فصلنامه زمین شناسی اقتصادی
سال پانزدهم شماره 4 (پیاپی 39، زمستان 1402)

Tozlou Pb-Zn mineralization, ~250-300m long, and ~50m thick, is hosted by limestone units of the Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Mineralization at Tozlou can be divided into five stages. Stage 1 is the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is categorized with dolomitization processes along with minor pyrite. Stage 3 occurred as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 includes late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes. Hydrothermal alterations include decarbonatization, carbonatization ± silicification, and late carbonatization. Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements pattern of ore samples, fresh and altered limestones is similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Characteristics of Tozlou occurrence are comparable with intermediate-sulfidation type of epithermal deposits.

Epithermal deposits are a group of base/precious-metal deposits that are formed by hydrothermal fluids in shallow environments under pressure/temperature changes and fluid-rock interactions (Hedenquist et al., 2000). Based on the host rock, epithermal deposits are divided into volcanic-hosted deposits and sedimentary-hosted deposits. According to the tectonic setting and magma type, they are divided into calc-alkaline magmas (including three subcategories of high-, intermediate-, and low-sulfidation) and alkaline magmas (White and Hedenquist, 1990; Cooke and Simmons, 2000; Hedenquist et al., 2000; Simmons et al., 2005). These types of deposits include a continuous range of deposits formed by magmatic/meteoric fluids and show different geometry, but have the same formation mechanism, especially the hydrothermal fluids circulation (Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Sedimentary rock-hosted deposits are divided into two groups: Carlin-type and sediment-hosted disseminated deposits. Carlin-type deposits are often formed as strata-bound or replacements at the boundary of rock units and are controlled by faults. They are distinguished by invisible Au in As-rich pyrite and arsenopyrite and do not show compatible spatial relationships to magmatic centers (Kuehn and Rose, 1992). Sediment-hosted disseminated deposits occurred as disseminated ore in sedimentary rocks (Hofstra and Cline, 2000). These deposits are physically and chemically comparable to Carlin-type deposits, but spatially and temporally are related to sub-volcanic porphyry intrusions (Theodore et al., 2000; Hofstra and Cline, 2000).
Tozlou Pb-Zn occurrence is 50km south of Qeydar in Zanjan province. This occurrence was first discovered/explored in 2017. Although general geological characteristics of Tozlou occurrence have been determined (Majidifard and Shafei, 2006), the mineralogy and origin of Tozlou occurrence have not been studied in detail. Here, detailed geology, mineralogy, alteration styles, and geochemistry of Tozlou occurrence are investigated to constrain the genetic model and type of its mineralization system. These results may have implications for future exploration of base-metal mineralization in this region and nearby areas. 

Comprehensive field and laboratory works have been carried out on Tozlou area. During the fieldwork, a detailed stratigraphic section of limestone units of Qom Formation was measured, sampled, and described. Fifty samples were collected from ore zones and limestone host rocks for laboratory analysis. Then, 34 thin and 15 polished-thin sections were prepared for mineralogical studies in the laboratory at the University of Zanjan, Iran. Fourteen typical samples from the ore zones and fresh/altered host limestone were analyzed for geochemical analysis using ICP–MS in Zarazma Analytical Laboratories, Tehran, Iran.

The main rock units exposed in Tozlou occurrence belong to Eocene sequence, Lower Red Formation, Qom Formation, and Quaternary units. Small outcrops of gabbro-gabbro diorite (gb) can also be seen in this region. Eocene strata include brown thin-bedded sandstone (Unit Es), alternating tuff and shale (Unit Etsh), and thin- to medium-bedded tuffs (Unit Et). Lower Red Formation includes a polygenetic conglomerate (Unit Ollrc) of Oligocene age. Qom Formation consists of massive- to medium-bedded cream-to-grey limestones (Unit OMql) and alternating marl and thin-bedded grey limestone (Unit OMqml). Quaternary units include terrigenous sediments.
Pb-Zn mineralization at Tozlou has ~250-300 m leng and ~50 m thick and is hosted by limestone units of Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Decarbonatization, carbonatization±silicic, dolomitization, and late carbonatization are hydrothermal alterations in Tozlou area. Mineralization processes at Tozlou can be divided into five stages. Stage 1 comprises the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is represented by the dolomitization of the limestone host rock, which is accompanied by minor pyrite. Stage 3 occurs as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 is characterized by late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes.
Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements patterns of ore samples, fresh and altered limestones, are similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Despite carbonate host rock, we think that mineralization at Tozlou is similar to the intermediate-sulfidation style of epithermal base metal deposits.

This study investigates the geochemical and mineralogical characteristics of Takht Coal Spoils in Minoodasht, Iran. For this purpose, six representative spoil samples were collected. The geochemistry of the samples were studied using XRF and ICP-OES analyses, microscopic studies, XRD, and SEM-EDX spectra. To examine the potential of Acid Mine Drainage (AMD) by the spoil samples, different static tests including pH and EC measurement of saturated paste, Acid-Base Accounting tests (ABA), and Net Acid Generation (NAG) / Net Acid Potential (NAP) test were applied. Based on the geochemical data, the studied samples are not enriched with Fe, Mn, Ni, Zn, low enriched with Cu and Cd, moderately enriched with Mo, significantly enriched with Sb and Pb, and strongly enriched with As. Quartz, muscovite, clinochlore and kaolinite are the major mineral phases in the studied samples. Static tests indicate that most of the samples are characterized by saturated paste pH<5.5, pH NAG<4.5, negative net neutralization potential (NNP), and positive NAPP values. NNP and NAG values as well as the position of the samples on the geochemical diagrams show that the formation of acid drainage is likely through the oxidation of spoils discarded around the mine. Regarding the environmental hazards imposed by acid mine drainage, the proper management of the spoils in the studied area deems necessary.

Coal is one of the most important fossil fuels that has been used by humans since ancient times due to its unique properties. However, coal extraction typically results in environmental problems such as land destruction, mine collapse, mine explosions, land subsidence, surface and groundwater pollution, soil and air pollution, and the production of Acid Mine Drainage (AMD). AMD is produced through the oxidation of metal sulfides (especially pyrite) present in waste rock dumps, processing wastes, underground mine tunnels, and open-pit mines. Oxygen, moisture, and ferric iron resulting from the oxidation of iron-bearing sulfides (especially pyrite) are the most important factors in sulfide oxidation (Munksgaard et al., 2012). AMD is one of the most important environmental problems in mining industry and one of the main causes of water pollution (Mohanty et al., 2018; Rezaie and Anderson, 2020), which reduces the pH and enhances the electrical conductivity (EC) of water and increases the concentration of potentially toxic elements (especially copper, zinc, arsenic, manganese, cobalt, nickel, lead, cadmium, barium, and mercury) in the surrounding areas (Pan et al., 2021; Kavehei et al., 2021). Moreover, the detrimental effects of AMD persist for decades and even centuries after mine closure. Coal spoils are among the most important sources of AMD production, because they usually contain high amounts of sulfidic minerals (e.g., pyrite, chalcopyrite, and arsenopyrite). Considering the negative impacts of AMD on the whole ecosystem, especially in coal mines where very large amounts of spoils are produced during extraction of coal, the prediction of AMD formation is of great importance that is useful in proper managing of spoil’s disposal and taking actions for preventing the formation of AMD (Kavehei et al., 2021). The aim of this study is investigating the geochemistry, mineralogy, and potential of AMD production by the coal spoils of Takht Coal Mine, located in Minoodasht County, Golestan Province, Iran. Coal extraction produces a large amount of waste materials, which are disposed around the mine tunnels. Since coal spoils is one of the most important sources for AMD production, examining their potential for acid generation is of great importance. Moreover, the geochemistry and mineralogy of the studied spoils were investigated by XRF and ICP analyses, microscopic studies, XRD, and SEM-EDX spectra of the representative samples.

Five representative samples were taken from the waste rock (spoil) dumps disposed near the extraction tunnels, and one representative sample was taken from the spoils discarded around Takht Coal Mine. To obtain a representative sample at each station, at least 30 sub-samples were collected and mixed together. The weight of each sub-sample was approximately 3 kg. To identify the minerals present in the samples, polished sections were prepared and studied, and X-ray diffraction (XRD) and SEM-EDX analyses were implemented. The geochemical compositions of the studied samples were studied by X-ray fluorescence (XRF) (for major oxides and sulfur) and ICP-OES (for major and trace elements) analyses. To predict the potential of AMD production by the studied samples, the most common statistic tests were conducted using standard methods 1) measuring pH and electrical conductivity (EC) of saturation pastes of the samples; 2) the modified Acid-Base Accounting (ABA) tests; and 3) Net Acid Generation (NAG) and Net Acid Potential (NAP) tests.
 

The results showed that the spoils of Takht Coal Mine is not enriched with Fe, Mn, Ni, and Zr, significantly enriched with Sb, Pb, Mo, and extremely enriched with As. The high enrichment of toxic elements (i.e., As, Sb, and Pb) in the studied samples is likely due to the presence of pyrite and chalcopyrite in the samples, as confirmed by the mineralogical studies in which pyrite presents as framboidal aggregates and semi-idiomorphic particles. Moreover, the high concentration of potentially toxic elements in the studied samples must be considered a potential risk which may result in serious environmental impacts on the surrounding areas. The statistic tests showed that the pH values of samples 1, 2, 3, and 4 in the net Acid Generation (NAG) test are <4.5. On the other hand, these samples have a positive Net Acid Production Potential (NAPP) and a negative Net Neutralization Potential (NNP). On the other hand, in samples 5 and 6, NAG pH is greater than 4.5, and the pH value of the saturation paste is approximately neutral. The two samples have the lowest sulfur among all samples. Moreover, XRD spectra showed that muscovite and quartz are present in theses samples, which can prevent acid production or neutralize the produced acid. The results of the static tests showed that samples 5 and 6 have a negative NNP and a positive NAPP. Therefore, the possibility of acid production in the waste materials is uncertain.

Considering the high concentrations of potentially toxic elements in the spoil samples of Takht Coal Mine, in the event of acid mine drainage formation, the surface and groundwater resources and soil of the studied area will be seriously affected. To reduce the environmental impacts of Takht Coal Mine’s spoils, taking proper measures is very relevant. Some possible measures include adding lime to the waste materials to neutralize the spoils, adding soil to the waste material, providing drainage channels under the waste dump bed to transfer produced acid into ponds containing lime materials, depositing waste material away from surface water paths, and separating pyrite from the waste material can be taken into account.

In central part of the Mesozoic Ashin ophiolite (Northwest of Anarak, Isfahan province, Iran), the Upper Eocene monzonitic stock cross cuts the Ashin ophiolite and Middle Eocene volcanic rocks. Amphibolite xenoliths are enclosed in the stock and associated Eocene volcanic rocks. Xenoliths are more abundant in the margin of the monzonitic stock. Rock-forming minerals of the stock are plagioclase with andesine to labradorite composition (An=34-60%), Alkali-feldspar with orthoclase composition (Or= 70.8 to 96.1%), diopsidic clinopyroxene with (Mg# =0.71-0.90), and phlogopite mica with (Fe#=0.3). Opaque minerals are magnetite and titanomagnetite (TiO2=1.6-4.4 wt.%). Main textures of samples from this intrusive body are granular, intergranular and poikilitic. Samples from the margin of this stock represent porphyritic texture. 
Geochemistry of minerals and whole rock samples of this stock indicate that they belong to the calc-alkaline magmatic series and are similar to the samples from the continental magmatic arcs.
These magmatic rocks possibly were formed by subduction of the CEIM (Central-East Iranian Microcontinent) confining oceanic crusts (Ashin and Nain oceanic crusts) during Mesozoic and Early Cenozoic eras.

Iran is a part of the Alpine-Himalayan orogenic system, including the Paleozoic to Cenozoic ophiolites, magmatic and metamorphic rocks (Takin, 1972; Berberian and King, 1981; Berberian et al., 1982; Dercourt et al., 1986; Alavi, 1994; Mohajjel et al., 2003; Shahabpour, 2007). The main pulse of the Paleogene and Neogene magmatic (volcanic and intrusive) activities of Iran can be attributed to the two Cenozoic subduction events, including the western Neo-Tethyan oceanic crust subduction beneath the Sanandaj-Sirjan block in the west and the eastern Neo-Tethyan oceanic crust subduction beneath the Central Iran (e.g., Shirdashtzadeh et al., 2022). The former subduction possibly caused to the formation of the Urumieh-Dokhtar Magmatic Arc, but the later subdution results is not well studied yet. 
In the this research, the target region is located in the west of the Yazd block (Central Iran), where the Eocene volcanic and plutonic rocks represent subduction-related characteristics (Jamshidzaei et al., 2021). The investigated subduction-related monzonitic stock that cross cuts the central part of the Ashin ophiolite in the Kuh-e-Kalut-e-Ghandehari region, in the northwest of Anarak (Isfahan Province, Iran). The main lithologies in the Kuh-e-Kalut-e-Ghandehari are Mesozoic lithologies of Ashin Ophiolite, Paleocene limestone, Eocene volcanic rocks, monzonitic stock, Lower Red Formation, and Akhoreh Formation. Ashin ophiolite was formed in the mesozoic (Shirdashtzadeh et al., 2022) and emplaced in the Late Paleocene (~60 Ma; Pirnia et al., 2020; Shirdashtzadeh et al., 2022), before than Eocene volcanism and plutonism. The studied monzonitic stock of the Kuh-e-Kalut-e-Ghandehari intrudes the Mesozoic Ashin ophiolite and Middle Eocene volcanic rocks.
The calc-alkaline affinity of the volcanic and plutonic rocks of the area, tectonic activity of the Great Kavir fault caused to the crushing and mylonitization of the surrounding rock units, as well as the alteration evidences in the field studies point to suitable conditions for the ore deposit exploration in the area (e.g., copper). In this research, the petrology, mineralogy, and whole rock geochemistry of the Upper Eocene monzonitic stock are considered. This research will expand our understanding of the geochemical nature of subduction-related Cenozoic magmatism in Central Iran.

After detailed field studies and sampling, the selected fresh samples were used for microscopic thin section and polished-thin section studies by the polarizing binocular microscope (Olympus BH-2). The microprobe analyses were performed at the School of Natural Systems, College of Science and Engineering, Kanazawa University (Kanazawa, Japan) using a wavelength dispersive electron probe microanalyzer (EPMA) (JEOL JXA-8800R). The mineral analysis was achieved under an accelerating voltage of 20 kV, a probe current of 20 nA, and a focused beam diameter of 3μm. 14 whole rock samples analyses were performed by Brucker S4 PIONEER XRF in the central laboratory of the University of Isfahan and 3 samples were analyzed in the Isfahan Nuclear Technology Center by neutron activation analysis (NAA).

Based on the field relation ships, this gray to light gray pluton intrudes into the Middle Eocene volcanic rocks and belongs to the Upper Eocene. The Middle Eocene volcanic rocks and Upper Eocene monzonitic stock crosscut the Ashin Ophiolite. This Eocene stock and volcanic rocks contain amphibolite xenoliths with the same mineralogy and petrography. Xenoliths are more abundant in the margin of the monzonitic stock. Gradual decreasing of modal plagioclase content indicates that the xenoliths range from amphibolite (plagioclase + amphibole) to hornblendite (only amphibole) in composition.
Rock-forming minerals of the stock are plagioclase with andesine to labradorite composition (An = 34-60 %), alkali-feldspar with orthoclase composition (Or = 70.8 to 96.1%), diopside clinopyroxene with Mg# = 0.71-0.90, and phlogopite mica with Fe# = 0.3. Opaque minerals are magnetite and titanomagnetite with TiO2 = 1.6-4.4 wt%. The main textures of samples from this intrusive body are granular, intergranular and poikilitic. Samples from the margin of this stock represent porphyritic texture. The SiO2 value in the whole rock compositions ranges from 47.9 to 61.65 wt.% (basic to intermediate). The average content of alkalis is 9.75 wt.%). The Kuh-e-Kalut-e-Ghandehari rocks show sodic affinity by higher Na2O than K2O, based on the Na2O/K2O versus SiO2 and K2O/Na2O versus SiO2 diagrams (Jaques et al., 1985). The Eocene intrusive and volcanic rocks of this area are similar in terms of mineralogy and texture. Petrography and whole rocks chemical analyses indicate that the studied stock is geochemically composed of gabbro, monzodiorite to monzonite in composition with metaluminous affinity. Monzonite is the predominant rock.

Various tectonomagmatic discrimination diagrams are used to determine the tectonomagmatic setting of the Kuh-e-Kalut-e-Ghandehari stock. Mineral chemistry and whole rock geochemistry of the Kuh-e-Kalut-e-Ghandehari monzonitic stock indicate a calc-alkaline magmatic series similar to the subduction-related magmas in the normal continental magmatic arcs formed during the mantle metasomatism. According to the the temporal and geological situation, as well as the geochemical characteristics of the Kuh-e-Kalut-e-Ghandehari stock, it is considered as a part of an arc magmatism, related to the subduction of Neo-Tethyan oceanic crust beneath the CEIM (Central–East Iranian Microcontinent) during the Late Mesozoic and Early Cenozoic eras.

We are grateful to the University of Isfahan and the Department of Geology of Kanazawa University (Japan) for their supports. We are also grateful to anonymous reviewers for their useful comments and suggestions that improved the quality of this paper.

Sagh mineral occurrence is located southeast of Torbat-e-Heydarieh, Khorasan Razavi province, and in the eastern part of the Khaf-Kashmar-Bardeskan magmatic belt. The rock units of area are divided into two categories: intrusions (monzonite, monzodiorite, diorite, and syenite) in the southern half, and conglomerate in the northern half. One square kilometer of continuous mineralization may be observed as stockwork, while there are other locations where it has a linear trend and is supported by intrusive rocks. Primary minerals include specularite, chalcopyrite, pyrite, galena, and sulfosalt, and secondary minerals include malachite, goethite, hematite, chalcosite, caveolite, and anglesite. The mineralization textures are vein-veinlet, disseminated, replacement, and cloform, mainly with a strong chloritic-silicified alteration. The average amount of copper is 0.8 with a maximum of more than 3%, the average amount of silver is 24.4 with a maximum of more than 113 ppm, and the average amount of gold is 44 with a maximum of 250 ppb. The average amount of lead is 761 ppm with a maximum of 0.4% and the average amount of zinc is 430 ppm with a maximum of 0.1%. The formation temperature of ore-forming fluid is between 159 and 328 °C and the salinity is between 7.2 and 16.7 wt.% equiv. NaCl. The mixing of magmatic fluids with meteoric waters with low temperatures and salinity was the most important mechanism of mineral formation. Based on the evidence of tectonic setting, lithology, type of alteration, shape, and state of mineralization, and the presence of abundant specularity with copper, silver, and gold anomalies, probably the Sagh area is iron oxide Cu-Ag±Au type. 

The geological settings, hydrothermal alteration, and mineralizing fluid compositions vary among the deposits of “IOCG-type” (Hitzman et al., 1992; Sillitoe, 2003). However, they belong to a family of Cu ±Au deposits that include substantial hydrothermal alkali (Na/Ca/K) alteration and a lot of low-Ti iron oxide (magnetite and/or hematite). According to Williams et al. (2005), these deposits likewise exhibit strong structural constraints and a temporal but not a tight geographical relationship with igneous rocks. They formed in rift or subduction settings (Hitzman, 2002) from the Late Archean to the Pliocene (Groves et al., 2010).
Sagh mineral occurrence is located the southeast of Torbat-e-Heydarieh, Khorasan Razavi province, and in the eastern part of the Khaf-Kashmar-Bardeskan magmatic belt (Fig.1). This belt has a high potential for iron oxide copper-gold type deposits and sometimes skarn and porphyry copper (Karimpour, 2004).
The purpose of this research is geological studies and determine the relationship of intrusions with mineralization, examine the total paragenesis sequence, geochemistry, fluid inclusions studies and finally determine the mineralization model, and the formation of mineral occurrences in the Sagh area, for the first time is done.

To investigate the lithology, alteration, and mineralization of the Sagh area, 61 samples were taken mainly from the intrusions. 32 samples for the thin section and 10 samples for the polished thin section and polished block were selected, prepared, and studied. Then, the geological and alteration-mineralization map with a scale of 1:5000 was prepared in Arc GIS software. Furthermore, for geochemical studies of mineralization zones and veins, 24 samples were taken and sent to the Zarazma laboratory for analysis. Analysis was done by the ICP-OES method. Furthermore, 11 samples were selected for gold analysis with Fire assay, and sent to Zarazma laboratory. Using a cooling and heating system made by Linkam Company, model THM 600, microthermometric tests and salinity determination were performed on 2 wafers of quartz minerals and 31 fluid inclusions at Ferdowsi University of Mashhad.

The rock units of the area are divided into two categories: subvolcanic and plutonic intrusions in the southern half and conglomerate units in the northern half. Intrusive rocks are composed of monzonite, monzodiorite, diorite and syenite. Mineralization can be seen in the form of stockwork in a wide and continuous zone with an area of about one square kilometer, but in some places, it has a linear trend (NE-SW and NW-SE trend) which is hosted by intrusive rocks. Primary minerals include specularite, chalcopyrite, pyrite, galena, and sulfosalt, and secondary minerals include malachite, goethite, hematite, chalcosite, covellite, and anglesite. Vein-veinlet, disseminated, replacement, and cloform mineralization textures are seen, with a dominant chloritic-silicified alteration. The average concentration of copper is 0.8%, with a maximum concentration of more than 3%, silver is 24.4 ppm, with a maximum concentration of more than 113 ppm, and gold is 44 ppb, with a maximum concentration of more than 250 ppb, according to geochemical data. The average amount of lead is 761 ppm with a maximum of 0.4% and the average amount of zinc is 430 ppm with a maximum of 0.1%. Based on fluid inclusions studies, the formation temperature of ore-forming fluid is between 159 and 328 °C, and the salinity is between 7.2 and 16.7 wt.% equiv. NaCl.

Comparing the characteristics of Sagh prospect area with other copper-bearing deposits shows that this area is very similar to iron oxide copper-gold deposits. An empiric definition of IOCG deposits is summarized as having the following five characteristics (Williams et al., 2005): (1) copper, with or without gold, as economic metals, (2) hydrothermal ore styles and strong structural controls, (3) abundant magnetite and/or hematite, (4) Fe oxides with Fe/Ti ratios greater than those in most igneous rocks and bulk crust, and (5) no clear spatial associations with igneous intrusions as, for example, displayed by porphyry and skarn ore deposits.
Sillitoe (2003) proposed a close genetic relationship between IOCG deposits in northern Chile, and dioritic plutons. Mineralization in the Sagh area has a close relationship with monzonitic, monzodiorite, and diorite, which are similar to Kuh-e-Zar, Bahariyeh, Namaq, Fadiheh, Chenar, and other KKBMB deposits (Table 3).
The main alteration related to mineralization in the Sagh is propylitic-silicified, and its propylitic alteration is characterized by chlorite mineral. Extensive chlorite alteration in the Sagh area is similar to Monteverde deposit in Peru (Vila et al., 1998), Mont-del-Aigle in Canada (Simard et al., 2006), Kuh-e-Zar Tarbat Heydarieh (Karimpour et al., 2017), and other IOCG type deposits in the KKBMB belt (Almasi et al., 2015; Taghadosi and Malekzadeh Shafaroudi, 2018; Najmi et al., 2023; Sahebi Khader et al., 2021; Behnamnia et al., 2023) and Qala Zari (Karimpour, 2005) in the Lut block, where the temperature and salinity of ore-fluid are lower than some IOCG type deposits in the world.
Based on the available evidence, the mineral occurrence of the Sagh includes 1) the presence of oxidant intrusions formed in the subduction zone in the KKBMB, 2) mineral paragenesis of specularity, chalcopyrite, pyrite, and galena, 3) structural control of mineralization, 4) copper, silver, gold, and lead geochemical anomaly, 5) chloritic-silicified alteration, which is very compatible with iron oxide copper-silver-gold systems. The location of this area in the KKBMB belt, which has great potential for IOCG deposits, and near other IOCG deposits that have many similarities (Almasi et al., 2015; Karimpour et al., 2017; Sahebi Khader et al., 2021; Najmi et al., 2023), is a confirmation of this claim.
Although monzonitic, monzodiorite, diorite, and syenitic intrusions are the host rock of mineralization and mineralization is controlled by structures and faults, this magmatism can be represented of source rock at deep. The mineral paragenesis of the Sagh and the abundance of specularity with sulphide minerals of copper, lead, and silver, which are associated with quartz and chlorite, show that mineralization generated from a high fO2, Fe-Si rich ore fluid.
The metal originated from an oxidan magmatism from deep, and moved up through faults, joints, and fractures. The mixing of magmatic ore solution with higher temperature and salinity with meteoric water with lower temperature and salinity has finally led to the deposition of sulfides, and the formation of mineralization. Temperature-salinity and alteration evidence show that we are currently in the upper parts of the system, and we need more information. The relevance of this magmatic belt in eastern Iran as a significant metallogenic zone for deposits of copper, gold, and silver is growing as more and more IOCG mineral occurrences are found there.

The intrusive body in the south of Vineh, located in the north of Karaj city, is one of the several late Eocene plutons that intruded into the volcano-sedimentary Karaj Formation in the south of Central Alborz. This intrusive body comprises monzogabbro, monzodiorite, monzonite, and syenite with an alkaline shoshonitic nature and geochemically is cogenetic, evolved through fractional crystallization. The rocks are medium to coarse-grained with a dominant hypidiomorphic granular texture and consist of plagioclase, olivine, clinopyroxene, amphibole, orthoclase, and quartz. Titanite, apatite, biotite, and opaque occur as accessory minerals, whereas, epidote, chlorite, calcite, and iddingsite as secondary minerals. Geochemical data such as LREE enrichment relative to HREE, Pb positive anomaly, and depletion of Nb, Ta, Zr, Ti, as well as major, minor, and trace element data indicate that primary magma of these rocks formed in an active continental margin under the influence of Neo-Thetys subduction components beneath Central Iranian microplate. Alternatively, based on tectonic discrimination diagrams, the study of plutonic rocks is mainly attributed to the post-collision tectonic regime. Therefore, it seems that the magma originated from a low degree of partial melting (3 to 5 percent) of phlogopite-spinel peridotite source at a depth of about 60 to 65 km in an extensional back-arc basin as a result of slab rollback in the late Eocene, following the subduction of Neo-Thetys in Central Iran. The generated melt during the ascent underwent assimilation and fractional crystallization in lower depth magma chamber. 

The intrusive body in the south of Vineh, located in the north of Karaj city, is one of the several Late Eocene bodies that intruded into the volcano-sedimentary Karaj Formation in the south of Central Alborz zone. The evolution of the Cenozoic Alborz Magmatic Arc Belt (AMAB) is regarded as the back arc of the Urumieh-Dokhtar Magmatic Belt (UDMB) which is related to the Neo-Tethys subduction and the continental collision between the Arabian and Eurasian plates (e.g., Asiabanha and Foden, 2012; Maghdour-Mashhour et al., 2015; Sepidbar et al., 2021). One of the most considerable episodes of magmatism in Iran was an extensive flare-up magmatism that developed principally in the UDMB and the AMAB throughout the Eocene-Oligocene (Berberian and King, 1981; Verdel et al., 2011; Asiabanha and Foden, 2012). This magmatism is distinguished by intermediate rock compositions from calc-alkaline to shoshonitic nature occurring in an extensional arc setting (Verdel et al., 2011; Agard et al., 2011; Shafaii Moghadam et al., 2018). In Central Alborz, several Late Eocene intrusive bodies intruded Karaj Formation such as Mobarakabad gabbro, Lavasan syenite, Shekarnab monzonite, and Karaj Dam basement gabbro to monzonite sill. In the south of Karaj Dam basement sill in Vineh village area, an outcrop of monzogabbro to syenite sill hosted by the Karaj Formation is investigated to clarify the petrological and geochemical characteristics. To achieve this purpose, field relationships, rock textures, and chemical analyses for different rock types are presented. The data and the findings of previous studies (e.g., Asiabanha and Foden, 2012; Maghdour-Mashhour et al., 2015; Sepidbar et al., 2021) are subsequently employed to infer the type of the geodynamic regime of the Alborz throughout the Cenozoic.

The study area is located in the north of Karaj city between the northern geographical latitude of 35° 51´ 02" and 35° 54´ 10", eastern longitude of 51° 00´ 23" and 51° 03´ 17", and geologically in southern-central Alborz structural zone (Figure 1). The dominant rock types in the area consist of basic lavas, tuffs, and clastic rocks accumulated from the Middle to Late Eocene, creating 3 to 5 km thick Karaj Formation in Central Alborz (Dedual, 1967). The Karaj Formation in the study area was intruded by Vineh sill that seems to be coeval with the Karaj Dam basement sill during Late Eocene-Early Oligocene (Maghdour-Mashhour et al., 2015). The contact of the intrusion with country rocks is sharp in the field.

Thirty rock specimens from different outcrops were collected from Vineh sill. Subsequently, based on field evidence and thin section petrography, 8 specimens were selected and analyzed by ICP-OES (major elements) and ICP-MS (trace elements) techniques at Zarazma Company. The accuracy of measurements was within 5% for major and 10%-15% for trace elements. Table 1 shows the results of chemical analyses.

Vineh intrusive rocks with mainly hypidiomorphic texture are composed essentially of plagioclase, clinopyroxene, and olivine as well as minor amphibole, biotite, and K-feldspar. In monzonite and syenite, amphibole, biotite, and K-feldspar are dominant in addition to plagioclase and clinopyroxene. Chlorite, calcite, epidote, and iddingsite are secondary minerals, whereas apatite, titanite, zircon, and opaque are minor. The rocks are porphyritic at the margin and have medium to coarse-grained equigranular texture in the center of the sill. The geochemistry of eight specimens plotted on the rock classification diagram of Middlemost (1994) shows monzodiorite, monzonite, and syenite (Figure 5A), and on the normative diagram of Streckeisen and LeMaitre (1979), monzogabbro, monzodiorite, monzonite, syenite, and alkali feldspar syenite (Figure 5B). This intrusive body with an alkaline shoshonitic affinity is geochemically cogenetic and evolved through fractional crystallization.

Geochemical data show that the rocks are alkaline and shoshonitic in nature and the chondrite-normalized REEs diagram, exhibits LREE enrichment relative to HREEs. In the primitive mantle-normalized multi-element diagram (Sun and McDonough, 1989), the patterns of rocks show enrichment of LILE (e.g., Ba and Rb), Pb positive anomaly, and depletion of HFSE (Nb, Ta, Ti, Zr), the outstanding characteristics of subduction-related magmatism. It seems that the magma originated from a low-degree partial melting (3 to 5 percent) of a phlogopite spinel-lherzolite mantle at a depth of 60 to 65 km in an extensional back-arc basin due to slab rollback following the subduction of Neo-Thetys beneath Central Iran. In other words, the parent magma formed as a result of fluids and sediments derived from the Neo-Tethys oceanic crust caused metasomatism of subcontinental lithospheric mantle followed by extension-related decompression melting of phlogopite spinel-lherzolite mantle by the heat supplied by rising of the asthenosphere. The generated melt during the ascent underwent assimilation and fractional crystallization in lower depth magma chambers.

The authors are very grateful to the reviewers of the Journal of Economic Geology for their constructive ideas in improving the scientific structure of the article.

The Lower Oligocene basic dikes are cropped out in the Chah-e-Alikhan area (Northeast of Isfahan province, North of the Daq-e-Sorkh desert). These dikes show NE-SW and NW-SE trends and cross cut the Eocene volcanic rocks and associated flysches. NW-SE dikes are younger and cut the NE-SW ones. These dikes are similar in petrography and are composed of plagioclase, clinopyroxene, olivine, sanidine, Cr-spinel and ilmenite. Zeolite, serpentine, calcite and magnetite are secondary minerals. These dikes represent the porphyritic, glomeroporphyritic, poikilitic and trachytic textures. Intergranular and granular textures can be seen at the center of the larger dikes. These basalts are enriched in alkalis (Na2O+K2O), LREE and LILE (Cs, Rb, Ba, Pb) and have high values of LREE/HREE ratio (La/Yb=8.9-10). In the classification diagrams, which are based on the incompatible elements and HFSEs, they are classified as alkali basalts. The primitive magma of these basaltic dikes has been produced by partial melting of a garnet-spinel lherzolite of the mantle previously suffered the carbonate metasomatism. The formation of the alkali basalt dikes of the Chah-e-Alikhan area can be ascribed to the former subduction of the Central- East Iranian Microcontinent (CEIM) confining oceanic crust and decompression melting induced by the extensional basin of the Anarak‒Jandaq area in Early Oligocene. The primary basaltic magma has been formed by low degree of partial melting of a metasomatised mantle lherzolite during continental crust extension episode in the lower Oligocene and has been ascent through the faults. 

In the Northwest of CEIM (Central-East Iranian Microcontinent), along the Great Kavir fault, volumes of alkali basalts with the lower Oligocene age are outcropped as volcanic and subvolcanic (Dike) rocks. In this research, the subvolcanic exposures of this basic magmatism in the the Chah-e-Alikhan area is discussed. The Lower Oligocene basic dikes are cropped out in the Chah-e-Alikhan area (Northeast of Isfahan, Northeast of Zavareh, and Northwest of the CEIM). These dikes show NE-SW and NW-SE trends and cross cut the Eocene volcanic rocks and associated flysches. In this paper, the geological and petrological aspects, as well as the geodynamic setting of alkali basalt dikes of the Chah-e-Alikhan area are discussed. Study of these dikes, as a part of the Cenozoic alkaline magmatism from Northwest of the CEIM, will be useful in understanding the geodynamical evolution of the Central Iran.

 The method of study is including petrography (field, library and microscopic studies) and whole rocks geochemical analysis of rocks. 13 fresh whole rock samples of alkali basalts from the Chah-e-Alikhan area were selected for the major and trace elements chemical analyses.
Whole rock geochemical analyses carried out by using a Bruker S4 Pioneer XRF at the Central Laboratory of the University of Isfahan. Trace element compositions of the selected samples were achieved by ICP-MS (Inductively coupled plasma-mass spectrometry) at the Zarazma Mineral Studies Company (Tehran, Iran). 

The rock-forming minerals of the Chahe-e-Alikhan basic dikes are Cr-spinel, olivine, clinopyroxene, plagioclase, sanidine and ilmenite. Zeolite, serpentine, calcite and magnetite are secondary minerals which are formed as a result of the alteration of primary minerals. Petrographical characteristics indicate that these dikes are alkali basalt and represent the porphyritic, glomeroporphyritic and trachytic textures. Intergranular and granular textures can be seen at the center of the larger dikes.
These basalts are enriched in alkalis (Na2O+K2O=4.5-5.4 wt%), LILEs (Cs, Rb, Ba, Pb) and have high values of LREE/HREE ratio (La/Yb=8.9-10). Trace elements ratio diagrams such as La/Nb versus La/Yb, Dy/Yb against La/Yb, Sm/Yb versus La/Yb (Bogaard and Worner, 2003) and Ce/Yb-Ce (Ellam, 1992) are used in order to determination of the depth, type and degree of partial melting of the source rock. Based on the geochemical characteristics and diagrams, the primitive magma of the Chah-e-Alikhan alkali basalts possibly have been produced by about 5 to 10 percent partial melting of a garnet-spinel lherzolite, which is located at the depth of about 105 km, as a part of a mixed asthenospheric–lithospheric mantle. The elevated values of the Zr/Hf ratio and the Na2O + K2O versus TiO2 diagram (Zeng et al., 2010) indicate that the primitive magma of the studied basic dikes previously suffered the carbonate metasomatism.
The Chah-e-Alikhan alkali basalts show high values of the Alkalis (Na2O + K2O), enrichment in LREE, HFSE and LILE. The subducted oceanic slab is the source of carbon and LILEs are the mobile components of subduction (Shaw et al., 2003). Considering that Cs is a highly fluid mobile element, enrichment in Cs relative to Rb suggests that the fluid phases derived from a subducting slab are probably the metasomatic agents.
The lower Oligocene alkaline magmatism in the Chah-e-Alikhan area and the enrichment of the mantle with incompatible elements (metasomatism) can be attributed to two oceanic crust subduction events: (1) Northeast ward Neotethys subduction along the Zagros Thrust Zone beneath the Central Iran from the Triassic to the Eocene (Torabi, 2010); and (2) Subduction of an oceanic crust along the Great Kavir Fault, which is situated to the western margin of the CEIM. The spreading of the last ocean crust started in the Triassic and ended in the Eocene. The remnants of this oceanic crust are found as ophiolitic melanges on the western side of the CEIM, such as the Nain, Surk, and Ashin ophiolites (Rajabi and Torabi, 2012; Torabi, 2010). The geological history and position of the Chah-e-Alikhan alkali basalt dikes suggests that the the carbonate metasomatism of the mantle peridotites can be attributed to the subduction of the CEIM confining oceanic crust.
Several tectonic discrimination diagrams have been used for determination of the tectonic setting of the Chah-e-Alikhan basalts. The La/Yb versus Th/Nb (Hollocher et al., 2012), Ta/Yb against Th/Yb (Gorton and Schandl, 2000) and DF1 versus DF2 (Verma and Agrawual, 2011) diagrams suggest a within-plate (continental) tectonic setting.
The activity of the major faults of the area such as Great Kavir, Chah Mishury and Chah Gireh Faults has been created a suitable inter-plate extensional system to ascending the Lower Oligocene alkali basalt magma in the Chah-e-Alikhan area.

The Lower Oligocene alkali basalts of the Chah-e-Alikhan area is a part of the intra-continental alkaline magmatism crosscuts the Eocene volcanic rocks. The area provides a setting to study the Cenozoic alkaline magmatism of the northwest of the CEIM.
These basalts are enriched in total Alkalis, TiO2, LREE and LILEs. They have been produced by about 5 to 10 percent degree of partial melting of a garnet-spinel bearing lherzolite of a mixed lithospheric-asthenospheric mantle which is previously metasomatised. The mantle enrichment can be ascribed to the subduction of the CEIM confining oceanic crust beneath the Central Iran from the Triassic to the Eocene. The Grate Kavir Fault and related faults have played an important role in the Lower Oligocene alkaline magmatism in northwest of the CEIM.

The authors thank the University of Isfahan for financial support.