University of Isfahan Petrological Journal 2228-5210 16 3 2025 09 23 Geology, geochemistry and origin of the Chore Nab IOA-type iron deposit in the Tarom metallogenic belt, northwestern of Iran Geology, geochemistry and origin of the Chore Nab IOA-type iron deposit in the Tarom metallogenic belt, northwestern of Iran 27 74 29731 10.22108/ijp.2025.144993.1358 FA Parisa Shahkarami Ph.D student, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran Reza Zarei Sahamieh Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran Mohammad Ebrahimi Associate Professor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran Ahmad Ahmadi Khalaji Associate Professor, Department of Geology, Faculty of Sciences, Lorestan University Khorramabad, Iran Ramin Sarikhani Associate Professor, Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran Journal Article 2025 04 26 Introduction The 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 Geology Chore 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 methods Field 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. Petrography Rocks 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. Geochemistry For 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 Conclusion Eocene 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. Acknowledgements The authors sincerely appreciate the esteemed editor and referees for their invaluable scientific advice and insightful comments, which significantly enriched this article. Introduction The 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 Geology Chore 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 methods Field 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. Petrography Rocks 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. Geochemistry For 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 Conclusion Eocene 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. Acknowledgements The authors sincerely appreciate the esteemed editor and referees for their invaluable scientific advice and insightful comments, which significantly enriched this article.

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