پترولوژی

IntroductionThe Hendou-Abad Cu(-Ag) deposit is located in the central part of the Urumieh-Dokhtar magmatic arc, approximately 110 km northeast of Isfahan, Iran. The deposit is hosted by upper Eocene volcanic rocks composed mainly of andesitic basalt, andesite, and subordinate trachyandesite and trachybasalt. Although copper mineralization in the area had previously been recognized, its geological controls, fluid evolution, and genetic characteristics had not been comprehensively investigated. This study integrates geological, mineralogical, geochemical, and fluid inclusion data to characterize the ore-forming processes and evaluate the relationship between the deposit and manto‑type copper systems.MethodologyField investigations, sampling, petrographic studies, XRD analyses, whole‑rock geochemistry, electron probe microanalysis (EPMA), and fluid inclusion microthermometry were conducted. Fifty‑seven representative samples were collected from mineralized and altered zones. Petrographic observations were used to determine mineral assemblages and paragenetic relationships, whereas XRD analyses identified alteration minerals. Whole‑rock geochemistry and EPMA were employed to investigate elemental distributions and ore mineral chemistry. Fluid inclusion studies on quartz, epidote, and calcite veins provided information on the evolution of temperature and salinity of the ore‑forming fluids.Geology and MineralizationThe oldest exposed rocks in the area are upper Eocene volcanic units consisting predominantly of andesitic basalt and andesite, with minor trachyandesite and trachybasalt. These rocks host the Cu(-Ag) mineralization and are intruded by mafic to intermediate dikes. Regional strike-slip fault systems, particularly the Kachomesqal and Zafarghand fault zones, acted as the principal pathways for hydrothermal fluid circulation.Mineralization occurs as veins, veinlets, stockworks, disseminations, cavity fillings, and replacement bodies. Three distinct breccia types are recognized: red, green, and white breccias. The red breccia contains rounded volcanic fragments cemented by a quartz‑calcite‑iron oxide matrix, whereas the white breccia consists of volcanic and red breccia fragments enclosed within a siliceous matrix. The green breccia is characterized by angular to sub-rounded fragments within an epidote-calcite-quartz matrix.Primary ore minerals include chalcocite, chalcopyrite, bornite, pyrite, and minor galena. Electron microprobe analyses also identified tetrahedrite, electrum, native gold, digenite, and accessory Ag‑bearing phases. Chalcocite, chalcopyrite, and bornite constitute the dominant copper sulfides. The average grades of copper and silver in mineralized samples are approximately 2.7 wt.% Cu and 62 ppm Ag, respectively.Hydrothermal alteration is closely associated with mineralization. A pervasive propylitic assemblage consisting of epidote, chlorite, calcite, tremolite-actinolite, and prehnite is particularly developed within the red breccias. In contrast, epidote-chlorite alteration is spatially associated with copper-bearing veins in the green and white breccias. Away from the mineralized zones, this alteration gradually changes into zeolite-bearing assemblages.DiscussionPetrographic observations, mineral chemistry, and fluid inclusion data indicate that mineralization developed through three successive stages. The first stage is represented by disseminated pyrite and minor chalcopyrite associated with pervasive propylitic alteration and Type I quartz within the red breccias. Fluid inclusions hosted by Type I quartz exhibit homogenization temperatures of 218–275°C and salinities ranging from 12.5 to 16.8 wt.% NaCl equivalent, indicating formation from relatively hot and moderately saline hydrothermal fluids.The second stage represents the principal Cu-Ag mineralization event and is responsible for most of the economic metal accumulation. Mineralization occurs as veins, veinlets, stockworks, and replacement bodies controlled primarily by E–W-trending structures. Ore minerals include chalcocite, bornite, chalcopyrite, tetrahedrite, electrum, native gold, and galena. This stage is associated with Type II epidote, Type II quartz, and Type II calcite. Fluid inclusion studies indicate homogenization temperatures between 95 and 237°C and salinities ranging from 2.90 to 12.96 wt.% NaCl equivalent. These lower temperatures and salinities indicate progressive cooling and dilution of hydrothermal fluids by meteoric water. Most copper and silver precipitation occurred during this stage.The third mineralization stage is characterized by low-temperature hydrothermal activity and chalcedonic quartz-calcite veinlets. This stage contributed little to the overall metal budget and is therefore economically insignificant.Whole-rock geochemical analyses reveal enrichment of Cu, Ag, Pb, Sr, and sulfur and depletion of Ba and Zn relative to host rocks. Strong positive correlations between Cu and Ag indicate a close genetic relationship between silver and copper sulfides. EPMA data show that silver is present in most copper sulfides but is preferentially concentrated in secondary sulfides. The highest silver concentrations were recorded in covellite, reaching approximately 0.7–1.08 wt.%.Supergene weathering subsequently modified the deposit and produced an enriched Cu-Ag zone. Oxidation and leaching of primary sulfides generated secondary chalcocite, covellite, Ag-bearing digenite, native copper, cuprite, tenorite, malachite, and azurite, significantly enhancing copper and silver grades.ConclusionsThe Hendou-Abad Cu(-Ag) deposit formed within upper Eocene volcanic rocks under strong structural control exerted by regional fault systems. Three successive mineralization stages are recognized, with the second stage representing the principal Cu-Ag event. Hydrothermal alteration evolved from widespread propylitic assemblages in the red breccias to epidote-chlorite alteration in the green and white breccias, grading outward into zeolite alteration. Fluid inclusion data demonstrate a progressive decrease in temperature and salinity from the first to the third stage, indicating increasing dilution by meteoric water. Chalcocite, chalcopyrite, and bornite constitute the primary copper ore minerals, whereas supergene processes generated secondary sulfides enriched in silver, particularly covellite. The geological setting, alteration characteristics, ore mineralogy, geochemical signatures, structural controls, and microthermometric data collectively indicate that the Hendou-Abad deposit shares strong similarities with manto-type copper deposits and represents an important example of volcanic-hosted Cu(-Ag) mineralization in the Urumieh-Dokhtar magmatic arc.

IntroductionThe Kushk Pb–Zn deposit in northeastern Bafq, Central Iran, is associated with Neoproterozoic–Early Cambrian magmatism related to the Proto-Tethyan continental arc system. These magmatic processes, accompanied by crustal extension and interaction between mantle-derived magmas and continental crust, played an important role in regional metallogeny. Therefore, investigating the origin and crystallization conditions of the host dacitic magma is crucial for understanding magma evolution and ore-forming processes in the Bafq district. In this study, whole-rock geochemistry together with zircon morphology and internal textures are used to evaluate the magma source, tectonic setting, and magmatic evolution. Because zircon preserves geochemical and crystallization features under different geological conditions, it is widely applied in petrogenetic studies.Regional GeologyThe Koushk Zn–Pb deposit is situated within the upper part of the Lower Cambrian volcano‑sedimentary sequences, in the central part of the Zarigan–Chahmir Basin (Figure 2). Two major stratigraphic sequences have been recognized in the area (Figure 3): (1) a mineralized sequence comprising the upper interval of the Lower Cambrian volcano‑sedimentary sequences at the base, and (2) an overlying volcano‑sedimentary sequence that includes Lower Paleozoic shales, argillaceous limestone, dolomitic units which host Fe-mineralization, as well as the rhyolitic and tuffaceous rocks (Gibbs, 1976). Rhyolitic and dacitic domes are present in the southeastern part of the deposit, adjacent to the mineralized sequence, as well as to the north and northwest of the deposit.Materials and MethodsIn this study, 65 samples were collected from the dacitic units hosting the Koushk Zn–Pb deposit. Petrographic and mineralogical investigations were carried out on 47 thin sections using an optical microscope at Shahid Beheshti University, Iran. To evaluate whole‑rock geochemistry, 27 samples of the rhyolites and rhyodacites hosting the Koushk Zn–Pb deposit were analyzed by XRF using a Philips PW 2404 instrument at Tarbiat Modares University, and a separate suite of 9 samples was processed for trace elements by ICP‑MS using a Perkin Elmer NexION 300 instrument at Zarazma Company Laboratory. Zircons were separated using a Wilfley shaking table, a Frantz magnetic separator, and heavy liquids, followed by handpicking under a binocular microscope at the Geological Survey of Iran. Zircon grains selected for CL and BSE‑SEM were mounted in epoxy resin and polished to expose their internal structures. CL images were obtained using a JEOL JXA 8900RL electron microprobe, and BSE‑SEM images were acquired using a Hitachi S3400N scanning electron microscope at Nagoya University, Japan, and Aria Electron Optics Co., Ltd.DiscussionExamination of the external and internal morphology of zircon can aid in identifying the origin of magmatic rocks, the degree of aluminum and alkali saturation (Pupin, 1980), and the temperature of the melt (Pupin and Turco, 1972). Temperature and Zr saturation are the main factors governing the relative growth of different prismatic zircon morphologies. Zircons crystallizing from alkali, water-poor, and tholeiitic melts fall within the (101) and (100) fields; those derived from peraluminous melts plot within the (101) field; and in the presence of high-water content in the melt, they occur within the (101) and (110) domains. Based on the above considerations, the examination of zircon crystals associated with the Koushk dacites indicates that they predominantly display prismatic faces (110) and (110) >> (100), along with pyramidal faces (101) and (211) >> (101). The development of prismatic forms (110) and (100) reflects a high-temperature crystallization index, whereas the dominance of the (101) pyramids suggests a high alkalinity index an interpretation that is further supported by the geochemical characteristics of the samples. Moreover, the morphological analysis reveals that some zircon crystals exhibit noticeable variations in their length-to-width ratios, indicating differences in growth dynamics during crystallization. This may be attributed to crystallization rate (Bussy and Cadoppi, 1996) or the possible presence of two zircon generations in these samples. However, based on the detrital zircon dating from the Koushk area, (Mahmoudi, 2022; Vickers-Rich et al., 2017), the presence of a single zircon generation in these samples is confirmed. Therefore, crystallization rate is likely the main factor responsible for the increased length-to-width ratio observed in these zircons.ConclusionThese crystals predominantly fall within the P2, P5, S5, and S25 fields, with fewer crystals plotting in the AB5, D, L5, P3, P4, R3, S10 and S20 domains. The minimum zircon crystallization temperatures in the studied dacites, based on zircon morphology and the temperature (I.T) and alkalinity (I.A) indices, are 740°C and 706.6°C, respectively. The temperature of the rhyolitic melt, based on zircon saturation thermometry, ranges from 703.49 to 830.74 °C (Watson and Harrison, 1983) and from 702.94 to 877.49 °C (Boehnke et al., 2013). Whole‑rock geochemical data yield a temperature range of 700 to 780 °C.The data show that rhyolitic magma was supersaturated with respect to Zr from the earliest stages of crystallization making zircon one of the first minerals to form-a temperature interval of 700 to 780 °C is inferred for zircon crystallization in the rhyolitic magma. The presence of zoning within zircon crystals likely reflects a decrease in HREE and an enrichment in LREE, U, Th, and Y in these zones. The presence of narrow and closely spaced zoning in both elongated needle‑like zircons and shorter crystals indicates that the magma remained supersaturated with respect to zircon from the earliest to the latest stages of crystallization. Internal structures of some zircon crystals reveal rounded cores with zoning patterns distinct from their rims, suggesting that these cores acted as non‑reactive mineral relics during partial melting. The zircons within the dacites also exhibit evidence of partial resorption, implying episodic intervals of zircon undersaturation in the melt. Structural and compositional characteristics, crystal growth conditions, zircon age and provenance and metamictization processes, can all contribute to reduced lattice order and, consequently, diminished or absent cathodoluminescence (CL) in zircon crystals. Based on geochemical studies, these rocks originate from crust‑derived melts, and their magmas correspond to A‑type granites, specifically the A2 subtype within the calc‑alkaline series. According to tectonic discrimination diagrams, the dacites are derived from volcanic arc granites.AcknowledgementsThe authors appreciate Shahid Beheshti University Research Council that supported this work.

Introduction Ophiolitic complexes—fragments of oceanic lithosphere tectonically emplaced onto continental margins—serve as crucial archives for reconstructing the formation and evolution of ancient ocean basins. The Sabzevar ophiolite in northeastern Iran represents one of the most significant remnants of Mesozoic Neotethyan oceanic lithosphere and provides a key window into the tectonic development of the northern Neotethys branch. Previous studies have assigned this ophiolite to diverse tectonic settings, including mid‑ocean ridge, supra‑subduction zone, and back‑arc environments (Khalatbari Jafari et al., 2013a, b; Rezaei et al., 2018; Jafari and Ghasemi, 2023). Nevertheless, the co‑occurrence of contrasting magmatic signatures within its volcanic sequences points to a polyphase magmatic history in a complex geodynamic framework (Omrani et al., 2018; Moghadam et al., 2025). This study investigates the pillow lavas and sheeted dikes exposed in the Sultanabad area, in the eastern sector of the Sabzevar ophiolite. Its primary aims are to characterize the geochemistry, constrain the crystallization ages of the volcanic units via zircon U–Pb geochronology, and assess their tectonomagmatic significance for the evolution of the Sabzevar oceanic basin. Geological Setting The Sabzevar ophiolite, situated in northeastern Iran, constitutes an integral component of the tectonic structure of the Central Iranian microcontinent (Alavi, 1994). It is widely interpreted as a relict of the northern Neotethyan oceanic realm, which formed within the Central Iranian terrane between Central Iran and the Alborz belt during the Mesozoic (Agard et al., 2005). The ophiolitic succession comprises ultramafic mantle rocks, layered ultramafic–mafic cumulates, sheeted dike complexes, pillow basalts, and pelagic sedimentary cover (e.g., Shojaat et al., 2003; Khalatbari Jafari et al., 2013a, b; Moghadam et al., 2025). The Sultanabad area hosts well‑preserved volcanic units, dominated by pillow basalts intercalated with sheeted dikes and minor massive lava flows. These rocks represent the uppermost levels of the oceanic crust. Field relations indicate that the pillow lavas erupted in a submarine setting and were subsequently affected by tectonic deformation during the Neotethyan closure and obduction of the ophiolitic complex onto the continental margin. Materials and Methods Representative samples of pillow basalts and sheeted dikes were collected from the Sultanabad area. Petrographic examination was performed using optical microscopy to characterize mineral assemblages and textural features. Whole‑rock major and trace element concentrations were determined via X‑ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP‑MS). Zircon grains were extracted from selected samples and subjected to U–Pb isotopic dating and trace element analysis using laser ablation‑inductively coupled plasma mass spectrometry (LA‑ICP‑MS). The geochemical data served to classify magma types, constrain magma sources, and discern tectonic affinities. Zircon trace element compositions were additionally examined to offer complementary constraints on magmatic processes and crystallization conditions. Results Petrographic observations reveal that the studied volcanic rocks consist predominantly of plagioclase, clinopyroxene, and secondary alteration minerals. The pillow lavas typically exhibit porphyritic to intersertal textures, whereas the sheeted dikes show fine‑grained to subophitic textures. Whole‑rock geochemical data indicate that the studied samples fall into three main magmatic series: alkaline, calc‑alkaline, and tholeiitic varieties. The alkaline basalts are enriched in incompatible elements and display pronounced LREE enrichment relative to HREE. Their trace element patterns are akin to those of ocean island basalts (OIB). The tholeiitic basalts and sheeted dikes exhibit relatively flat REE patterns and are marked by negative Nb and Ta anomalies, characteristic of magmas generated in supra‑subduction zone settings. Calc‑alkaline basalts show intermediate geochemical signatures between these two groups. Zircon U–Pb geochronology reveals that magmatic activity in the study area took place during the Cretaceous, yielding ages between ~113 and 90 Ma. The alkaline basalts record the oldest ages (~112–110 Ma), while the tholeiitic and calc‑alkaline rocks give slightly younger but overlapping ages of ~113–91 Ma. Trace element compositions of zircon grains show HREE enrichment and LREE depletion, consistent with a magmatic origin. Variations in elemental ratios such as Th/U and Eu/Eu* point to differences in magma composition and crystallization conditions across the studied rock types. Discussion The geochemical signatures of the studied rocks point to the involvement of multiple magma sources in generating the Sultanabad volcanic sequence. The alkaline basalts most likely originated from low‑degree partial melting of a garnet‑bearing enriched mantle source, consistent with an intraplate or seamount‑related affinity. By contrast, the tholeiitic basalts and sheeted dikes appear to have been derived from higher‑degree partial melting of a depleted mantle source metasomatized by slab‑derived fluids. The calc‑alkaline basalts exhibit geochemical features characteristic of subduction‑related magmatism and probably represent melts generated in a mantle wedge modified by slab‑derived fluids. The co‑occurrence of alkaline and supra‑subduction zone magmas within the same volcanic sequence implies that the Sabzevar oceanic basin underwent a complex tectonomagmatic history, encompassing both intraplate and subduction‑related processes. The zircon U–Pb ages obtained in this study show that magmatic activity persisted over a protracted interval during the Middle to Late Cretaceous. This prolonged magmatism likely reflects the progressive evolution of a supra‑subduction zone system linked to the initiation and advancement of subduction within the northern Neotethys. Conclusions Combined whole‑rock geochemistry and zircon U–Pb geochronology provide new constraints on the petrogenesis and tectonic evolution of the volcanic units in the eastern Sabzevar ophiolite. The investigated rocks fall into alkaline, calc‑alkaline, and tholeiitic suites, reflecting the contribution of multiple mantle sources and magmatic pathways. Zircon U–Pb dating restricts magmatism to ca. 113–90 Ma, i.e., the Middle–Late Cretaceous. Geochemical fingerprints suggest that the tholeiitic basalts and sheeted dikes formed in a supra‑subduction zone setting, whereas the alkaline basalts represent within‑plate‑related magmatism subsequently incorporated into the ophiolitic succession. Collectively, the results favor a model whereby the Sabzevar ophiolite developed within a complex supra‑subduction zone system during the evolution and final closure of the northern Neotethys Ocean.

IntroductionUrumieh–Dokhtar Magmatic Arc (UDMA) as a part of Zagros orogeny is the most important Cenozoic magmatic belt in Iran (Alavi, 1994; Babazadeh et al., 2024). Lithostratigraphic and age dating evidence indicates that magmatic activity in this belt initiated during Late Cretaceous-Paleocene and continued to Pliocene-Quaternary, with the peak of the magmatism in the Middle-Late Eocene. This was followed by extensive Oligocene-Miocene intrusive magmatism and subsequently renewed during Pliocene–Quaternary by scattered volcanism (Moghadam et al., 2022a, b; Babazadeh et al., 2024). In the southeastern segment of the UDMA, particularly along the Jebal-e-Barez mountains, regional geology and zircon U–Pb geochronology record multiphase, extensive arc related magmaism from the Eocene to the Oligocene-Miocene, locally extending to the Pliocene–Quaternary (Nazarinia et al., 2020; Atapour and Aftabi, 2021; Moghadam et al., 2022a, b; Babazadeh et al., 2024). Peak of the magma emplacement occurred during the Oligocene–Miocene, characterized by intermediate to felsic plutons of the Jebal-e-Barez mountains (Chiu et al., 2013; Babazadeh et al., 2024). Biotite, a major Fe–Mg-bearing constituent of the Jebal-e-Barez intrusive complex, has a substantial capacity for incorporating Ti and Al, making it an effective monitor of crystallization conditions (temperature, pressure, oxygen fugacity), as well as for classification and discrimination of granite tectonic settings and their mineralization potential (Wones and Eugster, 1965; Wones, 1989; Abdel-Rahman, 1994; Henry et al., 2005; Nachit et al., 2005; Jiang et al., 2002; Uchida et al., 2007; Anderson et al., 2008; Villaseca et al., 2017). Most previous studies on the Jebal-e-Barez intrusive complex have relied on whole-rock geochemistry for petrological purposes and economic fertility assessments, whereas mineral chemistry approaches such as biotite chemistry remain sparse.GeologyThe Sarbijan–Dalfard district, located northwest of Jiroft within the Jebal‑e‑Barez mountain range, represents the southern part of the UDMA. This major volcano‑plutonic complex developed in response to prolonged subduction of the Neotethys oceanic lithosphere beneath the Central Iran block, with magmatic activity persisting from the Late Cretaceous to the Neogene. In the southeastern segment of the UDMA, a compositionally diverse suite of intermediate‑felsic plutonic rocks—including diorite, monzodiorite, quartz diorite, granodiorite, and granite—intrudes the Eocene volcanic and volcano‑sedimentary rocks (Moghadam et al., 2022a, b; Babazadeh et al., 2024). The Jebal‑e‑Barez granitoids exhibit calc‑alkaline to high‑K calc‑alkaline affinities, consistent with an active continental arc setting. Moreover, the Oligocene–Miocene magmatism has been attributed to incipient collisional processes, crustal thickening, and partial melting of the oceanic slab and metasomatized mantle wedge, with variable crustal contamination (Moghadam et al., 2022a, b; Babazadeh et al., 2024).Research MethodsRepresentative specimens from the main lithological units (monzodiorites and granodiorites) were selected for mineral chemical analyses using a JEOL 8200 electron microprobe at the Microprobe Laboratory, University of Milan, Italy. Analyses were conducted at an accelerating voltage of 30 kV, beam currents ranging from 10⁻¹² to 10⁻⁵ A, and a counting time of 80 seconds. Biotite composition was normalized to 22 oxygens, and the Fe³⁺ content was calculated following Droop (1987) assuming charge balance within the biotite structure.PetrographyThe granitoid bodies of the Sarbijan–Dalfard district show a progressive fractionated series from diorite to granite. The diorites and monzodiorites exhibit coarse‑ to medium‑grained hypidiomorphic textures, characterized by plagioclase as the dominant mineral, alongside biotite and amphibole as the primary mafic phases. Granodiorites predominantly display anhedral granular textures, where plagioclase often shows polysynthetic twinning and evidence of secondary alteration. Granites are typically coarse‑grained and anhedral granular, and show granophyric and myrmekitic textures in alkali‑feldspar‑rich varieties, representing the late‑stage simultaneous crystallization of quartz and feldspar.DiscussionBiotite geochemistry in the Sarbijan–Dalfard granitoids provides key constraints on the physicochemical conditions (P, T, fO₂) of magma generation, crystallization, and emplacement, as well as classification (I, S, A), tectonic setting , and mineralization potential. Microprobe analyses of biotites in the Sarbijan–Dalfard granitoids indicate their Mg‑rich magmatic nature, crystallized under relatively high H₂O pressure and oxidizing conditions, reflecting a calc‑alkaline (I‑type) orogenic magma within a subduction‑related continental margin environment. Fe/(Fe+Mg) ratios and Al content indicate limited crustal contribution, while Ti concentrations suggest closure temperatures of 638 to 724°C, close to the crystallization conditions of granodiorite‑granite suites (Luhr et al., 1984; Henry et al., 2005). Total Al content in biotite implies emplacement pressures of 0.98–2.56 kbar, corresponding to depths of 3‑7 km in the upper crust (Uchida et al., 2007). High Mg# contents of biotites and their coexistence with Fe‑Ti oxides further support high fO₂ conditions, consistent with subduction‑related arc magmatism and minimal post‑emplacement re‑equilibration.ConclusionBiotites of the Sarbijan–Dalfard granitoids are Mg‑rich, magmatic, and largely unaltered, recording relatively oxidizing conditions during crystallization, consistent with Fe‑Ti oxide‑bearing calc‑alkaline I‑type magmas of a subduction‑related arc setting. Thermo‑barometry estimates based on Ti and Al‑in‑biotite suggest closure temperature ranges of 630‑725 °C and pressure ranges of 1‑2.5 kbar, indicating emplacement at shallow upper crustal depths. Integration of petrography, biotite chemistry, and thermo‑barometry calculations confirms that these granitoids were generated in an oxidizing, subduction‑related environment, with significant potential for Cu mineralization.AcknowledgmentsThis study forms part of the first author’s PhD dissertation, which was financially supported by the Research Vice‑Presidency of Shahrood University of Technology (SUT). The authors gratefully acknowledge SUT, the staff of the Microprobe Laboratories at the University of Milan, and the esteemed reviewers of the Petrological Journal for their valuable guidance and constructive comments.

IntroductionFormation and evolution of the continental crust is one of the fundamental subjects in Earth sciences studies, as these processes usually occurred during the Archean and Proterozoic (e.g., Condie, 1980; Taylor and McLennan, 1981). Regions with high-grade metamorphic rocks such as granulites are considered key parts of the lower continental crust (e.g., Smithson and Brown, 1977; Harley, 1989; Bohlen, 1991).Precambrian-Cambrian basement sequences in Iran are exposed in some structural zones such as Central Iran and the Sanandaj-Sirjan zone (e.g., Nadimi, 2007; Hosseini et al., 2015). In these zones, the Chapedony complex is considered the oldest basement complex in Iran, exposed between two major faults: the Chapedony Fault to the west and the Chatak-Neybaz Fault to the east.The Neybaz Crystalline Core, situated in the West Central Iranian Microcontinent, is a high-grade metamorphic zone composed of diverse lithologies ranging from Precambrian to Cenozoic in age. It has undergone multiple intense deformation phases (Valiei et al., 2025).The main goal of this research is to describe the petrography, geochemistry, and metamorphic conditions of the Neybaz Granulite Complex. Based on new data and comparison with other published models, we tried to determine the metamorphic history, tectonic settings, and origin of the old basement protoliths. These findings will help us understand the geodynamic evolution of the Precambrian basement of Central Iran.Analytical MethodsTen samples were analyzed for geochemical composition at the Zarazma Minerals Research Company laboratory (Tehran, Iran) using XRF and ICP-MS.Major oxide contents were determined by the alkaline fusion method (lithium borate fusion). In this method, samples were melted with lithium metaborate, and the resulting product was dissolved in dilute nitric acid. The final solution was then analyzed using an ICP-OES instrument to measure major oxide concentrations.FeO content was determined by the wet chemical method, and loss on ignition (LOI) was measured using the conventional gravimetric method. For trace and minor elements, samples were digested using a multi-acid digestion method with a microwave digestion system, and the resulting solutions were analyzed by ICP-MS.Results and DiscussionPetrographyThe occurrence of granulites in the high-grade crystalline core of the Neybaz area was first reported by Valiei et al. (2025). The studied granulites are dark gray to grayish-black in color. They are in contact with the amphibolite unit and, to a lesser extent, with migmatite gneisses. These granulites are exposed as irregular patches and have medium to coarse grain sizes.Macroscopic studiesThe high-grade crystalline core of the Neybaz area comprises several rock units, including metacarbonate, calc-silicate, garnet/cordierite schist, amphibole schist, migmatite, mylonitic gneiss, amphibolite, granulite, and anatectic granite.Microscopic studiesMicroscopic investigations reveal that the main minerals in the Neybaz granulites include orthopyroxene, clinopyroxene, plagioclase, amphibole, garnet, biotite, apatite, and opaque minerals. Gneissic fabrics are widespread at the microscopic scale, characterized by ferromagnesian minerals (pyroxene and amphibole) and stretched plagioclase.GeochemistryThe studied rock units exhibit a compositional range, with SiO₂ contents varying between 48.08 and 56.18 wt%, and TiO₂ contents between 0.21 and 1.05 wt%. Al₂O₃ contents show a wide range (14.81–24.35 wt%; mean: 17.60 wt%). The samples are enriched in CaO (9.10–13.97 wt%) and show variations in MgO and FeOT contents (MgO: 0.54–10.42 wt%; FeOT: 1.90–10.18 wt%). The contents of K₂O, Na₂O, and P₂O₅ range from 0.15 to 0.83, 1.71 to 5.66, and 0.06 to 0.29 wt%, respectively. Loss on ignition (LOI) in the studied granulites ranges from 0.63 to 1.76 wt%. The Mg number in these rocks ranges from 33.70 to 73.61. Trace element concentrations also show wide variations, including Rb (14–35 ppm), Ba (70–162 ppm), Sr (166.8–1064.6 ppm), Zr (9–36 ppm), V (6–227 ppm), Nb (<1–47.4 ppm), and Y (15.7–89 ppm).Conclusion The Neybaz high-grade metamorphic complex is located in the western domain of the Central Iranian microcontinent, situated between the Chatak-Neybaz and Chapedony basement faults. Within this complex, metamorphosed mafic rocks occur as small masses in contact with, and within, gneisses that exhibit granulite facies metamorphic grade. The high-grade metamorphism in these rocks led to the development of a mineral paragenesis primarily composed of clinopyroxene, orthopyroxene, euhedral garnets, amphibole, and plagioclase. Field, petrological, and geochemical studies on the metamorphic mafic rocks in the Neybaz crystalline core indicate that the garnet/pyroxene granulite has a basaltic to andesitic protolith and is metaluminous in composition.Geochemical investigations of these granulites indicate that their protoliths range from basalt to andesite and basaltic andesite, showing calc-alkaline and tholeiitic affinities. Lithogeochemical variation diagrams suggest that these rocks formed in a plate margin setting. Furthermore, the close association of the mafic granulites with gneisses—some of which have a metagraywacke protolith—points to their origin from an active plate margin.Primitive mantle- and chondrite-normalized spidergrams show enrichment in light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), along with enrichment of LILEs and depletion of HFSEs, confirming the involvement of both mantle and crustal sources in the formation of the protoliths.Based on the geochemical data and structural evidence, this study suggests that the formation of the mafic melts in the Neybaz complex was related to cratonization processes in an active margin environment during the Paleo- to Neoproterozoic era. The geochemical characteristics of these granulites, including negative Nb and Ti anomalies in the spidergrams, link their origin to arc magmatism (e.g., island arc tholeiites or calc-alkaline basalts).

IntroductionListvenite is a metasomatic rock mainly composed of Mg-rich carbonates and quartz, formed by the interaction of CO₂-rich fluids with ultramafic rocks. Its main carbonate phase is typically magnesite, with variable iron content, and locally dolomite or calcite. Potassium-bearing fluids can alter chromian spinel to Cr-bearing muscovite (e.g., fuchsite). Listvenite represents a fully carbonated ultramafic rock, where divalent cations are hosted in carbonates, silica occurs as quartz/chalcedony/opal, and remnants of the protolith, such as chromian spinel, are preserved. It forms progressive alteration sequences from carbonated serpentinite to talc–carbonate rocks and finally to carbonate–quartz rocks—under high CO₂ activity and sustained fluid flux. Listvenites are relatively rare, occurring as lens-shaped or vein-like bodies within ophiolitic complexes and altered ultramafic rocks. They develop along tectonic contacts and plate-boundary faults with high CO₂ flux and have formed throughout Earth’s history from the Archean to the presentRegional GeologyListvenites in the Babalou region occur as vein-like and lens-shaped bodies within the Khoy–Mako ophiolitic mélange, mainly along shear zones and faults, with mineralization trending parallel to the N50W orientation of the ophiolites. The mélange consists of Upper Cretaceous mafic and ultramafic fragments associated with pelagic limestones, and the listvenites are morphologically prominent due to their greater resistance to weathering and hard outcrops. In addition, metamorphosed intermediate to mafic rocks with dark grey to green colors are exposed within the colored mélange complexes of the area..Analytical methodsDuring fieldwork, samples were collected from metamorphic rocks, metamorphosed mafic–intermediate rocks of the ophiolite–mélange, listvenite alteration zones, and some sedimentary units, and the general geology of the area was investigated. A total of 30 thin sections and 10 polished sections were prepared for petrographic and mineragraphic studies. Based on these results, 10 listvenite samples and 6 metamorphosed mafic–intermediate samples were selected and analyzed by ICP–MS at Actlabs, Canada.Petrography, Mineralogy and Whole Rock Chemistry Metamonzodiorite–meta-Gabbro to Metadiorite– meta-Gabbro (DG)The rocks display a granoblastic texture and are dominated by plagioclase, K-feldspar, amphibole, clinopyroxene, and epidote, with sphene as the main accessory. Plagioclase commonly shows deformation (bending/kinking), while clinozoisite occurs as an alteration product of amphibole and plagioclase.Meta Quartz Monzodiorite (QD)The rocks are composed of plagioclase, K-feldspar, quartz, muscovite, and epidote (allanite/pistacite), with minor biotite and rutile. They have undergone significant silicic–carbonate alteration, resulting in secondary chlorite, epidote, muscovite, and malachite. Notably, amorphous brown allanite is observed partially altering to pistacite.Silicic–Carbonate ListveniteThese rocks are primarily composed of quartz and carbonate. Quartz shows deformation and some recrystallization, while carbonate occurs in the matrix, crystals, and veins. Two generations of muscovite are present, and fuchsite likely formed during the late stage of listvenitization.Silicic ListveniteThese rocks consist mainly of quartz and calcite, with minor muscovite and opaque minerals. Quartz occurs as crystalline quartz and chalcedony, commonly showing fracturing, brecciation, and cavity filling. Siliceous veins display radial to feather-like textures and may form geode-like structures. Carbonates are mostly calcite, with minor dolomite, occurring in grains, veins, and fractures.DiscussionListvenite formation in the Babalu region resulted from CO₂-rich, K-bearing hydrothermal fluids moving through faults and shear zones after ophiolite emplacement and tectonic activity. The alteration was controlled by temperature, pH, oxygen fugacity, and sulfur fugacity. This process occurred in three main stages: carbonatization, with formation of calcite, dolomite, chlorite, epidote, and tremolite; silicification, with addition of silica and formation of quartz; and mica formation in the late stage. Repeated veining shows multiple pulses of alteration, and pyrite and chalcopyrite formed during cooler or chemically favorable fluid conditions.The SiO₂–LOI and SiO₂–(CaO+MgO)–Fe₂O₃ ternary diagrams both classify the studied rocks as siliceous listvenites. In SiO₂–LOI space, they plot in the high silica, low LOI field. In the SiO₂–Fe₂O₃–(CaO+MgO) diagram, they lie near the SiO₂ apex along the (CaO+MgO)–SiO₂ edge, reflecting low Fe content and the scarcity of Fe-rich carbonates such as ankerite and siderite.Chondrite-normalized REE patterns distinguish the two listvenite types. Siliceous listvenites are very REE-poor, nearly flat, and show a strong positive Eu anomaly, likely from calcic plagioclase alteration. Siliceous–carbonate listvenites have slightly higher REE contents but no Eu anomaly, probably due to calcite. Their (La/Yb)n ratios indicate gentle to moderate fractionation. Tectonic data place the meta quartz monzodiorite in the VAG field and the meta monzodiorite–meta diorite–meta gabbro in the continental arc field, so neither is a likely ophiolitic source for the listvenites. The most probable source is another, unidentified ophiolitic rock in the area.AcknowledgementsThe authors sincerely thank all individuals who contributed in any way to this research and the preparation of this article, especially colleagues and reviewers whose constructive comments and suggestions helped improve the quality of the manuscript.

IntroductionThe Zagros orogeny occurred through four main geodynamic events of the Wilson cycle, leading to the formation of the Neotethys oceanic basin: (i) intracontinental rifting in the Carboniferous, (ii) oceanic basin development in the Permian–Triassic, (iii) subduction of oceanic lithosphere beneath the Central Iranian microcontinent from the Late Triassic to the Late Cretaceous, and (iv) collision of the Afro-Arabian plate with the Iranian (Eurasian) plate in the Oligocene–Miocene (Jafari et al., 2023). This orogeny formed three parallel structural zones from southwest to northeast: (1) the Zagros fold–thrust zone, (2) the Mesozoic Sanandaj–Sirjan metamorphic–magmatic zone, and (3) the Cenozoic Urumieh–Dokhtar magmatic belt (UDMB). The UDMB is a large linear subduction-related magmatic arc, approximately 2000 km long and 50–100 km wide, composed of tholeiitic, calc-alkaline, and high-K alkaline igneous rocks along the active margin of the Central Iranian plate (Jafari et al., 2023; Babazadeh et al., 2023).The southeastern UDMB, known as the Kerman Copper Belt or Dehaj-Sarduiyeh belt, contains Eocene–Oligocene to Miocene calc-alkaline rocks formed by northeastward subduction of the Neotethys beneath Central Iran (Shafiei et al., 2009; Chiu et al., 2013; Babazadeh et al., 2023). The Jebal-e-Barez granitoid complex is the latest major Oligocene–Miocene intrusive event of the UDMB. Studies indicate that these rocks have calc-alkaline, metaluminous, I-type characteristics, typical of a subduction zone setting (Shafiei et al., 2009; Rasouli et al., 2016; Hosseini et al., 2017; Behpour et al., 2019; Moghadam et al., 2022; Babazadeh et al., 2023). Here, the Mardehak granitoids in the southeastern Jebal-e-Barez complex are investigated for the first time using field, petrographic, geochemical, and U-Pb dating methods.GeologyThe Mardehak intrusive bodies, part of the Jebal-e-Barez complex, include diorite, quartz diorite, monzonite, quartz monzonite, granodiorite, granite, and alkali granite, and they intrude Eocene volcanic and volcaniclastic-sedimentary rocks (Shafiei et al., 2009; Rasouli et al., 2016). Field evidence shows three main emplacement phases: (i) dioritic/quartz dioritic bodies emplaced into Eocene volcanic and pyroclastic-sedimentary rocks, (ii) quartz monzonitic and granodioritic bodies intruding the previous phase and host rocks, and (iii) granitic/alkali granitic bodies emplaced into the previous phases, indicating normal compositional zoning. Mafic microgranular enclaves (MMEs), characteristic of subduction-related calc-alkaline I-type granitoids (Didier and Barbarin, 1991), are common. These centimeter- to decimeter-scale enclaves have dioritic composition and rounded to angular shapes, with sharp contacts with the host rocks.Research MethodsApproximately 100 hand specimens were collected from the study area. From these, thin sections, polished sections, and polished thin sections were prepared for petrographic and geochemical studies. Petrographic observations as well as major and trace element geochemistry (using XRF and ICP-MS) were carried out on 16 samples at the Zarazma Geochemistry Laboratory in Kerman, Iran. U-Pb geochronology was performed on six representative samples, including two quartz diorites, two granodiorites, one granite, and one alkali granite. Crushing, washing, and mineral separation were conducted at Shahrood University of Technology. Final zircon separation was carried out manually, and the separated zircons were mounted at the University of Pisa, Italy. Zircon U-Pb analysis was performed using a PerkinElmer NexION 2000 ICP-MS coupled with an ESI NWR-193 excimer laser at the University of Pisa.PetrographyThe studied samples include diorite, quartz diorite, quartz monzonite, granodiorite, granite, and alkali granite. The diorites exhibit granular, anhedral to subhedral, fine- to medium-grained textures, and occasionally show porphyritic, intergranular, granophyric, and trachytic textures. Plagioclase, hornblende, biotite, and clinopyroxene are the main constituent minerals in the diorites. The more differentiated parts (quartz diorite, monzodiorite, and quartz monzonite) contain higher amounts of quartz and orthoclase.The granodiorites display granular, anhedral to subhedral, medium- to coarse-grained, poikilitic, and sometimes granophyric textures. Their mineralogy consists of quartz, plagioclase, and alkali feldspar. The granites and alkali granites represent the late-stage felsic phase and are composed of quartz, plagioclase, orthoclase, and biotite. They exhibit anhedral granular, graphic, granophyric, aplitic, perthitic, antiperthitic, and poikilitic textures.DiscussionThe Mardehak granitoids range from intermediate to acidic (diorite to alkali granite) and are metaluminous to subalkaline. Harker diagrams show negative trends for FeO, MgO, CaO, MnO, TiO₂, Al₂O₃, Cr, Ni, V, Sr, Y, and Yb, and positive trends for Na₂O, K₂O, La, Ce, Rb, and Ba, suggesting fractional crystallization. REE patterns show LREE enrichment relative to MREE and HREE, with a weak negative Eu anomaly, steep LREE and flat MREE-HREE segments. The rocks display high LILE enrichment (Sr, K, Rb, Ba) and HFSE depletion (Ta, Nb, Ti, Zr, Hf, Y).Discrimination diagrams indicate I-type granites (CI group) formed by partial melting of the subducted Neotethys slab in the amphibolite facies. These rocks lack adakitic features and are normal arc granites. Fluids from slab dehydration metasomatized the mantle wedge, the source for these granitoids. Abundant MMEs, large plagioclase with resorption rims, and inherited Late Eocene–Early Oligocene zircons within the Late Oligocene phase provide evidence of magma mixing. Tectonic discrimination diagrams indicate syn- to post-collisional granites emplaced in an active continental margin.Similar to other UDMB parts, these granitoids exemplify I-type magma genesis in an active continental margin, reflecting a transition from subduction to syn- to post-collisional regimes. U-Pb zircon geochronology reveals two phases. The first phase (Late Eocene–Early Oligocene, 35–29 Ma) is pre- to syn-collisional and reflects continued magmatic flare-up from partial melting of the subducting oceanic slab (amphibolitic source) and metasomatized mantle wedge. The second phase (Late Oligocene, 25–24 Ma) is post-collisional and accompanied crustal thickening. Both phases produced intermediate to felsic rocks with normal zoning, consistent with previous reports. According to Babazadeh et al. (2023) and Moghadam et al. (2022), magmatic activity in the southeastern UDMB results from a flare-up caused by slab retreat or break-off, asthenospheric upwelling, and decompression melting.ConclusionThe geochemical characteristics of the Mardehak granitoids (calc-alkaline, metaluminous, LILE enrichment, and HFSE depletion) indicate that they are I-type (CI) granitoids formed within an active continental margin subduction zone under a syn- to post-collisional tectonic regime. Their parental magma originated from partial melting of an amphibolitic source and the overlying metasomatized mantle wedge. This melting was triggered by metamorphism and dehydration of the subducting oceanic slab during the Eocene–Oligocene subduction of the Neotethys beneath the Central Iranian microcontinent.AcknowledgementsThis research is part of the first author's PhD dissertation entitled "Petrogenesis and Mineralization Potential of the Granitoid Bodies of the Mardehak Area, East Jiroft, Kerman," carried out with the support of the Office of the Vice-Chancellor for Research of Shahrood University of Technology and in collaboration with Kavak Aray Novin Madan Company, Kerman. The authors are grateful for this support.

IntroductionTourmaline exhibits a broad range of chemical variability (Hawthorne and Henry, 1999). This diverse and complex chemistry reflects a clear genetic link between tourmaline and the environment from which it crystallized. Such a relationship provides a reliable and robust indicator for determining the origin and evolution of hydrothermal systems responsible for ore formation, and serves as an effective guide in exploration for ore deposits (Jiang et al., 1995). The Astaneh and Aligudarz granitoid plutons are situated within the Sanandaj–Sirjan zone. A brief overview of relevant studies carried out around the investigated areas is provided below: Tahmasebi et al. (2009) investigated tourmalinization within the Astaneh granitoid pluton. The relatively flat REE patterns observed in tourmaline nodules reflect mobilization of light rare earth elements due to alteration processes. Esna-Ashari et al. (2012) conducted geochemical and geochronological studies on the Aligudarz granitoid complex. They suggest that these granitoids are analogous to I-type, crust-derived granitoids formed in continental arc settings. U–Pb zircon isotopic data yield a crystallization age of 165 Ma (Jurassic) for the granites. Given the geological significance of this mineral, the objective of the present study is to investigate the petrography and mineralogy of tourmaline, to evaluate its paragenetic relationships, to characterize the geochemical features of the tourmalines, to determine their structural formulas, and to reconstruct the conditions of formation in Aligudarz and Astaneh regions.Regional GeologyThe Astaneh granitoid pluton, in the Markazi Province, intruded the Jurassic shales and sandstones, which gave rise to contact metamorphism. Biotite granites represent another lithological unit in the region which exhibit minimal alteration and appears to be younger than the surrounding rock units. Geological features of this pluton include quartz–sulfide and quartz–tourmaline veins. Circulating meteoric and magmatic fluids have induced hydrothermal alteration within the intrusive body and resulted in the development of various alteration zones, including phyllic, propylitic, intermediate argillic, and silicic alteration. The Aligudarz granitoid complex formed during the Middle Jurassic along an active continental margin (Esna-Ashari et al., 2012). The lithological composition of this complex varies from quartz diorite to granodiorite and granite. Tourmalinization in these outcrops occurs within alteration halos adjacent to intrusive bodies and is directly related to hydrothermal systems generated by the interaction of the intrusion with pelitic host rocks.Materials and MethodsSome standard thin sections were prepared and examined using an OLYMPUS BH2 polarizing microscope. Six tourmaline samples were analyzed using a CAMECA SX-100 electron probe microanalyzer (EPMA) in Iranian Mineral Processing Research Center (Karaj) under operating conditions of 15 kV accelerating voltage and 20 nA beam current. Sixteen analytical spots were measured for each sample, and the results were reported as oxide concentrations of the constituent elements.Petrography Tourmalines in the study area can be categorized into the following types: 1. Nodular tourmalines: This type occurs as discrete nodules developed on the surfaces of granitoid rocks and its formation is attributed to the crystallization of late-stage magmatic fluids filling the fractures of the host rocks (Rozendaal and Bruwer, 1995; Morgan). 2. Layered tourmalines: developed within metamorphosed rocks of the region and are found at the contact zone between the intrusive body and the host rocks. 3. Disseminated tourmalines: appear as fine-grained disseminations within the groundmass of the rocks. Potassic alteration has affected plagioclase crystals, leading to their transformation into tourmaline and orthoclase. The released Na is incorporated into the tourmaline structure, whereas K becomes part of the orthoclase lattice. 4. Pegmatitic Tourmalines: These tourmalines occur within pegmatitic veins located in the contact zone between the intrusive body and the host rocks. 5. And finally patchy (irregular) tourmalines: appear in hand specimens as irregularly shaped grains that vary from coarse- to fine-grained.Chemical CompositionBased on the dominant ions occupying the X site, specifically Na⁺(K), Ca, and the degree of X-site vacancy, the analyzed tourmalines fall into alkali tourmaline group. The concentration of K + Na in the X site is significantly higher than that of Ca, and that the X site in the studied tourmalines is partially vacant. The X-site vacancy in the samples ranges from 0.26 to 0.49. To determine tourmaline type, binary diagrams of Na/(Na + Ca) and Fe/(Fe + Mg) were used (Trumbull and Chaussidon, 1999). In these diagrams, samples from the Astaneh area plot mainly within the schorl field, while those from Aligudarz area fall largely within the dravite field, trending towards schorl.DiscussionBased on the variations of FeO/(FeO+MgO) relative to MgO, all tourmalines from the Astaneh and a portion of Aligudarz samples represents compositions intermediate between magmatic and hydrothermal origins, indicating their formation during the mixing of magmatic and hydrothermal fluids. In contrast, several tourmalines from the northern Aligudarz region, corresponding to tourmalines formed at greater distances from the intrusive body. As the Figure 11 displays, the tourmalines fall within the compositional field of metapsammites coexisting with an Al-saturated phase. This suggests that the fluids responsible for their formation were aluminum-rich, consistent with derivation from Al-enriched hydrothermal solutions.ConclusionThe studied tourmalines occur in several distinct forms, including nodular, layered, disseminated, pegmatitic, and patchy/irregular varieties.The analyzed tourmalines belong to the alkali group, reflecting the dominance of K + Na over Ca in the X site and the presence of a measurable X-site vacancy. The tourmalines under study represent compositions within the schorl–dravite solid-solution series, exhibit chemical zoning, and display Al substitution in the Y site. According to FeO/(FeO+MgO) versus MgO systematics, all samples from the Astaneh region and a portion of those from Aligudarz indicating combined magmatic and hydrothermal influences, with meteoric water involvement during the final stages of formation. Several tourmalines from northern Aligudarz consistent with formation farther from the intrusive body. The primary source of boron is interpreted to be metapelites and metapsammites. Their assimilation into the granitoid magma likely contributed essential components such as B, F, Al, Mg, and Fe, trace amounts of other elements, thereby facilitating tourmaline formation within the investigated regions.

IntroductionDelkan iron mine, geologically, located in the south of Bardeskan city. It is geologically located in the eastern part of the Central East Iran Microcontinent. Regarding structural division, the Delkan iron mine lies in the northeast of the Kashmar-Kerman tectonic zone and on the northeastern ridge of Kuh-e-Sarhangi. Some of the most important iron mines in Iran are located in the Kashmar-Kerman structural zone, for example, the Bafgh iron mines with a total reserve of 5 billion tons (Torabian, 2007).Geology of the AreaThe rock units in the study area are predominantly the metamorphosed units of schist, quartzite, limestone, dolomite, and amphibolite, belonging to Precambrian and the Cambrian units composed of limestone, dolomite, carbonaceous shales, schist, and quartzite. These rock units were subjected to intrusion of a plutonic stock, which gave rise to contact metamorphism halo and iron mineralization during the Silurian.Materials and MethodsFollowing the field investigations, for structural studies, 37 fault planes were structurally sampled, and 284 rock samples were taken from the surface and the archive of drilled cores in the mine for petrology, mineralogy, and mineralization studies. 73 microscopic sections of the samples were studied with an Olympus BX60F5 microscope at the University of Isfahan. Maps of the area were drawn using ArcGIS software. To measure the main oxides, 36 rock samples were taken and after preparation using the peroxide fusion method, were analyzed by the use of the ICP-OES technique. δ18O stable isotope analyses were carried out on 2 magnetite and 2 quartz samples. Also, δ 34 S stable isotope analysis were performed on 2 pyrite samples. All isotope analyses were carried out at the Stable Isotope Research Laboratory of Arak University (SIRL).Mineralization, Alterations, Mineralogy and MineralographyIron mineralization in the Delkan mine is observed in the two forms: 1) Iron oxide apatite with disseminated and veinlet texture within the monzonite intrusive stock, 2) Massive proximal and distal magnetite without apatite.Alterations observed in the Delkan deposit can be divided into prograde skarn, sodic, calcic, phyllic-silicic, and secondary carbonate alteration in order of occurrence. The intensity and spread of Prograde calc-silicate skarn alteration in the area are extremely limited.Pyrite occurs in two forms, pentagonal and anhedral to cubic. Primary quartz is pentagonal and secondary quartz is anhedral. Metamorphic garnets are red, isotropic, and metasomatic garnets are brown to green, and anhedral to euhedral. Albite is often replaced by other minerals and can be seen as pseudomorphs. Acicular actinolite with fibrous textures, and anhedral to subhedral apatite, euhedral to anhedral magnetite with massive, disseminated, and replacement textures are noticeable. In the central parts of the deposit, magnetite mineralizations are present in massive form without apatite, but at the margins of the intrusive stock, disseminated magnetite mineralized with apatite. Hematite is seen with disseminated, replacement, and martitization textures; in some cases, it is replaced by goethite or limonite. Chalcopyrite is observed in an anhedral shape.Galena and sphalerite mineralizations were also observed in shallow quartz veins of Delkan (Shabani et al., 2015).Fault Patterns and Their Relationship with Iron MineralizationTwo main fault distributions are extended in the mining area, including longitudinal faults trending northeast-southwest parallel to the extension of the Kuh-e-Sarhangi and NW-SE trending transverse faults almost perpendicular to the first group. According to studies (Sahandi et al., 2010; Nozaem, 2012), the Kuh-e-Sarhangi and Delkan areas have undergone multiple tectonic regime shifts between transpressional tectonic phases and extensional phases accompanied by volcanism and mineralization. It seems that the Silurian extensional phases in the longitudinal faults of the area under study have played a significant role in creating a suitable space for the intrusion of monzonite stock, which ultimately gave rise to the formation of proximal IOA and massive magnetite mineralization. Transverse faults have also played the role of escape routes for part of the hydrothermal fluid, caused the formation of distal mineralizations.Geochemistry of stable isotopesThe isotopic values of δ18O for magnetite samples in ranges from 8.6 and 10‰. According to several people (Einaudi et al., 1981; Bowman, 1998; Meinert et al., 2005), these values indicate a Juvenile origin for the hydrothermal fluid that caused the mineralization of massive magnetites without apatite.The values of δ18O for quartz samples are between 15.6 and 16.2‰. These values indicate isotopic equilibrium between the hydrothermal fluid and the host rock during the gradual cooling processes of the fluid.The isotopic δ34S values for pyrite samples ranging from 20.1 to 20.6‰. According to (Einaudi et al., 1981; Meinert et al., 2005), we consider the studied sulfur sources in the area of study to be non-magmatic and related to isotopic changes in the hydrothermal fluid in equilibrium with marine sulfates and host rocks as well.Discussion and ConclusionTwo types of iron mineralizations (skarn and kiruna) occurred in the Delkan mine, but most iron reserves in this deposit share similar characteristics to iron skarn deposits. Mineralization in the Delkan iron deposit has been subjected by several factors, of which the most important are the following:A) The tectonic regime shifts between the transtensional and transcompressional regimes, which played a key role in intrusion and trapping of the intrusive stock,B) The direction and patterns of faults have been effective in determining the intrusion paths for both the plutonic stock and the juvenile hydrothermal fluids, mineralization type and locations of mineralizations,C) Differences in Oxidation state between the intrusive stock and the host rocks (especially the black carbonaceous phyllite layers that are highly reduced) plays a key role in the consumption of dissolved oxygen in the juvenile hydrothermal fluid due to intensity of decarbonation reactions between the fluid and these reducing layers, and as a result, the increase in the CO2 fugacity of the fluid, which will decrease the intensity of calc-silicate alterations (prograde skarn) and also a decrease in the amount of iron skarn mineralizations.

IntroductionGeographically, the granitoid intrusion under investigation is located in Ardestan, in the northeastern part of Isfahan Province and to the north of the Nain ophiolitic complex, between longitudes 52°50′ to 53°03′ E and latitudes 33°09′N to 33°13′N. With a general northwest–southeast trend, this body is considered part of the Urumieh–Dokhtar magmatic arc. Previous studies conducted in or around the area include: Akbari (1999) conducted a petrographic and petrological study of the Sohail Pakouh and Golshaknan intrusive bodies and, based on the regional lithology, classified the intrusion as an I-type granite. Yeganehfar (2007) investigated the petrogenesis of the Tertiary rocks south of Ardestan and argued that these volcanic rocks display the characteristics of island-arc magmatism, exhibiting indications of evolution toward an active continental margin setting Rahmani (2018), studied the petrology, geochemistry, and tectonomagmatic setting of the Qah Sareh granitoids located in southeastern Ardestan. Babazadeh (2017), who also worked on the petrogenesis of the Tertiary rocks south of Ardestan. In this study, the similarities in major and trace elements as well as Sr–Nd isotopic characteristics of the plutonic and volcanic rocks of Ardestan indicate derivation from a common magma source. The author proposed a subduction model involving the Neo-Tethyan slab beneath the Central Iran mantle.Tourmaline has proven to be a highly useful mineral for petrological studies (Manning, 1982; London, 1999) due to its ability to crystallize under diverse pressure-temperature regimes and geological environments, and its stability across a wide range of metamorphic conditions and weathering. Given the lack of detailed geochemical investigation on the tourmalines of this area, this study aims to conduct petrographic analysis, determine the chemical composition, and elucidate the origin and formation conditions of the tourmalines present in the regional granitoids.Regional GeologyThe studied intrusive body lies within the western segment of the Central Iranian Zone and the central part of the Urumieh–Dokhtar magmatic arc, trending NW–SE (Fig. 1). Based on geographical distribution, it can be divided into the Sohil Pakouh, Goleshkanan, and Hajiabad subareas. These intrusive bodies, as part of the Urumieh–Dokhtar magmatic belt, have intruded into Eocene volcanic and volcaniclastic rocks in the northwestern part of the Nain ophiolite zone. Their emplacement has been dated to the Oligocene–Miocene (Amidi, 1975). The thermal impact of these intrusions has caused low- to very low-grade contact metamorphism in the host rocks.Analytical MethodsAfter sampling the granitoid rocks, 25 thin sections were prepared for mineralogical and textural analysis using an Olympus BH2 polarizing microscope. Following petrographic investigations, selected tourmaline grains were analyzed by electron microprobe at the University of Oklahoma, USA, to determine their elemental compositionPetrographyThe studied intrusions mainly consist of granodiorite, tonalite, diorite, and monzodiorite, appearing both as veins and dikes, as well as larger plutonic bodies. Dominant minerals include quartz, plagioclase, alkali feldspar, amphibole, biotite, and tourmaline. The average crystal size ranges from 4 to 9 mm. The rocks exhibit a granular texture, with subordinate poikilitic, perthitic, and granophyric textures. Late-stage intrusive activity after the Eocene led to thermal alteration of the regional Eocene volcanic rocks, forming siliceous–argillic breccias with white, yellow, to pink coloration. Petrographic evidence of metasomatism includes late-stage feldspar veinlets within quartz grains, brecciated textures in quartz, and partial replacement of plagioclase by potassium feldspar at grain margins. Electron microprobe analysis of adularia confirms the composition of the potassium feldspar. Adularia appears to have formed at the final crystallization stage of the granitoid as vein fillings, indicating pervasive potassium metasomatism driven by hydrothermal fluids.DiscussionThe rocks are primarily granodioritic, with occurrences of diorite, monzodiorite, and tonalite. The igneous rocks in southeastern Ardestan are mainly calc-alkaline in character, with metaluminous to peraluminous compositions, and are geochemically consistent with subduction-related tectonic settings. The chemical composition of tourmaline provides valuable insights into the physicochemical conditions of the host rock’s formation (Manning, 1982; Henry and Guidotti, 1985; London, 1999). To determine the structural formulae of the tourmalines, multiple grains from the granitoid samples were analyzed via electron microprobe. The calculated formulae are presented in Table 1. Analyses were conducted from the rim to the core of the tourmaline grains. The core and rim compositions are as follows:Core composition: (Na, K) 0.72 (Fe²⁺, Mn, Ti) 2.84 Mg1.5 Al4.85 B3 Si6 O27 (OH, F)4Rim composition: (Na, K)0.72 (Fe²⁺, Mn, Ti) 1.63 Mg1.73 Al5.7 B3 Si6 O27 (OH, F)4The tourmalines are thus members of the schorl–dravite solid solution series. Based on substitutions at the X site, tourmalines are classified into calcic, alkali, and X-site-vacant types depending on the relative proportions of Na+(K), Ca, and site vacancies (Hawthorne and Henry, 1999). According to this classification and as shown in Figure 7, most of the analyzed tourmalines fall within the alkali group, indicating high K and Na contents relative to Ca and minimal X-site vacancies. Alkali tourmalines typically form under acidic and lower-temperature conditions (Collins, 2010). In the Fe vs. Mg diagram, all samples plot above the ∑(Fe+Mg) = 3 line within the schorl–dravite field, indicating a deficiency of Al in the Z-site and its absence from the Y-site. The R1+R2 vs. R3 diagram [(Ca+Na)+(Fe+Mg+Mn) vs. Al+1.33Ti] of Manning (1982) (Fig. 11) reveals Al-involved substitutions, suggesting the presence of aluminous tourmaline, foitite, X-site vacancies, and olenite. In this diagram, the samples trend from the schorl–dravite composition toward uvite, indicating substitutions involving Ca, Mg, and Fe [(Ca (Fe, Mg) ↔ NaAl)].Based on the Fe–Mg–Ca ternary diagram (Henry and Guidotti, 1985), which is used to infer the nature of the fluids involved in tourmaline crystallization, most samples plot within the field of low-Ca metapelites and meta psammites and quartz-tourmaline rocks, while a few are positioned within the compositional field of lithium-deficient granitoids. (Fig. 12). In diagram 13, the tourmalines lie within fields B to C, indicating crystallization from environments ranging from proximal to intermediate, and even distal relative to the granitoid body. The FeO/(FeO + MgO) ratio is a key indicator of system openness and source characteristics. A ratio of 0.8–1 suggests a closed magmatic system with minimal external fluid involvement. Ratios <0.6 imply formation in distal, hydrothermal systems with external fluid input. Intermediate ratios (0.6–0.8) indicate mixed magmatic–hydrothermal environments with both internal and external fluid contributions (Pirajno and Smithies, 1992). In the studied granitoids, this ratio ranges from 0.60 to 0.75 (mean: 0.69), suggesting formation of tourmaline in an environment transitional between magmatic and hydrothermal regimes, likely reflecting fluid mixing involving magmatic-hydrothermal fluids and meteoric water during the final stages of crystallization.

IntroductionThe Chah Gonbad area is located 125 km southwest of Birjand, 90 km southwest of Khousf, and about 40 km southwest of Khour village, between the longitudes 58º07ʹ30ʺ–58º14ʹ50ʺ and the latitudes 32º36ʹ23ʺ–32º42ʹ40ʺ. Based on the 1:100, 000 map of Seh Changi prepared by Eftekharnejad and Stöcklin (1975), the studied area is located in the northeast of Sechangi, north of the Lut Block. Access to the area is possible via the main Birjand–Khousf–Khour–Kerman road and the Khour–Chah Gonbad–Sechangi side road (Figure 1). There are various opinions about the formation of the volcanic rocks of the Lut Block (Eftekharnejad, 1972; Darvishzadeh, 1976; Jung et al., 1983; Camp and Griffis, 1982; Tirrul et al., 1983; Tarkian et al., 1983; Pang et al., 2013; Omidianfar, et al., 2018; Kalatbari Jafari et al., 2019, 2020, 2021; Fotoohi Rad et al., 2022; Yousefzadeh and Chahkandinezhad, 2023). The studied rocks range from basic/intermediate to acidic compositions. The main purpose of this research is therefore to provide detailed petrological and geochemical information on volcanic rocks in the Chah Gonbad area to constrain the tectonic setting of these rocks and to identify the geology of the Lut Block in eastern Iran.Regional GeologyThe Tertiary volcanic rocks are extensively exposed in the north of Chah Gonbad. These volcanic and pyroclastic rocks, which cover most of the region, include tuff, perlite, and ignimbrite (Paleogene), as well as rhyolite, dacite (associated pyroclastics), and andesite/ basaltic andesite (Neogene) (Figure 2).Research Method In order to carry out this research, reports, geological and topographic maps, satellite images of the region, and references related to the research topic were first prepared and reviewed. In the next step, during 8 days of fieldwork, rock sampling was carried out by examining their field relationships. In the third step, 79 thin sections were prepared, and their mineralogical and textural descriptions were identified using a polarizing Leitz microscope. Then, 10 samples with the least alteration were selected and sent to Acme Canada Laboratory for analysis of major elements by the ICP-ES method and analysis of trace elements by the ICP-MS method. GCDKit, Excel (@2007), Grapher, and ArcGIS software were used to draw the diagrams and geological map. To calculate the amounts of Fe₂O₃ and FeO, Minpet software was used following the method of Irvine and Baragar (1971).PetrographyThe Chah Gonbad area has extensive outcrops of volcanic rocks with basic/intermediate to acidic compositions. The studied rocks range from basaltic andesite to rhyolitic compositions (basaltic andesite/andesite, rhyolite, dacite, perlite, and ignimbrite), with a peak in acidic compositions. These rocks are dominated by porphyritic texture with microlitic groundmass, glomeroporphyritic, hyaloporphyritic, poikilitic, perlitic, and spherolitic textures. Plagioclase (oligoclase–andesine), sanidine, pyroxene, hornblende, biotite, and quartz are common minerals. Evidence of disequilibrium, including sieve texture, chemical zoning and resorption margins in plagioclase, opacified margins in hornblende, and rounded or embayed edges in quartz and sanidine, are observed in these rocks.Geochemistry and PetrogenesisBased on various diagrams, the samples from Chah Gonbad fall within the range of andesite/basalt, andesite, trachyandesite, dacite, trachydacite, and rhyolite. These rocks have calc-alkaline, high-potassium calc-alkaline, and shoshonitic affinities (Figure 9C). In the Co versus Th diagram (Hastie et al., 2007), which is used for volcanic rocks, the samples show consistent trends. The Sun and McDonough diagram (1989) was used to normalize trace elements to the primitive mantle (Figure 10A). The overall geochemical characteristics, including depletion in Ba, Nb, P, Ti, and Ta, enrichment in LILEs (i.e., Cs, Th, U, K, Rb) relative to HFSEs (i.e., Nb, P, Zr, Ti, Ta), negative anomalies of Nb, Ti, and Ta, and high LILE/HREE ratios in the studied rocks, are features associated with subduction zone magmas. The observed negative Nb anomaly in these samples is an indicator of continental rocks and may suggest crustal participation in magmatic processes (Rollinson, 1993). Depletion of HFSEs such as Nb, P, Ta, and Ti is a prominent feature of arc environments and may result from magma derived from subducted oceanic crust and the overlying mantle wedge, which underwent fractional crystallization, assimilation, and contamination with crustal materials (Saunders et al., 1992; Nagudi et al., 2003). To study the behavior of rare earth elements in samples from the region, a normalized spider diagram with chondrites was used (Boynton, 1984) (Figure 10B). In this diagram, LREEs show enrichment relative to HREEs. According to Winter (2010), the enrichment in LREEs indicates formation in subduction zones. The low Eu depletion in these rocks could be due to high oxygen fugacity during formation and crystallization. Based on Nb versus Zr, Ta/Yb versus Th/Yb, and Yb versus Th/Ta ratios (Figures 11A-11E), the studied rocks are located in a subduction–post -collision setting and in the active continental margin. Geochemical characteristics and tectonic discrimination diagrams suggest that these volcanic rocks presumably formed in an immature continental arc setting (Figure 12). Considering the geological setting and petrological and geochemical evidence, it can be concluded that these rocks were formed in a post-collisional zone during delamination of the continental lithosphere in the Lut Block.ConclusionThe depletion of Ti, Nb, and Ta in the rocks of the region, along with low HREE and high LREE contents, indicates magmatism in a subduction zone. These rocks belong to the active continental margin. Depletion in Ti, Nb, and Ta (TNT) and Ba enrichment in Cs, Th, U, and Rb provide evidence of the role of continental crust in magmatic processes. Low amounts of Ni (>20) and Co (0.6–24.8), Mg# values less than 40 (12–40), and Nb/Ta ratios greater than 1 (8.9–23.5) indicate the prominent role of the crust in the formation or evolution of the parent magma. Based on geochemical evidence, the volcanic rocks of the Chah Gonbad region were formed in a post-collisional zone during thinning of the continental lithosphere in the Lut Block and in an immature continental margin arc.

Introduction The Central Iran zone represents one of the most significant geological domains of Iran, characterized by a wide diversity of igneous, metamorphic, and sedimentary rocks formed through prolonged tectonic and magmatic processes. In the southeastern part of this zone, the Talahoueieh area, located north of Bam, occupies a structurally central Iranian position but is geodynamically situated along the active margin of the Urumieh–Dokhtar magmatic arc (UDMA). The development of this magmatic arc is attributed to the subduction of the Neo-Tethyan oceanic lithosphere beneath the Central Iran plate during the Cenozoic, making it one of the most important volcanic–plutonic and metallogenic belts in Iran (Berberian and King, 1981; Shahabpour, 2005). The Talahoueieh area comprises a suite of Eocene volcanic and volcaniclastic rocks, andesitic–dacitic dykes, and shallow to semi-deep intrusive bodies of granodioritic and monzonitic composition. These lithological assemblages clearly reflect multiple pulses of magmatic activity within an active tectonic setting. In several parts of the area, the igneous units are affected by widespread hydrothermal alteration, including silicic, argillic, chloritic, and carbonate assemblages. Field observations, petrographic characteristics, and preliminary geochemical data suggest a close genetic relationship between magmatism and base- and precious-metal mineralization The presence of extensive alteration zones, quartz vein–veinlet systems, and sulfide minerals such as pyrite, sphalerite, galena, and chalcopyrite indicates a strong potential for intermediate-sulfidation epithermal mineralization. Such deposits are commonly associated with calc-alkaline subvolcanic intrusions emplaced along active fault zones and are characterized by intense hydrothermal alteration. Accordingly, the Talahoueieh area represents a promising exploration target in the southeastern part of the Central Iran zone. In this study, whole-rock geochemical data obtained by ICP-MS and XRF analyses, together with detailed petrographic and ore microscopic studies, are used to constrain the petrogenesis, magma evolution, crystallization and differentiation processes, and their genetic links to alteration and mineralization. The ultimate goal is to develop a comprehensive model for the origin, evolution, and metallogenic role of igneous rocks in the Talahoueieh area. Research Method The study was conducted through fieldwork and laboratory analyses. A 1:10,000 geological map of the area was prepared, and 62 rock samples were collected. Of these, 35 were used for petrographic studies, while 19 representative samples (5 intrusive and 14 volcanic) were analyzed by XRF and ICP-MS at the Zarazma Laboratory (Kerman, Iran). The geochemical data were processed using Excel and GCDkit software to evaluate the geochemical and tectonic characteristics of the studied rocks. Regional Geology Magmatic activity in the UDMA lasted from the Eocene to the Quaternary, peaking in the Eocene. A shift from calc-alkaline to adakitic magmas in the early Miocene enhanced magma fertility, promoting porphyry mineralization. In the southeastern UDMA (Kerman copper belt), mineralization occurred mainly during the late Oligocene to Miocene. Key volcanic complexes include Bahr Aseman (Middle Eocene), Razak (Late Eocene), and Hazar (Middle Oligocene), showing a near-complete Cenozoic volcanic–sedimentary succession, with Eocene units being the most significant. In the Talahoueieh area, exposed rocks are dominated by volcano-sedimentary units (tuffaceous shale, conglomerate, and limestone), with central volcanic tuffs and dacitic–andesitic rocks forming elevated areas. Intrusive bodies are limited but locally associated with skarn-type mineralization. Alteration and Mineralization In the Talahoueieh deposit, hydrothermal alteration is widespread and, dominated by argillic, silicic, chloritic, and advanced argillic types, with argillic alteration being the most extensive and closely linked to mineralized zones. This reflects mid- to late-stage acidic hydrothermal activity. Potassic and phyllic alterations were not observed. Polymetallic vein-type mineralization (Cu, Pb, Zn, Ag) mainly occurs in Eocene volcanic units, especially pyroclastic tuffs and andesites, in the form of veins, veinlets, replacement, and open-space fillings, and is structurally controlled by structural features. Key minerals include chalcopyrite, bornite, malachite, azurite, chrysocolla, galena, cerussite, sphalerite, and hemimorphite. Copper mineralization shows oxidized zones at the surface and sulfide zones at depth, while Pb and Zn occurrences are sporadic. Mineralization is controlled by a combination of structural, lithological, and hydrothermal factors, emphasizing its economic potential and guiding future exploration. Discussion Calc-alkaline magmas typically form in subduction-related volcanic arcs and are characterized by high SiO₂, low Fe/Mg ratios, and mineral assemblages including plagioclase, hornblende, and biotite. These magmas are commonly associated with porphyry Cu–Au systems. In contrast, shoshonitic magmas have higher K₂O and K₂O/Na₂O ratios, are enriched in LILE and LREE, and are often linked to epithermal Au mineralization. The intrusive and volcanic rocks of the Talahoueieh area (granite, granodiorite, rhyolite, dacite, and andesite) exhibit high Al₂O₃ and K₂O contents, reflecting partial melting of a metasomatized mantle source and subduction-related arc magmatism. The coexistence of calc-alkaline and shoshonitic compositions indicates an active arc environment and late-stage magmatic evolution, providing favorable conditions for widespread alteration zones and hydrothermal systems. These geochemical characteristics highlight the economic potential of the area, particularly for porphyry Cu–Au and epithermal Au–Ag mineralization. Conclusion In the Talahoueieh polymetallic deposit, the exposed rock units mainly consist of Eocene volcano-sedimentary rocks, particularly tuffs, along with minor Quaternary deposits, while volcanic (andesite, rhyolite, dacite) and intrusive (granite, granodiorite) bodies are limited and scattered. The area is dominated by pyroclastic units, with intrusive and volcanic rocks playing a marginal tectonic role. Extensive hydrothermal activity has produced argillic, advanced argillic, propylitic, and silicic alterations, primarily hosted in pyroclastic units and structurally aligned along a NW–SE trend. This indicates strong structural control by faults and fractures that served as fluid pathways. Geochemical features, including low Nb/Ti ratios, negative Ti anomalies, and high K₂O, Al₂O₃, and LILE/HFSE ratios, suggest a continental arc volcanic environment with a close genetic link to calc-alkaline and shoshonitic magmas. Magmatic evolution in the area, driven by subduction-related processes and arc volcanism, created favorable conditions for the development of hydrothermal systems and polymetallic mineralization.

Introduction The Chah Gaz Pb-Zn ore deposit is an inactive mineralization located approximately 70 km southwest of Shahr-e Babak in Kerman Province, Iran. It lies within the geologically significant Sanandaj-Sirjan zone, a region renowned for its massive sulfide deposits and thus the focus of extensive previous research (Mousivand et al., 2007; Badrzadeh, 2009; Mousivand, 2011). Numerous consulting engineering companies have studied the Chah Gaz deposit in the past, primarily with an exploratory focus (Sabzehei and Afrooz, 1989; Kavoshgaran Co., 1990; Tehran Padir Co., 1991; Minook Co., 1993; Sabzehei et al., 1993). The most recent scientific research by Mousivand (2011) indicated that, based on a brine pool model, the Chah Gaz deposit closely resembles the siliciclastic felsic type or Bathurst-type deposits, such as those in the Bathurst mining district in Canada and the Iberian Pyrite Belt in Spain and Portugal. The deposit also shows strong geological similarities to volcano-sedimentary volcanogenic Kuroko deposits (Soleimani Alh-Dadi, 2017). Kuroko-type volcanogenic massive sulfide (VMS) deposits are significant submarine hydrothermal mineralizations formed in back-arc basins, associated with bimodal volcanic activity. They are key sources of base metals such as copper and zinc, characterized by low- to medium-temperature hydrothermal fluids and bimodal magmatism. These genetic features are essential for identifying exploration targets and understanding metallogenic processes in extensional tectonic settings (Ohmoto, 1996). The principal objectives of this study were to investigate the genesis of the deposit through an integrated approach, including geochemistry, petrography, trace element distribution, and fluid inclusion studies. Additionally, the Chah Gaz deposit is compared to global massive sulfide analogues based on key characteristics such as host rock sequences, mineral paragenesis, and tectono-magmatic setting. Method The concentrations of 23 trace elements and 14 rare earth elements were determined in the ore and metamorphic host rocks using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), conducted by ZarAzma Mineral Studies. Six ore samples were analyzed for gold content using Fire Assay and ICP methods. Eleven samples of ore and associated alteration rocks were examined via X-ray Diffraction (XRD) to identify major and minor minerals. Temperature-pressure measurements of fluid inclusions were carried out using a Linkam heating-cooling stage model THMSG600, TMS94, with a temperature range of -196 to +600 °C, equipped with a computer-linked simultaneous imaging system for video and slide recording. Results and Discussion Regional Geology The Chah Gaz Pb-Zn ore deposit is situated southwest of Shahr-e Babak, within the southern Sanandaj-Sirjan structural zone. This area comprises metamorphosed rocks such as slate, schist, metarhyolite, metabasalt, and gneiss. The gneisses are likely metamorphosed Cambrian granites transformed into orthogneisses. These rocks are metamorphosed to the greenschist facies and display diverse structures including boudinage, foliation, and mylonitization. The studied host rocks are mainly weakly to moderately metamorphosed and include semi-gneiss, schist, mineralized mylonite, quartzite, metarhyolite, and metabasalt. The schists exhibit chloritic and sericitic alteration, with chlorite contributing to preferred foliation. Black slates contain mica and quartz minerals with relatively weak foliation. Rhyolites in the area have been tectonically transformed into mylonites, showing secondary mineralization such as sericite and goethite veinlets, identified by XRD due to their fine grain size. Mineralization Both hypogene and supergene mineralization are present. Hypogene minerals include sphalerite, galena, pyrite, and chalcopyrite, while supergene minerals comprise covellite, chalcocite, smithsonite, cerussite, malachite, and iron oxides, especially in the oxidized zone. The gangue minerals mainly consist of sericite, quartz, chlorite, feldspar, siderite, ankerite, dolomite, and barite. Pyrite is the most abundant primary sulfide in the hypogene zone, occurring as euhedral, vein, and cataclastic forms, indicating intense deformation and metamorphic processes. Secondary pyrite appears rregular and veinlet-like, with iron oxide inclusions reflecting asynchronous sulfide and oxide phases. Chalcopyrite forms after pyrite as fracture-fillings, while sphalerite is a secondary sulfide enriched in zinc. Covellite is the dominant supergene oxidation mineral, formed by the alteration of chalcopyrite along its fractures. Azurite and malachite are observed in oxidized zones alongside goethite and limonite. Geochemistry The highest concentrations of major elements in the host rocks are silica, aluminum, iron, potassium, and magnesium. The elevated Al₂O₃ and LOI values in the host rocks are attributed to clay alteration, resulting from the formation of minerals rich in volatile components such as illite, halloysite, montmorillonite, and other hydrated minerals, consistent with XRD results. The highest average concentrations of minor elements include zinc (5.2 wt%), lead (4.1 wt%), copper (1.9 wt%), sulfur (9.5 wt%), calcium (0.06 wt%), and barium (3.6 wt%), indicating the abundance of sulfide minerals such as galena, sphalerite, chalcopyrite, and barite. The anomalous arsenic content in most ore samples suggests the presence of gold in the area. Fire assay analysis of six sulfide ore samples revealed an average gold content of 8 ppm, exceeding the economic threshold. In contrast, the silver content in the sulfide ore is significantly below the economic grade, with an average concentration of 0.003574 wt%, compared to the economic grade of 0.01 wt%. The absence of silver in this deposit may serve as an important indicator for determining the ore deposit type (Santagulda and Hannington, 1996; Tajeddin et al., 2019). Conclusion The Chah Gaz deposit represents a typical Kuroko-type volcanogenic massive sulfide system formed in a back-arc basin setting, characterized by acidic volcanic host rocks, stratiform to semi-massive sulfide mineralization, and a paragenetic sequence dominated by chalcopyrite, sphalerite, galena, and abundant barite. It contains economically significant lead, zinc, and copper, with gold concentrations reaching up to 8 ppm. The mineralizing fluids exhibit moderate salinities of 10–15 wt% NaCl and are associated with intense sericitic alteration. Unlike previous classifications as Bathurst-type, Chah Gaz differs by its higher gold -to -silver ratio (~1.4), moderate fluid salinity (vs. >25 wt% NaCl in Bathurst), dominance of sulfide minerals over sulfosalts, and a distinctive abundance of barite. These geological, geochemical, and mineralogical features support the reclassification of Chah Gaz as a Kuroko-type massive sulfide deposit.

IntroductionIran constitutes a critical segment of the Alpine-Himalayan orogenic belt, formed through the collision of the Arabian, Indian and Eurasian tectonic plates (Rolland et al., 2002; Stampfli and Hochard, 2009; von Raumer et al., 2003; Yin and Harrison, 2000). The Urmia-Dokhtar magmatic arc (UDMA), extending northwest-southeast across Iran, records Neo-Tethyan subduction and subsequent continental collision (Chiu et al., 2013; Verdel et al., 2011). Magmatism within this arc is predominantly calc-alkaline, with localized adakitic affinities (Delavari et al., 2020; Lechmann et al., 2018; Omrani et al., 2008). The Salafchegan-Tafresh region, situated in the central UDMA, comprises diverse lithological units, including Paleogene to Neogene volcanics and pyroclastics as well as calc-alkaline intrusions dated at 19–22 Ma (Raeisi et al., 2020). These units reflect UDMA magmatism associated with Neo-Tethyan subduction processes. Additionally, the region is intruded by various dykes, exhibiting predominantly intermediate to mafic composition. These dykes are inferred to be of Miocene–Pliocene age, and their geochemical and structural analysis provides critical insights into the region’s tectonic evolution.Analytical methodsWhole-rock geochemical analyses were performed at Zarazma lab company (Tehran, Iran) using inductively coupled plasma-optical emission spectroscopy (ICP-OES) for major elements and inductively coupled plasma-mass spectrometry (ICP-MS) for trace elements. Sample preparation involved fusion with lithium metaborate followed by dissolution in nitric acid. The analytical precision yielded a detection limit of ~0.05 wt.% for major oxides. To analyze trace elements, sample digestion was performed via acid dissolution (HF-HNO₃-HClO₄). Detection limits ranged between 0.05 and 1 ppm. To ensure data accuracy and reproducibility, replicate analyses and international reference standards were employed.Results and discussionPetrographyThe investigated dykes can be categorized into basaltic andesite and andesite. In the basaltic andesite, plagioclase constitutes the dominant mineral phase, accounting for up to 50 vol.% in some samples, and typically occurs as subhedral to euhedral laths within a fine-grained groundmass. Clinopyroxene and amphibole are present as subordinate phases, often exhibiting partial alteration to secondary minerals. The andesite dykes are characterized by a higher relative abundance of plagioclase, which forms the principal framework of the rock. Ferromagnesian minerals (e.g., pyroxene, amphibole) occur in lesser proportions compared to the basaltic andesite group, suggesting either differences in melt composition or crystallization conditions. Opaque minerals, predominantly Fe-Ti oxides, are ubiquitously present as accessory phases in both groups, typically disseminated throughout the groundmass or as inclusions within major silicate phases.GeochemistryThe studied dykes exhibit a compositional range with SiO2 contents varying between 51.75 and 64.97 wt%. In the Zr/Ti versus Nb/Y diagram, the samples plot within the basaltic andesite and andesite fields, displaying a calc-alkaline affinity. Low Mg#, Ni, and Cr values suggest significant geochemical modification and derivation from evolved melts. Harker diagrams reveal coherent geochemical trends and decreasing trends in TiO₂, Al₂O₃, MnO, MgO, CaO, Sc, and V with increasing SiO2. Chondrite-normalized rare earth element (REE) patterns exhibit enrichment in REEs, with light REEs (LREEs) showing the highest enrichment (~52× chondrite), followed by middle REEs (MREEs; ~16×) and heavy REEs (HREEs; ~14×). The Lan/Smₙ (7.6–9.2) and Lan/Ybₙ (10–3.4) ratios indicate LREE enrichment relative to MREEs and HREEs. The Smn/Ybₙ ratio (0.8–1.9) suggests a flat to gently sloping pattern in the MREE-HREE segment, implying limited HREE depletion. Primitive mantle-normalized multi-element diagrams display enrichment in large ion lithophile (LIL) elements (e.g., Rb, K) and depletion in high field strength (HFS) elements (e.g., Nb, Ta).Petrogenetic ModelingFractional crystallization modeling was conducted using one sample (TT22) as the parental melt. Trace element modeling indicates that the more evolved compositions can be derived through 20–80% fractional crystallization of plagioclase, clinopyroxene, olivine, and Fe-Ti oxides.Regional Tectonomagmatic ImplicationsThe Urmia-Dokhtar magmatic arc (UDMA) exhibits distinct temporal variations in magmatism. Eocene and Neogene magmatism displays arc-related signatures, sourced from a metasomatized lithospheric mantle. Oligo-Miocene magmatism is alkaline, likely derived from asthenospheric upwelling. The temporal shift in melt composition from calc-alkaline in the Eocene to alkaline in the Oligo-Miocene, followed by a return to calc-alkaline magmatism in the Neogene within the Urmia-Dokhtar magmatic arc, reflects significant changes in subduction dynamics, crustal interactions, and tectonic regime. The Eocene calc-alkaline magmatism is interpreted as a product of arc-related processes in an active subduction zone, driven by the subduction of the Neotethys oceanic plate beneath the Central Iranian continental margin. In such a setting, calc-alkaline melts are typically generated through partial melting of a hydrated mantle wedge, metasomatized by slab-derived fluids (Delavari and Damghani, 2022; Verdel et al., 2011; Verdel, 2009). This magmatism is consistent with a supra-subduction zone extensional regime, where slab rollback facilitated asthenospheric upwelling, enhancing heat transfer to the mantle lithosphere and triggering widespread partial melting. During the Oligo-Miocene, magmatism transitioned to an alkaline affinity. Continued slab rollback may have induced asthenospheric upwelling and decompression melting, generating melts with oceanic island basalt (OIB)-like characteristics with weak to negligible subduction-related fluid signatures. The resurgence of calc-alkaline magmatism in the Neogene suggests a renewed influence of subduction-related processes, possibly linked to a post-collisional setting. Lithospheric thickening, driven by the convergence of the Arabian and Eurasian plates, may have facilitated partial melting of the mantle lithosphere. Regional fault systems played a critical role in controlling the spatial distribution and geometry of magmatic intrusions. These faults served as conduits for magma transport, localizing magmatic activity along their trends.ConclusionThe Salafchegan-Tafresh dykes, exhibiting basaltic andesite to andesite compositions, provide critical insights into the Urmia-Dokhtar magmatic arc's (UDMA) evolution. Geochemical signatures indicate calc-alkaline affinities, LREE enrichment, and LILE/HFSE fractionation, consistent with subduction-modified melts. Fractional crystallization of plagioclase, clinopyroxene, and Fe-Ti oxides explains compositional variations. The temporal shift from Eocene calc-alkaline to Oligo-Miocene alkaline magmatism reflects slab rollback and asthenospheric upwelling, while Neogene calc-alkaline resurgence suggests renewed subduction influence. Regional faults facilitated magma transport, highlighting the interplay between tectonics and magmatism in the UDMA. These findings underscore the complex geodynamic evolution of the Neo-Tethyan subduction-collision system.

IntroductionThe study area, situated 5 km northeast of Zanjan, is a component of the Tarom magmatic subzone within the Tarom-Hashtjin metallogenic province. This province is characterized by a variety of deposit types, including porphyry, skarn-type iron, IOCG, volcanic-sedimentary, and IOA deposits, all located in the Western Alborz magmatic arc (Nabatian et al., 2015; Ghasemi Siani and Ebrahimifard, 2023). Previous research in the Tarom-Hashtjin subzone has largely concentrated on intrusive igneous bodies (Nabatian et al., 2014a, 2014b; Aghazadeh et al., 2015; Saeedi et al., 2018; Ghasemi Siani et al., 2020), with less emphasis on the geochemical and petrological aspects of volcanic rocks. Specific iron deposits identified include skarn types (Qozlu, Arjin, Gozel Darreh- Moghaddasi et al., 2019; Mokhtari et al., 2019; Shafaiepour et al., 2020), iron oxide-apatite types (Zaker, Sorkheh Dizaj, Morvarid - Nabatian et al., 2014a; Nabatian and Ghaderi, 2013), volcanic-sedimentary types (Shah Bolaghi, Hossein Abad, Reyhan- Mokhtari et al., 2019), and placer type (Zarnan - Ebrahimi et al., 2016, 2017). Some studies highlight the influence of intrusive igneous masses on regional mineralization. For instance, Ghasemi Siani et al. (2020) suggest that the internal igneous masses of Tarom provided the necessary heat and chemical composition for hydrothermal fluids responsible for epithermal mineralization. The Eocene-Oligocene Alborz magmatism cycle, particularly in the Tarom-Hashtjin province, yielded diverse intrusive, semi-volcanic, and volcanic-sedimentary rocks, spanning acidic to intermediate compositions and belonging to calc-alkaline, high-potassium calc-alkaline, and shoshonitic series (Ghasemi Siani and Ebrahimifard, 2023).Given the debated origin of iron ore deposits, this study undertakes detailed geological and mineralogical research in the Chore Nab region. It aims to investigate the petrology of igneous and volcanic rocks to ascertain their role in iron mineralization, analyze the textures, structures, mineralogy, formation, and types of iron mineralization, and establish the magmatic series and tectonic setting of the local rock masses. Comprehensive geochemical and rare earth element studies will be conducted using XRF, XRD, ICP-MS, SEM, and EDS analyses.Regional GeologyChore Nab is located in the central part of Zanjan Province, Iran. The study area, covering approximately 20 km2, is located 5 km northeast of Zanjan city, with geographical coordinates of 36° 41′ 10′′ to 36° 43′ 40′′ N and 48° 32′ 25′′ to 48° 35′ 19′′ E. According to Tarom’s 1:100,000 geological map, several rock units with outcrops are present in the study area. These rocks are Eocene volcanic and pyroclastic rocks, including basalt, dacite, andesite basalt, andesite, sandstone and green tuff in the lower part(unit E5k.a), light green tuff breccia and lapilli tuff(E6k.a) and andesitic lavas with tuff breccia, green tuff, sandstone, and mudstone(unit E8k.a) The Late Eocene granitoid rocks have a lithological composition of quartz monzodiorite, quartz monzonite, quartz syenite(unit Qm), and microquartz diorite porphyry(unit P). Quaternary deposits consist of old alluvial terraces (unit Q1t) and new alluvial terraces (unit Q2t).Analytical methodsField sampling of rock units was performed, resulting in 50 collected samples. From these, 36 thin sections and 22 polished thin sections were prepared for petrographic, mineralogical, and alteration studies at Bu-Ali Sina University. Following this, 14 samples were chosen for chemical analysis. Zar Azma Company in Tehran conducted ICP-MS analysis for rare earth and trace elements, and XRF analysis for major and minor element oxides on these 14 samples. Additionally, SEM and EDS analyses were performed on ten mineral samples, and eight samples were selected for X-ray diffraction studies at Lorestan University.PetrographyRocks in the area are classified into volcanic rocks (basalt, andesite, dacite), intrusive masses (monzonite, quartz monzodiorite), and Quaternary sediments. Volcanic rocks primarily display porphyritic and glomeroporphyritic textures, while granitoid intrusives are predominantly granular, with some anti-rapakivi and granophyric textures. Exsolution texture in pyroxenes and sieve texture in plagioclases were noted. Main minerals are plagioclase and pyroxene in volcanics, and quartz, alkali feldspar, and plagioclase in intrusives. Amphibole, epidote, and chlorite are common mafic minerals; apatite and monazite are minor. Laboratory studies reveal extensive mineralization and alteration in volcanic rocks. Magnetite mineralization appears as massive and dispersed grains, accompanied by secondary hematite, limonite, goethite, and copper minerals (malachite, chalcocite). Field studies confirmed significant limonite and goethite alteration. GeochemistryFor geochemical analysis, 14 minimally altered rock samples from the study area underwent whole-rock analysis using XRF and ICP-MS. Intrusive masses plot as quartz monzodiorite and monzodiorite on the SiO2 versus (Na2O + K2O) diagram. Volcanic masses appear as andesite-basalt, andesite, trachyandesite, and subalkaline basalt on the Nb/Y versus Zr/TiO2 diagram, and as andesite, andesite-basalt, trachyandesite, and basalt on the Nb/Y versus Zr/Ti diagram. The trace element Co versus Th diagram, along with the AFM diagram, indicate all samples are calc-alkaline. On the SiO2 versus K2O diagram, samples fall within the high-potassium calc-alkaline range. All samples are meta-aluminous based on the A/CNK versus A/NK diagram. Negative Ti and Nb anomalies suggest subduction-related magmatism and crustal involvement. Studied samples are enriched in LREE relative to HREE, showing a high LREE/HREE ratio and a subtle negative Eu anomaly.Discussion and ConclusionEocene igneous rocks in the Chore Nab region are linked to iron mineralization. The Chore Nab mine specifically features iron oxide-apatite mineralization in lenses, veins, and as disseminations within intrusive and, to a lesser extent, volcanic-sedimentary rocks. The region’s rocks are high-potassium calc-alkaline and meta-aluminous, with granitoids being Type I. Intrusive masses formed in an active continental margin setting during collision, while granitoids are associated with volcanic arcs. Volcanic masses are found in orogenic environments related to continental arcs. Geochemical diagrams (Th/Ta versus Ta/Yb, Th/Ta versus Yb, Nb versus Y) place the intrusive masses within active continental margin and volcanic arc settings, respectively. Geochemically, the mineralization falls within the range of iron apatite and titaniferous iron deposits based on Ni, V, Ti, and Fe content.AcknowledgementsThe authors sincerely appreciate the esteemed editor and referees for their invaluable scientific advice and insightful comments, which significantly enriched this article.

IntroductionThe Asagi igneous complex is located in the northwest of Zahedan city (Figure 1A) and is part of a southeast–northwest trending magmatic belt. The igneous rocks of this belt were formed during at least two distinct periods. In the first period, Oligocene igneous rocks occur as extrusive (lava and pyroclastic), intrusive, and subvolcanic bodies that are mostly potassic. In the second period, Pliocene igneous rocks appear as sodic extrusive lavas (Camp and Griffis, 1982; Piri, 2018; Boomeri et al., 2020, 2022; Moradi et al., 2016; Nazari et al., 2022). Based on these studies, the Oligocene rocks belong to alkaline, calc-alkaline, high-potassium calc-alkaline, and shoshonitic magmatic series. These rocks are attributed to subduction-related and post -collisional tectonic settings.The aim of this paper is to investigate the geology, petrography, and geochemistry of volcanic and subvolcanic rocks in the southern part of the Asagi igneous complex. It also explores the tectonic setting and magma origin.GeologyThe Asagi igneous complex lies within the Sistan Suture Zone (Figure 1B), situated between the Lut and Afghan blocks. This zone includes two ophiolite complexes—Neh in the west and Ratuk in the east —separated by the Sefid-Abeh sedimentary basin (Tirrul et al., 1983). The Neh and Ratuk complexes contain Upper Cretaceous ophiolites and locally metamorphosed flysch-type sedimentary rocks of Upper Cretaceous to Eocene age. These complexes are commonly intruded by Cenozoic igneous rocks. The Sefid-Abeh basin consists of clastic rocks and limestone deposited in shallow to deep marine environments, with a thickness of approximately eight kilometers (Tirrul et al., 1983). This basin also hosts numerous intrusive and extrusive igneous bodies, indicating multiple magmatic phases during the Cenozoic (Camp and Griffis, 1982; Boomeri et al., 2021; Nazari et al., 2022). Strike-slip faults have played a key role in controlling magmatism in the region (Bagheri and Damani Gol, 2020). The study area is located within the Sefid -Abeh basin, where small outcrops of ophiolitic and sedimentary rocks are intruded by larger outcrops of basic to acidic volcanic and subvolcanic rocks, most of which have undergone hydrothermal alteration (Figures 2 and 3).Research MethodTwenty-four thin sections were prepared from collected samples for petrographic analysis. Thirteen relatively unaltered samples were selected for geochemical analysis of major, minor, and rare earth elements. Major and some minor elements were measured using X-ray fluorescence (XRF) at Tarbiat Modares University, while rare earth and trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) at Novin Shimiyar Laboratory in Tehran.PetrographyPetrographic studies (Figure 4) reveal that the igneous rocks in the study area include andesite, andesiticbasalt, dacite, trachyte, quartz monzonite, and diorite porphyry. These rocks predominantly exhibit porphyritic textures. The main minerals are plagioclase (with or without quartz), orthoclase, hornblende, biotite, and augite. Secondary, opaque, and accessory minerals are present in most samples. Some primary minerals show disequilibrium textures, such as resorption and zoning. Secondary minerals include calcite, quartz, sericite, and clay minerals, occasionally accompanied by chlorite, epidote, orthoclase, and biotite. Opaque minerals mainly consist of pyrite, hematite, magnetite, and iron hydroxides.GeochemistryThe SiO₂ content in the studied rocks ranges from 53.66 to 66.34 wt.% (Table 1). In Harker diagrams, SiO₂ shows a negative correlation with P₂O₅, TiO₂, CaO, MgO, Fe₂O₃, and Al₂O₃, and a positive correlation with K₂O (Figure 5). These trends likely reflect magma differentiation and fractionation processes (Rollinson, 1993). The correlation between SiO₂ and Na₂O is weak, possibly due to weathering and hydrothermal alteration effects.The rocks belong to alkaline and subalkaline magmatic series (Figure 7B). Alkaline samples are potassium-rich and fall within the shoshonitic series (Figure 8), while subalkaline samples are mainly high -K calc- alkaline. Overall, the samples are classified as high -potassium calc-alkaline and shoshonitic.Geochemically, the rocks exhibit high Sr/Y (>40) and (La/Yb)N (>20) ratios, low Y (<18 ppm) and Yb (<1.9 ppm), and high Sr (>400 ppm), along with very low HFSE (Nb, Ta, Ti)—features characteristic of adakitic rocks (Castillo, 2006).Discussion and ConclusionsShoshonitic, adakitic, high -K calc-alkaline, and calc-alkaline rocks are typically associated with convergent plate boundaries, including continental margins, island arcs, and collision/post-collision zones (Morrison, 1980; Torabi, 2011). Low-K adakites are commonly found in active subduction zones.Tectonic discrimination diagrams confirm that the studied volcanic and subvolcanic rocks are related to convergent plate settings (Figure 9), specifically continental margins. Primitive mantle -normalized diagrams show enrichment in LILE relative to HFSE (Figure 10). Spider diagrams reveal positive anomalies in Cs, Pb, Th, U, and K, and negative anomalies in Rb, Nb, Ti, and P. Chondrite-normalized REE diagrams indicate enrichment in LREE over HREE, with weak negative Eu anomalies in all samples. These geochemical features are typical of high-K calc-alkaline, adakitic, and shoshonitic magmas formed in subduction-related continental margins (Wilson, 1989; Rollinson, 1993; Tatsumi and Eggins, 1995). The magmas are likely contaminated by crustal material (Wilson, 1989) and derived from an enriched mantle source (Figures 12A and B). The host rocks are garnet lherzolites enriched in phlogopite, with partial melting rates below 20 % (Figure 13). Although the geochemical signatures resemble those of magmas formed in continental margin subduction zones, considering the age, it is likely that these rocks formed in a post-collisional tectonic setting within a supra-subduction zone.AcknowledgementWe thank the reviewers for their valuable comments on an earlier draft of this paper

IntroductionThe Nain ophiolite in Central Iran has been the subject of numerous petrological investigations, particularly focusing on its ultramafic rocks. The present study examines the crystal chemistry of pyroxenes in harzburgite massifs from the southern Separab area in order to compare with those of the central (near Sucheh village) and eastern parts of the Nain ophiolite (Darreh Deh region). Understanding mantle heterogeneity is crucial for interpreting the tectonomagmatic conditions of forearc oceanic lithosphere (Ishii et al., 2019a; Zheng, 2019a).This study examines the oceanic lithosphere remnants of Nain ophiolite in the northwest of Central East Iranian Microcontinent (CEIM), where mantle peridotites record suprasubduction zone (SSZ) processes (Mehdipour et al., 2010; Pirnia et al., 2013; Shirdashtzadeh et al., 2014). Previous work documented a lherzolite-harzburgite-dunite transition (Pirnia, 2007; Shirdashtzadeh, 2014) formed by melt-rock interactions in a suprasubduction setting (Pirnia et al., 2010, 2018). While peridotites from the central and southern sections have been studied (e.g., Mehdipour et al., 2010; Pirnia et al., 2013), the western exposures near Separab (or Separo) village remain poorly characterized. A preliminary study by Safdari and Shirdashtzadeh (2024) have shown compositional heterogeneity for the olivines in the various harzburgite massifs of the aforementioned ophiolite. Chemical analysis of constituent minerals in these rock units provides critical insights into the origin and the nature of the oceanic lithospheric mantle sequence. Among these, pyroxenes - particularly clinopyroxene - serve as important petrogenetic indicators due to their refractory nature and high chemical/physical resistance, especially against alteration processes. As demonstrated in numerous studies (e.g., Aldanmaz, 2012; Mohamed et al., 2013; Nishio et al., 2022; Ghorbani et al., 2024), their chemistry has been extensively used to determine the nature and the origin of host rocks. Therefore, this study conducts detailed petrographic and chemical analyses of clinopyroxene and orthopyroxene in harzburgite outcrops south of Separab village to investigate the nature and the evolution of the mantle beneath the Neotethyan oceanic lithosphere. The obtained results are then compared with previously studied harzburgite samples from other sections of this ophiolite by various researchers.Geological BackgroundThe Nain ophiolite, located in central Iran, is a part of the larger Central Iranian tectonic zone representing the remnants of the Neotethyan oceanic lithosphere. The ophiolitic sequence includes harzburgites, which are key to understanding mantle processes during subduction initiation. The studied harzburgites from Separab, Suché, and Darreh Deh exhibit variations in mineralogy and geochemistry, suggesting different tectonic settings. The Separab harzburgites are dominated by olivine, orthopyroxene, and minor clinopyroxene (<5 vol%) and spinel, whereas the Sucheh and Darreh Deh harzburgites show greater evidence of subduction-related metasomatism. These differences imply that the Separab harzburgites may represent an earlier stage of forearc mantle evolution, while the Sucheh and Darreh Deh harzburgites reflect a more mature SSZ environment.Analytical MethodsField sampling was conducted to collect fresh, least-altered samples. Thin sections were prepared using resin mounts (without coverslips) and examined under an Olympus BH-2 polarizing microscope at Tarbiat Modares University. Selected polished thin sections were analyzed for major elements compositions of clinopyroxene and orthopyroxene using a JEOL JXA8800R electron microprobe (accelerating voltage: 15 kV; beam current: 15 nA; spot size: 3 µm) at Kanazawa University, Japan. Structural formulas and end-member components of pyroxenes were calculated based on 6 oxygen atoms per formula unit using Excel spreadsheets. Mineral abbreviations follow Warr (2021).DiscussionThe geochemical differences between the Separab harzburgites and those from Sucheh and Darreh Deh suggest two possible models for their formation: Two-Stage Formation Model: The Separab harzburgites may be older, originating in a Jurassic mid-ocean ridge (MOR) setting, while the Sucheh and Darreh Deh harzburgites formed later in a Late Cretaceous SSZ-like forearc environment above the subducting Neotethyan slab. Given that the pyroxene chemistry in all the studied harzburgites resembles that of the harzburgites from subduction-related zones (though the subduction-related chemical indicators are less pronounced in the Separab area compared to other regions), this model may not be valid for the formation of these harzburgites. Therefore, the harzburgites in the southern Separab were likely not formed in an ancient mid-ocean rift environment during the Jurassic period. Single-Stage Formation with Progressive Subduction Influence: The Separab harzburgites formed in a young forearc rift (MOR-like FAB) during the initial stages of subduction, where the mantle wedge was less affected by slab-derived fluids. In contrast, the Sucheh and Darreh Deh harzburgites formed later in the same Late Cretaceous period but under greater subduction influence (SSZ-like FAB), as the mantle wedge became more metasomatized by slab-derived fluids. The chemical composition of pyroxenes (Figs. 5-10), lower oxygen fugacity, higher temperatures (1456–1487°C) recorded in Separab pyroxenes suggest lower mantle partial melting with minimal influence of subduction-related fluids, whereas the Sucheh and Darreh Deh pyroxenes reflect more hydrated conditions of mantle wedge (e.g., chemistry of pyroxenes (Figs. 5–10), higher oxygen fugacity, lower melting temperatures) that is typical characteristics of SSZ settings. Various compositional plots for pyroxenes (Figs. 5–10) clearly distinguish the initial MOR-like FAB nature of Separab harzburgites from the SSZ-like nature of Sucheh and Darreh Deh harzburgites, supporting the interpretation of a heterogeneous mantle wedge beneath the oceanic lithosphere in this forearc basin.ConclusionThe Nain ophiolite, situated north of Nain city in the Central Iranian zone, contains harzburgite units exposed in various sections, including the northwestern area near Separab village. This harzburgite consists mainly of olivine and orthopyroxene, with minor clinopyroxene (<5 vol%) and spinel. Geochemical analyses reveal that the Separab harzburgite pyroxenes (Cr#>0.3, Na₂O >0.1 wt%) formed at higher temperatures (1456–1487°C) and lower oxygen fugacity (higher AlVI/AlIV), indicating lower degrees of mantle wedge partial melting. These features suggest an initial forearc setting resembling mid-ocean ridge-like forearc basalt (MOR-like FAB). In contrast, harzburgites from the eastern (Darreh-Deh) and southern (Sucheh) sections developed under lower temperatures and higher oxygen fugacity, reflecting a mature forearc setting with subduction-related signatures (SSZ-like FAB). These compositional differences highlight temporal heterogeneities in the sub-arc mantle, driven by the advancing stages of slab subduction. The Nain ophiolite thus, records a transition from early, MOR-like forearc magmatism to later, SSZ-dominated conditions, documenting the evolution of the subduction system.

Introduction Granitoids represent the primary components of orogenic belts with a wide range of compositional variations (Kaygusuz et al., 2008). Therefore, analyzing the composition of granitoids contributes significantly to the understanding of continental crust formation and evolution (Barbarin, 1999). Mineral compositions provide insights into the pressure-temperature conditions and the nature of the magma during granite emplacement, and estimating these parameters for a magmatic body is crucial for interpreting petrogenesis and regional tectonic settings (Abdel-Rahman, 1994; Moazzen and Droop, 2005; Gomes and Neiva, 2005; Zhang et al., 2006; Mazhari et al., 2008; Shabani et al., 2010; Sahin et al., 2010). Mineral composition reflects the pressure, temperature, and magmatic characteristics during granite emplacement, and determining these physical and chemical conditions is essential for accurately interpreting petrogenetic processes and understanding the broader tectonic framework of a region (Mazhari et al., 2008; Shabani et al., 2010; Sahin et al., 2010). The mineral assemblage and its chemical composition within igneous rocks are significantly influenced by the original magma composition and the prevailing physicochemical conditions during the crystallization process. The minerals analyzed in this study—namely plagioclase, biotite, and amphibole—exhibit geochemical signatures that offer valuable insights into magmatic crystallization dynamics and melt evolution. The purpose of this study is to investigate the chemistry of plagioclase, biotite, and amphibole minerals and to determine the magmatic origin on the base of chemical composition of aforementioned minerals. Geological Setting The Bagh pain granitoids are located between the geographical longitudes of 46'35°6'E and 46'33°46'E and the geographical latitudes of 36'25°36'N and 36'26°36'N, 50 km south of Shahin dej County and 50 km north of Takab City in the Sanandaj-Sirjan Zone. Based on geological maps and uranium-lead dating studies, the granitoid rocks of the region belonging to Late Cretaceous, were probably generated under the influence of the Late Laramide and Cimmerian orogenic phases. The rocks under study are classified as volcanic arc type and I-type granite. Materials and Methods In this study, a total of 120 samples were collected from all intrusive units during a field visit to the area, and the most intact specimens were selected based on minimal weathering. Subsequently, 40 thin sections were prepared at Bu-Ali Sina University in Hamedan, where petrological investigations were carried out using a polarizing microscope. In addition, 9 representative samples, carefully selected from over one hundred analyzed points, were sent to the University of Vienna, Austria, for detailed microprobe analysis. These samples were subsequently examined using high-resolution electron microscopy and backscattered electron (BSE) imaging techniques. After carbon coating, they underwent rapid semi-quantitative elemental analysis using a CAMECA SX Five Electron Microprobe equipped with a field emission cathode and an energy-dispersive X-ray (EDX) system, operating at an accelerating voltage of 20 keV, a probe current of 25 nanoamperes, and a beam diameter of 60 μm, in the Lithosphere Research Group laboratory at the University of Vienna. Discussion Abdel-Rahman (1994) through the analysis of MgO, Al₂O₃, and FeO oxides in biotite minerals, proposed several geochemical classification diagrams to categorize granitoid rocks into three distinct magma series, which correspond to three tectonic zones. These classifications are derived from the type and relative concentrations of iron, magnesium, and aluminum present within the mineral structure. Zone A corresponds to alkaline, non-orogenic igneous rocks. The C range encompasses calc-alkaline magmas typically generated in subduction-related orogenic settings and is representative of I-type granites, whereas the P range includes peraluminous magmas formed in collisional orogenic environments, which are characteristic of S-type granites. Based on the geochemical discrimination diagrams utilized in this study, all analyzed samples plot within the C range, thereby indicating that the biotites in the investigated area are genetically linked to subduction-related calc-alkaline magmatic systems. Considering the relative concentrations of Na₂O and Al₂O₃ compared to TiO₂, it is inferred that the amphiboles exhibit alkaline and pseudo-alkaline characteristics. Pseudo-alkaline amphiboles typically contain lower levels of Ti, Na, and Al than alkaline types. Accordingly, the amphiboles present in the regional granitoid rocks exhibit a pseudo-alkaline character, which is consistent with the whole-rock geochemical data. Moreover, the TiO₂ versus Al₂O₃ discrimination diagram clearly demonstrates the involvement of both mantle-derived magmatic input and crustal contributions in the genesis and subsequent evolution of these granitoid formations. Conclusion The Bagh-Pain granitoid body comprises granite, granodiorite, diorite, and aplite units, containing quartz, plagioclase, alkali feldspar, amphibole, and biotite as major minerals, along with zircon and apatite as accessory mineral phases. Detailed chemical analyses of biotite and plagioclase indicate that the plagioclases are oligoclase and andesine, while the biotites are magnesium-rich and re-equilibrated. This mineralogical composition corresponds with the green coloration of biotites in the region, their weak pleochroism, and the association of their source rocks with subduction-related tectonic settings. Additionally, the amphiboles are identified as calcium-rich edenite and pargasite types. Based on mineral chemistry data, these rocks are closely linked to calc-alkaline magmatism and are interpreted to have originated from mantle-derived magma that was subsequently modified by crustal contamination.

IntroductionEconomic chromite deposits are very common in ophiolite belts. These deposits usually occur in the uppermost horizons of the ophiolite mantle sequence or within the ultramafic cumulitic rocks at the base of the crustal sequence (González-Jiménez et al., 2014a; González-Jiménez et al., 2014b; Uysal et al., 2018; Arai, 2021).The largest chromite deposit in Iran lies within the Sorkhband Ultramafic Complex (Faryab chromite mine). In addition, numerous peridotite masses are exposed within the Bajgan Complex and the Colored-mélange Complex, as well as around Rudan, which are host for minor chromite deposits. In this study, chromite masses from different areas of the Bajgan Complex and the Colored-mélange Complex in western Makran were sampled and their field characteristics, petrography and chemical composition were studied. These data were applied to identify the nature of the rocks, the petrological changes and the tectono-magmatic setting as well.Field Evidence and PetrographyThe study area located in the south of Kerman Province and the western part of the Makran Zone. The peridotite outcrops occurred within the Bajgan metamorphic complex and around Kahnuj, Kuhshah, Kuh-e-Sefid, and Rudan. These rocks mainly contain minor chromite reserves. These peridotite masses occur as relatively small to large blocks ranging in size from a few meters to several kilometers, often in fault contact with metamorphic units of the Bajgan Complex. The southwestern Kahnuj peridotite outcrop with a dunite composition covers an area of ov 10 square kilometers. The Kuhshah peridotite masses cover an area of over 50 square kilometers consisting mainly of dunite and to a lesser extent harzburgite, pyroxenite and wehrlite.Dunites exhibit a variety of textures, including porphyroclastic, granoblastic, and mylonitic, reflecting varying degrees of deformation and recrystallization. Harzburgites consist mainly of olivine (80-85 %Vol), orthopyroxene (10-15 %Vol), clinopyroxene (less than 2-3 %Vol) and spinel (1-3 %Vol). Harzburgites often have a porphyroclastic texture, and the effects of plastic deformation in olivine and orthopyroxene crystals are visible as wave extinction and kink bands. Chromitites often occur as irregular lenses or masses within dunite units. These rocks are mostly massive to semi-massive and disseminated in texture. Analytical Methods Following the mineralogical studies using Polarized light microscopy, polished thin sections were prepared from a number of mantle peridotite and chromitite samples. In order to determine the chemical composition of chromite minerals, point analysis of minerals was carried out in the Experimental Laboratory of Geophysics and Volcanology, Department of Seismology and Tectonophysics, INGV, Rome (Italy). In this method, the main elemental composition of the minerals was obtained by Jeol JXA 8200 electron microprobe (EMP). The analysis conditions included an accelerating voltage of 15 keV, a sample current of about 7.5 nA, a counting time of 10s and 5s on the peaks and background, respectively, and a beam size of 2-3 mm.GeochemistryIn the dunites, the Al2O3 content of the chromian spinels varies from 21.89 to 25.26 wt.% and Mg# [Mg/ (Mg + Fe2+)] varies from 0.19 to 0.63 (Table 1), while in the harzburgite chromian spinels, the Al2O3 and Mg# contents are higher (Al2O3: 43.01 to 48.28 wt.%; Mg#:0.71 to 0.76). The value of Cr# [Cr/ (Cr + Al)] in the dunites and harzburgites, varies from 0.50 to 0.75 and 0.24 to 0.30, respectively. In chromitites, the Cr# content has a relatively wide range, based on which they are classified into two groups: high-Cr and high-Al chromitites. The Kutak chromitite has relatively high amounts of Al2O3 (20.52 to 23.63 wt%), while the Al2O3 content in the Kuhshah, Faryab and colored-mélange chromitites varies between 2.45 and 10.47 wt.%. Similarly, the Cr2O3 content in the Kutak chromitites varies between 45.96 and 52.26, while it is higher in other chromitites in the region, it has a higher value and varies between 60 and 70.93 wt.%. Therefore, Kutak chromitite with Cr# between 0.57 and 0.63 are in the high-Al chromitites range, and Kuhshah, Faryab and colored-mélange chromitites (Cr# between 0.80 and 0.95) are in the high-Cr chromitites group. DiscussionThe chemical composition of chromian spinel is widely used to determine the origin of magma and also to determine the tectonic setting of peridotites (Dick and Bullen, 1984; Kamenetsky et al., 2001). The chromian spinel in the ophiolitic peridotites and chromitites studied in the western Makran region shows a relatively wide range in terms of Cr# content. The high Mg# and low Cr# content in the chromian spinels of harzburgite rocks indicate the remnants of a relatively depleted mantle melt. The Cr# content of the chromian spinels in dunites and high-Al chromitites can often be explained by melt-rock reaction and chemical equilibrium with similar MORB melts, while the Cr# content in high-Cr chromitites points to the effective role of Mg-rich magmas or boninitic melts in the melt-rock reaction. The chemical compositions of chromite as well as the chemistry of the parental magma calculated using the Al2O3 content and the FeO/MgO ratio indicate that the genesis of the mantle peridotites of the Bajgan complex evolved in a supra-subduction environment (SSZ). As the obtained data of this study display the chemical diversity of chromites indicates a complex history of chemical and tectonic evolution, which is related to the heterogeneity of the mantle origin, different degrees of partial melting of the host rock, the compositional diversity of the reacting melts (MORB-like melts to boninitic melts), the evolution of the tectonic setting during the initial stages of subduction, and the development of the fore-arc tectonic environment.ConclusionThe study of chromite deposits in the Bajgan complex and colored-mélange complex in western Makran reveals significant variations in chromian spinel chemistry, reflecting diverse magmatic and tectonic processes. High-Al chromitites (e.g., Kutak) suggest melt-rock reactions with MORB-like melts, while high-Cr chromitites (e.g., Kuhshah, Faryab) indicate interaction with boninitic melts in a supra-subduction zone (SSZ) setting. The chemical diversity of chromites points to a complex mantle evolution involving heterogeneous sources, varying degrees of partial melting, and changing tectonic conditions during subduction initiation and fore-arc development. These findings enhance understanding of ophiolite formation and chromite genesis in the Makran zone.

IntroductionDogan mining area is located on the northern edge of Iran's central desert plain and northwest of Toroud village. Structurally, the area is a part of Central Alborz, Eastern Alborz, and Central Iran zones, which gave rise to the formation of deposits and a diverse metallogenic environment. Geologically, this area is a part of Toroud‐Chah Shirin (TCS) belt, a Tertiary base metal and gold-silver mineral region in northern Iran. The TCS belt consists mainly of Eocene volcanic and pyroclastic rocks, equivalent to subvolcanic and intrusive bodies, although there are scattered outcrops of metamorphosed Paleozoic and Mesozoic rocks. Structural patterns are controlled by two principal strike-slip faults, Anjilow in the north and Toroud in the south, both trending NE. So far, no detail study has been carried out on the study area in terms of separation and investigation of intrusive bodies, and only one subvolcanic microdiorite body has been introduced in the previous studies in this area. While, the overall data obtained from detailed field surveys, drilling core as well as petrographic studies indicate that at least three subvolcanic bodies have been identified injected in the area in a telescopic form, and all three are the carriers of copper mineralization as disseminated and vein-veined forms. Therefore, the petrographic and geochemical characteristics of, these bodies are the purpose of the present study.Regional GeologyThe main volume of rock units in the study area, based on 1:1000 geological map of Dogan area, includes andesitic lavas, pyroclastic tuffs, and various subvolcanic bodies. The subvolcanic bodies are relatively diverse in composition, and the greatest areal extent of these bodies is in the northeastern, central, and southeastern parts of the region. The nature of these subvolcanic bodies are as follows:Porphyritic quartz monzonite to quartz monzodiorite (Qmz): A large part of the central part of the study area is surrounded by porphyritic body, which is older than the other bodies and is injected into Eocene units.Porphyritic diorite to microdiorite (Dr): This unit lies in the central part of the area with a less extensive distribution than that of the Porphyritic quartz monzonite body. This body in the central part cuts the Porphyritic quartz monzonite body and is, therefore, younger in age, but its cutting by the dykes of the porphyritic quartz diorite body indicating it is older than this body.Porphyric quartz diorite to granodiorite (Qdr): As the youngest body as well as less extensive area than that of the existing bodies, is exposed in the central part of the area.Analytical methods In this study, after field investigations and sampling of drill cores, about 200 thin sections were prepared from the collected samples for petrographic studies and about 60 polished sections for mineralogy studies. After microscopic studies and separation of intrusive units, 15 samples with minimal alteration were analyzed in the laboratory of Zar Azma Company to measure the main oxides and determine the abundance of trace and rare earth elements by XRF and ICP-MS methods.PetrographyPorphyritic quartz monzonite to quartz monzodiorite (Qmz): Microscopically, this porphyry body ranges from quartz monzonite to quartz monzodiorite, exhibiting a porphyritic texture with a fine-grained matrix. Main minerals include plagioclase, K-feldspar, and quartz, with accessory amphibole, biotite, apatite, zircon, and opaque minerals. Plagioclase and K-feldspar phenocrysts are pseudomorphed by sericite and carbonate, while ferromagnesian minerals (amphibole, biotite) are altered to chlorite and magnetite. Secondary minerals including sericite, chlorite, carbonate, and iron oxides result from alteration.Porphyritic diorite to microdiorite (Dr): These rocks dominated by the presence of plagioclase and amphibole and small volume of quartz, apatite, zircon, and opaque minerals. They display a microlithic porphyritic texture, with subhedral plagioclase phenocrysts (showing mixed zoning) in a microlithic matrix of plagioclase and quartz. Plagioclase is altered to sericite and clay minerals, while amphibole phenocrysts are pseudomorphed by chlorite and iron oxides. Secondary biotite, actinolite, and ore accumulations occur, alongside potassic alteration.Porphyritic quartz diorite to granodiorite (Qdr): The essential minerals of this body’ are plagioclase, K-feldspar, and quartz, with accessory zircon and apatite as well as porphyritic texture with a fine-grained matrix. Plagioclase exhibits mixed zoning; amphibole is partly altered to chlorite. Biotite appears as primary (magmatic, altered to chlorite and iron oxides) and thesecondary (hydrothermal, flaky, brown). Chloritization and iron oxide precipitation are common.DiscussionAs the SiO2 versus Zr/TiO2 diagram display the subvolcanic bodies in the Dogan mining area are dominated by granodiorite, tonalite, and diorite/. These I-type granitoids are calc-alkaline to high-K calc-alkaline and metaluminous to peraluminous nature formed in a continental arc setting. Geochemical data show depletion in Sm, Nd, Ti, and Y and enrichment in LILEs (Ba, Rb, Cs, K), consistent with subduction-related magmatism. The REE patterns display LREE enrichment over HREE, further supporting a subduction origin. Low Th/Nb and Ba/Th ratios point out to subduction zone fluids/melts and crustal contamination. The elevated Y/Rb ratios may reflect subduction enrichment or crustal input.The parental magma likely originated from a metasomatized mantle wedge, influenced by fluids from subducting oceanic lithosphere, and underwent fractionation and crustal contamination during ascent. On Y versus Sr/Y and Ybn versus (La/Yb)n diagrams, the rocks show adakite-like signatures. Given the association of high Sr/Y magmas with porphyry systems, these subvolcanic rocks may be linked to porphyry mineralization.AcknowledgmentsThis article is part of the studies carried out for the first author’s Ph.D. thesis, which is being conducted at the University of Tabriz, and part of its costs were covered by the University of Tabriz and the Shahid Arefi Complex. Therefore, I would like to express my deepest gratitude and appreciation to the respected management of the Graduate Studies Department of the University of Tabriz and the management of the Shahid Arefi Complex.