Urumieh-Dokhtar Magmatic Belt Research Articles

Correlation between Mo mineralization and faults using geostatistical and fractal modeling in porphyry deposits of Kerman Magmatic Belt, SE Iran

Kerman Magmatic Belt (KMB) is located in the southern part of Urumieh-Dokhtar Magmatic Belt (UDMB), SE Iran. There are many Cu-Mo porphyry deposits which may have correlation with existing faults. The aim of this study is determination of correlation between Mo mineralization in the porphyry deposits of the KMB and faults based on fractal and geostatistical modeling. Fault density (FD) was calculated and classified by Concentration-Area (C-A) fractal model. Moreover, the Mo values in the porphyry deposits were classified by Concentration-Number (C-N) fractal model. However, the variograms and anisotropic ellipsoids for Mo, Cu and FD show that there is a proper relationship between Mo mineralization and FD trends. Consequently, the correlation between Mo mineralization and faults was calculated by logratio matrix. Based on the results derived via the fractal and geostatistical modeling, the Mo mineralization in Cu-Mo porphyry deposit have good correlation with faults in the KMB especially in the central part of the region including Sarcheshmeh mine and Nowchun deposit. Areas with extremely FD may be prospects for exploration of new porphyry deposits.

Zircon U-Pb ages and emplacement history of the Nodoushan plutonic complex in the central Urumieh-Dokhtar magmatic belt, Central Iran: Product of Neotethyan subduction during the Paleogene

The Nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in Iran. Diorite porphyry, diorite, granodiorite and granite intrusives belong to the central part of the Urumieh–Dokhtar magmatic belt, which is part of the Alpine-Himalayan orogenic belt. Monzogabbroic members of the complex are instead located within the bordering Sanandaj–Sirjan magmatic-metamorphic zone. These plutons were emplaced into Permian and lower Cretaceous sedimentary units and Eocene calc-alkaline volcanic and subvolcanic rocks. New U-Pb zircon ages reveal that the plutonic complex was assembled incrementally over ca. 15m.y. during three main episodes at 40.487±0.063Ma near the Middle/Late Eocene boundary, at 30.52±0.11Ma and 30.06±0.10Ma in the Early Oligocene (Middle Rupelian) and at 24.994±0.037 and 24.13±0.19Ma in the Late Oligocene (latest Chattian). The activity recorded in the Nodoushan plutonic complex represents the final stages of subduction-related magmatism prior to the eventual Miocene collision between the Arabian and Eurasian blocks.

Age revision of the Neotethyan arc migration into the southeast Urumieh-Dokhtar belt of Iran: Geochemistry and U–Pb zircon geochronology

The Urumieh-Dokhtar magmatic belt of Central Iran runs parallel to the Zagros orogenic belt and has been resulted from Neotethys ocean subduction underneath Eurasia. The Bahr Aseman volcanic-plutonic complex (BAC), covering an area ~2000km2 in the Kerman magmatic belt (KMB) in the southern section of the Urumieh-Dokhtar belt, has long been considered as the earliest manifestation of extensive Cenozoic arc magmatism in KMB. The nature and timing of the magmatism, however, is poorly constrained. An area ~1000km2, in BAC and adjacent Razak volcaniclastic complex and Jebal Barez-type granitoids, was mapped and sampled for geochemistry and geochronology. Andesite and basaltic andesite are the main volcanic components in the study area; plutonic bodies vary from tonalite to quartz diorite, granodiorite and biotite-granite. The rocks in BAC display dominantly normal calc-alkaline character. On spider diagrams, the rocks are characterized by enrichments in LILE relative to HFSE and enrichments in LREE relative to HREE. These features suggest a subduction related setting for the BAC. LaN/YbN ratios for the intrusive and volcanic rocks range from 1.41 to 5.16 and 1.01 to 6.42, respectively. These values are lower than those for other known granitoids in KMB, namely the abyssal, dominantly Oligocene Jebal Barez-type (LaN/YbN=1.66–9.98), and the shallow, dominantly late Miocene Kuh Panj-type (LaN/YbN=12.97–36.04) granitoids. This suggests a less evolved magma source for the BAC igneous rocks. In Y vs. Nb and Th/Yb vs. La/Yb discrimination diagrams, an island-arc setting is defined for the BAC rocks. The rocks further plot in primitive island-arc domain in Nb vs. Rb/Zr and Y/Nb vs. TiO2 diagrams.The BAC volcanic and plutonic rocks yielded zircon U–Pb ages of 78.1 to 82.7Ma and 77.5 to 80.8Ma, respectively. Zircon U–Pb dating of volcanic rocks and granitoids from the adjacent Razak complex and the Jebal Barez-type granitoids indicated 48.2Ma and 26.1Ma ages, respectively, consistent with earlier works on similar rocks elsewhere in KMB.The new data allow a revision of the chronostratigraphy/tectonic history of KMB. In Late Cretaceous, a back arc rift developed extending from Nain to Baft (NB back arc) to the northeast of the Sanandaj-Sirjan magmatic arc. Along with shrinking of the Neotethys Ocean, the dip angle of the subducting slab decreased during the Late Cretaceous, and arc magmatism moved from the Sanandaj-Sirjan zone landward. Meanwhile, Bahr Aseman volcanic-plutonic complex formed as an island-arc in NB back arc rift. Later with arc shift, due to shallowing of subducted slab, magmatism moved toward continent leading to extensive volcanism in Kerman magmatic arc during Eocene and Oligocene, represented by volcanic-sedimentary Razak and Hezar Complexes, respectively.

Petrogenesis of Soheyle- Pakuh and Golshekanan granitoid based on mineral chemistry of ferromagnesian minerals (north of Nain), Iran

The Middle Oligocene I-Type Soheyle- Pakuh and Golshekanan granitoid (SPGG) occurs in Urumieh-Dokhtar magmatic belt and north of Nain in central part of Iran. The dominant studied intrusive rocks are diorite, quartz-diorite, tonalite, granodiorite and granite which petrographically are characterized by the presence of plagioclase, quartz, K-feldspar, amphibole, pyroxene, biotite, apatite, titanite, zircon, tourmaline, allanite and opaques. The pyroxenes comprise calc-alkaline augite, calcic amphiboles and Fe-rich biotite. Using Fe2+/Fe2++Mg and Al (tot) for primary amphiboles, an average pressure of 2 Kbar was estimated corresponding to the depth of between 3.63 and 10.88 km. Further, the low Na2O and TiO2 contents of these phases suggest subduction environment (S-Amph). Distribution of aluminum in clinopyroxenes suggests that these minerals formed at <5 kbar pressure and their water content was between 5 to over 10 percent. Biotites from gabbroic diorite, diorite and tonalite, using Ti and Mg/Mg + Fe diagram, crystallized at temperature of about 720 °C whereas, the pyroxenes and enclaves solidified in the range of 1100–1175 °C. The overall geochemical data suggests that the SPGG are high temperature, I- type, calc-alkaline developed in high oxygen fugacity in an orogenic tectonic setting related to volcanic arc environment consistent with the subduction of Neotethys oceanic underneath the Central Iranian microcontinent during Upper Cretaceous to Paleogene.

Utilization of ASTER Data and Spectral Analysis to Discriminate Hydrothermally Altered Areas over Rabor, South of Kerman, Iran

This study attempts to evaluate the capability of the advanced spaceborne thermal emission and reflection radiometer (ASTER) and the advantages of ground knowledge for generating maps portraying hydrothermally altered areas in relation to porphyry copper deposits. The northern part of the Rabor area in the Urumieh–Dokhtar magmatic belt, containing some copper mineralization occurrences, was investigated as a case study. Several image processing techniques, namely minimum noise fraction, pixel purity index, and n-dimensional visualization, contributed to the extraction of pure pixels as endmembers. The spectra of some rock samples collected around the well-known altered zones of the study area were resampled to ASTER bands and used to identify the image-extracted endmembers. Spectral analysis of the endmembers and ground sample spectra led to the identification of three types of hydrothermal alterations: (1) phyllic, (2) propylitic, and (3) argillic. The identified endmembers were used as the specified targets for mapping hydrothermal alteration zones over the study area by using a mixture tuned match filtering algorithm. Results demonstrate that high abundances within pixels correspond closely to the altered areas. Field observations, thin section, and X-ray diffraction of collected samples confirmed the accuracy of the alteration maps prepared by the application of the proposed methods. The final classified hydrothermal alteration maps showed the overall accuracy and kappa coefficient values of 85.41 and 0.72%, respectively. These results ascertain that ASTER data that use suitable image processing techniques appear consistent in mapping out the distribution of hydrothermally altered areas. In addition, ground knowledge data can act as a valuable information source to increase the image classification accuracy and reliability.

Examination of chloritization of biotite as a tool for reconstructing the physicochemical parameters of mineralization and associated alteration in the Zafarghand porphyry copper system, Ardestan, Central Iran: mineral-chemistry and stable isotope analyses

The chloritization of biotite and stable isotopes of silicate have been studied for the Zafarghand porphyry copper deposit, Ardestan, Iran. The studied area, in the central part of the Urumieh–Dokhtar magmatic belt, contains porphyry-style Cu mineralization and associated hydrothermal alteration within the Miocene (19–26 Ma, Zircon U-Pb age) granodioritc stock and adjacent andesitic to rhyodacitic volcanic rocks (ca. 56 Ma, zircon U-Pb age). The primary and secondary biotite that formed during potassic alteration in this porphyry and these volcanic host rocks are variably chloritized. Chloritization of biotite pseudomorphically is characterized by an increase in MgO, FeOt, and MnO, with decreasing in SiO2, K2O, and TiO2. Based on the Ti-in-biotite geothermometer of Henry et al. (Am Mineral 90:316–328, 2005) and Al-in-chlorite geothermometer of Cathelineau (Clay Miner 23:417–485, 1988), crystallization temperatures of primary biotite representative of magmatic conditions and later chloritization temperature range from 617° to 675 °C ± 24 °C and 177° to 346 °C, respectively. Calculated isotopic compositions of fluids that chloritized primary and secondary biotite display isotopic compositions of 1.1 to 1.7 per mil for δ18O and −19.9 to −20.5 per mil for δD consistent with meteoric water. Sericite, barren, and A-type-quartz veins from phyllic alteration were produced by mixed magmatic and meteoric water with δ18O values from −2.8 to 2.5 and δD values of ∼ −23 per mil; the narrow range of δD values of the propylitic epidote may be due to a meteoric water with δ18O values from 0.8 to 1.6 and δD values from −14.6 to −16.9 per mil.

Application of fractal modeling and PCA method for hydrothermal alteration mapping in the Saveh area (Central Iran) based on ASTER multispectral data

The aim of this study is determination and separation of alteration zones using Concentration-Area (C-A) fractal model based on remote sensing data which has been extracted from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images. The studied area is on the SW part of Saveh, 1:250,000 geological map, which is located in Urumieh-Dokhtar magmatic belt, Central Iran. The pixel values were computed by Principal Component Analysis (PCA) method used to determine phyllic, argillic, and propylitic alteration zones. The C-A fractal model is utilized for separation of different parts of alteration zones due to their intensity. The log-log C-A plots reveal multifractal nature for phyllic, argillic, and propylitic alteration zones. The obtained results based on fractal model show that the main trend of the alteration zones is in NW-SE direction. Compared to the geological map of the study area and copper mineralizations, the alteration zones have been detected properly and correlate with the mineral occurrences, intrusive rock, and faults.

Mineral chemistry of a Cenozoic igneous complex, the Urumieh-Dokhtar magmatic belt, Iran: Petrological implications for the plutonic rocks

The Niyasar plutonic complex, one of the Cenozoic magmatic assemblages in the Urumieh-Dokhtar magmatic belt, was the subject of detailed petrographic and mineralogical investigations. The Niyasar magmatic complex is composed of Eocene to Oligocene mafic rocks and Miocene granitoids. Eleven samples, representing the major rock units in the Niyasar magmatic complex and contact aureole were chosen for mineral chemical studies and for estimation of the pressure, temperature, and oxygen fugacity conditions of mineral crystallization during emplacement of various magmatic bodies. The analyzed samples are composed of varying proportions of quartz, plagioclase, K-feldspar, hornblende, biotite, titanite, magnetite, apatite, zircon, garnet, and clinopyroxene. Application of the Al-in-hornblende barometer indicates pressures of around 0.2 to 0.4 kbar for the Eocene–Oligocene mafic bodies and around 0.5 to 1.7 kbar for the Miocene granitoids. Hornblende-plagioclase thermometry yields relatively low temperatures (661–780 °C), which probably reflect late stage re-equilibration of these minerals. The assemblage titanite–magnetite–quartz as well as hornblende composition were used to constrain the oxygen fugacity and H2O content during the crystallization of the parent magmas in the Miocene plutons. The results show that the Miocene granitoids crystallized from magmas with relatively high oxygen fugacity and high H2O content (~5 wt% H2O). The Miocene granitoids show similar range of oxygen fugacity, H2O contents and mineral chemical compositions, which indicate a common source for their magmas. Although the crystallization pressures of the Miocene plutons discriminate various categories of plutonic bodies emplaced at depths of about 5.7–6.5 km (Marfioun pluton), about 4.2 km (Ghalhar pluton) and 1.9–2.3 km (Poudalg pluton), they were later uplifted to the same level by vertical displacement of faults. The emplacement depths of the Niyasar plutons suggest that the central part of the Urumieh-Dokhtar magmatic belt has experienced an uplift rate of ca. 0.25–0.4 mm/yr from the Miocene onwards. Urumieh-Dokhtar火成岩帯の新生代火成岩類の一つであるNiyasar深成複合岩体について詳細な記載岩石学・鉱物学的研究を行った.Niyasar火成複合岩体は始新世から漸新世のマフィック岩と中新世の花崗岩類からなる.Niyasar火成複合岩体とその接触変成帯から採取した11試料について鉱物組成を分析し,各岩体の定置時の晶出温度・圧力,酸素分圧を推定した.分析試料は石英,斜長石,カリ長石,普通角閃石,黒雲母,チタナイト,磁鉄鉱,燐灰石,ジルコン,ザクロ石,単斜輝石からなる.普通角閃石Al圧力計は始新世―漸新世マフィック岩体について0.2―0.4 kbar,中新世花崗岩類について0.5―1.7 kbarを示す.普通角閃石―斜長石温度計は比較的低温(661–780 ˚C)を示すが,これは後の再平衡によるものと思われる.中新世深成岩類のチタナイト―磁鉄鉱―石英組合せと普通角閃石組成からマグマが固化した時の酸素分圧と含水量を制約した.その結果,中新世花崗岩類は比較的高い酸素分圧と高含水量(およそ5 wt%)のマグマから晶出したことがわかった.中新世花崗岩類は同様の酸素分圧,含水量,鉱物組成を示すことから,同じ起源物質に由来すると考えられる.中新世深成岩類の晶出圧力は様々な定置深度5.7―6.5 km(Marfioun深成岩体), ~4.2 km(Ghalhar深成岩体),1.9–2.3 km(Poudalg深成岩体)を示すが,後の断層運動によって同じ深さにまで上昇した.Nayasar深成岩体の定置深度はUrumieh-Dokhtar火成岩帯中央部が中新世以降年間0.25―0.4 mmの速度で上昇したことを示唆する. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Tectonic evolution of the Zagros Orogen in the realm of the Neotethys between the Central Iran and Arabian Plates: An ophiolite perspective

The Zagros Orogenic Belt includes the Fold and Thrust Belt, the High Zagros Belt, the Outer Zagros Ophiolitic Belt, the Sanandaj–Sirjan Metamorphic Belt, the Inner Zagros Ophiolitic Belt, and the Urumieh–Dokhtar Magmatic Belt. We divide the High Zagros evolutionary history into five stages: (1) triple junction formation, (2) continental lithosphere rifting, (3) generation, spreading, and maturation of the Neotethys Ocean, (4) subduction of the oceanic lithosphere, and (5) collision. The Neotethys triple junction, located at the southeastern corner of the Arabian Plate, formed during the Late Silurian–Early Carboniferous. Subsequently, this triple junction became a rift basin due to normal faulting and basalt eruption. The rifting stage occurred during the Late Carboniferous–Early Permian. Thereafter, extension of the basin continued, leading to spreading and maturation of the Neotethys oceanic basin during the Late Permian–Late Triassic. Probably at the end of the Late Triassic, closure of the Paleotethys...

Investigation of copper and gold prospects using index overlay integration method and multifractal modeling in Saveh 1:100,000 sheet, Central Iran

Abstract This study aims at prospecting copper and gold promising areas in Saveh 1:100,000 sheet, situated in Urumieh-Dokhtar magmatic belt (Central Iran). Geographic information system (GIS) is effective in recognition of probable mineral resources by collecting, processing, exploration layer weighting and integrating thematic maps. As there is no certainty in different geological phenomena, modeling and integrating information layers are used to obtain suitable results for determining potential areas. In this study, index overlay method, which is a combination of software processing and expertise knowledge, was used. The survey layers consist of the lithologic units, geophysical data, mineralization, faults and structures and alteration. For more exact survey, concentration-area (C-A) fractal modeling was applied to the map of results obtained from integration. Applying fractal model to this map, the results of the original map were prioritized and became more limited. In the end for assessing the validity of determined promising areas, the results were compared with geochemical anomaly maps of stream sediments and also field observation was performed. Areas with high exploration priority with limited extend exist in center, west and some parts of NW, conformed to granodiorite intrusives and also next priority exists in center, west, NE and NW conformed to granite, diorite, and also subvolcanic rocks respectively. These prioroties are related to fault systems. In order to perform X-ray Diffraction (XRD), Inductively Coupled Plasma – Mass Sepctrometry (ICP-MS) analyses and microscopic studies, lithogeochemical samplings were done. All investigations indicate the possibility of pyrite, chalcopyrite and galena epithermal mineralizations resulted from post magmatic fluids, and also secondary products like hematite, goethite, and malachite as a result of oxidation processes in these areas.

Geochemistry of enclaves and host granitoids from the kashan granitoid complex, central iran: Implications for enclave generation by interaction of cogenetic magmas

The major and trace elements and Sr-Nd-Pb isotopes of Miocene host granitoid rocks and their mafic microgranular enclaves (MMEs) were studied to understand the petrogenesis of MMEs in the Kashan complex, which is part of the Urumieh-Dokhtar magmatic belt (Iran). The host rocks consist of quartz-diorite and tonalite associated with a dioritic intrusion. The enclaves show microgranular texture and the same mineralogy as their respective host with plagioclase, quartz and biotite. MMEs have a diorite to quartz-diorite composition and show geochemical characteristics mostly between their granitoid host and the diorite intrusion. Chondrite-normalized REE patterns of all samples are moderately fractionated [(La/Yb)N=2.1 to 12.9]. The MMEs display in part small negative Eu anomalies (Eu/Eu*=0.54 to 0.99), with enrichment of LILE and depletion of HFSE. The enclaves show emplacement depth of ~4 to 6 km which is comparable with the host rocks. Moreover, the Hornblende-plagioclase equilibrium temprature of MMEs yields average temperatures of 795°C which is slightly higher than the host ones. Identical mineral compositions and Nd-Sr-Pb isotopic features of MME-host granitoid pairs indicate interactions and parallel evolution of MME and enclosing granitoid in the Kashan plutons. Additionally, the geochemical and isotopic investigations of host and dioritic intrusions suggest a common source for their genesis. A thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower crust to generate Kashan granitoid rocks.

Application of ASTER data for exploration of porphyry copper deposits: A case study of Daraloo–Sarmeshk area, southern part of the Kerman copper belt, Iran

The Cenozoic Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran is a major host to porphyry Cu±Mo±Au deposits (PCDs). Most known PCDs in the UDMB occur in the southern section of the belt, also known as the Kerman Copper Belt (KCB). Three major clusters of PCDs are distinguished in the KCB and include the Miduk, Sarcheshmeh and Daraloo clusters. The Daraloo and Sarmeshk deposits occur in a northwest–southeast-trending fault zone that is characterized by the presence of a narrow zone of alteration–mineralization that contains a series of Oligocene granitoids and Miocene porphyritic tonalite–granodiorite plutons that cut Eocene andesitic lava flows and pyroclastic rocks. Here we use various techniques, including different ratio images, minimum noise fraction, pixel purity index, and matched filter processing to process ASTER data (14 bands) and generate maps that portray the distribution of hydrothermal minerals (e.g., sericite, kaolinite, chlorite, epidote and carbonate) related to PCD alteration zones. In order to validate the ASTER data, follow-up ground proofing and related mineralogical work was done which, in all cases, proved to be positive. The results of this work have identified the regional distribution of hypogene alteration zones (i.e., phyllic, argillic, propylitic and silicic), in addition to areas of secondary Fe-oxide formation, which are coincident with known sites of PCDs. The regional distribution and extent of the alteration zones identified also highlighted the role of regional structures in focusing the mineralizing/altering fluids. These results demonstrate very convincingly that ASTER imagery that uses the appropriate techniques is reliable and robust in mapping out the extent of hydrothermal alteration and lithological units, and can be used for targeting hydrothermal ore deposits, particularly porphyry copper deposits where the alteration footprint is sizeable.

Delineation of Cu prospects utilizing multifractal modeling and stepwise factor analysis in Noubaran 1:100,000 sheet, Center of Iran

The aim of this study is to separate and subsequently determine geochemical anomalies for exploration of Cu mineralization in Noubaran 1:100,000 sheet, situated in the Urumieh-Dokhtar magmatic belt, Center of Iran. To do this, stepwise factor analysis and also a Concentration-Number (C-N) fractal modeling were used. Stepwise factor analysis can be effective in exact recognition of reciprocal genetic correlation between elements and data classification based on distinct elements associated with the studied deposit. Accordingly, after applying four steps of factorization, all the noise elements which had no role in the formation of geochemical processes were eliminated, and finally, factor score of Bi, Ag, and Cu were calculated. A C-N log-log plot for factor scores were plotted, and five threshold values were determined in order to delineate mineral potential maps of the target elements. The designated regions on the mineral potential map are in the NE, S, more limited in the SE, and the central parts of the area which show clear correlation with alteration zones. Field observation, mineralographical and petrographical studies of the polished and thin sections, and also AAS, ICP-MS, XRD analyses indicate pyrite, chalcopyrite, chalcocite, covellite, and bornite mineralizations are associated with sub-volcanic and intrusive rocks. Considering the evidence, it can be deduced that the effect of the postmagmatic fluids on Eocene pyroclastic units has led to the creation of the alterations and sulfide mineralized siliceous vein-veinlet.

Kuh-e Dom Fe–Cu–Au prospect, Anarak Metallogenic Complex, Central Iran: a geological, mineralogical and fluid inclusion study

The Kuh-e Dom Fe–Cu–Au prospect is located in the Urumieh-Dokhtar Magmatic Belt, and is characterized by copper–iron oxide and gold veins, stockworks and breccias hosted by the Eocene Kuh-e Dom arc intrusion. Mineralization is located within NE–SW to WNW–ESE sinistral faults and likely formed in a subduction-related continental margin that is typical of IOCG deposit systems. The deposits have a distinct metal composition of Fe, Cu, Bi, Co, Mo and LREE with gold (up to 3 g/t), and the mineral assemblages are quartz, hematite, pyrite, chalcopyrite, emplectite, magnetite, free gold, calcite, barite, chlorite, and tourmaline. Three paragenetic stages of mineralized quartz veins are distinguished in the Kuh-e Dom prospect, including: (i) hematite-bearing quartz veins, (ii) quartz-sulfide stockwork and breccia veins, and (iii) quartz-calcite±sulfide infilling veins. Sodic (albitization), potassic, and quartz–calcite±chlorite pervasive alterations are commonly associated with these three mineralization stages. Three types of fluid inclusions have been identified at Kuh-e Dom, including: aqueous two-phase (H2O−NaCl−CaCl2±FeCl2), halite-saturated aqueous (H2O−NaCl±KCl), and CO2-bearing (H2O–CO2±CH4 and CO2±CH4) fluid inclusions. A hypersaline (~35 wt% NaCl equiv.), aqueous magmatic fluid was released at about 400 °C and a pressure of nearly 4 kbar, forming early hematite-bearing quartz veins. These high salinity fluids were progressively diluted further away from Kuh-e Dom intrusion due to substantial input of meteoric water and mixing with the magmatic components during the middle and late stages of mineralization. The mineralogy, alteration, and fluid composition of the Kuh-e Dom Fe–Cu–Au prospect compared well with Fe oxide Cu–Au (IOCG) deposits worldwide.

Crustal lineament control on mineralization in the Anarak area of Central Iran

The Anarak mining area in Iran is identified as one of the best known examples of mineralization located at the intersection of two important crustal-scale lineaments, which are the E_W striking Great Kavir fault and the NW–SE trending Urumieh-Dokhtar Magmatic Belt. The objective of this research is to investigate the role of the lineaments and their subsidiaries at Anarak area in the genesis of mineral deposits. Lineaments are long-lived features which control or affect ancient as well as young crustal sequences. Lineaments are also deep-seated, because they commonly control the emplacement of deep crustal or mantle-derived magmas. Metallogenic areas of up to ~1000km2 might be observed in areas where broad structural zones intersect, because they can facilitate the localization of magmatic or hydrothermal centers. The two lineaments that intersect in the Anarak area were both very active during mineralization. Therefore, it is likely that pull-apart basins or other dilatational sites at the intersection point were not preserved for substantial lengths of time, and single large magma conduits would have been divided into smaller conduits for magma penetration and hydrothermal circulation. The presence of these small conduits in addition to a small magma input could produce conditions for the circulation of mainly meteoric waters, in which the magmatism has acted as a heat source for the mineralization system. This phenomenon has led to the generation of a metallogenic area with several similar small deposits within a circular area of radius ~30km centered at the intersection point. The two most famous deposits in this area are Talmessi and Meskani in which mineralization had occurred in two separate stages: first stage — fissure-filling copper sulfide mineralization associated with Eocene magmatism (veins, veinlets, and stockworks). The second is an overprinting stage which occurred after a fairly long interval which involves the formation of Ni–Co arsenides and U oxide minerals.

Mineral chemistry and isotopic composition of magmatic, re-equilibrated and hydrothermal biotites from Darreh-Zar porphyry copper deposit, Kerman (Southeast of Iran)

Abstract The Darreh-Zar porphyry copper in the southeastern part of the Urumieh–Dokhtar magmatic belt developed as a consequence of hydrothermal alteration related to the Darreh-Zar granodioritc porphyry stock intruded into mafic volcanic rocks. Hydrothermal alteration and Cu–Mo mineralization are focused on the Darreh-Zar porphyry pluton belonging to Miocene time and the neighboring basaltic country rocks. A core zone of potassic alteration is enclosed by a peripheral zone of chlorite–sericite, sericitic, argillic and propylitic alteration. Judging by petrographic features as well as chemical composition, the biotites studied display variable size, color, and shape and occur as magmatic (M), re-equilibrated (R) and hydrothermal (H) types. The M and R-type biotites are found in the Darreh-Zar porphyry and the H-type formed during potassic alteration within the Darreh-Zar porphyry and the volcanic host rocks as well. The hydrothermal biotites are characterized by the highest amounts of Al 2 O 3 and K 2 O whereas the magmatic types are hosted by high level of TiO 2 (up to 4.38 wt.%). X Mg values vary between 0.31 and 0.61 which is increased from M to R-biotites then decreased toward low temperature potassic alteration zone. Fluorine and chlorine contents from biotite types also vary between 0.07 to 0.56 wt.% and 0.14 to 0.38 wt.% respectively. These values change to 2.94 to 2.15 wt.% and − 3.6 to − 4.4 wt.% for IV(F) and IV(Cl) respectively. In all types of biotites, positive correlation is observed between X Mg , Al 2 O 3 , Na 2 O + K 2 O + BaO and F but with FeO and Cl it is negative. The TiO 2 content clearly decreases from the M to R and H-type (Average: 3.98, 2.9 and 2.4 wt.% respectively). A direct relation may be noted between Mg# and oxygen fugacity. Log ( f H 2 O/ f HF) and log ( f H 2 O/ f HCl) values range from 6.24 to 5.46 and 4.49 to 4.12 wt.% respectively. Oxygen fugacity increases during formation of re-equilibrated biotites but it decreases in the course of potassic alteration. Crystallization temperatures range from 600° to 650 °C, 550 to 600 °C and 450 to 550 °C for magmatic, re-equilibrated and hydrothermal biotites respectively. The M-biotites from Darreh-Zar have the δD values of − 89 to − 101‰ and the calculated δD values of the aqueous fluids (− 66 to − 78‰) in equilibrium with the biotites are consistent with a large component of magmatic fluid which shows similarities with the biotite originated from the primary mantle source. The δ 18 O also varies between 7.4 to 8.2‰ for fluids in equilibrium with biotites. The obtained M-biotite data from Darreh-Zar porphyry indicates that there is no clear correlation between δD values, Fe and Mg contents but for δD values, Al and Fe 3 + /Fe 2 + some affinities were observed. The isotopic data indicate that M-biotites are formed at high temperature (620 ± 20 °C) from fluids with the highest δ 18 O H 2 O (7.8 ± 0.4‰) in comparison with the biotites from some other copper porphyries.

SHRIMP zircon U–Pb and biotite and hornblende Ar–Ar geochronology of Sungun, Haftcheshmeh, Kighal, and Niaz porphyry Cu–Mo systems: evidence for an early Miocene porphyry-style mineralization in northwest Iran

The Cenozoic Urumieh–Dokhtar magmatic belt (UDMB) extends for over 2,000 km from northwest to southeast Iran and is characterized by dominantly calc-alkaline volcanic, pyroclastic, and intrusive rocks. The UDMB hosts numerous porphyry-type Cu ± Mo deposits, mostly distributed in two separate areas, one known as the Kerman copper belt (KCB) in the south, and the other, here referred to as the Arasbaran Metallogenic Zone (AMZ), in the north, of the UDMB. The two areas are represented by two world-class Cu–Mo deposits, Sarcheshmeh (1,200 Mt of ore at 0.69 % Cu and 300 ppm Mo) and Sungun (>500 Mt of ore at 0.69 % Cu and ~250 ppm Mo), respectively. Chronology data were obtained for the Sungun, Haftcheshmeh, Kighal, and Niaz deposits in the AMZ. The Sungun deposit is associated with a suite of porphyritic granodiorite to monzodiorite stocks and late dykes intruding older andesitic lavas and limestones. SHRIMP zircon U–Pb data indicate that the host andesites were emplaced at 27.65 ± 0.51 Ma (±0.2σ). The main Sungun porphyritic intrusion crystallized at 20.69 ± 0.37 (±0.2σ) Ma. The Haftcheshmeh deposit is associated with a porphyritic granodiorite body intruding an older gabbro-diorite intrusion. Primary magmatic hornblende from the gabbro-diorite host rock yielded a 40Ar/39Ar plateau age of 27.47 ± 0.17 Ma. The main porphyritic intrusion crystallized at 19.46 ± 0.39 Ma. The Kighal porphyry system is associated with a porphyritic monzonite body intruding into older andesitic and dacitic lavas, and the Niaz porphyry system is associated with a porphyritic granodiorite stock cutting through an older monzodiorite intrusion. For the Kighal and Niaz, secondary biotite concentrates collected from potassic alteration zones in the parent porphyritic bodies yielded plateau ages of 20.1 ± 1.8 and 22.14 ± 0.13 Ma, respectively. The timing of the porphyritic intrusions and the associated mineralizations in the AMZ is considerably older than that in KCB in southern UDMB (14–7 Ma). There is evidence that the AMZ formed on a separate arc related to the southern lesser Caucasus subduction zone. The arc extends from northwest Iran to Armenia and Azerbaijan to the north. Similar deposits of the same age have been discovered in Armenia, exemplified by Kajaran and Dastakert.

Relative contributions of crust and mantle to generation of Oligo-Miocene medium-K calc-alkaline I-type granitoids in a subduction setting—a case study from the Nabar Pluton, central Iran

The Nabar pluton with the age of Oligo-Miocene located northwest of Isfahan, the Urumieh-Dokhtar magmatic belt, is composed of gabbro, gabbro diorite, diorite, quartz diorite, tonalite, and quartz monzonite. These rocks contain plagioclase, quartz, alkali-feldspar, magnesiohornblende, actinolite, tremolite-hornblende, actinolite-hornblende, anthophyllite, biotite, and Na-poor pyroxene. Application of the Al-in-hornblende barometry indicates pressures of 2–2.15 kbar, whereas the clinopyroxene barometry shows a pressure of 5 kbar. The temperature (i.e., 750–800°C) is estimated using the amphibole-clinopyroxene thermometry in a dioritic sample. Magmatic water content was greater than 10% at the time of formation of dioritic rocks in the Nabar pluton.

Petrochemistry of ultrapotassic tephrites and associated cognate plutonic xenoliths with carbonatite affinities from the late Quaternary Qa’le Hasan Ali maars, central Iran

The Quaternary Qa’le Hasan Ali (QHA) maars in central Iran occur at the intersection of the north–south Nayband fault, which defines the western boundary of the Lut micro-continental block, and a system of northwest–southeast faults, subparallel to the Zagros suture zone, that formed during the Arabian–Eurasian collision. These post-collisional maars intrude Eocene volcanic rocks of the Urumieh–Dokhtar magmatic belt, which was generated by the subduction of Neotethys oceanic lithosphere below Iran. The highly potassic, Ti-phlogopite+Mg-rich (Fo89–92) olivine+diopside-augite+aegirine–augite basanite tephrites forming the tuff rims of the QHA maars contain tephrite-coated plutonic xenoliths, some of which are interpreted as co-genetic with the tephrites based on their similar mineralogy and Sr isotopic composition (87Sr/86Sr=0.70590). Cognate plutonic xenoliths have up to ∼20vol% calcite, considered to be magmatic calcite because of (1) its grain size, which is similar to feldspars and aegirine–augite pyroxenes in these rocks, (2) the occurrence of fine-grained inclusions of pyroxene and apatite within these calcite grains, and (3) the similarity of the Sr-isotopic composition of this calcite with the other minerals in these rocks. The fact that the magmatic calcite has remained intact and did not volatilize during the transport of these xenoliths to the surface in the hot tephrite magma implies a short transit time, indicating that they are samples of a shallow plutonic complex, as does the presence of anorthoclase in these plutonic xenoliths. Their high modal proportion of magmatic calcite suggests that this shallow plutonic complex has affinities with carbonatites. The magmatic calcite-bearing plutonic xenoliths have high LREE/HREE ratios and contain REE-rich allanite (with up to ∼20wt% LREE) and britholite (∼60wt% LREE) that make up ∼3 modal percent of the most calcite-rich samples. Similar to many post-collisional highly potassic rocks formed in the Alpine–Himalayan collision zone, the highly potassic basanite tephrites of the QHA maars have high 87Sr/86Sr and low C̵Nd (−1.3 to −3.4), distinct from convecting asthenosphere, and they are depleted in Nb and Ta relative to Ba and La. They formed by small degrees of partial melting of lower continental lithospheric mantle metasomatized by both H2O and CO2-rich fluids derived from subducted Neotethys oceanic crust and sediments during the collision of the Arabian and Eurasian plates.

Stable isotope record of hydrothermal sulfate, sulfide and silicate minerals in the Darreh-Zar porphyry copper deposit in Kerman, southeastern Iran: Implications for petrogenesis and exploration

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 0.8wt.% Cu ores. A ~50-m-thick supergene zone containing 0.8 to 1.5wt.% 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.