rocks to the Kahak deposit include andesite and tuff, and the geometry of mineralization is stratabound. Mineralographical studies show that the ore minerals are pyrite, chalcopyrite, chalcocite, native copper, bornite, galena, covellite, digenite, and malachite accompanied by magnetite, and hematite. Based on mineralogical studies, two types of alteration are recognized in the volcanic rocks of the area, general alteration, and ore mineral alteration. The propylitic alteration is an indication of general alteration. The main alteration types in the mineralized zone of the deposit include carbonatization, silicification, chloritization, epidotization, and zeolitic. Dissemination, open space filling, vein-veinlet, pseudo-lamination, and replacement are the major textures and structures of the ore minerals at Kahak. Two major stages are distinguished for mineralization at the Kahak deposit. The first stage is volcanism and pyrite formation in the host rocks (andesite and tuff), producing reduction state. The second stage involves diagenesis and entering Cu-rich oxidant fluids replacing Cu for Fe in the pyrite and forming Cu-sulfides and hematite and mineralization. The Kahak copper deposit shows high similarities in geometry, host rock, mineralogy, texture and structure and genetic model with the Manto-type copper deposits worldwide.
Negin Fazli; Majid Ghaderi; David Lentz; Jianwei Li
Abstract
The North Narbaghi deposit is located approximately 26 km northeast of the city of Saveh in the central part of Urumieh-Dokhtar magmatic arc of Iran. In this area, the Oligo-Miocene intrusive rocks cut the Eocene volcano-sedimentary rocks intruding into the surrounding rocks causing extensive alteration ...
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The North Narbaghi deposit is located approximately 26 km northeast of the city of Saveh in the central part of Urumieh-Dokhtar magmatic arc of Iran. In this area, the Oligo-Miocene intrusive rocks cut the Eocene volcano-sedimentary rocks intruding into the surrounding rocks causing extensive alteration zones such as phyllic, argillic, propylitic and tourmalinization. The intrusive rocks include diorite, monzodiorite, megadiorite with calc-alkaline nature which formed as a result of subduction of the Neo-Tethyan oceanic crust beneath the Central Iranian block. The epithermal Ag-Cu mineralization at North Narbaghi, with vein-veinlet and breccia geometries is mainly hosted in andesite, lithic tuff, diorite and monzodiorite. At the North Narbaghi deposit, ore minerals can be divided into four groups: sulfides (chalcopyrite, pyrite, sphalerite, bornite), sulfosalts (tetrahedrite, tennantite), carbonates (azurite, malachite) and oxides (hematite, goethite). The alteration shows a relative concentration pattern at the North Narbaghi deposit; the argillic, sericitic and calcite alteration types are in close connection with the Ag-Cu mineralization and the propylitic and tourmalinization alteration types occur at the margin of mineralization. The main characteristics of mineralization such as geodynamic environment, host rocks, mineralogy, metal content, geometry, alteration and comparing these features with the characteristics of epithermal deposits, show that the North Narbaghi deposit can be classified as a typical intermediate-sulfidation (IS) epithermal mineralization.
Economic Geology
Hadi Mohammaddoost; Majid Ghaderi; Jamshid Hassanzadeh
Abstract
Sulfur isotope data on pyrite, chalcopyrite and molybdenite in the A, B and D type veinlets in porphyry systems of the Meiduk cluster, located in northwestern part of the Kerman copper belt, show that these systems have near zero δ34S values. Sulfur isotope composition for the Chah-Firouzeh and ...
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Sulfur isotope data on pyrite, chalcopyrite and molybdenite in the A, B and D type veinlets in porphyry systems of the Meiduk cluster, located in northwestern part of the Kerman copper belt, show that these systems have near zero δ34S values. Sulfur isotope composition for the Chah-Firouzeh and Iju deposits and Serenu, God-e-Kolvari and Kader prospects is from -1.4 to +2.5 (average +0.31), -1.3 to +1.1 (average +0.07), +0.1 to +2.4 (average +0.87), -1.5 to +0.2 (average -0.1) and -4.1 to +1 (average -1.04), respectively. These results suggest a magmatic source for sulfur. Also, limited range of isotopic variations and analogous isotopic composition for the three types of veinlets reveals that with evolution of the hydrothermal system, no significant changes occurred in the primary and relatively homogenous source of sulfur. Comparison between the data for the Meiduk cluster with available data from other deposits in middle and southern parts of the Kerman belt suggested that in porphyry systems of the northwestern, and to some extent southern parts, of the Kerman Cenozoic magmatic arc, sulfur was provided by a mafic magma originated from metasomatized subcontinental lithospheric mantle (SCLM) which was affected by assimilation with continental crust; while in the southern parts, processes related to subduction and fluids from seawater and associated sediments had a major role in their sulfur isotope composition.
S Afzali; N Nezafati; M Ghaderi
Abstract
The Gazestan magnetite–apatite deposit is located 78 km east of Bafq, in the Bafq-Poshtebadam subzone of the Central Iran structural zone. The rock units in the area belong to the Rizou series and consist of carbonate rocks, shale, tuff, sandstone and volcanic rocks. Intrusive rocks in the form ...
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The Gazestan magnetite–apatite deposit is located 78 km east of Bafq, in the Bafq-Poshtebadam subzone of the Central Iran structural zone. The rock units in the area belong to the Rizou series and consist of carbonate rocks, shale, tuff, sandstone and volcanic rocks. Intrusive rocks in the form of stock and dyke crop out as granodiorite and granite in various places. Trachytic and dacitic rocks in the area are green due to chloritic alteration and host iron and phosphate mineralization. The main alteration types are chloritic and argillic, while sericitic, potassic, and silicic alterations as well as tourmalinization and epidotization are also found in the rock units. Five forms of mineralization are distinguished in the Gazestan deposit, including massive iron ore with minor apatite, apatite-magnetite ore, irregular vein-veinlets (stockwork) in the brecciated green rock and disseminated and monomineralic massive apatite veins. Fluid inclusion studies were conducted on the apatites of two stages. According to these studies, temperature and salinity values in the stage-I apatite are higher than those in stage-II apatite. Lower salinity values in the stage-II apatite could be due to contamination of magmatic fluids with meteoric waters during later stages of mineralization. Oxygen, hydrogen and carbon stable isotope composition of magnetite, quartz, apatite and calcite; and calculation of oxygen isotope composition in the fluid equilibrated with the oxide minerals suggest mixing the magmatic fluids with basin brines in mineralization of the Gazestan deposit.
S. M. Heidari; M. Ghaderi; H. Kouhestani
Abstract
Arabshah gold deposit formed through hydrothermal activity with an age of ~11 Ma (based on zircon U-Pb dating by LA-ICP-MS), in northwestern Iran. This hydrothermal activity is a part of the Urumieh-Dokhtar magmatic arc (UDMA), leading to mineralization in this area, similar to Zarshouran, Aghdarreh ...
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Arabshah gold deposit formed through hydrothermal activity with an age of ~11 Ma (based on zircon U-Pb dating by LA-ICP-MS), in northwestern Iran. This hydrothermal activity is a part of the Urumieh-Dokhtar magmatic arc (UDMA), leading to mineralization in this area, similar to Zarshouran, Aghdarreh and Sarigunay gold deposits. Host rocks are a series of lower Paleozoic sedimentary sequences, cut by calc-alkaline to alkaline (high potassium) dacitic domes. Gold mineralization is mainly observed as vein-veinlets, open space filling, disseminated and brecciation in the deposit. The mineralization in terms of hydrothermal alteration (decalcification, minor argillic, sulfidization, dolomitization and silicification) and mineralization development process is associated with brecciation and deposition of base metal sulfides, iron, arsenic and antimony, similar to deposits associated with geothermal systems (low sulfidation epithermal) in volcanic arcs, but the host rock here is sedimentary. Sulfide minerals in the ore include pyrite, arsenopyrite, orpiment and realgar, stibnite, galena, sphalerite and minor amounts of chalcopyrite. Gold mineralization occurred in the form of released grains of oxidized pyrite, the tiny (invisible) in the sulfide phases such as arsenian pyrite for solid solution. The Arabshah deposit shows characteristic alteration assemblages and ore minerals (As, Sb, Hg, base metals) of epithermal low sulfidation deposits. It has been formed in relation to the mid-upper Miocene, high-level magmatic-hydrothermal activity within an extensional regime at the last stages of the UDMA activity in northwestern Iran.
Economic Geology
A. Baharvandi; M. Lotfi; M. Ghaderi; M. R. Jafari; H. A. Tajeddin
Abstract
Shekarbeig barite deposit is located 46 km southwest of Mahabad in northwestern part of the Sanandaj-Sirjan zone. The outcropped rock units in the area are Late Protrozoic metamorphosed volcano-sedimentary rocks, equivalent to Kahar Formation. The main ore mineral occurs as stratiform barite lenses in ...
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Shekarbeig barite deposit is located 46 km southwest of Mahabad in northwestern part of the Sanandaj-Sirjan zone. The outcropped rock units in the area are Late Protrozoic metamorphosed volcano-sedimentary rocks, equivalent to Kahar Formation. The main ore mineral occurs as stratiform barite lenses in three horizons accompanied by sulfide minerals as massive and/or parallel bands within metamorphosed rhyolitic tuffs (metatuff). The deposit footwall is composed of phyllite and slate crosscut by silicic and sulfide-bearing barite veins and veinlets (stringer zone). Primary minerals in the ore are mainly barite, pyrite, marcasite, chalcopyrite and bornite and secondary minerals are chalcocite, covellite, malachite, siderite, goethite, hematite and other iron hydroxides. Gangue minerals include quartz, sericite, calcite, dolomite, feldspar and chlorite. In terms of metallic ores, the Shekarbeig deposit does not vary much having only pyrite and chalcopyrite. Types of fluid inclusions in the Shekarbeig deposit are two-phase liquid-vapour (LV), mono-phase vapour and mono-phase liquid; two-phase liquid-vapour being the dominant type in both stringer and stratiform parts. Sulfur isotope data indicate that seawater was the main mineralizing fluid for Shekarbeig mineralization. These data suggest that complete reduction of recent seawater sulfate and the rate of mixing of hydrothermal solution with cold waters in deep parts of the basin may result in precipitation of large amount of sulfides in the stringer and stratifrom zones. On the other hand, partial reduction of recent seawater sulfates provided required sulfur for the deposition of barite. Geological evidence, evaluation, lithostratigraphy, mineralization geometry and the results of fluid inclusion and sulfur isotope studies for samples from the Shekarbeig deposit indicate derivation of the hydrothermal fluids of low salinity and moderate temperature from seawater and circulation and upward movement by a heating source (probably subvolcanic intrusions) and finally cooling and deposition of the fluids as sulfate and sulfide on the sea floor due to mixing with seawater, similar to massive sulfide Kuroko-type deposits.
T Salehi; M Ghaderi; N Rashidnejad-Omran
Abstract
Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located in northwestern part of Urumieh-Dokhtar volcano-plutonic zone, 90 km southwest of Zanjan. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene dacitic subvolcanic dome, rhyodacitic volcanics and ...
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Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located in northwestern part of Urumieh-Dokhtar volcano-plutonic zone, 90 km southwest of Zanjan. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene dacitic subvolcanic dome, rhyodacitic volcanics and andesite porphyry dykes. The main mineralization at Gomish-Tappeh deposit has occurred in a steeply deeping normal fault and fracture system defined by NE-SW trend in three stages including hydrothermal breccias, silicic-sulfidic, silicic-sulfidic-carbonate veins and veinlets and late banded veins (rich in silica and specularite). Host rocks to mineralization include dacitic crystal lithic tuff, dacitic subvolcanic dome, and specifically acidic tuff. Paragenetic minerals at the deposit consist of pyrite, arsenopyrite, chalcopyrite, bornite, galena, low-Fe sphalerite, tetrahedrite, tennantite and specularite. The main alteration types at the area are silicic, silicic-sulfidic, sericitic, carbonate, argillic and propylitic. Based on element distribution and frequency patterns in the ore samples, among base metals, Zn, Pb, Cu and Ag show the highest concentrations. Average grades in the ore veins at Gomish-Tappeh deposit are: 6% Zn, 4% Pb, 2% Cu, 88 ppm Ag and 44 ppb Au. Fluid inclusion microthermometric studies on quartz crystals of the first and second stages of mineralization indicate homogenization temperatures of 260-367 °C, salinities of 9.1-16.9 wt% NaCl equiv., and approximate mineralization depth of 956 m below the paleowater table. Considering high salinity fluids and base metal contents, it is likely that base metals and silver were transported by chloride complexes. Fluid inclusion studies, hydrothermal breccias, banded-colloform-crustiform textures and amorphous silica indicate that boiling is the main factor for instability of the complexes and eventually, ore deposition.
N Mazhari; A Malekzadeh Shafaroudi; M Ghaderi
Abstract
The Senjedak-I prospect area is one of the six eastern anomalies of Sangan iron mine. Geologic units in the area consist of Jurassic shales and sandstones, skarn rocks and Tertiary biotite monzonite and biotite syenogranite intrusive rocks. Due to the severe alteration of biotite monzonite porphyry intrusive, ...
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The Senjedak-I prospect area is one of the six eastern anomalies of Sangan iron mine. Geologic units in the area consist of Jurassic shales and sandstones, skarn rocks and Tertiary biotite monzonite and biotite syenogranite intrusive rocks. Due to the severe alteration of biotite monzonite porphyry intrusive, geochemical studies have focused on the biotite syenogranite.
This granular intrusive consists of alkali feldspar, plagioclase, quartz, biotite and accessory minerals such as zircon, sphene, apatite and magnetite, with weak sericitic, argillic and silicic alteration. Biotite syenogranite rock is rich in silica (68.7 to 77.2 wt.%) and is chemically peraluminous and has generated by fractional crystallization from an I-type granitic magma poor in P (average 0.1% P2O5). This intrusive rock falls in the range of I-type granites and is oxidized. REE values indicate negative Eu anomaly, mild enrichment of LREE, a positive pattern close to flat HREE, negative anomalies of Ba, Sr, La, Ce, Ti, and Eu. On the basis of Rb, Nb, Yb, Hf, and Ta, tectonic setting of samples fall in Volcanic Arc Granite (VAG) and Post Collision Granite (post-COLG) divisions.
The most important event in Senjedak-I area is the penetration of Fe-bearing fluids in carbonate rocks, their recrystallization, skarnification (prograde and retrograde), and iron ore deposition that could be explained by the occurrence of calc-silicate minerals.
The skarn has been separated into 4 zones on the basis of abundance of the calc-silicates: garnet skarn, phlogopite skarn, epidote skarn, and amphibole skarn.
According to Electron Probe Micro Analysis (EPMA), the composition of garnets is andradite-grossular (An 100-42.6 Gr 0-55.32 Sps 0-1.39) and pyroxenes are diopside-hedenbergite (Di 63-92 Hd 4-35 Jo 0.5-3.9).
Mineralization in this prospect area formed as stratabound and massive bodies in the carbonate rocks. The main ore mineral is magnetite (40%) with minor amounts of pyrite. Secondary minerals are hematite and malachite. The FeO in the magnetite is 91.7% and the S content is 0.03%. The Senjedak-I anomaly places along the eastern part of Dardvay deposit (in central division of Sangan mine) and the geochemical similarities of intrusive rocks, chemistry of skarn minerals, and pyroxene and garnet composition confirms that the Senjedak-I is a part of Dardvay, which is separated by a main fault with southeast-northwest trend.
M Alimohammadi; S Alirezaei; M Ghaderi; D.J Kontak
Abstract
The Daraloo and Sarmeshk copper deposits lie in a northwest-trending fault zone, 10 km long and 0.5-1 km wide in the southern section of the Kerman copper belt, south Iran. The area is marked by a series of Late Eocene-Oligocene granodiorite and Miocene porphyritic tonalite-granodiorite intrusions that ...
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The Daraloo and Sarmeshk copper deposits lie in a northwest-trending fault zone, 10 km long and 0.5-1 km wide in the southern section of the Kerman copper belt, south Iran. The area is marked by a series of Late Eocene-Oligocene granodiorite and Miocene porphyritic tonalite-granodiorite intrusions that cut Eocene andesitic and basaltic lava flows and pyroclastic rocks. Mineralization in both deposits is associated with the Miocene porphyritic intrusions. Both volcanic and plutonic rocks are intruded by post-mineralization diabasic, andesitic and rhyolitic dykes. Representative samples from various rocks were analyzed for major oxides and a wide range of elements. The samples display calc-alkaline affinities; the volcanic rocks are metaluminous, and the intrusive rocks are peraluminous. On primitive mantle- and chondrite-normalized plots, all rocks are characterized by enrichment in large ion lithophile elements and light rare earth elements, relative to high field strength elements and heavy rare earth elements. The features, combined with the negative anomalies for Nb, Ta, and Ti, are characteristic of the subduction- related magmas.The Miocene tonalites are most fractionated, with LaN/YbN ratios ranging between 7.81 and 18.21. This ratio in granitoid rocks is between 6.61 and 7.56. The volcanic rocks are least fractionated, with LaN/YbN ratios from 1.52 to 5.16 .The geochemical attributes of the intrusive bodies from both Daraloo and Sarmeshk are consistent with significant contribution from sediments and crustal materials in the source area, compared to that introduced by fluids released from a subducting slab. The volcanic rocks are, however, appear to have been least affected by crustal materials, but slightly influenced by slab-derived fluids. Plots of samples from all plutonic and volcanic rocks on various discrimination diagrams indicate a transition from an island-arc setting in Paleocene-Eocene to a continental margin volcanic arc setting in Neogene. This is in agreement with earlier works on the evolution of the Kerman belt.
H Mohammaddoost; M Ghaderi; N Rashidnejad-Omran
Abstract
Qamsar cobalt deposit is located 26 km south of Kashan, in the middle part of Urumieh-Dokhtar magmatic arc. Exposed rock units in the area include Eocene volcanics, Qom Formation marine sediments and plutonic bodies. The intrusive bodies have quartz-diorite to granodiorite composition as well as porphyry ...
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Qamsar cobalt deposit is located 26 km south of Kashan, in the middle part of Urumieh-Dokhtar magmatic arc. Exposed rock units in the area include Eocene volcanics, Qom Formation marine sediments and plutonic bodies. The intrusive bodies have quartz-diorite to granodiorite composition as well as porphyry microdiorite. Intruding bodies into the Eocene volcanics and Qom Formation units caused recrystallization and metamorphism and formed assemblages of skarn minerals such as garnet, pyroxene, epidote, tremolite and actinolite. Mineralization occurred as endo-skarn and exo-skarn in massive, vein, brecciated, open space filling and diffusion forms. Magnetite is the main ore mineral and is accompanied by cobaltite, chalcopyrite and pyrite. Fluid inclusion microthermometry studies were performed on prograde stage garnet and pyroxene and retrograde stage quartz. Microthermometry studies show homogenization temperatures from 400 to more than 600°C and from 180 to 200°C as well as salinities between 12 and 20% and between 5.8 and 11.9% wt NaCl equiv. for prograde and retrograde phases, respectively. Isotopic thermometry on pyrite-chalcopyrite pair minerals gives 241 to 528°C and that for quartz-magnetite pair minerals gives 441 to 549 °C. Sulfur and oxygen isotopic ratios offer magmatic origin which mixed with basinal fluid for this mineralization.
S Shahbazi; M Ghaderi; N Rashidnejad-Omran
Abstract
The Bashkand iron deposit is located in 16 km southwest of Soltanieh, in Central Iran Structural Zone. The rock units in the area include alternations of metamorphosed sedimentary rocks of the Kahar Formation, Khorramdarreh granite and an andesitic dike. The major alteration types are argillic, potassic, ...
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The Bashkand iron deposit is located in 16 km southwest of Soltanieh, in Central Iran Structural Zone. The rock units in the area include alternations of metamorphosed sedimentary rocks of the Kahar Formation, Khorramdarreh granite and an andesitic dike. The major alteration types are argillic, potassic, chloritic, sericitic and quartz-carbonatic in composition. N30-50W trend and S30-50W dip mineralization conforms primary bedding, foliation of phyllites as well as parallel faults. Mineralogical paragenesis includes: 1) Grossularite, pyroxene, idocrase; 2) Andradite, pyroxene, forsterite, phlogopite, magnetite; 3) Tremolite, serpentine, epidote, talc, biotite, magnetite, specularite and sulfides, and they have been cut by quartz-carbonate veins. The presence of magnetite synchronous with quartz and feldspar in the intrusive body, unconformity in behavior pattern of Fe2O3 with SiO2 and Al2O3, and its conformity with other major oxides as well as Cu and Zn, similarity of REE pattern in the ore, the intrusive body and skarnized host rocks as well as no similarity with the less altered host rocks, are the signs of sourcing ore from the intrusive-deriven fluids. Mixing of these fluids with meteoric water together with increasing in oxygen fugacity in the retrograde metasomatism stage led to ore mineralization.
S.M Heidari; M Ghaderi; H Kouhestani; M Hosseini
Abstract
The Touzlar epithermal gold deposit formed within the high-K calc-alkaline (shoshonitic) andesitic volcanic units in northwestern Iran. The volcanic complex is in fact a part of magmatism related to the Urumieh-Dokhtar Magmatic Belt crosscutting northeastern rim of the Sanandaj-Sirjan Metamorphic-Magmatic ...
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The Touzlar epithermal gold deposit formed within the high-K calc-alkaline (shoshonitic) andesitic volcanic units in northwestern Iran. The volcanic complex is in fact a part of magmatism related to the Urumieh-Dokhtar Magmatic Belt crosscutting northeastern rim of the Sanandaj-Sirjan Metamorphic-Magmatic Zone. This magmatic system is composed of pyroclastics and lava flow sequences. The volcanic and subvolcanic rocks of the complex constitute a part of the volcano-sedimentary sequence of the Qom Formation, which formed in an extensional regime of basement uplifting and intra-continental basin. Zircon LA-ICP-MS U-Pb dating shows age between 18.4±1.0 and 18.7±0.55 Ma (Lower Miocene) for the volcanism. The hydrothermal alteration types (propylitic, argillic, phyllic, sericitic, advanced argillic and silicification) and evolving mineralization in relation to brecciation and deposition of copper sulfides and sulfosalts imply that the mineralization at Touzlar is similar to that of high sulfidation deposits in volcanic settings. The gold mineralization textures in the Touzlar deposit appear as disseminated, open space filling, veins and veinlets. The main sulfide minerals are pyrite, chalcopyrite, bornite, as well as small amounts of enargite, chalcocite, covellite, digenite, tetrahedrite, galena and sphalerite. The gold in this mineralization occurs as freed from oxidized pyrite grains, also in quartz in hydrothermal breccias as well as solid solution in other minerals such as sulfides and sulfosalts. The main difference in the formation of Touzlar with high sulfidation deposits is in its setting. The formation setting for this mineralization confirms its genesis at low depth and pressure. The deposit formed at the shallow submarine environment of the Qom basin in relation to extensional tectonic regime, while high sulfidation epithermal deposits usually form in subaerial environments related to tensional settings. Structural, host rock type, alteration, paragenesis and Au-Ag (Cu) ore mineralization characteristics of the deposit suggest that Touzlar is most similar to subvolcanic intrusion-related epithermal (high sulfidation) gold deposits formed in intra-arc extensional settings.
H Kouhestani; M.H Ghaderi; M.H Emami; S Meffre; V Kamenetsky; J McPhie; Kh Zaw
Abstract
The Chah Zard Ag-Au deposit, a typical breccia-hosted low- to intermediate-sulfidation epithermal system, is located within late Miocene andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar magmatic belt. The orebodies are emplaced in breccia bodies dominantly hosted by ...
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The Chah Zard Ag-Au deposit, a typical breccia-hosted low- to intermediate-sulfidation epithermal system, is located within late Miocene andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar magmatic belt. The orebodies are emplaced in breccia bodies dominantly hosted by rhyolite porphyries. Systematic whole-rock geochemical investigations on the volcanic rocks show that both intermediate and felsic rocks are characterized by significant Large Ion Lithophile Elements (LILE) and Light Rare Earth Elements (LREE) enrichment coupled with High Field Strength Elements (HFSE) depletion. These geochemical data indicate subduction-related magmatic arc affinity for the volcanic rocks, and suggest that hornblende fractionation appears to be an important controlling factor on the evolution of mineralized subvolcanic rocks. Although the rhyolite porphyry has relatively high 87Sr/86Sr ratios, the volcanic rocks have similar Sr and Nd isotopic compositions, displaying 87Sr/86Sr range of 0.704910-0.705967 and εNd(i) values of +2.33 to +2.70. These data suggest that the rhyolitic magmas probably represent the final diffetentiates of parental andesitic magmas with minor crustal contamination. The andesitic magmas generated from partial melting of a mixture of an incompatible element depleted anhydrous asthenospheric mantle source and a hydrous LILE and LREE enriched lithospheric mantle source in response to slab-break-off and upwelling of asthenospheric mantle. The rhyolite porphyry is inferred to have supplied heat that drove the convective hydrothermal system at Chah Zard deposit, but also provided some of the fluid sources responsible for the development of the Chah Zard epithermal system.
Majid Ghaderi; H. Kouhestani; M. H. Emami; K. Zaw
Abstract
The breccia-hosted epithermal Ag-Au deposit of Chah Zard is located within an andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar magmatic belt. At this location, magmatic and hydrothermal activity was associated with local extensional tectonics, formed in the Dehshir-Baft ...
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The breccia-hosted epithermal Ag-Au deposit of Chah Zard is located within an andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar magmatic belt. At this location, magmatic and hydrothermal activity was associated with local extensional tectonics, formed in the Dehshir-Baft strike-slip fault system. The host rocks of the volcanic complex consist of Eocene sedimentary and volcanic rocks covered by Miocene sedimentary rocks. LA-ICP-MS U–Pb zircon geochronology yields ages between 6.36±0.14 and 6.19±0.24 Ma, and a mean age of 6.23±0.16 Ma for magmatic activity at Chah Zard. Breccias and veins were formed during and after the waning stages of strong explosive eruption of magmatic-hydrothermal and phreatomagmatic brecciation events due to shallow emplacement of the rhyolite porphyry. Detailed systematic mapping leads to the recognition of three distinct breccia bodies: the volcaniclastic breccia with a dominantly clastic matrix, the gray polymict breccia with a greater proportion of hydrothermal cements, and the mono-polymict breccia with argillic groundmass matrix. The polymictic breccias generated bulk-mineable ore, whereas the volcaniclastic breccia is relatively impermeable and largely barren. Variable hydrothermal alteration occurs in outcrops, covering about 9 km2 at Chah Zard. Hydrothermal alteration assemblages are zoned around the breccias and veins, consisting of secondary quartz, illite, pyrite, adularia, chlorite, various carbonate minerals, and minor K-feldspar. Iron oxide-hydroxide, jarosite, gypsum, kaolinite, halloysite and rare alunite are the supergene alteration minerals replacing primary minerals, and filling the fractures and vugs. Precious metals occur with sulfide and sulfosalt minerals as disseminations in the veins and breccia cement. There is a progression from pyrite-dominated (stage 1) to pyrite-base metal sulfide and sulfosalt-dominated (stages 2 and 3) to base metal sulfide-dominated (stage 4) breccias and veins. Deposition of gangue minerals progressed from illite-quartz to quartz-adularia, carbonate and finally gypsum-dominated assemblages. Free gold occurs in stages 2 and 4, principally as intergrown with pyrite, quartz, chalcopyrite, galena, sphalerite, and Ag-rich tennantite-tetrahedrite; and also as inclusions in pyrite. The U-Pb zircon age of 6.19±0.24 Ma for emplacement of the rhyolitic magmas represents the maximum age of mineralization at Chah Zard. It may indicate that there was a previously unrecognized mineralization event in Urumieh-Dokhtar at this time.
A. Najafi; M.H. Karimpour; M. Ghaderi
Abstract
Based on data processing for 51 stream sediment, 115 rock and 22 heavy mineral samples, together with field evidence for mineralization and alteration, mineralization pattern for Rahimi copper-gold prospecting area was analyzed. Twelve primary and secondary geochemical halo maps for Au-Ag-As-Ba-Cu-Co-Hg-Mo-Pb-Sb-W-Zn ...
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Based on data processing for 51 stream sediment, 115 rock and 22 heavy mineral samples, together with field evidence for mineralization and alteration, mineralization pattern for Rahimi copper-gold prospecting area was analyzed. Twelve primary and secondary geochemical halo maps for Au-Ag-As-Ba-Cu-Co-Hg-Mo-Pb-Sb-W-Zn as well as maps showing iron-oxide minerals in heavy mineral samples were analyzed using new geological and mineralization field evidence for the area. Therefore, two distinct promising areas, with IOGC and porphyry copper mineralization patterns were proposed for semi-detailed studies.
M. E. Moslempour; M. Khalatbari-Jafari; T. Morishita; M. Ghaderi
Abstract
Mantle sequences exposed in west of Fannuj-Maskutan area comprise of lherzolite and porphyroclastic cpx-bearing harzburgite in the lower part and recrystallized fine-grained lherzolite with chromitite lenses in the upper parts of the sequence. Petrography studies and microprobe data show evidence ...
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Mantle sequences exposed in west of Fannuj-Maskutan area comprise of lherzolite and porphyroclastic cpx-bearing harzburgite in the lower part and recrystallized fine-grained lherzolite with chromitite lenses in the upper parts of the sequence. Petrography studies and microprobe data show evidence of melt/peridotite interactions, post-melting processes and subsolidus interactions associated with the appearance of two generations of deformed primary pyroxene-olivine and fine-grained pyroxene-olivine-amphibole neoblasts. Second generation of minerals formed as inclusion, interstitial and fine-grained. These two groups of minerals have different geochemical characteristics, i.e., the first group are comparable with abyssal peridotites and the second group are comparable to suprasubduction peridotites. Therefore, the chemical compositions of different generations of minerals show different petrogenesis for ultramafic rocks of the Fannuj-Maskutan ophiolitie complex. Interpretation of whole rock chemical data indicate that these rocks have a depleted MORB mantle source which underwent 5-15% partial melting. Rare earth element patterns normalized with chondrite standard values and compared with patterns of depleted MORB mantle (DMM), indicate enrichment in LREE/MREE ration and show U-shape patterns. Thus, the peridotites of the Fannuj-Maskutan ophiolitie have experienced multistage evolution and show characteristics of abyssal environment to suprasubduction zone. It might be said that transition from abyssal environment to suprasubduction has been affected by fluids derived from the subducted slab.
M. Abdi; Majid Ghaderi; N. Rashidnejad-Omran; E. Rastad
Abstract
Azna tungsten (copper) ore occurrence is located 2 km west of Azna, in Lorestan province. The region is placed in Sanandaj-Sirjan structural zone of Iran, at the complex deformation sub-zone. In this area, tungsten-copper mineralization occurs as stratiform-stratabound in mylonitic meta-rhyolite and ...
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Azna tungsten (copper) ore occurrence is located 2 km west of Azna, in Lorestan province. The region is placed in Sanandaj-Sirjan structural zone of Iran, at the complex deformation sub-zone. In this area, tungsten-copper mineralization occurs as stratiform-stratabound in mylonitic meta-rhyolite and semi-pelitic country rock within upper Triassic volcano sedimentary sequence. The sequence consists of meta-rhyodacite, amphibolite (basic meta-volcanic), black schist, meta-rhyolite and pelitic schist with a predominance of volcanics over sediments. Ore mineral textures cover a wide variety from laminated, disseminated, choloform, bounded to open space filling. Mineralization occurs in several stages concentrated through regional (medium to high grade facies) metamorphism, folding and mylonitization of shear zone (ductile) and fractures of brittle deformation events. In this ore occurrence, metamorphism and deformations process had confused detection of proximal or distal mineralization. But base of comparison of Azna tungsten mineralization with both typical proximal on Felbertal and Austroalpine and distal on Broken Hill and Kleinarltal tungsten mineralizations has shown that they are more similar to the proximal mineral deposits.
Ghodratollah Rostami Paydar; M. Lotfi; M. Ghaderi; A. Amiri; M. Vossoughi-Abedini
Abstract
Baba-Ali and Galali iron deposits in west of Hamedan are emplaced within the Songhor volcano-sedimentary sequence of Sanandaj-Sirjan geological-structural zone. Mineralography and SEM-EDAX analyses on magnetite iron ores at both deposits for better understanding of mineralogy and crystal-chemistry of ...
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Baba-Ali and Galali iron deposits in west of Hamedan are emplaced within the Songhor volcano-sedimentary sequence of Sanandaj-Sirjan geological-structural zone. Mineralography and SEM-EDAX analyses on magnetite iron ores at both deposits for better understanding of mineralogy and crystal-chemistry of the ores have shown some interesting results. Studies on concentrations of some trace elements such as V, Co, Ni, Cu, Cr, Ti, Au, PGE as well as S and P impurities in the ore indicate that only some of the primary pyrites have considerable concentrations of Pt. It seems that other generations of pyrite and magnetite are depleted in these trace elements. Late stage hydrothermal fluids that lead to mineralization of pyrite in calcite-quartz gangue veins, have also been impotant for gold mineralization and pyrite has actually acted as a favorable carrier for Au. Detection of abundant phlogopite and trace element concentration patterns at Galali iron ore have strengthened volcanogenic magnesian skarn hypothesis.
M. Shirkhani; Majid Ghaderi; N. Rashidnejad-Omran; R. Mohammadi-Niaei
Abstract
AyQalesi polymetal deposit is located 30 km southeast of Takab in Orumieh-Dokhtar structural zone. For Enzyme LeachSM analysis at the deposit, 723 samples were collected from B-horizon soils. Based on the analytical results and data interpretation, six oxidation anomalies, A through F, have been defined. ...
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AyQalesi polymetal deposit is located 30 km southeast of Takab in Orumieh-Dokhtar structural zone. For Enzyme LeachSM analysis at the deposit, 723 samples were collected from B-horizon soils. Based on the analytical results and data interpretation, six oxidation anomalies, A through F, have been defined. Five of these are recommended as drill targets while one, anomaly C, is not recommended for drilling because it appears to represent a buried intrusion without significant Zn enrichment. Anomalies B, D and E have very high Zn values. For anomaly D, this is because of outcropping Zn mineralization and the presence of mine waste at surface. Anomalies B and E may occur above shallowly buried mineralized zones. Anomalies A, C and F contain much less Zn. Anomaly A may overlie a concealed zone of Zn mineralization that could be buried to a substantial depth. Anomaly F is not recommended for drilling because it appears to be a quite narrow mineralized zone.
H.R. Vatanpour; A. Khakzad; M. Ghaderi
Abstract
Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic ...
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Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic evaluation of chromite deposits specifically in ophiolitic complexes. Chondrite-normalized PGE patterns of the chromitites related to ophiolites have a negative slope suggesting that during initial stages of magma crystallization, chromite preferentially removed compatible PGE from the magma. These patterns in the Sabzevar chromitites imply that these rocks are related to ophiolitic complexes (Alpine type). Chromite ore bodies which exhibit a relatively high incompatible/compatible element (Pd/Ir, Cu/Ni) ratios are derived from a more evolved magma with a lower fractional melting degree and do not seem to be of economic importance; this ratio in Al-rich chromites is higher than that of Cr-rich type. Pd/Ir ratio in Sabzevar chromitites on the average is less than 1, similar to many important chromite ore bodies related to ophiolitic complexes throughout the world. This ratio being low, as well as high chromium number (Cr/Cr+Al>0.60) suggests that this complex can be considered to contain a significant potential for economic and metallurgical chromite. Furthermore, the complex does not contain chromitites of uniform composition in chalcophile elements. PGE patterns of peridotites in the study area also show that these units in upper parts of the Gaft area are similar to ultramafic cumulates of oceanic crust, while in lower parts of Faroumad area related to mantle sequences.
A. R. Ghiasvand; M. Ghaderi; N. Rashidnejad-Omran
Abstract
The iron deposits in north of Semnan are located in the south of Central Alborz structural zone. Stratigraphically, the area consists of Paleozoic to Quaternary rock series exposures. The area has been affected by Semnan, Darjazin, Attari and Diktash faults. An intermediate to acidic granitoid body of ...
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The iron deposits in north of Semnan are located in the south of Central Alborz structural zone. Stratigraphically, the area consists of Paleozoic to Quaternary rock series exposures. The area has been affected by Semnan, Darjazin, Attari and Diktash faults. An intermediate to acidic granitoid body of calc-alkaline and metaluminous composition, representing I-type granite characteristics, has intruded the Eocene volcanopyroclastic rocks in the north of Semnan. Skarn development and iron mineralization have occurred at the contact of the intrusive body and the volcanopyroclastic rocks. Mineral Paragenesis consists of magnetite accompanied by hematite, oligist, pyrite, chalcopyrite, garnet, pyroxene and epidote. Geometry of the ore bodies is massive, lenticular and vein type and their texture is disseminated, brecciated, vein-veinlet and massive. Dominant alterations in the area are propylitic, argillic, silicic, sericitic, chloritic and pyritic, respectively. The intrusive body has many similarities with intrusive bodies which form Fe-skarn deposits. Variations in the calculated parameters for REE indicate contribution of magmatic origin hydrothermal fluids to mineralization and that the intrusive body has had the dominant role as source of the skarn ore materials. Along with the intrusion, emplacement and crystallization of intrusive body, Fe-bearing fluids have intruded the volcanopyroclastic rocks, forming sodic metasomatism and deposited iron ores in the north of Semnan which have many similarities with calcic Fe-skarn deposits.
M. Abdi; Majid Ghaderi; N. Rashidnejad-Omran; A. Najafi
Abstract
Two cases of tungsten-copper vein-type mineralization have been studied in the Nezam-abad and Deh-hossein areas, in southwest of Shazand. The hydrothermal quartz-tourmaline mineralized veins have different host rocks (biotitic-granite and meta-sandstone). Considering similar ore metals (tungsten-copper-tin-lead-zinc) ...
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Two cases of tungsten-copper vein-type mineralization have been studied in the Nezam-abad and Deh-hossein areas, in southwest of Shazand. The hydrothermal quartz-tourmaline mineralized veins have different host rocks (biotitic-granite and meta-sandstone). Considering similar ore metals (tungsten-copper-tin-lead-zinc) in the Nezam-abad and Deh-hossein areas, same mineralogy of veins (quartz-dravite) and similar REE variation patterns in the two areas, it is suggested that the Nezam-abad and Deh-hossein mineralized veins have the same origin. It means, when the Br-bearing fluids were active, they caused the quartz-tourmaline vein-type mineralization in this area. Considering the barren intrusions in the area and other mineralogical-geochemical evidences in this study, it could be concluded that tungsten and other metallic elements in the Nezam-abad and Deh-hossein ore-bearing veins have a sedimentary/metamorphic origin.