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Petrological Journal (22285210) 15(1)pp. 159-184
Rahmani, F. ,
Varas-reus, M.I. ,
Marchesi, C. ,
Noghreyan, M. ,
Makizadeh, M.A. ,
Garrido, C.J. International Geology Review (00206814) 65(21)pp. 3388-3411
The Sabzevar ophiolite is the most extensive and best-exposed section of oceanic lithosphere in NE Iran. In this study, we examined the mantle section of the eastern part of the Sabzevar ophiolite, where mantle peridotites are the most widespread rock type and are crosscut by pyroxenite veins and mafic dykes. Major and trace element compositions (minerals and whole-rock) of lherzolites are akin to those of abyssal peridotites from mid-ocean ridges (MOR), whereas those of harzburgites evidence formation in a supra-subduction zone (SSZ) setting. Rare-earth element (REE) patterns of whole-rock and clinopyroxene of lherzolites and harzburgites suggest polybaric melting, with initial melting in the garnet peridotite field (~5–6%), followed by ~5–15% melting for lherzolites and ~10–20% for harzburgites in the spinel peridotite field. Harzburgites show LREE enrichment incompatible with partial melting models, indicating significant interaction with SSZ-related melts, whereas analysed lherzolites experienced limited melt-rock interaction. Pyroxene dissolution and olivine precipitation in residual peridotites resulting from reaction with island arc tholeiite and/or boninite melts led to the formation of dunites. These melts eventually intruded as dykes and veins in the mantle and crustal sections of the ophiolite. In addition, boninite melts are inferred to be responsible for forming olivine pyroxenite veins within the harzburgites. We conclude that the mantle section of the Sabzevar ophiolite formed in an intra-oceanic arc setting and experienced a geochemical evolution from a MOR-like to SSZ setting. The intra-oceanic subduction of the Neotethys oceanic lithosphere and shifting conditions of melting during the development of subduction beneath the incipient island arc were responsible for the geochemical heterogeneity of mantle peridotites and the generation of SSZ-related magmas within the Sabzevar oceanic lithosphere. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Indian Journal of Geosciences (22293574) 76(1)pp. 59-84
The mantle sequence of Nain ophiolite in Central East Iran Microplate is composed of harzburgite, dunite, chromitite pods and lherzolite with major minerals of olivine, orthopyroxene, clinopyroxene and chromite. The studied chromites were classified as high chromium (Cr#>0.6) and high aluminum (Al2O3 average content ≈ 17.5wt%; Cr#<0.6). The high Cr-chromite plots fall in the boninitic field but the high-Al ones are mostly closer to abyssal peridotites and mid-oceanic ridge fields. The Cr# of chromite in dunite and chromitite varies between 0.77-0.83 and 0.86-0.89 respectively and show a boninitic nature for the parental melts. These characteristics prove that they were generated in an arc setting. High-Al harzburgites seem to have originated or been modified by boninitic magmatism which is taken place in the mid ocean ridge basalt environment due to melt-rock or melt-melt interactions. Also, the studied chromites occupy the field of supra-subduction zone (SSZ) peridotites with a tendency towards a MORB-type setting can be inferred. Hence, hydrous fluids which released from a subducted plate might have played an important role in Nain ophiolite petrogenetic evolution. MORB-like melts sourced from an arc environment and melting associated with a supra-subduction zone are primary factors for chromite occurrences in this area. © 2022 Geological Survey of India. All rights reserved.
Journal of Economic Geology (20087306) 12(1)pp. 93-109
In porphyry copper deposits, turquoise is considered to be a supergene oxidation product (John et al., 2010; Chavez, 2000). Based on Rezaian et al., 2003; Zarasvandi et al., 2005 and Eslamizadeh, 2004, the Aliabad index is introduced as a porphyry copper system. The first published report on turquoise events around Ali-Abad was presented by Momenzadeh et al., 1988. This area is located 57 km southwest of Yazd. Alterations often include siricitization, advanced argillization. Kaolinization and silicification have occurred frequently in the arkose and microcan glomerate of the Sangestan formation. The aim of this research study is to try to reconstruct and investigate the formation and origin of turquoise by using the latest mineralogical and geochemical data. Field evidence shows occurrence of turquoise in the form of a veinlet and nodules, with blue-green and blue-white colors. Jarosite, alunite, quartz and iron oxides are found together with turquoise. © 2020 Ferdowsi University of Mashhad. All rights reserved.
Acta Geodynamica et Geomaterialia (12149705) 17(1)pp. 61-87
The Mollaahmad pass bentonite deposit occurs within an area of about 10 km2 with Oligo-Miocene age (Isfahan-Iran). This bentonite deposit with two general lenticular and layered forms has extended in the tuff, conglomerates and sandstones (including volcanic fragments). XRD studies are demonstrating that montmorillonite, montmorillonite-illite, nontronite, albite, anorthite and quartz are major and clinoptilolite, heulandite, sanidine, orthoclase, calcite, microcline and actinolite are minor constituent minerals in studied bentonite deposit. Moreover, mineral chemistry indicates that Mollaahmad pass bentonite deposit has intermediate to di-octahedral smectites, so it can be classified as Wyoming bentonite type. Based on geochemical studies, transform process of parent rocks into bentonite was accompanied by enrichment of Cr, Sb, Se and REEs, and also enrichment or depletion of other major and trace elements. More geochemical studies have shown positive to negative Eu and Ce anomalies. This can be related to change in rate of oxidation and alteration intensity in altered system. In addition, study of rare earth elements indicates high differentiation of LREEs from HREEs that related to egress of HREEs from environment in form of carbonate complexes. It seems that six factors including discrepancy in rate of alteration intensity of the source materials, incorporation in crystal lattice, complex-forming ligands, surface adsorption and difference in stability of primary minerals are able to control mobilization, differentiation and distribution of elements in studied bentonites. This bentonite deposits has formed in margin of lacustrine environment. © 2020, Academy of Sciences of the Czech Republic,. All rights reserved.
Geoscience Frontiers (16749871) 11(6)pp. 2347-2364
The Late Cretaceous Sabzevar ophiolite represents one of the largest and most complete fragments of Tethyan oceanic lithosphere in the NE Iran. It is mainly composed of serpentinized mantle peridotites slices; nonetheless, minor tectonic slices of all crustal sequence constituents are observed in this ophiolite. The crustal sequence contains a well-developed ultramafic and mafic cumulates section, comprising plagioclase-bearing wehrlite, olivine clinopyroxenite, olivine gabbronorite, gabbronorite, amphibole gabbronorite and quartz gabbronorite with adcumulate, mesocumulate, heteradcumulate and orthocumulate textures. The crystallization order for these rocks is olivine ± chromian spinel → clinopyroxene → plagioclase → orthopyroxene → amphibole. The presence of primary magmatic amphiboles in the cumulate rocks shows that the parent magma evolved under hydrous conditions. Geochemically, the studied rock units are characterized by low TiO2 (0.18–0.57 wt.%), P2O5 (<0.05 wt.%), K2O (0.01–0.51 wt.%) and total alkali contents (0.12–3.04 wt.%). They indicate fractionated trends in the chondrite-normalized rare earth element (REE) plots and multi-element diagrams (spider diagrams). The general trend of the spider diagrams exhibit slight enrichment in large ion lithophile elements (LILEs) relative to high field strength elements (HFSEs) and positive anomalies in Sr, Pb and Eu and negative anomalies in Zr and Nb relative to the adjacent elements. The REE plots of these rocks display increasing trend from La to Sm, positive Eu anomaly (Eu/Eu∗ = 1.06–1.54) and an almost flat pattern from medium REE (MREE) to heavy REE (HREE) region [(Gd/Yb)N = 1–1.17]. Moreover, clinopyroxenes from the cumulate rocks have low REE contents and show marked depletion in light REE (LREE) compared to MREE and HREE [(La/Sm)N = 0.10–0.27 and (La/Yb)N = 0.08–0.22]. The composition of calculated melts in equilibrium with the clinopyroxenes from less evolved cumulate samples are closely similar to island arc tholeiitic (IAT) magmas. Modal mineralogy, geochemical features and REE modeling indicate that Sabzevar cumulate rocks were formed by crystal accumulation from a hydrous depleted basaltic melt with IAT affinity. This melt has been produced by moderate to high degree (~15%) of partial melting a depleted mantle source, which partially underwent metasomatic enrichment from subducted slab components in an intra-oceanic arc setting. © 2020 China University of Geosciences (Beijing) and Peking University
Neues Jahrbuch fur Mineralogie, Abhandlungen (00777757) 196(1)pp. 1-18
The Dehshir listvenites are located in the Dehshir–Baft suture zone, central Iran. This suture zone includes a sequence of Cretaceous ophiolite rocks, pieces of altered upper mantle rocks, serpentinites and Cenozoic volcanic rocks. The listvenites (both para-and ortho-listvenites) formed close to shear zones, faults and fractures and occur as continuous and discontinuous veins and masses. Based on mineralogical and geochemical studies three types of listvenites can be distinguished (1) carbonate listvenite, (2) silica listvenite and (3) silica–carbonate listvenite. The listvenites contain a wide range of silicate and carbonate minerals related to different hydrothermal fluid compositions and different rock types. The chemical composition of the listvenites was controlled by shear zones and reactions between country rocks and hydrothermal solutions under variable pT-conditions. Listvenites of the study area have high potential for sulfide mineralization compared to ordinary serpentinite. Silica listvenites are more variable in mineralogy compared to carbonate listvenites and enrichment of metals, such as Au content, increases with silica content. Fluid inclusion studies of the Dehshir listvenites indicate the former presence of a low salinity and high temperature (115 – 300 °C) hydrothermal fluid during listvenitization. © 2019 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.
Journal of Economic Geology (20087306) 11(2)
Turkish Journal Of Earth Sciences (1303619X) 27(4)pp. 294-317
Medium- and high-K calc-alkaline magmatism of the Shurab (southeast Qom city) and Garmsar (northwest Garmsar city) areas occurred within the Lower Red Formation in the Central Basin behind the Urumieh-Dokthar Magmatic Arc. In terms of whole-rock geochemical analyses and in agreement with the petrographic features, all representative samples of the Shurab area are classified into three groups: group 1 with mainly intergranular texture comprises basalt/trachybasalt, while groups 2 and 3 with trachytic and porphyritic textures, respectively, have basaltic trachyandesite composition. The overall major constituents are plagioclase with composition in the range from An49Ab23 to An75Ab47, clinopyroxene with composition in the range Wo43-45En39-45Fs9-15, and olivine with composition in the range from Fo58Fa31 to Fo67Fa40. Minor minerals consist of opaque minerals and K-feldspar in the range Or41-65Ab33-50An0.69-8. The characteristic accessories are apatite and sphene. In the Garmsar area, rocks are seen as subvolcanic with mafic (basalt) and intermediate (trachybasalt/basaltic trachyandesite) compositions. The Garmsar area rocks represent intergranular, granular, ophitic, and subophitic textures. In these rocks, major mineral phases are plagioclase and clinopyroxene. The minor constituents are olivine, opaque minerals, amphibole, biotite, and quartz. Apatite is the most important accessory mineral. The rocks of both areas display REE patterns characterized by LREE-enriched and HREE-depleted segments typical of arc lavas. Primitive mantle-normalized trace element patterns for samples of both areas exhibit high ratios of strongly incompatible elements with similar bulk partition coefficients (e.g., Th/ Ta and Th/Ce), enrichment in large-ion lithophile elements (LILEs: Cs, Ba, Rb, Th) relative to the high field-strength elements (HFSEs: Ti, Hf, Zr, and REEs), and troughs for Nb, Ta, Ti, and Zr and peaks for Cs, Th, K, and Sr, all of which are indicators for subductionrelated magmatism. Subduction of the Neo-Tethys beneath the Eurasian margin led to upper mantle deformation and metasomatism. Once the Arabian plate collided with the Eurasian margin, subduction ended through a slab breakoff process, and thermal flux of asthenospheric origin uprising through the slab tear induced the thermal erosion of the mantle metasomatized during the previous subduction event and triggered its partial melting. Also, the late Eocene-early Oligocene collision of Eurasian with Arabian plates led to the subsidence and formation of faults and extensions in the Central Basin (i.e. the Shurab and Garmsar areas) such that eruption of medium- and high-K metasomatic magmatism along these faults and extensions caused postcollision volcanism in the Central Basin. © TÜBİTAK.
Ore Geology Reviews (01691368) 95pp. 680-694
Magnetite bodies of the Late Cretaceous Nain ophiolite mélange (Central Iran) are hosted by a small volume of a serpentinized peridotite nappe. These ore bodies and their host peridotites have been studied in detail with respect to their mode of occurrence, petrography and mineral chemistry. The investigated ore deposits consist of m-scale lenses and pods of massive magnetite rocks exposed along a semi-brittle shear zone between pervasively serpentinized harzburgites, upper one with higher-Cr# [=Cr/(Cr + Al), 0.6–0.7] spinel and lower one with lower Cr# (0.5). Silicate mesostasis of the ore bodies is composed of stringy serpentine and chlorite. Cr-spinel grains are occasionally found dispersed within the magnetite rocks. Serpentines of the host serpentinized harzburgites show mesh and bastite textures, and were in part replaced by fibrous serpentine showing an interpenetrating texture. The Cr-spinels show a wide range of Cr# (0.5–0.7) and Mg# [=Mg/(Mg + Fe2+), 0.5–0.7], low TiO2 contents (<0.1 wt%), and relatively high contents of ZnO (0.11–0.26 wt%) and MnO (0.33–0.43 wt%). The magnetites are close in chemistry to the end-member Fe3O4, but some grains show high-SiO2 (up to 1.5 wt%) cores. They strongly resemble accessory Cr-spinels in the host serpentinized harzburgites in chemistry. The magnetite rocks have total precious-metal abundances (ΣPGE + Au = 66–262 ppb) analogous to those of mantle peridotites from other Mesozoic ophiolites. They are poor in PGE (21–67 ppb) relative to Au (45–195 ppb). Our analyses and observations are inconsistent with an igneous origin for the Nain magnetite deposits, but indicate a replacement origin from harzburgite, not from chromitite, via hydrothermal fluids. Overall data indicate that the Nain magnetite bodies were generated by multi-episodic serpentinization of harzburgites. The magnetite ore deformation style itself indicates syn-kinematic emplacement of the ore bodies within the semi-brittle shear zone, where the serpentinization-derived fluid/(altered) peridotite ratio became so high that eventually caused precipitation of magnetite at the ore level. © 2018 Elsevier B.V.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 286(3)pp. 303-328
The Sabzevar ophiolite is the largest and most complete ophiolitic sequence in northeastern Iran. Its eastern part contains a well-developed ultramafic and mafic cumulates section, comprising plagioclase bearing wehrlite, olivine gabbronorite, gabbronorite, amphibole gabbronorite and quartz gabbronorite with layers of clinopyroxenite and thin layers of anorthosite. These rocks have adcumulate, mesocumulate, heteradcumulate and orthocumulate textures and consist of olivine, clinopyroxene, orthopyroxene, plagioclase and amphibole. The crystallization order in these rocks is olivine (Fo89.8-80.0) ± chromian spinel, clinopyroxene [100∗Mg/(Mg + Fe+2) = 98-77], plagioclase (An93.1-87.6), orthopyroxene [100∗Mg/(Mg + Fe+2) = 93-75] and amphibole. The whole-rock geochemistry of the cumulative rocks suggests that they can be classified as low-Ti ophiolite and originated from an island arc tholeiitic magma source. The crystallization order and existence of orthopyroxene and clinopyroxene with very high Mg numbers, compared with those of coexisting olivines, and plagioclase with extremely high anorthite contents in the ultramafic and mafic cumulate samples, except for quartz gabbronorite samples, are in good agreement with products of high-pressure crystal fractionation of primary basaltic melts beneath an intra-oceanic island arc/supra-subduction zone setting. In contrast, the quartz gabbronorite samples in the upper crustal level show evidence of a low-pressure crystal fractionation within the same tectonic setting. We suggest that the arc crust of the Sabzevar ophiolite was thick, with the active magma chamber situated at the base of the crust at a pressure of 8-13 kbar for the highpressure cumulates, and a related active shallower level magma chamber for the low-pressure rocks. © 2017 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Journal of African Earth Sciences (1464343X) 125pp. 191-201
Mineralogy, minerals paragenesis and evolution of polygenic marbles were investigated in the Baqi-Abad region (Yazd province). The area is located in the central Iran. Studied marbles are classified as calcitic marbles, brucite-bearing marbles and forsterite- serpentine bearing marbles. The following mineral assemblages have been determined: calcite + dolomite + forsterite + serpentine + talc + brucite + hydromagnesite. Based on calcite twin's geometry, marbles underwent the temperature formation between 200 and 300°C. Two mineral assemblages which have been defined in marbles are related to two stages of contact- metamorphism and metasomatism. In the first stage, de-carbonation reactions have been taken place in high fCO2 so anhydrous minerals are formed. The Second stage is characterized by invading H2O bearing fluids, leading to the formation of hydrous paragenesis. Brucite is probably formed by the de-silicification of serpentines at the first stage. On the other hand, due to the influence of hydrothermal fluids, olivines can be directly altered to brucite. It is obvious that hydromagnesite was formed at the expense of dolomite, brucite and serpentine. Its formation is associated with final carbonation reactions. As a whole, it can be concluded that based on the paragenetic relationships of minerals, there are four stages in mineral evolution system including carbonation, dehydration, de-carbonation and final dehydration processes. © 2016 Elsevier Ltd
Geochemistry International (00167029) 54(5)pp. 423-438
Grossular-andradite (grandite) garnets, precipitated from hydrothermal solutions is associated with contact metamorphism in the Kal-e Kafi skarn show complex oscillatory chemical zonation. These skarn garnets preserve the records of the temporal evolution of contact metasomatism. According to microscopic studies and microprobe analysis profiles, the studied garnet has two distinct parts: the intermediate (granditic) composition birefringent core that its andradite content based on microprobe analysis varies between 0.68–0.7. This part is superimposed with more andraditic composition, and the isotropic rim which its andradite content regarding microprobe analysis ranges between 0.83–0.99. Garnets in the studied sample are small (0.5–2 mm in diameter) and show complex oscillatory zoning. Electron microprobe analyses of the oscillatory zoning in grandite garnet of the Kal-e Kafi area showed a fluctuation in chemical composition. The grandite garnets normally display core with intermediate composition with oscillatory Fe-rich zones at the rim. Detailed study of oscillatory zoning in grandite garnet from Kal-e Kafi area suggests that the garnet has developed during early metasomatism involving monzonite to monzodiorite granitoid body intrusion into the Anarak schist- marble interlayers. During this metasomatic event, Al, Fe, and Si in the fluid have reacted with Ca in carbonate rocks to form grandite garnet. The first step of garnet growth has been coeval with intrusion of the Kal-e Kafi granitoid into the Anarak schist- marble interlayers. In this period of garnet growth, change in fluid composition may cause the garnet to stop growing temporarily or keep growing but in a much slower rate allowing Al to precipitate rather than Fe. The next step consists of pervasive infiltration of Fe rich fluids and Fe rich grandite garnets formation as the rim of previously formed more Al rich garnets. Oscillatory zoning in the garnet probably reflects an oscillatory change in the fluid composition which may be internally and/or externally controlled. The rare earth elements study of these garnets revealed enrichment in light REEs (LREE) with a maximum at Pr and Nd and a negative to no Eu anomaly. This pattern is resulted from the uptake of REE out of hydrothermal fluids by growing crystals of calcsilicate minerals principally andradite with amounts of LREE controlled by the difference in ionic radius between Ca++ and REE3+ in garnet x site. © 2016, Pleiades Publishing, Ltd.
Mehvari, R. ,
Noghreyan, M. ,
Sharifi, M. ,
Makizadeh, M.A. ,
Tabatabaei s.h., S.H. Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 281(3)pp. 283-311
The Nabar kaolin deposit is located 29 km south of Kashan in the Isfahan province and is part of the Iranian Central structural zone. Field evidence and geochemical study shows that the Nabar deposit is an alteration product of Eocene volcanic rocks. The major minerals are quartz, kaolinite, dickite, illite, montmorillonite, albite,muscovite, along with lesser amounts of anatase, diaspore, goethite and alunite. Element mass change calculations, assumingAl as the low to immobile index element, indicate that leaching and fixation are two prominent factors controlling the concentration of major, minor, trace, and rare earth elements.Geochemical studies show that variation of the negative to weak positive Eu anomalies (0.57-1.10) and negative toweak positive Ce anomalies (0.77-1.04) at Nabar were, respectively, controlled by the degree of feldspar alteration and changes in the rate of oxidation potential of the environment. From the geochemical data it can be inferred that hypogene alteration features were overprinted by supergene alteration in the course of deposit formation, indicating both deep fluid source and shallow chemical leaching took place. Element distribution modes in the deposit indicate that the element behavior during kaolinization of volcanic rocks was primarily controlled by porosity and permeability, but also by factors such as pH, redox potential, temperature variations, high fluid/ rock ratios, scavenging and fixation by clays and iron oxides, discrepancies in the stability rate of minerals, abundance of complex-forming ions, and isomorphic substitution. Further geochemical considerations show that oxides and hydroxides of Fe and Mn along with secondary phosphates are the potential hosts for REE in the deposit. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Arabian Journal of Geosciences (discontinued) (18667538) 8(5)pp. 2967-2981
The Esfordi iron oxide–apatite deposit is located in the Bafq district, Central Iran. The ore body is hosted by the Lower Cambrian succession of rhyolite, rhyolitic tuff, cherty dolomite, and limestone. Calc-silicate assemblages occur locally in altered host rocks as stratigraphically controlled patches. The main hydrothermal minerals include apatite, magnetite–hematite, actinolite, garnet, clinopyroxene, talc, calcite, and quartz. The prograde calc-silicate mineral paragenesis manifests as garnet (Ad96.7, Gr1.88) and clinopyroxene (Di76.14, Hd22.65, Jo1.21), whereas apatite, magnetite, hematite, tremolite–actinolite, chlorite, talc, epidote, quartz formed during retrograde episode. Microthermometric results yield a temperature range for 222–465 ° C, with a salinity of 8 to 21 wt% NaCl for apatite that coexists with retrograde mineral assemblage. δ18O isotopic variations of apatite (1.23–14.9 ‰), magnetite (6.8–8.3 ‰), and quartz (13.8–15.8 ‰) suggests that mixing of magmatic and meteoric fluids occurred during mineralization. Calc-silicates prograde stage is believed to have formed at T < 550 °C and high ƒO2 conditions. The field, mineralogical, and geochemical evidence indicate distal calcic skarn type alteration occurred locally in the Esfordi hydrothermal system. © 2014, Saudi Society for Geosciences.
Zahedi, A. ,
Boomeri, M. ,
Nakashima, K. ,
Makizadeh, M.A. ,
Ban, M. ,
Lentz, D.R. Resource Geology (17513928) 64(3)pp. 209-232
The Khut copper skarn deposit is located at about 50km northwest of Taft City in Yazd province in the middle part of the Urumieh-Dokhtar magmatic arc. Intrusion of granitoid of Oligocene-Miocene age into carbonate rocks of the Triassic Nayband Formation led to the formation of marble and a calcic skarn. The marble contains high grade Cu mineralization that occurs mainly as open space filling and replacement. Cu-rich sulfide samples from the mineralized marble are also anomalous in Au, Zn, and Pb. In contrast, the calcic skarn is only weakly anomalous in Cu and W. The calcic skarn is divided into garnet skarn and garnet-pyroxene skarn zones. Paragenetic relationships and microthermometric data from fluid inclusions in garnet and calcite indicate that the compositional evolution of skarn minerals occurred in three main stages as follows. (i) The early prograde stage, which is characterized by Mg-rich hedenbergite (Hd53.7Di42.3-Hd86.1Di9.5) with Al-bearing andradite (69.8-99.5mol% andradite). The temperature in the early prograde skarn varies from 400 to 500°C at 500 bar. (ii) The late prograde stage is manifested by almost pure andradite (96.2-98.4mol% andradite). Based on the fluid inclusion data from garnet, fluid temperature and salinity in this stage is estimated to vary from 267 to 361°C and from 10.1 to 21.1 wt% NaCl equivalent, respectively. Pyrrhotite precipitation started during this stage. (iii) The retrograde stage occurs in an exoskarn, which consists of an assemblage of ferro-actinolite, quartz, calcite, epidote, chlorite, sphalerite, pyrite, and chalcopyrite that partially replaces earlier mineral assemblages under hydrostatic conditions during fracturing of the early skarn. Fluids in calcite yielded lower temperatures (T<260°C) and fluid salinity declined to ∼8 wt% NaCl equivalent. The last stage mineralization in the deposit is supergene weathering/alteration represented by the formation of iron hydroxide, Cu-carbonate, clay minerals, and calcite. Sulfur isotope data of chalcopyrite (δ34S of +1.4 to +5.2‰) show an igneous sulfur source. Mineralogy and mineral compositions of the prograde assemblage of the Khut skarn are consistent with deposition under intermediately oxidized and slightly lower fS2 conditions at shallow crustal levels compared with those of other typical Fe-bearing Cu-Au skarn systems. © 2014 The Society of Resource Geology.
Parsapoor a., ,
Dilles j.h., ,
Khalili m., M. ,
Makizadeh, M.A. ,
Maghami m., Journal of Geochemical Exploration (03756742) 143pp. 103-115
The Darreh-Zar porphyry copper deposit is found together with other porphyries such as Sar-Cheshmeh and Sungun in the Cenozoic age Urumieh-Dokhtar magmatic belt that is related to the subduction of the Arabian plate beneath Central Iranian microcontinent. The deposit is associated with Miocene granodiorite porphyry intrusions into Eocene basaltic volcanic rocks. The principal hydrothermal facies of the area are a core zone of potassic alteration enclosed by a peripheral zone of propylitic alteration. Chlorite-sericite, sericitic, advanced argillic and intermediate argillic alteration zones cut the upper part of the potassic zone and are developed near the interface between the potassic and propylitic zones. Chalcopyrite, pyrite or local bornite, and associated anhydrite are the chief hypogene sulfide minerals, and constitute <. 0.1 to 0.8. wt.% Cu ores. A ~. 50-m-thick supergene zone containing 0.8 to 1.5. wt.% Cu, characterized by covellite and chalcocite, underlies an oxidized and partially leached ~. 20-m-thick zone containing chrysocolla, malachite and azurite.The hydrogen isotopic composition of biotite from Darreh-Zar ranges from δD of -89 to -101‰, and the calculated aqueous fluids (δD of -66 to -78‰) in equilibrium with biotite are consistent with a large component of magmatic fluid. Epidote varies from δD of -56 to -53‰, and yields calculated fluids responsible for the propylitic alteration that range from -22 to -19‰. Oxygen isotopic data for the studied quartz, biotite, anhydrite and epidote vary between δ18O of 0.8 to 9.0‰. The calculated δ18O values for aqueous fluids in equilibrium with the biotite, quartz (from barren type and A veins), anhydrite (from B veins) and epidote are 7.8±0.4, 5.1±0.6, 2.6±0.5 and -1.1±0.1‰, respectively. This marked decrease likely reflects a change from magmatic-derived fluids in central potassic zone to meteoric or sedimentary-derived fluids in the outer propylitic zone. Sulfur isotope compositions are 11.8 to 14.0‰, for anhydrite (n=3), 2.4‰ for molybdenite (n=1), 1.7 to 3.9‰ for pyrite (n=17), and 1.6 to 2.9‰ for chalcopyrite (n=2). The sulfide data, alone, suggest a conventionally 'magmatic' value of about 1.6 to 2.9‰ for Darreh-Zar sulfur. However, the fairly oxidized granitic parental magma shows relatively heavy bulk sulfur (δ34SσS≈+5‰) and sulfate-sulfide sulfur isotopic fractionation is consistent with an approach to isotopic equilibrium at calculated temperatures of 520±50°C for most of the coexisting anhydrite-pyrite pairs (n=4). An exploration implication is that the identification of isotopically high sulfur isotopic compositions of gypsum from near-surface samples determines a hydrothermal system that contains deeper hypogene anhydrite, a common indicator of large porphyry Cu-Mo deposits. In contrast, isotopically low sulfur isotopic values similar to and derived from weathering of pyrite and other sulfides are common in many hydrothermal environments. © 2014 Elsevier B.V.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 272(1)pp. 61-77
The Kuh-Zar Cu-Au-turquoise deposit is located within the Torud-Chah Shirin magmatic arc (middle Eocene). The rocks exposed in the mining area consist of andesite, dacite, pyroclastics and diorite to granodiorite. Petrological studies show they have a typical arc geochemical signature. Based on their main mineral assemblages that encompass quartz, sericite, pyrite, tourmaline, alunite, turquoise, jarosite, the following hydrothermal alteration zones have been identified: propylitic, argillic, phyllic, advanced argillic and sillicic. The rare association of tourmaline and turquoise is an outstanding feature of this deposit. Electron probe microanalysis indicates that the tourmaline belongs to the schorlite-dravite group. The B-bearing fluids were sourced from metapelites and metapsammites coexisting with Al- saturated phases. It is probable that the tourmaline was generated from hydrothermal fluids affecting sericites from the phyllic alteration zone. Mineral reactions and stable isotope data (d18O and dD) for turquoise indicate that a final oxidation stage of primary sulfides resulted in the development of an acid-sulfate mineral assemblage (including turquoise) on overgrowing pre-existing mineral assemblages. © 2014 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Iranian Journal of Science and Technology, Transaction A: Science (10286276) 37(A1)pp. 11-22
The Ali-Abad porphyry copper deposit is located in the Central Iranian magmatic belt. As a result of subduction magmatism, Oligo-Miocene leucogranitoid rocks have intruded into conglomerates of lower Cretaceous age. Due to contact metamorphism the following mineral assemblage has occurred in the altered conglomerate: Garnet (andradite-grossular) + epidote+ quartz + calcite + pyrite Skarnification have only occurred in reactive carbonate clasts of the conglomerates. Chemical composition of garnets and classic discrimination scheme imply the porphyry copper related skarn-type mineralization. Garnets are characterized by abrupt chemical zoning area and thin bands. REE pattern of skarn garnet and host granite have similar trends, so it is concluded that garnets are hydrothermal in origin. The garnet mineralization episode occurred during skarnification, giving hydrothermal fluid temperatures of 422-472 °C, likely this episode corresponds to the fluid boiling and high fO2 of garnet forming processes in the skarn system. Probably, the temporal decrease of hydrothermal fluid pressure led to rapid growths of andradite zones i.e., extensive hydrofracturing, porosity of conglomerate could be the dominant conditions which led to boiling of hydrothermal fluids and precipitation of andradite garnet.
Taghipour, S. ,
Khalili m., M. ,
Makizadeh, M.A. ,
Kananian, A. ,
Taghipour, B. Geological Magazine (14695081) 150(1)pp. 72-88
The Kaj-Rostam Abad, Dashtak and Doab diapirs are part of the Precambrian-Cambrian Hormuz series that are rich in igneous inclusions concentrated by dissolution of diapiric salt. They are situated in the Iran-Pakistan salt range and commonly associated with inclusions of basalt, trachyte, andesite, micro-gabbro, gypsum and anhydrite, with lesser amounts of carbonate rocks. The mineral assemblage in these inclusions developed in three stages: (I) magmatic stage (diopside, Ti-augite, kaersutite, plagioclase, apatite, biotite and opaque minerals), (II) late magmatic stage (biotite, quartz, chlorite, albite, calcite, titanite, epidote, actinolite and opaque minerals) and (III) vein mineralization (quartz, chlorite, albite, calcite, garnet, epidote, opaque minerals and actinolite). Clinopyroxene is diopside to Ti-augite. Actinolite, kaersutite, albite and pycnochlorite are constituents of the metasomatic rocks of the area. Chlorite geothermometry yielded a temperature of 330-500 °C for chlorite formation. Clinopyroxene thermobarometry ranges from 960 ≤ T ≤ 1440 °C and 1 ≤ P ≤ 10 kbar. The presence of halite-bearing fluid inclusions in hydrothermal quartz veins with homogenization temperatures between 320 and 350 °C points to strong evidence of hydrothermal events. The salinity of these fluids is 39.8-42.7 wt% NaCl. δ18O data on hydrothermal quartz veins range from 14.89 to 22.09 ‰ (SMOW), indicating that the studied samples were affected by fluids originated from sedimentary-evaporitic rocks. Meteoric water that penetrated the evaporitic rocks likely mixed with late magmatic fluids while subjected to magmatic heat, when buried to depths of several kilometres by the Phanerozoic cover sequence. Whole-rock geochemistry data for the studied rocks emphasize their alkaline to sub-alkaline affinities, in a transitional magmatic series. Copyright © 2012 Cambridge University Press.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 265(3)pp. 235-248
The Eocene green tuff belt of the Alborz structural unit, the so-called Karaj Formation, is composed mainly of a pyroclastic succession with some carbonate rocks. Pyroclastics are genetically linked to calc-alkaline magmatism of the back arc extensional setting. The belt is a part of the broad Arabian-Central Iran collision zone. The petrographic data has shown that glass shards of various shapes and sizes are the main component of tuffs. The geochemical characteristics indicate that these rocks are trachyandesites, rhyodacites and rhyolites. Based on the detailed microscopy, XRD, and electron microprobe analysis (EMPA), the following main minerals have been identified: clinoptilolite, montmorillonite and crystobalite. The glass shards are filled with clinoptilolite as a result of their alteration. According to the Si/Al classification of the zeolite group derived from the chemical data, clinoptilolite is the main component. The zeolitization developed in the glass-rich tuffaceous Karaj Formation as a stratabound form. This type of zeolite occurrence could be of marine to lacustrine origin. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 259(2)pp. 217-229
In Central Iran, granodiorite of the Cenozoic magmatic arc intruded into Cretaceous carbonate rocks causing various generations of skarn to be formed. Two occurrences of the rare mineral clintonite were studied in the Shir-kuh and Feshark polygenic skarns. Characteristical assemblages were found to be garnet+spinel+clintonite+phlogopite+vesuvianite (Feshark area) and fassaite+spinel+clintonite+melilite+phlogopite+vesuvianite (Shir-kuh area). The genesis of clintonite was investigated in detail on the basis of the textural relationships between spinel, clintonite, garnet and pyroxene. Gradual and pseudomorphic replacement of grossular and fassaite by spinel was evident. These reactions suggest a temporal Al-leaching process in the skarn evolution stages. Spinel or other minerals could then take part in another reaction to form clintonite. © 2011 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen (00777749) 256(2)pp. 129-139
In the Cenozoic magmatic belt of Central Iran, the Eocene volcanics and pyroclastics from the Shahrzad area underwent extensive hydrothermal alteration. Major alteration zones show inclusions of propylite, quartz sericite, advanced argillic and silicified zones. Shahrzad alunites are mainly porcelaneous and their compositions show a solid solution between alunite and jarosite. In alteration zones, the mineral assemblage is characterized by alunite-jarosite + quartz + sericite + alkali feldspars + chlorite ± turquoise ± barite ± iron oxides. There are numerous alunite and jarosite occurrences, mainly as veinlets, in parts of the advanced argillic zone. Alunite δ18O and δD values range from -1.76 to 8.81 %o and from -52.86 to -129.26 %o respectively. Field observations, mineralogical evidence and results from light element stable isotope data (δ18O, δD and δ34S) indicate that the Shahrzad alunitization is of supergene origin. © 2010 Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.
Journal of Asian Earth Sciences (18785786) 34(2)pp. 123-134
The rhyolitic dome in the Rangan area has been subjected to hydrothermal alterations by two different systems, (1) A fossil magmatic-hydrothermal system with a powerful thermal engine of a deep monzodioritic magma, (2) An active hydrothermal system dominated by meteoric water. Based on mineralogical and geochemical studies, three different alteration facies have been identified (phyllic, advanced argillic and silicic) with notable differences in REE and other trace elements behaviour. In the phyllic alteration zone with assemblage minerals such as sericite, pyrite, quartz, kaolinite, LREE are relatively depleted whereas HREE are enriched. The advanced argillic zone is identified by the presence of alunite-jarosite and pyrophyllite as well as immobility of LREE and depletion in HREE. In the silicic zone, most of LREE are depleted but HREE patterns are unchanged compared to their fresh rock equivalents. All the REE fractionation ratios (La/Yb)cn, (La/Sm)cn, (Tb/Yb)cn, (Ce/Ce*)cn and (Eu/Eu*)cn are low in the phyllic altered facies. (Eu/Eu*)cn in both advanced and silicic facies is low too. In all alteration zones, high field strength elements (HFSE) (e.g. Ti, Zr, Nb) are depleted whereas transition elements (e.g. V, Cr, Co, Ni, Fe) are enriched. Geochemically speaking, trace and rare earth elements behave highly selective in different facies. © 2008.
Central European Geology (17882281) 51(1)pp. 85-98
The Keshe area is a part of Cenozoic magmatic belt of Central Iran. Some volcanics in this area underwent hydrothermal alteration including kaolinitization and alunitization. The altered rocks are characterized by an assemblage of alunite, kaolinite and quartz, which is typical in advanced argillic alteration. The mineralogical study suggests that the hydrothermal alteration in this area occurred in a magmatic hydrothermal environment. © 2008 Akadémiai Kiadó.
Neues Jahrbuch fur Mineralogie, Abhandlungen (00777757) 184(2)pp. 117-129
The Cheshmeh-Sefid granitoid complex, hosted by metasedimentry and meta-igneous rocks, north of Golpayegan, Sanandaj-Siran zone of Iran, is a heterogeneous pluton that comprises mainly quartz-monzonite, quartz-syenite, granite and syenite rocks. Geochemically, the granitoids are mostly peralkaline to metaluminous. The2y have similar trace element abundances over a range of SiO2 from 57 to 72.4 wt.%, and have a distinctive A-type chemistry characterized by high contents of Na2O + K2O, Nb, Zr, LREE and low MgO. The P-T conditions of crystallization of the granitoids were determined from amphibole-bearing samples using amphibole-plagioclase thermometry and Al-in-hornblende barometry. Aluminum-in-hornblende geobarometry indicates crystallization pressures of about 5 to 6 kbar; corresponding to intrusion depths of 17 to 20 km. Hornblende-plagioclase geothermometry indicates hornblende crystallization temperatures of 750 to 790 °C. Also, the Zr saturation temperature based on zircon solubility reflects a mean temperature of 776 °C. © by E. Schweizerbart'sche Verlagsbuchhandlung 2007.
Carbonates and Evaporites (08912556) 20(1)pp. 34-41
The zeolite deposits in Central Alborz, north of Iran display several features typical of their formation in hypersaline basins. Clinoptilolite, a predominant zeolite mineral in saline, alkaline lake deposits, occurs as a most common zeolite species in the zeolitized tuffs of the study area. Furthermore, the high concentration of chlorine (up to 0/5 wt%) and Sr (>1500 ppm) in zeolite deposits indicate that brackish water has presumably some bearing on the genesis of these deposits in north of Iran.
