Ferdowsi University of MashhadJournal of Economic Geology2008-730614420221222Geology, geochemistry, fluid inclusion and genesis of the Arabshah magnetite-apatite mineralization, SE TakabGeology, geochemistry, fluid inclusion and genesis of the Arabshah magnetite-apatite mineralization, SE Takab1294151610.22067/econg.2021.69859.1015FAMir Ali Asghar MokhtariAssociate Profesor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran0000-0002-5359-416XHosein KouhestaniAssociate Profesor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran0000-0002-3031-9042Soheila Aghajani MarsaM.Sc., Mineralogy Lab., Iran Mineral Processing Research Center (IMPRC), Tehran, IranJournal Article20210415The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone in southeast of Takab. The oldest rock units in the mineralization area include sedimentary succession of the Qom Formation that was intruded by the Pliocene Ayoub Ansar volcanic dome. Magnetite- apatite mineralization at the Arabshah occurs as vein-veinlets with E-W stright within the Ayoub Ansar dacitic dome. Brecciated zones containing narrow magnetite vein- veinlets occur at footwall and hanging wall of the main vein. Hydrothermal alterations include sodic-calcic, silicification and argillic. Magnetite is the only ore mineral in this mineralization which is accompanied with apatite, clinopyroxene, albite and quartz as gangue minerals. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement. REEs concentration within apatite crystals are more than 1%, and demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies which is indicative for Kiruna- type iron ores. The result of fluid inclusion studies indicates the presence of two-phase and poly-phase inclusions include LV, VL, LVH, LVS and LVHS fluid inclusions with homogenization between 230-550 °C. The salinity of halite bearing poly-phase fluid vary between 35-60 wt.% NaCl equiv. Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Evidences like mineral assemblages, hydrothermal alteration, ore structure and textures, geochemical characteristics and fluid inclusion data, indicate that the Arabshah magnetite-apatite mineralization can be classified as Kiruna-type iron ores.<br /> <br /> <br /><strong>Introduction</strong><br />Iron oxide-apatite deposits (IOA) are considered to be Kiruna-type iron ores which have formed between Protrozoic to Tertiary eras in different parts of the world. Apatite occurs as a major constituent of these deposits which is accompanied by magnetite and some actinolite. Higher concentration of REEs is one of the important features of these deposits (Frietsch and Perdahl, 1995). The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone within the Sanandaj-Sirjan zone which is located about 15 km southeast of Takab. During the past years, some exploration works were done on the Arabshah Fe mineralization, but its geological characteristics, mineralogy, texture, geochemistry, characteristics of mineralized fluids and genesis have not been studied yet. Recognition of characteristics of the Arabshah magnetite-apatite deposit as the first explored deposit of the Kiruna type mineralization in the Takab area is useful for exploration of this type of mineralization in NW Iran.<br /> <br /><strong>Materials and methods</strong><br />This research study can be divided into two parts including field and laboratory studies. Field work includes recognition of different lithological units and ore veins along with sampling for laboratory studies. During field work, 34 samples were selected for petrographical, mineralogical and analytical studies. 10 thin sections and 5 thin-polished sections were used for petrographical and mineralogical studies. For geochemical studies, 6 samples from ore vein were analyzed by ICP–MS methods at the Geological Research Center, Karaj, Iran. Microthermometric measurements were performed on 2 samples using a Linkam THMS-600 heating–freezing stage attached to a ZIESS microscope in the fluid inclusion laboratory of the Iran Minerals Processing Research Center.<br /> <br /><strong>Results</strong><br />The oldest rock units in the Arabshah area include Oligo-Miocene sedimentary succession of the Qom Formation that was intruded by the E–W-trending Pliocene Ayoub Ansar volcanic dome. Based on petrographic studies, the Ayoub Ansar volcanic dome has porphyritic, felsophyric and glomeroporphyritic textures and it is composed of plagioclase, amphibole and some quartz and K-feldspar phenocrysts set in a quartz-felspathic groundmass, and it is compositionally classified as dacite-rhyodacite. These rocks have medium-K calc-alkaline affinity and are classified as metaluminous I-type granitoids. They have been formed in an active continental margin to post-collisional tectonic setting and demonstrate geochemical characteristics similar to high silica adakites (Sabzi et al., 2018).<br />Fe mineralization at the Arabshah mineralization occurs as vein-veinlets of magnetite-apatite within the Ayoub Ansar dacitic dome. Brecciated zones occur at footwall and hanging wall of the main vein. The ore vein has east- west trend and crops out in 50 m length and maximum 1 m width. Coarse-grained euhedral apatite crystals are mainly present at the margins of the main vein. Hydrothermal alterations around the mineralized veins include sodic-calcic, silicification and argillic alterations. Mineralogically, the ore minerals include magnetite along with apatite, clinopyroxene, albite and quartz as gangue minerals. Goethite was formed during supergene alteration. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement form. Apatite crystals have high concentrations of REEs (about 1%). Condrite-normalized REE patterns for apatite crystals, magnetite-apatite ores and magnetite ore without or with minor apatite demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies.<br />Based on phase relationships at room temperature, three types of fluid inclusion including two-phase (LV and VL), three-phase (LVH and LVS) and polyphase (LVHS) are present within the apatite crystals at the Arabshah mineralization. Microthermometric measurements indicate that LV and VL fluid inclusions have homogenized between 253-550 °C and 363-490 °C, respectively. Tree-phase LVH fluid inclusions have been homogenized between 278-508 °C and have salinities between 35-59.8 wt.% NaCl equiv. Three-phase LVS fluid inclusions have been homogenized between 240-520 °C. Polyphase LVHS fluid inclusions have been homogenized between 230-520 °C and have salinities between 36-59 wt.% NaCl equiv.<br /> <br /><strong>Discussion</strong><br />Similar REE patterns of apatite crystals and mineralized samples with samples from host dacitic dome demonstrate a genetic link between magnetite-apatite mineralization and dacites. Furthermore, REE patterns of the Arabshah mineralization is similar to other iron oxide-apatite deposits from the Tarom–Hashtjin metallogenic belt (Mokhtari et al., 2018), and those of Central Iranian iron ores (Mokhtari et al., 2013). Moreover, REE patterns of the Arabshah deposit are similar to REE patterns of the Kiruna-type iron ores (Frietsch and Perdahle, 1995).<br />Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Positive correlations between salinity and homogenization temperatures indicate that mineralization at the Arabshah deposit involved mixing of magmatic fluids and a dilute and cooler meteoric fluid.<br />Totally, based on mineral assemblages, hydrothermal alteration, textures, geochemical characteristics and fluid inclusion data, the Arabshah magnetite-apatite mineralization can be classified to be of the Kiruna-type iron ores.<br /> <br /><strong>Acknowledgment</strong><br />This research study was made possible by a grant from the office of vice-chancellor of research and technology, University of Zanjan. We hereby acknowledge their generous support. The Journal of Economic Geology reviewers and editor are also thanked for their constructive comments.The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone in southeast of Takab. The oldest rock units in the mineralization area include sedimentary succession of the Qom Formation that was intruded by the Pliocene Ayoub Ansar volcanic dome. Magnetite- apatite mineralization at the Arabshah occurs as vein-veinlets with E-W stright within the Ayoub Ansar dacitic dome. Brecciated zones containing narrow magnetite vein- veinlets occur at footwall and hanging wall of the main vein. Hydrothermal alterations include sodic-calcic, silicification and argillic. Magnetite is the only ore mineral in this mineralization which is accompanied with apatite, clinopyroxene, albite and quartz as gangue minerals. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement. REEs concentration within apatite crystals are more than 1%, and demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies which is indicative for Kiruna- type iron ores. The result of fluid inclusion studies indicates the presence of two-phase and poly-phase inclusions include LV, VL, LVH, LVS and LVHS fluid inclusions with homogenization between 230-550 °C. The salinity of halite bearing poly-phase fluid vary between 35-60 wt.% NaCl equiv. Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Evidences like mineral assemblages, hydrothermal alteration, ore structure and textures, geochemical characteristics and fluid inclusion data, indicate that the Arabshah magnetite-apatite mineralization can be classified as Kiruna-type iron ores.<br /> <br /> <br /><strong>Introduction</strong><br />Iron oxide-apatite deposits (IOA) are considered to be Kiruna-type iron ores which have formed between Protrozoic to Tertiary eras in different parts of the world. Apatite occurs as a major constituent of these deposits which is accompanied by magnetite and some actinolite. Higher concentration of REEs is one of the important features of these deposits (Frietsch and Perdahl, 1995). The Arabshah Fe mineralization is the only known magnetite-apatite mineralization at the Takab–Takht-e-Soleyman–Angouran subzone within the Sanandaj-Sirjan zone which is located about 15 km southeast of Takab. During the past years, some exploration works were done on the Arabshah Fe mineralization, but its geological characteristics, mineralogy, texture, geochemistry, characteristics of mineralized fluids and genesis have not been studied yet. Recognition of characteristics of the Arabshah magnetite-apatite deposit as the first explored deposit of the Kiruna type mineralization in the Takab area is useful for exploration of this type of mineralization in NW Iran.<br /> <br /><strong>Materials and methods</strong><br />This research study can be divided into two parts including field and laboratory studies. Field work includes recognition of different lithological units and ore veins along with sampling for laboratory studies. During field work, 34 samples were selected for petrographical, mineralogical and analytical studies. 10 thin sections and 5 thin-polished sections were used for petrographical and mineralogical studies. For geochemical studies, 6 samples from ore vein were analyzed by ICP–MS methods at the Geological Research Center, Karaj, Iran. Microthermometric measurements were performed on 2 samples using a Linkam THMS-600 heating–freezing stage attached to a ZIESS microscope in the fluid inclusion laboratory of the Iran Minerals Processing Research Center.<br /> <br /><strong>Results</strong><br />The oldest rock units in the Arabshah area include Oligo-Miocene sedimentary succession of the Qom Formation that was intruded by the E–W-trending Pliocene Ayoub Ansar volcanic dome. Based on petrographic studies, the Ayoub Ansar volcanic dome has porphyritic, felsophyric and glomeroporphyritic textures and it is composed of plagioclase, amphibole and some quartz and K-feldspar phenocrysts set in a quartz-felspathic groundmass, and it is compositionally classified as dacite-rhyodacite. These rocks have medium-K calc-alkaline affinity and are classified as metaluminous I-type granitoids. They have been formed in an active continental margin to post-collisional tectonic setting and demonstrate geochemical characteristics similar to high silica adakites (Sabzi et al., 2018).<br />Fe mineralization at the Arabshah mineralization occurs as vein-veinlets of magnetite-apatite within the Ayoub Ansar dacitic dome. Brecciated zones occur at footwall and hanging wall of the main vein. The ore vein has east- west trend and crops out in 50 m length and maximum 1 m width. Coarse-grained euhedral apatite crystals are mainly present at the margins of the main vein. Hydrothermal alterations around the mineralized veins include sodic-calcic, silicification and argillic alterations. Mineralogically, the ore minerals include magnetite along with apatite, clinopyroxene, albite and quartz as gangue minerals. Goethite was formed during supergene alteration. Mineralization textures in the Arabshah deposit include vein-veinlet, brecciated, disseminated, and replacement form. Apatite crystals have high concentrations of REEs (about 1%). Condrite-normalized REE patterns for apatite crystals, magnetite-apatite ores and magnetite ore without or with minor apatite demonstrate LREE enrichment with high LREE/HREE ratio and distinctive negative Eu anomalies.<br />Based on phase relationships at room temperature, three types of fluid inclusion including two-phase (LV and VL), three-phase (LVH and LVS) and polyphase (LVHS) are present within the apatite crystals at the Arabshah mineralization. Microthermometric measurements indicate that LV and VL fluid inclusions have homogenized between 253-550 °C and 363-490 °C, respectively. Tree-phase LVH fluid inclusions have been homogenized between 278-508 °C and have salinities between 35-59.8 wt.% NaCl equiv. Three-phase LVS fluid inclusions have been homogenized between 240-520 °C. Polyphase LVHS fluid inclusions have been homogenized between 230-520 °C and have salinities between 36-59 wt.% NaCl equiv.<br /> <br /><strong>Discussion</strong><br />Similar REE patterns of apatite crystals and mineralized samples with samples from host dacitic dome demonstrate a genetic link between magnetite-apatite mineralization and dacites. Furthermore, REE patterns of the Arabshah mineralization is similar to other iron oxide-apatite deposits from the Tarom–Hashtjin metallogenic belt (Mokhtari et al., 2018), and those of Central Iranian iron ores (Mokhtari et al., 2013). Moreover, REE patterns of the Arabshah deposit are similar to REE patterns of the Kiruna-type iron ores (Frietsch and Perdahle, 1995).<br />Fluid inclusion data indicates that Arabshah magnetite-apatite mineralization originated from magmatic fluids. Positive correlations between salinity and homogenization temperatures indicate that mineralization at the Arabshah deposit involved mixing of magmatic fluids and a dilute and cooler meteoric fluid.<br />Totally, based on mineral assemblages, hydrothermal alteration, textures, geochemical characteristics and fluid inclusion data, the Arabshah magnetite-apatite mineralization can be classified to be of the Kiruna-type iron ores.<br /> <br /><strong>Acknowledgment</strong><br />This research study was made possible by a grant from the office of vice-chancellor of research and technology, University of Zanjan. We hereby acknowledge their generous support. The Journal of Economic Geology reviewers and editor are also thanked for their constructive comments.https://econg.um.ac.ir/article_41516_eb51cc512f00c3043a538787ba7a9256.pdfFerdowsi University of MashhadJournal of Economic Geology2008-730614420221222Origin of magnetite and apatite ores in the Esfordi magnetite-apatite ore deposit NE of Bafq, south Yazd: insights from mineralogy, geochemistry, microthermometry, O-H stable and U-Pb and Nd-Sm non-stable isotopesOrigin of magnetite and apatite ores in the Esfordi magnetite-apatite ore deposit NE of Bafq, south Yazd: insights from mineralogy, geochemistry, microthermometry, O-H stable and U-Pb and Nd-Sm non-stable isotopes31884315910.22067/econg.2022.76456.1045FAKiamars HosseiniPh.D. student, Department. of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran0000-0002-2796-8340Mohammad Ali RajabzadehProfessor, Department of Earth Sciences, School of Science, Shiraz University, Shiraz, Iran0000-0002-4167-7152Journal Article20220519Petrographic and mineralogical data indicate the widespread presence of five generations of apatite, two generations of monazite with minor xenotime in the Esfordi deposit. The O-H isotopic studies on the 1<sup>st</sup>- and 2<sup>nd</sup>-generations of apatites and massive fine-grained and vein-type apatites as well as their Sr and Mn contents, showed that the source of phosphorous was the sedimentary phosphorites. The ratio of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O, and the difference of Nd isotopic ratios in the massive fine-grained and vein-type apatites indicate that they are not reproductively related to the host rhyolite and diorite. The similarity of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub> in the 1<sup>st</sup>- and 2<sup>nd</sup>-generations of apatite and the host rocks indicated that recrystallization of the apatites occurred during the magmatic and hydrothermal fluids circulation which were derived from the felsic to intermediate subvolcanic rocks. Difference in the age of the 2<sup>nd</sup>-generation apatites and the paragenetic- monazites ( <sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb dating), the crystalline apatites and magnetite, the ilmenite exclusions in the magnetites, the dissolution evidences of different apatites and monazites generations, the content of Ti vs V, Al+Mn vs Ti+V and Mg+Al+Si vs Ti, and the O-H isotopes of the magnetite-apatite ores, all indicate the mixing of high-temperature magmatic and hydrothermal fluids rich in REE, P with Ca ±Fe evaporatic brines in different time periods, which caused a polygenic origin for the Esfordi deposit.<br /> <br /><strong>Introduction</strong><br />The origin of the magnetite-apatite ore deposits in the Bafq mining district has been explained by a variety of mineralization models, including: a) metasomatic-hydrothermal (IOCG) related to Kiruna-type iron ore deposits (Mehrabi et al., 2019; Ziapour et al., 2021), b) orthomagmatic Kiruna-type (Mehdipour Ghazi et al., 2020; Vesali et al., 2021), and c) Ediacarian-paleoglacial BIF (Aftabi et al., 2021). This study combines evidence from mineralogy, geochemistry, stable isotopes, and apatite and magnetite ores from the Esfordi ore deposit to investigate the origin of mineralizing fluids for the first time. The results of this research could be used to explain the mineralization mechanisms of magnetite-apatite ore deposits in the Bafq mining district.<br /> <br /><strong>Materials and methods</strong><br />Twenty samples of crystalline apatite of the first and second generations, twenty-two samples of massive fine grained apatite ore, and twenty-three magnetite-apatite samples were collected from different ores sections. Petrographic and mineralogical studies were carried out on 47 microscopic thin sections. Scanning Electron Microscopy (SEM) (18 samples) and XRD analyses (7 samples) were used to analyze the representative samples. ICP-OES and ICP-MS techniques were used at the Iranian Mineral Processing Research Center to analyze representative samples from apatite ores (12 samples), magnetite ores (12 samples), hematite ores (2 samples), jaspilite (10 samples), rhyolite (6 samples), rhyolitic tuff (5 samples), and metasomatized host rocks (5 samples). Fluid inclusion investigations on Twelve apatite crystals were conducted at Tehran's Zaminriz Kavan Research Company and the Geological Survey of Iran. Six samples of apatite ore were submitted to Hungaria laboratory for O-H isotopic analysis, and three samples were sent to Queensland University in Australia for Nd-Sm isotope analysis in order to conduct the isotopic analysis. Laser Ablation Coupled Plasma Mass Spectrometry was also used at Tasmania University in Australia to analyze four samples of apatite ores.<br /> <br /><strong>Results</strong><br />This research reveals the Esfordi apatite ores are derived from the sedimentary phosphorites. The O-H isotopic data and the Sr and Mn content of the first and second generations as well as the massive fine-grained apatites, display the role of evaporitic brines in their formation.<sup> </sup>According to the contents of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub>, as well as the variety in Nd isotopic ratios, the massive fine grained apatites, which forms the majority of the apatite mineralization (>95%), lacks a clear genetic relationship in terms of provenance with the rhyolitic, dioritic, and microdioritic host rocks. The similarity of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub> in the first and second generations of apatites and the host rocks demonstrated that the recrystallization of apatite rocks occurred under the influence of magmatic and hydrothermal fluids originating from the felsic to intermediate subvolcanic rocks in the area, which resulted in an increase in εNd values.<br />The differences in age between the second-generation apatite and the paragenetically related monazites, using <sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb dating methods, besides dissolution evidence in different generations of apatites and monazites, Ti vs V, Al+Mn vs Ti+V and O-H isotopes of the magnetite-apatite ores, indicated the role of high temperature magmatic and hydrothermal fluids along with evaporitic brines in mineralization in different time spans. This processes lead to a diversity of mineralization and a polygenic origin for the Esfordi apatite-magnetite ore deposit.<br /> <br /><strong>Discussion</strong><br />The Esfordi ore deposit contains three different forms of apatites mineralization, including vein-type, fine grained massive and disseminated ores according to field observations. There were five generations of apatite, according to petrographic data. Numerous rare earth element minerals, including alanite, parisite-synchysite, bastenasite, and britolite, as well as two generations of monazite and one generation of limited xenotime, were identified in the Esfordi ore deposit according to investigations on the first and second generation apatites. Stable H-O and radiogenic Nd-Sm isotopic studies on the first and second generation apatites and massive fine grained apatite ores along with the similarity between εNd contents in apatite and phosphorites in Soltanieh Formation and phosphorite nodules of the Eastern European platform (Ediacarne and Lower Cambrian deposits) as well as Lower Cambrian sedimentary phosphate deposits in Siberia, Western Mongolia, Baltic, South Kazakhstan, South China, Australia, West Newfoundland, North Greenland and East Greenland confirms that the investigated apatites were formed from leaching of old or contemporaneous sedimentary phosphorites of Soltanieh Formation while magmatic and hydrothermal fluids originated from granitoid masses circulated in massive fine grained apatite ores. By the way, these crystalline apatites have been enriched in εNd content under the influence of magmatic and hydrothermal fluids originated from deep to sub-volcanic felsic and intermediate intrusions in this region.<br />Investigation using the radiometric dating methods (<sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb) on the second-generation apatite and the paragenetically related monazites showed that these minerals were formed between 494-528 Ma and 514-556 Ma, respectively. Some monazites are older than apatites (approximately 28 Ma), which indicates that they were formed before apatite ore and it has been affected by hydrothermal fluids in the structure of apatite. The dating, for a limited number of monazites, indicates a time span between 23 to 33 and a time span of 104 to 153 Ma. The age differences between the apatite and monazite inclusions can be due, not only, to late alteration of deep to sub-volcanic bodies originated hydrothermal fluids, but also, to separation of U-Pb from this system or the formation of young monazites during orogenesis in different time spans. The presence of recrystalized apatite and magnetite, zoning and dissolution evidence in some monazites, dendritic texture in actinolite, ilmenite exsolutions and stable isotopes of magnetite and apatite ores indicates the mixing of magmatic and high temperature hydrothermal fluids with evaporatic brines enriched in REE, P, Ca ±Fe resulting in a diversity of processes involved in formation of the Esfordi ore deposit.<br /> <br /><strong>Acknowledgements</strong><br />The authors appreciate Shiraz University Research Council for support of this work. The Director General and personal of the Esfordi Mine Company are acknowledged for their assistance in the field works.Petrographic and mineralogical data indicate the widespread presence of five generations of apatite, two generations of monazite with minor xenotime in the Esfordi deposit. The O-H isotopic studies on the 1<sup>st</sup>- and 2<sup>nd</sup>-generations of apatites and massive fine-grained and vein-type apatites as well as their Sr and Mn contents, showed that the source of phosphorous was the sedimentary phosphorites. The ratio of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O, and the difference of Nd isotopic ratios in the massive fine-grained and vein-type apatites indicate that they are not reproductively related to the host rhyolite and diorite. The similarity of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub> in the 1<sup>st</sup>- and 2<sup>nd</sup>-generations of apatite and the host rocks indicated that recrystallization of the apatites occurred during the magmatic and hydrothermal fluids circulation which were derived from the felsic to intermediate subvolcanic rocks. Difference in the age of the 2<sup>nd</sup>-generation apatites and the paragenetic- monazites ( <sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb dating), the crystalline apatites and magnetite, the ilmenite exclusions in the magnetites, the dissolution evidences of different apatites and monazites generations, the content of Ti vs V, Al+Mn vs Ti+V and Mg+Al+Si vs Ti, and the O-H isotopes of the magnetite-apatite ores, all indicate the mixing of high-temperature magmatic and hydrothermal fluids rich in REE, P with Ca ±Fe evaporatic brines in different time periods, which caused a polygenic origin for the Esfordi deposit.<br /> <br /><strong>Introduction</strong><br />The origin of the magnetite-apatite ore deposits in the Bafq mining district has been explained by a variety of mineralization models, including: a) metasomatic-hydrothermal (IOCG) related to Kiruna-type iron ore deposits (Mehrabi et al., 2019; Ziapour et al., 2021), b) orthomagmatic Kiruna-type (Mehdipour Ghazi et al., 2020; Vesali et al., 2021), and c) Ediacarian-paleoglacial BIF (Aftabi et al., 2021). This study combines evidence from mineralogy, geochemistry, stable isotopes, and apatite and magnetite ores from the Esfordi ore deposit to investigate the origin of mineralizing fluids for the first time. The results of this research could be used to explain the mineralization mechanisms of magnetite-apatite ore deposits in the Bafq mining district.<br /> <br /><strong>Materials and methods</strong><br />Twenty samples of crystalline apatite of the first and second generations, twenty-two samples of massive fine grained apatite ore, and twenty-three magnetite-apatite samples were collected from different ores sections. Petrographic and mineralogical studies were carried out on 47 microscopic thin sections. Scanning Electron Microscopy (SEM) (18 samples) and XRD analyses (7 samples) were used to analyze the representative samples. ICP-OES and ICP-MS techniques were used at the Iranian Mineral Processing Research Center to analyze representative samples from apatite ores (12 samples), magnetite ores (12 samples), hematite ores (2 samples), jaspilite (10 samples), rhyolite (6 samples), rhyolitic tuff (5 samples), and metasomatized host rocks (5 samples). Fluid inclusion investigations on Twelve apatite crystals were conducted at Tehran's Zaminriz Kavan Research Company and the Geological Survey of Iran. Six samples of apatite ore were submitted to Hungaria laboratory for O-H isotopic analysis, and three samples were sent to Queensland University in Australia for Nd-Sm isotope analysis in order to conduct the isotopic analysis. Laser Ablation Coupled Plasma Mass Spectrometry was also used at Tasmania University in Australia to analyze four samples of apatite ores.<br /> <br /><strong>Results</strong><br />This research reveals the Esfordi apatite ores are derived from the sedimentary phosphorites. The O-H isotopic data and the Sr and Mn content of the first and second generations as well as the massive fine-grained apatites, display the role of evaporitic brines in their formation.<sup> </sup>According to the contents of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub>, as well as the variety in Nd isotopic ratios, the massive fine grained apatites, which forms the majority of the apatite mineralization (>95%), lacks a clear genetic relationship in terms of provenance with the rhyolitic, dioritic, and microdioritic host rocks. The similarity of <sup>143</sup>Nd/<sup>144</sup>Nd vs <sup>147</sup>Sm/<sup>144</sup>Nd and εNd vs P<sub>2</sub>O<sub>5</sub> in the first and second generations of apatites and the host rocks demonstrated that the recrystallization of apatite rocks occurred under the influence of magmatic and hydrothermal fluids originating from the felsic to intermediate subvolcanic rocks in the area, which resulted in an increase in εNd values.<br />The differences in age between the second-generation apatite and the paragenetically related monazites, using <sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb dating methods, besides dissolution evidence in different generations of apatites and monazites, Ti vs V, Al+Mn vs Ti+V and O-H isotopes of the magnetite-apatite ores, indicated the role of high temperature magmatic and hydrothermal fluids along with evaporitic brines in mineralization in different time spans. This processes lead to a diversity of mineralization and a polygenic origin for the Esfordi apatite-magnetite ore deposit.<br /> <br /><strong>Discussion</strong><br />The Esfordi ore deposit contains three different forms of apatites mineralization, including vein-type, fine grained massive and disseminated ores according to field observations. There were five generations of apatite, according to petrographic data. Numerous rare earth element minerals, including alanite, parisite-synchysite, bastenasite, and britolite, as well as two generations of monazite and one generation of limited xenotime, were identified in the Esfordi ore deposit according to investigations on the first and second generation apatites. Stable H-O and radiogenic Nd-Sm isotopic studies on the first and second generation apatites and massive fine grained apatite ores along with the similarity between εNd contents in apatite and phosphorites in Soltanieh Formation and phosphorite nodules of the Eastern European platform (Ediacarne and Lower Cambrian deposits) as well as Lower Cambrian sedimentary phosphate deposits in Siberia, Western Mongolia, Baltic, South Kazakhstan, South China, Australia, West Newfoundland, North Greenland and East Greenland confirms that the investigated apatites were formed from leaching of old or contemporaneous sedimentary phosphorites of Soltanieh Formation while magmatic and hydrothermal fluids originated from granitoid masses circulated in massive fine grained apatite ores. By the way, these crystalline apatites have been enriched in εNd content under the influence of magmatic and hydrothermal fluids originated from deep to sub-volcanic felsic and intermediate intrusions in this region.<br />Investigation using the radiometric dating methods (<sup>238</sup>U/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb) on the second-generation apatite and the paragenetically related monazites showed that these minerals were formed between 494-528 Ma and 514-556 Ma, respectively. Some monazites are older than apatites (approximately 28 Ma), which indicates that they were formed before apatite ore and it has been affected by hydrothermal fluids in the structure of apatite. The dating, for a limited number of monazites, indicates a time span between 23 to 33 and a time span of 104 to 153 Ma. The age differences between the apatite and monazite inclusions can be due, not only, to late alteration of deep to sub-volcanic bodies originated hydrothermal fluids, but also, to separation of U-Pb from this system or the formation of young monazites during orogenesis in different time spans. The presence of recrystalized apatite and magnetite, zoning and dissolution evidence in some monazites, dendritic texture in actinolite, ilmenite exsolutions and stable isotopes of magnetite and apatite ores indicates the mixing of magmatic and high temperature hydrothermal fluids with evaporatic brines enriched in REE, P, Ca ±Fe resulting in a diversity of processes involved in formation of the Esfordi ore deposit.<br /> <br /><strong>Acknowledgements</strong><br />The authors appreciate Shiraz University Research Council for support of this work. The Director General and personal of the Esfordi Mine Company are acknowledged for their assistance in the field works.https://econg.um.ac.ir/article_43159_0ec5228eade4e987d1cf40b81cc4647c.pdfFerdowsi University of MashhadJournal of Economic Geology2008-730614420221222The role of sulfidation of Fe-carbonate rocks in increasing gold contents at the Zarshuran deposit (northern Takab), Takab-Angouran metallogenic districtThe role of sulfidation of Fe-carbonate rocks in increasing gold contents at the Zarshuran deposit (northern Takab), Takab-Angouran metallogenic district891144276710.22067/econg.2022.75417.1042FASharareh HeshmatniaM.Sc., Department of Geology, Faculty of Science, Bu-Ali Sina University, Hamedan, IranEbrahim Tale FazelAssistant Professor, Department of Geology, Faculty of Science, Bu-Ali Sina University, Hamedan, Iran0000-0002-8776-1405Abbas OrojiPh.D. Student, Department of Geology, Faculty of Science, Bu-Ali Sina University, Hamedan, IranJournal Article20220219Iron and arsenic sulfides are considered as the most important gold hosts in the sediment-hosted disseminated invisible gold deposits. The Zarshuran gold deposit (155 tons Au with average grade of 2.63 g/t) is formed in the Lower Cambrian black shale and siltstone (Zarshuran unit) and Fe-rich carbonates (Chaldagh unit) host rocks. As-sulfide (e.g., realgar and orpiment) and arsenian pyrites are the most important host minerals of gold in this deposit. Based on EPMA data, pyrite with As content below the detection limit to 3.99 wt% occurs in six different types, respectively, Py0 (gold content of 0.01 ppm), Py1 (gold content of 0.02 ppm), Py2 (gold content of 0.03 ppm), Py3 (gold content of 0.02 ppm), Py4 (gold content of 0.04 ppm), and Py5 (gold content of 0.01 ppm). According to the evidences, gold can be present as participating in chemical bounded (Au<sup>+</sup> and Au<sup>+3</sup>) or nanoparticle inclusions (Au<sup>0</sup>). The weak geochemical correlation (R<sup>2</sup> = −0.6) between As and S elements in pyrites indicates that there is pyrite with a complex composition [Fe(S,As)<sub>2</sub>Au<sub>2</sub>S<sup>0</sup>], which As<sup>−</sup> has replaced S<sup>2−</sup>. Mineralogy and the abundance of Fe and S in the rock units suggest that gold mineralization in the Zarshuran deposit is well occurs in response to sulfidation process. Sulfidation occurs when H<sub>2</sub>S-rich ore-forming fluids react with Fe-bearing carbonate host rock to form pyrite, marcasite, and pyrrhotite minerals.<br /> <br /><strong>Introduction</strong><br />Sediment-hosted disseminated gold deposits with high gold grade (> 1000 g/t) are known to contain gold as participating in chemical bounded (Au<sup>+</sup> and Au<sup>+3</sup>) or nanoparticle inclusions (Au<sup>0</sup>)in the pyrite composition (Deditius et al., 2014). The Zarshuran gold deposit (155 t @ 2.63 g/t Au; Madan-Zamin Company, 2020) is situated 35 km north of Takab in the Takab-Angouran metallogenic district, NW Iran. According to Mehrabi et al. (1999) and Asadi et al. (2000), gold mineralization in the Zarshuran deposit is in many respects like the Carlin-style and Carlin-like gold deposits, respectively. Gold substitution has been reported to be below detection limit to a maximum of 0.64 wt.% and 3 wt.% in arsenian pyrite and arsenopyrite lattice, respectively (Voute et al., 2019). Here, we examine the relationship between geochemistry and textures of pyrite, with a view to constraining the mechanism of gold precipitation. We use electron probe microanalysis (EPMA) to study the composition of different pyrite types. The results show that distribution of ferrous iron (Fe<sup>2+</sup>) is controlled by the initial diagenesis of Fe-C-S systems.<br /> <br /><strong>Materials and methods</strong><br />During field studies, mineralization outcrops and their associated host rocks were identified. After preparing thin and thin-polished sections, mineralogical studies were carried out by transmitted and reflected polarizing ZIESS Axioplan2 microscope. To identify and classify different pyrite types and investigate the possibility of presence of gold and trace minerals, eight thin-polished sections were prepared, and carbon coated. This study was carried out by scanning electron microscope (SEM) with EVO MA15 model in the Central Laboratory of Kharazmi University (Tehran, Iran). Then, to achieve the chemical composition of different types of pyrite, 104 points were examined by EPMA (model JEOL JXA-8530F) in the Laboratory of Geo Forschungs Zentrum (GFZ). Spot analysis was performed with a voltage of 20 kV, electron beam current of 10 nA, X-ray diameter of 2 μ and radiation time of 5 to 20 seconds. The standard examples used to calibrate the various elements in this experiment were as follows: FeS<sub>2</sub> (for Fe and S), CoAsS (for As and Co), and free gold (for Au). The detection limits of the elements are Fe (300 ppm), As (200 ppm), S (300 ppm) and Au (200 ppm). To identify rare minerals such as mackinawite (Fe<sub>9</sub>S<sub>8</sub>), HR microscopic confocal Raman technique was used in the Central Laboratory of Shiraz University (Shiraz, Iran). The experiment was performed with an X50 laser, a wavelength of 785 nm with a power of 100 mw and a radiation time of 20s.<br /> <br /><strong>Results and discussion</strong><br />Based on SEM and optical-microscopic studies, six types of pyrite have been identified in the Zarshuran deposit. They are (1) framboidal pyrite (Py0) (avg. = 30 μm in diameter), (2) fine-grained disseminated pyrite (Py1) (< 20 μm in diameter), (3) coarse-grained euhedral pyrite (Py2) (avg. = 100 μm in diameter), (4) porous/sponge pyrite (Py3) (avg. = 300 μm in diameter), (5) colloform pyrite (Py4) (avg. = 550 μm in diameter), (6) vein pyrites (Py5) (avg. = 55 μm in thickness). Decalcification and sulfidation of host rocks are two important mechanisms in genesis of sediment-hosted gold deposits, and the importance of sulfidation depends on the reactivity of Fe<sup>2+</sup> and H<sub>2</sub>S rocks (Voute et al., 2019). The interaction of H<sub>2</sub>S-rich hydrothermal fluids with reactive iron originating from the host rocks (Cail and Cline, 2001) or through hydrothermal fluids added to the environment (Reich et al., 2005) which results in formation of Au(-As)-rich pyrite. Arsenic in pyrite can occur in various oxidation states that correspond to different crystallographic sites in the lattice and different substitution mechanisms. As<sup>−</sup> substitution for S<sup>2−</sup> is found in reducing conditions and often in sediment-hosted gold deposits; while As cations (As<sup>2+</sup>, As<sup>3+</sup>, As<sup>5+</sup>) replace Fe<sup>2+</sup> under oxidation conditions (Reich et al., 2005; Deditius et al., 2014). The diagram of arsenic versus sulfur in the Zarshuran deposit shows that the concentration of As in the formed pyrites is strongly related to the decrease in concentration of S. Based on this, it can be concluded that As replaces S in the pyrite structure and in the form of As<sup>−..</sup>; Moreover, As species are common in pyrites of gold deposits with sedimentary host rocks. In the Zarshuran deposit the occurrence of gold in As-Hg-Sb sulfides in late drusy quartz veins (Daliran et al., 2018) is more important than the presence of gold in various pyrites. Finally, all evidence suggest that gold mineralization in the Zarshuran deposit occurs well in response to sulfidation process of Fe-bearing carbonate rocks. The correlation between gold content and degree of sulfidation in the Zarshuran deposit indicates that sulfidation process is a much more important mechanism to gold precipitation relative to addition of pyrite (pyritization).Iron and arsenic sulfides are considered as the most important gold hosts in the sediment-hosted disseminated invisible gold deposits. The Zarshuran gold deposit (155 tons Au with average grade of 2.63 g/t) is formed in the Lower Cambrian black shale and siltstone (Zarshuran unit) and Fe-rich carbonates (Chaldagh unit) host rocks. As-sulfide (e.g., realgar and orpiment) and arsenian pyrites are the most important host minerals of gold in this deposit. Based on EPMA data, pyrite with As content below the detection limit to 3.99 wt% occurs in six different types, respectively, Py0 (gold content of 0.01 ppm), Py1 (gold content of 0.02 ppm), Py2 (gold content of 0.03 ppm), Py3 (gold content of 0.02 ppm), Py4 (gold content of 0.04 ppm), and Py5 (gold content of 0.01 ppm). According to the evidences, gold can be present as participating in chemical bounded (Au<sup>+</sup> and Au<sup>+3</sup>) or nanoparticle inclusions (Au<sup>0</sup>). The weak geochemical correlation (R<sup>2</sup> = −0.6) between As and S elements in pyrites indicates that there is pyrite with a complex composition [Fe(S,As)<sub>2</sub>Au<sub>2</sub>S<sup>0</sup>], which As<sup>−</sup> has replaced S<sup>2−</sup>. Mineralogy and the abundance of Fe and S in the rock units suggest that gold mineralization in the Zarshuran deposit is well occurs in response to sulfidation process. Sulfidation occurs when H<sub>2</sub>S-rich ore-forming fluids react with Fe-bearing carbonate host rock to form pyrite, marcasite, and pyrrhotite minerals.<br /> <br /><strong>Introduction</strong><br />Sediment-hosted disseminated gold deposits with high gold grade (> 1000 g/t) are known to contain gold as participating in chemical bounded (Au<sup>+</sup> and Au<sup>+3</sup>) or nanoparticle inclusions (Au<sup>0</sup>)in the pyrite composition (Deditius et al., 2014). The Zarshuran gold deposit (155 t @ 2.63 g/t Au; Madan-Zamin Company, 2020) is situated 35 km north of Takab in the Takab-Angouran metallogenic district, NW Iran. According to Mehrabi et al. (1999) and Asadi et al. (2000), gold mineralization in the Zarshuran deposit is in many respects like the Carlin-style and Carlin-like gold deposits, respectively. Gold substitution has been reported to be below detection limit to a maximum of 0.64 wt.% and 3 wt.% in arsenian pyrite and arsenopyrite lattice, respectively (Voute et al., 2019). Here, we examine the relationship between geochemistry and textures of pyrite, with a view to constraining the mechanism of gold precipitation. We use electron probe microanalysis (EPMA) to study the composition of different pyrite types. The results show that distribution of ferrous iron (Fe<sup>2+</sup>) is controlled by the initial diagenesis of Fe-C-S systems.<br /> <br /><strong>Materials and methods</strong><br />During field studies, mineralization outcrops and their associated host rocks were identified. After preparing thin and thin-polished sections, mineralogical studies were carried out by transmitted and reflected polarizing ZIESS Axioplan2 microscope. To identify and classify different pyrite types and investigate the possibility of presence of gold and trace minerals, eight thin-polished sections were prepared, and carbon coated. This study was carried out by scanning electron microscope (SEM) with EVO MA15 model in the Central Laboratory of Kharazmi University (Tehran, Iran). Then, to achieve the chemical composition of different types of pyrite, 104 points were examined by EPMA (model JEOL JXA-8530F) in the Laboratory of Geo Forschungs Zentrum (GFZ). Spot analysis was performed with a voltage of 20 kV, electron beam current of 10 nA, X-ray diameter of 2 μ and radiation time of 5 to 20 seconds. The standard examples used to calibrate the various elements in this experiment were as follows: FeS<sub>2</sub> (for Fe and S), CoAsS (for As and Co), and free gold (for Au). The detection limits of the elements are Fe (300 ppm), As (200 ppm), S (300 ppm) and Au (200 ppm). To identify rare minerals such as mackinawite (Fe<sub>9</sub>S<sub>8</sub>), HR microscopic confocal Raman technique was used in the Central Laboratory of Shiraz University (Shiraz, Iran). The experiment was performed with an X50 laser, a wavelength of 785 nm with a power of 100 mw and a radiation time of 20s.<br /> <br /><strong>Results and discussion</strong><br />Based on SEM and optical-microscopic studies, six types of pyrite have been identified in the Zarshuran deposit. They are (1) framboidal pyrite (Py0) (avg. = 30 μm in diameter), (2) fine-grained disseminated pyrite (Py1) (< 20 μm in diameter), (3) coarse-grained euhedral pyrite (Py2) (avg. = 100 μm in diameter), (4) porous/sponge pyrite (Py3) (avg. = 300 μm in diameter), (5) colloform pyrite (Py4) (avg. = 550 μm in diameter), (6) vein pyrites (Py5) (avg. = 55 μm in thickness). Decalcification and sulfidation of host rocks are two important mechanisms in genesis of sediment-hosted gold deposits, and the importance of sulfidation depends on the reactivity of Fe<sup>2+</sup> and H<sub>2</sub>S rocks (Voute et al., 2019). The interaction of H<sub>2</sub>S-rich hydrothermal fluids with reactive iron originating from the host rocks (Cail and Cline, 2001) or through hydrothermal fluids added to the environment (Reich et al., 2005) which results in formation of Au(-As)-rich pyrite. Arsenic in pyrite can occur in various oxidation states that correspond to different crystallographic sites in the lattice and different substitution mechanisms. As<sup>−</sup> substitution for S<sup>2−</sup> is found in reducing conditions and often in sediment-hosted gold deposits; while As cations (As<sup>2+</sup>, As<sup>3+</sup>, As<sup>5+</sup>) replace Fe<sup>2+</sup> under oxidation conditions (Reich et al., 2005; Deditius et al., 2014). The diagram of arsenic versus sulfur in the Zarshuran deposit shows that the concentration of As in the formed pyrites is strongly related to the decrease in concentration of S. Based on this, it can be concluded that As replaces S in the pyrite structure and in the form of As<sup>−..</sup>; Moreover, As species are common in pyrites of gold deposits with sedimentary host rocks. In the Zarshuran deposit the occurrence of gold in As-Hg-Sb sulfides in late drusy quartz veins (Daliran et al., 2018) is more important than the presence of gold in various pyrites. Finally, all evidence suggest that gold mineralization in the Zarshuran deposit occurs well in response to sulfidation process of Fe-bearing carbonate rocks. The correlation between gold content and degree of sulfidation in the Zarshuran deposit indicates that sulfidation process is a much more important mechanism to gold precipitation relative to addition of pyrite (pyritization).https://econg.um.ac.ir/article_42767_db71252afec605cc7cad0b5aa0be30c0.pdfFerdowsi University of MashhadJournal of Economic Geology2008-730614420221222Petrology and geochemistry of high temperature I type granitoids in Nusha region, Mazandaran provincePetrology and geochemistry of high temperature I type granitoids in Nusha region, Mazandaran province1151484340710.22067/econg.2023.79859.1060FAFarbood Hakimi BandboonPh.D. Student, Department of Geology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran0000-0001-6529-1804Saeed TakiAssistant Professor, Department of Geology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran0000-0002-2785-1089Mohamad ModarresniaAssistant Professor, Faculty of Basic Sciences, Rasht Branch, Islamic Azad University, Rasht, Iran0000-0002-8728-5881Journal Article20221209The study area is located about 30 km south of Ramsar, in the central Alborz zone. In addition to the Nusha granitoids (with an age of about 56 million years), the outcrops in this area, mainly include Paleozoic and Mesozoic rock units. Petrographically, the Nusha granitoids have diorite, syenite, monzonite, monzodiorite, granodiorite and quartz monzonite compositions. Moreover, mineralogically, feldspar is the principal mineral, and the texture superiority in them belongs to the granular type. In terms of magmatic series these rocks are metaluminous and range from high K calcalkaline to shoshonitic. The geochemical characteristics of the major and rare elements, as well as the petrographic ones indicate that these granitoids are I type granites, and at the same time they belong to high temperature ones based on the behavior of Ba, Ce and Y elements. Enrichment in LILE and LREE and low concentrations of heavy rare earth elements HREE and high field strength elements HFSE, together with Nb and Ti negative anomaly in the spider diagrams are signs of magmas related to the subduction zone. The high temperature nature and characteristics such as Y/Nb, Rb/Sr and Rb/Ba ratios show that the Nusha granitoids have the geochemical properties of both crustal and mantle origin materials with different ratios. Based on tectonomagmatic discrimination diagrams and trace element compositions, these granitoids belong to an active continental margin environment. The parental magma has originated from melting of an enriched mantle source and contaminated with continental crust during ascent.<br /> <br /><strong>Introduction</strong><br />The study area is part of the Alborz-Azerbaijan magmatic belt. Many of the intrusive masses present in this area are high potassium calc-alkaline to shoshonite and are of I type granitoids (Aghazadeh, 2009; Aghazadeh et al., 2013; Nabatian et al., 2014; Taki, 2011). In this research study, we seek to determine the nature of the granitoids of the Nusha region by using geochemical characteristics and determine their origin and tectonomagmic setting. Exposed rock units in the study area, in addition to intrusive igneous rocks, include sedimentary carbonate and detrital rocks belonging to the Mobarak (Carboniferous), Dorood (Lower Permian), Ruteh (Upper Permian), Nesen (Upper Permian), Elika (Lower-Middle Triassic), Shemshak (Upper Triassic-Lower Jurassic) Formations and Cretaceous sedimentary and volcanic rocks. In this area, the granitoid intrusive masses have northwest-southeast trends and have intruded during the Eocene (56±2 million years ago) (Axen et al., 2001). The outcrop of the Nusha granitoids starts from the western slope of Sehezar Valley and extends north-westward to the south-west of Nusha. The granitoid unit is separated into two masses by a dextral fault. The southern border of this mass is completely faulted. This has resulted that the Upper Paleozoic assemblage has been thrusted onto the granitoids. Its northern border is also mainly faulted. The only normal contact present in the western part with Lower and Middle Jurassic sediments.<br /> <br /><strong>Research method</strong><br />After sampling of intrusive rocks and petrographic studies of the study area, 10 samples of rocks related to intrusive masses were sent to the Zarazma company in Iran for chemical analysis and 7 samples were sent to the Actlabs company in Canada. In the laboratory of these companies, the ICP-OES method is used to measure the major elements and some minor elements, and the ICP-MS method is used to evaluate the abundance of rare and trace elements. In this research study, since iron is reported unseparated, the Irvine and Baragar method (1971) was used to calculate divalent and trivalent iron.<br /> <br /><strong>Results and discussion </strong><br />The granitoids of the study area are petrographically composed of diorite, syenite, monzonite monzodiorite, granodiorite and quartz monzonite. Mineralogically, feldspar is the principal mineral and the granular is superior texture. Based on several geochemical characteristics such as aluminum saturation [the molar (Al<sub>2</sub>O<sub>3</sub>/(CaO+Na<sub>2</sub>O+K<sub>2</sub>O)) or ASI] and agapiitic [A.I.=molar (Na+K)/Al] indices, Na<sub>2</sub>O/K<sub>2</sub>O ratio, range of SiO<sub>2</sub> content, Na<sub>2</sub>O weight percentages in acidic terms, average values of Na<sub>2</sub>O, Zr, Y, Ce and Rb/Sr, and diagrams of ANK-ACNK, normative corundum and P<sub>2</sub>O<sub>5</sub> versus Rb, (A/CNK-Fe2O3+FeO), Th-Rb and P<sub>2</sub>O<sub>5</sub>-SiO<sub>2</sub> as well as petrographic features like, petrographical composition ranges and the nature of enclaves and ferromagnesian minerals in the studied samples all confirm the I type nature of the Nusha granitoids. At the same time, the variations of Ba, Ce and Y elements in the Nusha granitoids are such that they first increase and then decrease with increase of silica content. Thus, they are high temperature I type granite and must have been originated from the melting of mafic rocks of crust or evolved mantle.<br />These rocks have high K calc-alkaline to shoshonite magmatic series nature. REE patterns of all the studied samples are parallel and similar (so they have a common origin) and relatively highly enriched (than primitive mantle) and have no Eu anomaly (due to the participation of feldspar in the magma during partial melting of the source rock or lack of differentiation of this mineral during the fractional crystallization of the parental magma). Like many other active continental margin calc-alkaline rocks, these rocks have negative slope on the LREE side and are flat on the HREE side. Enrichment in LILE and LREE and low concentration of HREE and HFSE, along with negative anomaly of Nb and Ti in the spider diagrams are indicators of magmas related to the subduction zone. The very distinct Nb-Ta trough in the arc systems spider diagrams is due to crustal contamination or retention of these elements in the source during partial melting. Positive Pb-K anomalies and overall enrichment of LILE are also indicators of crustal contamination. The extreme U and Th enrichment in the spider diagrams indicate addition of pelagic sediments or altered oceanic crust in the melting process.<br />The high Th/Ta and relatively low Nb/Th ratios indicate formation of magma in an arc environment, and the tectonomagmatic discrimination diagrams show continental arc one as well and according to their age, like many Cenozoic igneous rocks in the Alborz, Western Alborz-Azerbaijan and South Caucasus must have resulted from subduction of the Neotethys oceanic crust. In the Nb versus Rb/Zr diagram, the Nusha granitoids are in the range of normal to mature continental arcs. On the Sm/Yb-La/Sm and Rb-Sr diagrams, the continental crust is about 45 km and shows enriched mantle at the parental magma generation source. The wide range of variations in Y/Nb ratios indicates that the study area granitoids have the geochemical characteristics of both crustal and mantle origin materials. According to the Rb/Sr versus Rb/Ba diagram, the mantle to crust materials ratios are between 20 and 50%. The low Tb/Yb ratio and the multiple concentration of rare earth elements compared to the primitive mantle in the Nusha granitoids indicate a mantle source with the composition of spinel bearing peridotite without garnet origin.The study area is located about 30 km south of Ramsar, in the central Alborz zone. In addition to the Nusha granitoids (with an age of about 56 million years), the outcrops in this area, mainly include Paleozoic and Mesozoic rock units. Petrographically, the Nusha granitoids have diorite, syenite, monzonite, monzodiorite, granodiorite and quartz monzonite compositions. Moreover, mineralogically, feldspar is the principal mineral, and the texture superiority in them belongs to the granular type. In terms of magmatic series these rocks are metaluminous and range from high K calcalkaline to shoshonitic. The geochemical characteristics of the major and rare elements, as well as the petrographic ones indicate that these granitoids are I type granites, and at the same time they belong to high temperature ones based on the behavior of Ba, Ce and Y elements. Enrichment in LILE and LREE and low concentrations of heavy rare earth elements HREE and high field strength elements HFSE, together with Nb and Ti negative anomaly in the spider diagrams are signs of magmas related to the subduction zone. The high temperature nature and characteristics such as Y/Nb, Rb/Sr and Rb/Ba ratios show that the Nusha granitoids have the geochemical properties of both crustal and mantle origin materials with different ratios. Based on tectonomagmatic discrimination diagrams and trace element compositions, these granitoids belong to an active continental margin environment. The parental magma has originated from melting of an enriched mantle source and contaminated with continental crust during ascent.<br /> <br /><strong>Introduction</strong><br />The study area is part of the Alborz-Azerbaijan magmatic belt. Many of the intrusive masses present in this area are high potassium calc-alkaline to shoshonite and are of I type granitoids (Aghazadeh, 2009; Aghazadeh et al., 2013; Nabatian et al., 2014; Taki, 2011). In this research study, we seek to determine the nature of the granitoids of the Nusha region by using geochemical characteristics and determine their origin and tectonomagmic setting. Exposed rock units in the study area, in addition to intrusive igneous rocks, include sedimentary carbonate and detrital rocks belonging to the Mobarak (Carboniferous), Dorood (Lower Permian), Ruteh (Upper Permian), Nesen (Upper Permian), Elika (Lower-Middle Triassic), Shemshak (Upper Triassic-Lower Jurassic) Formations and Cretaceous sedimentary and volcanic rocks. In this area, the granitoid intrusive masses have northwest-southeast trends and have intruded during the Eocene (56±2 million years ago) (Axen et al., 2001). The outcrop of the Nusha granitoids starts from the western slope of Sehezar Valley and extends north-westward to the south-west of Nusha. The granitoid unit is separated into two masses by a dextral fault. The southern border of this mass is completely faulted. This has resulted that the Upper Paleozoic assemblage has been thrusted onto the granitoids. Its northern border is also mainly faulted. The only normal contact present in the western part with Lower and Middle Jurassic sediments.<br /> <br /><strong>Research method</strong><br />After sampling of intrusive rocks and petrographic studies of the study area, 10 samples of rocks related to intrusive masses were sent to the Zarazma company in Iran for chemical analysis and 7 samples were sent to the Actlabs company in Canada. In the laboratory of these companies, the ICP-OES method is used to measure the major elements and some minor elements, and the ICP-MS method is used to evaluate the abundance of rare and trace elements. In this research study, since iron is reported unseparated, the Irvine and Baragar method (1971) was used to calculate divalent and trivalent iron.<br /> <br /><strong>Results and discussion </strong><br />The granitoids of the study area are petrographically composed of diorite, syenite, monzonite monzodiorite, granodiorite and quartz monzonite. Mineralogically, feldspar is the principal mineral and the granular is superior texture. Based on several geochemical characteristics such as aluminum saturation [the molar (Al<sub>2</sub>O<sub>3</sub>/(CaO+Na<sub>2</sub>O+K<sub>2</sub>O)) or ASI] and agapiitic [A.I.=molar (Na+K)/Al] indices, Na<sub>2</sub>O/K<sub>2</sub>O ratio, range of SiO<sub>2</sub> content, Na<sub>2</sub>O weight percentages in acidic terms, average values of Na<sub>2</sub>O, Zr, Y, Ce and Rb/Sr, and diagrams of ANK-ACNK, normative corundum and P<sub>2</sub>O<sub>5</sub> versus Rb, (A/CNK-Fe2O3+FeO), Th-Rb and P<sub>2</sub>O<sub>5</sub>-SiO<sub>2</sub> as well as petrographic features like, petrographical composition ranges and the nature of enclaves and ferromagnesian minerals in the studied samples all confirm the I type nature of the Nusha granitoids. At the same time, the variations of Ba, Ce and Y elements in the Nusha granitoids are such that they first increase and then decrease with increase of silica content. Thus, they are high temperature I type granite and must have been originated from the melting of mafic rocks of crust or evolved mantle.<br />These rocks have high K calc-alkaline to shoshonite magmatic series nature. REE patterns of all the studied samples are parallel and similar (so they have a common origin) and relatively highly enriched (than primitive mantle) and have no Eu anomaly (due to the participation of feldspar in the magma during partial melting of the source rock or lack of differentiation of this mineral during the fractional crystallization of the parental magma). Like many other active continental margin calc-alkaline rocks, these rocks have negative slope on the LREE side and are flat on the HREE side. Enrichment in LILE and LREE and low concentration of HREE and HFSE, along with negative anomaly of Nb and Ti in the spider diagrams are indicators of magmas related to the subduction zone. The very distinct Nb-Ta trough in the arc systems spider diagrams is due to crustal contamination or retention of these elements in the source during partial melting. Positive Pb-K anomalies and overall enrichment of LILE are also indicators of crustal contamination. The extreme U and Th enrichment in the spider diagrams indicate addition of pelagic sediments or altered oceanic crust in the melting process.<br />The high Th/Ta and relatively low Nb/Th ratios indicate formation of magma in an arc environment, and the tectonomagmatic discrimination diagrams show continental arc one as well and according to their age, like many Cenozoic igneous rocks in the Alborz, Western Alborz-Azerbaijan and South Caucasus must have resulted from subduction of the Neotethys oceanic crust. In the Nb versus Rb/Zr diagram, the Nusha granitoids are in the range of normal to mature continental arcs. On the Sm/Yb-La/Sm and Rb-Sr diagrams, the continental crust is about 45 km and shows enriched mantle at the parental magma generation source. The wide range of variations in Y/Nb ratios indicates that the study area granitoids have the geochemical characteristics of both crustal and mantle origin materials. According to the Rb/Sr versus Rb/Ba diagram, the mantle to crust materials ratios are between 20 and 50%. The low Tb/Yb ratio and the multiple concentration of rare earth elements compared to the primitive mantle in the Nusha granitoids indicate a mantle source with the composition of spinel bearing peridotite without garnet origin.https://econg.um.ac.ir/article_43407_7d5517e0eb6b773e927e5dd17acd3238.pdfFerdowsi University of MashhadJournal of Economic Geology2008-730614420221222Determination of physicochemical conditions of causative intrusion in the Masjeddaghi Cu-Au porphyry-epithermal deposit: constraints on chemical composition of biotiteDetermination of physicochemical conditions of causative intrusion in the Masjeddaghi Cu-Au porphyry-epithermal deposit: constraints on chemical composition of biotite1491744343810.22067/econg.2023.79377.1056FAShohreh HassanpourAssociate Professor, Department of Geology, Payame Noor University, Tehran, Iran0000-0002-4779-267XZohreh RahnamaPh.D., Department of Earth Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran0000-0001-8460-5549Susan EbrahimiAssistant Professor, Department of Mineral Exploration, Faculty of Mining Engineering, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran0000-0002-1323-2391Journal Article20221106The Masjeddaghi porphyry-epithermal Cu-Au deposit has located in the western part of the Alborz-Azarbaijan zone; in the south margin of Lesser Caucasus. The Eocene porphyritic quartz diorite intrusion has intruded into the andesite volcanic rocks and formed the main host rock of Cu-Au mineralization. Hydrothermal alteration types consisted dominantly of potassic, phyllic, argillic, and propylitic, and local silicification around the veins. Electron microprobe studies indicated that the Masjeddaghi biotites has been located in the phlogopite field and fall into the field of re-equilibrated primary biotite. Moreover, these biotites indicate the tectonomagmatic setting and magma characteristics related to calk-alkaline granitoids which were originated from mantle sources. The temperature of biotites from Masjeddaghi indicated a range between 417 ºC -641ºC. The conditions of oxygen fugacity in the magmatic biotites are in the range of hematite-magnetite (HM) and nickel-nickel oxide (NNO), which indicate high oxygen fugacity of the magma in this ore deposit. In the Masjeddaghi biotites, there is no linear/parallel trend between halogen fugacity,d log (ƒH<sub>2</sub>O/ƒHF), log (ƒH<sub>2</sub>O/ƒHCl) and log (ƒHF/ƒHCl) lines. Therefore, it is possible that biotites have not formed under the same conditions and were in equilibrium in a wide range of temperatures and compositions with hydrothermal fluids.<br /> <br /><strong>Introduction</strong><br />The Masjeddaghi porphyry-epithermal Cu-Au deposit is located in the margin of the Arasbaran Belt, in the Alborz-Azarbaijan structural zone in the NW of Iran. The host rock of mineralization is diorite porphyry, which has been intruded into the andesitic volcanic rocks. Paleocene andesitic and lavas crop out in the southeastern and eastern parts of the area. Paleocene andesitic rocks, including lavas, dikes, pyroclastic, and epiclastic rocks overlying on the Permian-Triassic rocks. The mineralized host rocks composed of the dioritic stocks that have formed the main mass of Masjeddaghi and is dated at 54 Ma (Hassanpour and Alirezaei, 2017). The Middle Eocene diorite porphyry includes granular to porphyry texture and with some dikes extending with east - west trend in the northern and eastern parts of the Masjeddaghi district. It is called the main Masjeddaghi Porphyry. This magmatic sequence and associated Cu-Mo-Au mineralization and alterations have been dated at about 54 Ma (Hassanpour and Alirezaei, 2017).<br />The hydrothermal alteration types consist dominantly of potassic, phyllic, argillic, propylitic and locally of silicification around the veins (Ebrahimi et al., 2021; Hassanpour and Alirezaei, 2017; Ebrahimi et al., 2017). The chemical composition of biotite is sensitive to chemical and physical factors which are related to magmatic and hydrothermal activities such as halogens (e.g., F and Cl) and metals compositions, elemental distributions, water concentrations, temperature and pressure. Geological and geochemical features of porphyry-epithermal Cu-Au Masjeddaghi ore deposit have been studied in detail by Ebrahimi et al., 2021; Hassanpour and Alirezaei, 2017; Ebrahimi et al., 2017. In this research study we attempt to characterize the physicochemical attributes of causative magma in the Masjeddaghi porphyry ore deposit, by using biotite mineral chemistry.<br /> <br /><strong>Material and methods</strong><br />All samples are from the least altered diorite intrusion and from potassic alteration zone were collected from the surface and drill cores (up to 700m) in the Masjeddaghi area. More than 150 thin and thin-polished sections were studied and subsequently, four samples were selected for EMPA (Electron Micro-Probe Analyses) analysis. Twenty-six points of biotite grains were selected and analyzed by using a Cameca SX-100 instrument in czechoslovakia (central European laboratory). The analyses were conducted with 15 kV accelerating voltage and 10 nA beam current. The results were processed by using the MICA<sup>+</sup> software. <br />(Yavuz, 2003).<br /> <br /><strong>Results</strong><br />On the basis of petrographic studies, diorite porphyry consists of plagioclase, hornblende, biotite and quartz minerals. Biotite phynocrysts are within fine grained matrix and biotite chemistry can be used as an important indicator to evaluate magma crystallization condition (Selby and Nesbitt, 2000). Three kinds of biotites have been recognized in the samples: magmatic, re-equilibrated and hydrothermal type. On the basis of Mg, (Mn+Fe<sup>2+</sup>) vs. (Al<sup>VI</sup>+Fe<sup>3+</sup>+Ti), Fe<sup>2+</sup>/(Fe<sup>2+</sup>+Mg) vs. Al<sup>IV</sup><sup> and</sup> (Mg-Li) vs. Fe<sub>T</sub> + Mn + Ti-Al<sup>VI</sup>) diagrams all plotted in the phlogopite field. The samples in the MgO-10×(TiO<sub>2</sub>) -(FeO+MnO) diagram fall into the field of re-equilibrated primary biotite (Nachit et al., 2005). The temperature of biotites in diorite samples varies between 417-522 ºC (Bean, 1974) and 516-641 ºC (Henry et al., 2005).<br /> <br /><strong>Discussion</strong><br />Biotites in the Masjeddaghi Cu-Au porphyries are mainly Plogopite and are dominantly from the samples taken from potassic alteration zone and situated in the re-equilibrated biotites field. The ore deposit tectonically is related to the calk-alkaline magma. Generally, biotites are calk-alkaline, with high content of MgO and reducedAl<sub>2</sub>O<sub>3</sub> which refers to Al and Mg replacements in an ochtahedral setting. This ore deposit has a Magnesium rich calk-alkaline magma. The oxygen fugacity of biotites is in the range of hematite-magnetite (HM) and nickel-nickel oxide (NNO), which indicates high oxygen fugacity of the magma in this ore deposit. In the Masjeddaghi biotites, there is no linear/parallel trend between halogen fugacity and log (ƒH<sub>2</sub>O/ƒHF), log (ƒH<sub>2</sub>O/ƒHCl) and log (ƒHF/ƒHCl) lines. Therefore, it is possible that biotites have not formed under the same conditions and were in equilibrium in a wide range of temperatures and compositions with hydrothermal fluids. Halogen ratios of the Masjeddaghi biotites with other porphyry deposits in the world show similarity with Bingham and Santa Rita ore deposits. Moreover, these biotites indicate the calk-alkaline signature and mantle source for the magma.The Masjeddaghi porphyry-epithermal Cu-Au deposit has located in the western part of the Alborz-Azarbaijan zone; in the south margin of Lesser Caucasus. The Eocene porphyritic quartz diorite intrusion has intruded into the andesite volcanic rocks and formed the main host rock of Cu-Au mineralization. Hydrothermal alteration types consisted dominantly of potassic, phyllic, argillic, and propylitic, and local silicification around the veins. Electron microprobe studies indicated that the Masjeddaghi biotites has been located in the phlogopite field and fall into the field of re-equilibrated primary biotite. Moreover, these biotites indicate the tectonomagmatic setting and magma characteristics related to calk-alkaline granitoids which were originated from mantle sources. The temperature of biotites from Masjeddaghi indicated a range between 417 ºC -641ºC. The conditions of oxygen fugacity in the magmatic biotites are in the range of hematite-magnetite (HM) and nickel-nickel oxide (NNO), which indicate high oxygen fugacity of the magma in this ore deposit. In the Masjeddaghi biotites, there is no linear/parallel trend between halogen fugacity,d log (ƒH<sub>2</sub>O/ƒHF), log (ƒH<sub>2</sub>O/ƒHCl) and log (ƒHF/ƒHCl) lines. Therefore, it is possible that biotites have not formed under the same conditions and were in equilibrium in a wide range of temperatures and compositions with hydrothermal fluids.<br /> <br /><strong>Introduction</strong><br />The Masjeddaghi porphyry-epithermal Cu-Au deposit is located in the margin of the Arasbaran Belt, in the Alborz-Azarbaijan structural zone in the NW of Iran. The host rock of mineralization is diorite porphyry, which has been intruded into the andesitic volcanic rocks. Paleocene andesitic and lavas crop out in the southeastern and eastern parts of the area. Paleocene andesitic rocks, including lavas, dikes, pyroclastic, and epiclastic rocks overlying on the Permian-Triassic rocks. The mineralized host rocks composed of the dioritic stocks that have formed the main mass of Masjeddaghi and is dated at 54 Ma (Hassanpour and Alirezaei, 2017). The Middle Eocene diorite porphyry includes granular to porphyry texture and with some dikes extending with east - west trend in the northern and eastern parts of the Masjeddaghi district. It is called the main Masjeddaghi Porphyry. This magmatic sequence and associated Cu-Mo-Au mineralization and alterations have been dated at about 54 Ma (Hassanpour and Alirezaei, 2017).<br />The hydrothermal alteration types consist dominantly of potassic, phyllic, argillic, propylitic and locally of silicification around the veins (Ebrahimi et al., 2021; Hassanpour and Alirezaei, 2017; Ebrahimi et al., 2017). The chemical composition of biotite is sensitive to chemical and physical factors which are related to magmatic and hydrothermal activities such as halogens (e.g., F and Cl) and metals compositions, elemental distributions, water concentrations, temperature and pressure. Geological and geochemical features of porphyry-epithermal Cu-Au Masjeddaghi ore deposit have been studied in detail by Ebrahimi et al., 2021; Hassanpour and Alirezaei, 2017; Ebrahimi et al., 2017. In this research study we attempt to characterize the physicochemical attributes of causative magma in the Masjeddaghi porphyry ore deposit, by using biotite mineral chemistry.<br /> <br /><strong>Material and methods</strong><br />All samples are from the least altered diorite intrusion and from potassic alteration zone were collected from the surface and drill cores (up to 700m) in the Masjeddaghi area. More than 150 thin and thin-polished sections were studied and subsequently, four samples were selected for EMPA (Electron Micro-Probe Analyses) analysis. Twenty-six points of biotite grains were selected and analyzed by using a Cameca SX-100 instrument in czechoslovakia (central European laboratory). The analyses were conducted with 15 kV accelerating voltage and 10 nA beam current. The results were processed by using the MICA<sup>+</sup> software. <br />(Yavuz, 2003).<br /> <br /><strong>Results</strong><br />On the basis of petrographic studies, diorite porphyry consists of plagioclase, hornblende, biotite and quartz minerals. Biotite phynocrysts are within fine grained matrix and biotite chemistry can be used as an important indicator to evaluate magma crystallization condition (Selby and Nesbitt, 2000). Three kinds of biotites have been recognized in the samples: magmatic, re-equilibrated and hydrothermal type. On the basis of Mg, (Mn+Fe<sup>2+</sup>) vs. (Al<sup>VI</sup>+Fe<sup>3+</sup>+Ti), Fe<sup>2+</sup>/(Fe<sup>2+</sup>+Mg) vs. Al<sup>IV</sup><sup> and</sup> (Mg-Li) vs. Fe<sub>T</sub> + Mn + Ti-Al<sup>VI</sup>) diagrams all plotted in the phlogopite field. The samples in the MgO-10×(TiO<sub>2</sub>) -(FeO+MnO) diagram fall into the field of re-equilibrated primary biotite (Nachit et al., 2005). The temperature of biotites in diorite samples varies between 417-522 ºC (Bean, 1974) and 516-641 ºC (Henry et al., 2005).<br /> <br /><strong>Discussion</strong><br />Biotites in the Masjeddaghi Cu-Au porphyries are mainly Plogopite and are dominantly from the samples taken from potassic alteration zone and situated in the re-equilibrated biotites field. The ore deposit tectonically is related to the calk-alkaline magma. Generally, biotites are calk-alkaline, with high content of MgO and reducedAl<sub>2</sub>O<sub>3</sub> which refers to Al and Mg replacements in an ochtahedral setting. This ore deposit has a Magnesium rich calk-alkaline magma. The oxygen fugacity of biotites is in the range of hematite-magnetite (HM) and nickel-nickel oxide (NNO), which indicates high oxygen fugacity of the magma in this ore deposit. In the Masjeddaghi biotites, there is no linear/parallel trend between halogen fugacity and log (ƒH<sub>2</sub>O/ƒHF), log (ƒH<sub>2</sub>O/ƒHCl) and log (ƒHF/ƒHCl) lines. Therefore, it is possible that biotites have not formed under the same conditions and were in equilibrium in a wide range of temperatures and compositions with hydrothermal fluids. Halogen ratios of the Masjeddaghi biotites with other porphyry deposits in the world show similarity with Bingham and Santa Rita ore deposits. Moreover, these biotites indicate the calk-alkaline signature and mantle source for the magma.https://econg.um.ac.ir/article_43438_abfb77d5a350c407b1f3479902a46fa3.pdfFerdowsi University of MashhadJournal of Economic Geology2008-730614420221222Mineral chemistry, Thermobarometry, Geochemistry and tectonic setting of Tertiary andesitic lavas in the Shourestan area (west of Sarbisheh), Southern KhorasanMineral chemistry, Thermobarometry, Geochemistry and tectonic setting of Tertiary andesitic lavas in the Shourestan area (west of Sarbisheh), Southern Khorasan1752134364910.22067/econg.2023.80746.1065FASeyyed Saeid MohammadiProfessor, Department of Geology, Faculty of Science, University of Birjand, Birjand, Iran0000-0003-1018-2955Sun-Lin ChungProfessor, Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan; Professor, Department of Geosciences, National Taiwan University, Taipei, Taiwan0000-0002-5362-4496Malihe NakhaeiAssistant Professor, Department of Mining Engineering, Faculty of Civil, Mining and Chemistry, Birjand University of Technology, Birjand, Iran0000-0003-1371-7767Arash IslamipanahM.Sc., Department of Geology, Faculty of Science, University of Birjand, Birjand, IranJournal Article20230123In the Shourestan area, 14 kilometers west of Sarbisheh city, in South Khorasan province, volcanic rocks with pyroxene-andesite composition belonging to Eocene-Oligocene are exposed. The constituent minerals of these rocks include plagioclase and pyroxene. The composition of plagioclases have range from Ab<sub>32</sub>, An<sub>68</sub> to Ab<sub>58</sub>, An<sub>42</sub> and are andesine-labradorite type. Clinopyroxene and orthopyroxene have diopside-like augite and enstatite composition, respectively. The crystallization temperature for clinopyroxene and orthopyroxene were about 1175 and 1200 °C respectively and the pressure (for both types) was 2 to 5 kb. The geochemical data of whole rocks show that the andesitic lavas of Shourestan have high potassium calc-alkaline nature and the amount of Mg# in them varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. These rocks show signs of differentiation including LREE/HREE ((La/Yb)<sub>N</sub>) between 9.95 to 12.42, LREE/MREE ((La/Sm)<sub>N</sub>) between 3.53 to 6.55, MREE/HREE ((Sm/Yb)<sub>N</sub>) between 1.89 to 2.99. High ratios of Zr/Nb (9.81-22.10), Th/Nb (0.68-1.79), Th/Ta (7.29-24), and Nb/Ta (9.69-15.66) along with the pattern of LIL elements, support the possibility of different degrees of crustal contamination-assimilation of magma during its ascent to the earth's surface. The studied rocks have low ratios of Ce/Y (2.44-3.48), (Tb/Yb)<sub>N</sub> (1.17-1.39), Sm/Yb (1.92-2.78), and relatively flat MREE-HREE pattern that confirms the melting of the subcontinental lithospheric mantle in the field of spinel stability and at a depth of fewer than 75 kilometers.<br /> <br /><strong>Introduction</strong><br />Calc-alkaline magmas are commonly active in convergent plate margins and their petrogenesis is crucial for understanding the origin and evolution of the andesitic continental crust. The generation of calc-alkaline magmatic series in oceanic subduction zones has been primarily attributed to the partial melting of enriched mantle sources with the involvement of fluids and/or melts from the subducted oceanic lithosphere or the partial melting of metasomatized sub-continental lithospheric mantle that had been modified by previous plate subduction (Cheng et al., 2020). Andesite is the second most common volcanic rock type on earth and provides abundant information about the interaction between the mantle and crust in the subduction zones. However, the petrogenesis of subduction-related andesite is being debated, since andesite can form via different processes, such as (1) magma mixing between felsic and mafic/ultramafic melt; (2) fractional melting or assimilation fractional crystallization from basaltic composition; (3) partial melting of the hydrated mantle wedge peridotite (Li et al., 2013). Experimental investigation demonstrates that plagioclase and clinopyroxene composition can be used to estimate the P-T condition of volcanic rock crystallization. The chemical composition of pyroxene in volcanic rocks shows the nature of the host lava and is used to determine the magmatic series, tectonic environment, and origin of the igneous rock (Putirka, 2008).<br />In the Shourestan area, 14 kilometers west of Sarbisheh city in South Khorasan province, Eocene-Oligocene volcanic rocks with pyroxene-andesite composition are exposed. Based on the results of previous studies, the Tertiary lavas in the Sarbisheh area have calc-alkaline nature and are related to active continental margins (Mohammadi and Nakhaei, 2022). In this research, the chemical composition of minerals has been used to determine the nature of magma, tectonic setting and evaluation of the temperature and pressure conditions for the crystallization of andesitic lavas. Also, by using the geochemical data of the whole rock, the geochemical characteristics, tectonic setting, and origin of these rocks have been investigated.<br /><strong>Materials and Methods</strong><br />Microprobe analysis of pyroxene and plagioclase minerals was done at the institute of Earth sciences in Academia Sinica, Taipei, Taiwan. A scanning electron microscope (JEOL SEM JSM-6360LV) was used to observe micro-scale texture. Identification of mineral phases was done by an energy dispersive spectrometer equipped with SEM, under the beam conditions of 15 kV, and 0.2 nA for the acceleration voltage, and beam current, respectively. Mineralogical investigation was carried out by an electron probe micro analyzer (JEOL EPMA JXA-8900R) equipped with four wave-length dispersive spectrometers. For geochemical investigations, 8 samples were analyzed in Acme laboratory in Canada by ICP method (for major elements) and ICP-MS (for trace and rare earth elements) and 3 samples in ZarAzma Company (Tehran, Iran) by alkaline melting method (for major elements) and ICP-MS (for trace and rare earth elements).<br /> <br /><strong>Results</strong><br />The constituent minerals of these rocks include plagioclase and pyroxene. The composition of plagioclases changes from Ab<sub>32</sub> An<sub>68</sub> to Ab<sub>58</sub> An<sub>42</sub> and are andesine-labradorite type. Clinopyroxene and orthopyroxene have diopside-like augite and enstatite composition, respectively. The crystallization temperature for clinopyroxene and orthopyroxene were about 1175 and 1200 °C respectively and the pressure was 2 to 5 kb. The geochemical data of whole rocks show that the andesitic lavas of Shourestan have high potassium calc-alkaline nature and the amount of Mg# in them varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. These rocks show signs of differentiation including LREE/HREE ((La/Yb)<sub>N</sub>) from 9.95 to 12.42, LREE/MREE ((La/Sm)<sub>N</sub>) from 3.53 to 6.55, MREE/HREE ((Sm/Yb)<sub>N</sub>) from 1.89 to 2.99. High ratios of Zr/Nb (9.81-22.10), Th/Nb (0.68-1.79), Th/Ta (7.29-24), and Nb/Ta (9.69-15.66) along with the pattern of LIL elements, support the possibility of different degrees of crustal contamination-assimilation of magma during its ascent to the earth's surface. The studied rocks have low ratios of Ce/Y (2.44-3.48), (Tb/Yb)<sub>N</sub> (1.17-1.39), Sm/Yb (1.92-2.78), and relatively flat MREE-HREE pattern that confirms the melting of the subcontinental lithospheric mantle in the field of spinel stability and at a depth of fewer than 75 kilometers.<br /> <br /><strong>Discussion</strong><br />Petrographic studies show that the volcanic rocks of the Shourestan area have pyroxene-andesite composition. After plagioclase, pyroxene is the most abundant mineral in Shourestan andesitic lavas. The values of Mg# in clinopyroxene and orthopyroxene are 72-78 and 71-77, respectively. High values of Mg# in pyroxenes indicate the role of mantle components in the magma source. Based on the chemistry of clinopyroxene, andesitic lavas of the Shourestan area have sub-alkaline nature and are located in the field of volcanic arc basalts. The anorthite content of plagioclases in andesitic lavas of Shourestan (52-66%) and Mg# of clinopyroxenes (72-78) indicate the low amount of water during the formation of these minerals from primary magma. The formation temperature of investigated clinopyroxene and orthopyroxene was about 1200 °C and the calculated pressure at the time of their crystallization was determined 2 to 5 kb. The volcanic rocks of Shourestan were located in the range of andesite with high potassium calc-alkaline nature. The amount of Mg# in these rocks varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. The presence of negative Ti, Nb, and P anomalies in trace element diagrams of the studied samples, confirms the formation of these rocks in subduction zones. Relatively low values of Yb<sub>N</sub> in the samples (8.42 to 10.05 ppm) indicate low amounts of garnet in the source. Geochemical characteristics of the Shourestan andesitic rocks such as K<sub>2</sub>O/P<sub>2</sub>O<sub>5</sub> ratio >2 along with high Al<sub>2</sub>O<sub>3</sub> and Th enrichment can be related to crustal contamination or magma formation from a heterogeneous metasomatized mantle source. In addition, Th/Ta (7.29-24), Nb/Ta (9.69-15.66) and Ta/La (0.02-0.05) ratios also indicate different degrees of the crustal contamination-assimilation of magma during the ascent to the surface of the earth. Based on various element ratios, the Shourestan andesitic lavas originated from a subcontinental lithospheric mantle that evolved during subduction. The geochemical characteristics of the investigated rocks, such as the high ratio of LILE/HFSE and LREE/HREE, as well as the different tectonic discriminant diagrams, confirm active continental margin tectonic setting.In the Shourestan area, 14 kilometers west of Sarbisheh city, in South Khorasan province, volcanic rocks with pyroxene-andesite composition belonging to Eocene-Oligocene are exposed. The constituent minerals of these rocks include plagioclase and pyroxene. The composition of plagioclases have range from Ab<sub>32</sub>, An<sub>68</sub> to Ab<sub>58</sub>, An<sub>42</sub> and are andesine-labradorite type. Clinopyroxene and orthopyroxene have diopside-like augite and enstatite composition, respectively. The crystallization temperature for clinopyroxene and orthopyroxene were about 1175 and 1200 °C respectively and the pressure (for both types) was 2 to 5 kb. The geochemical data of whole rocks show that the andesitic lavas of Shourestan have high potassium calc-alkaline nature and the amount of Mg# in them varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. These rocks show signs of differentiation including LREE/HREE ((La/Yb)<sub>N</sub>) between 9.95 to 12.42, LREE/MREE ((La/Sm)<sub>N</sub>) between 3.53 to 6.55, MREE/HREE ((Sm/Yb)<sub>N</sub>) between 1.89 to 2.99. High ratios of Zr/Nb (9.81-22.10), Th/Nb (0.68-1.79), Th/Ta (7.29-24), and Nb/Ta (9.69-15.66) along with the pattern of LIL elements, support the possibility of different degrees of crustal contamination-assimilation of magma during its ascent to the earth's surface. The studied rocks have low ratios of Ce/Y (2.44-3.48), (Tb/Yb)<sub>N</sub> (1.17-1.39), Sm/Yb (1.92-2.78), and relatively flat MREE-HREE pattern that confirms the melting of the subcontinental lithospheric mantle in the field of spinel stability and at a depth of fewer than 75 kilometers.<br /> <br /><strong>Introduction</strong><br />Calc-alkaline magmas are commonly active in convergent plate margins and their petrogenesis is crucial for understanding the origin and evolution of the andesitic continental crust. The generation of calc-alkaline magmatic series in oceanic subduction zones has been primarily attributed to the partial melting of enriched mantle sources with the involvement of fluids and/or melts from the subducted oceanic lithosphere or the partial melting of metasomatized sub-continental lithospheric mantle that had been modified by previous plate subduction (Cheng et al., 2020). Andesite is the second most common volcanic rock type on earth and provides abundant information about the interaction between the mantle and crust in the subduction zones. However, the petrogenesis of subduction-related andesite is being debated, since andesite can form via different processes, such as (1) magma mixing between felsic and mafic/ultramafic melt; (2) fractional melting or assimilation fractional crystallization from basaltic composition; (3) partial melting of the hydrated mantle wedge peridotite (Li et al., 2013). Experimental investigation demonstrates that plagioclase and clinopyroxene composition can be used to estimate the P-T condition of volcanic rock crystallization. The chemical composition of pyroxene in volcanic rocks shows the nature of the host lava and is used to determine the magmatic series, tectonic environment, and origin of the igneous rock (Putirka, 2008).<br />In the Shourestan area, 14 kilometers west of Sarbisheh city in South Khorasan province, Eocene-Oligocene volcanic rocks with pyroxene-andesite composition are exposed. Based on the results of previous studies, the Tertiary lavas in the Sarbisheh area have calc-alkaline nature and are related to active continental margins (Mohammadi and Nakhaei, 2022). In this research, the chemical composition of minerals has been used to determine the nature of magma, tectonic setting and evaluation of the temperature and pressure conditions for the crystallization of andesitic lavas. Also, by using the geochemical data of the whole rock, the geochemical characteristics, tectonic setting, and origin of these rocks have been investigated.<br /><strong>Materials and Methods</strong><br />Microprobe analysis of pyroxene and plagioclase minerals was done at the institute of Earth sciences in Academia Sinica, Taipei, Taiwan. A scanning electron microscope (JEOL SEM JSM-6360LV) was used to observe micro-scale texture. Identification of mineral phases was done by an energy dispersive spectrometer equipped with SEM, under the beam conditions of 15 kV, and 0.2 nA for the acceleration voltage, and beam current, respectively. Mineralogical investigation was carried out by an electron probe micro analyzer (JEOL EPMA JXA-8900R) equipped with four wave-length dispersive spectrometers. For geochemical investigations, 8 samples were analyzed in Acme laboratory in Canada by ICP method (for major elements) and ICP-MS (for trace and rare earth elements) and 3 samples in ZarAzma Company (Tehran, Iran) by alkaline melting method (for major elements) and ICP-MS (for trace and rare earth elements).<br /> <br /><strong>Results</strong><br />The constituent minerals of these rocks include plagioclase and pyroxene. The composition of plagioclases changes from Ab<sub>32</sub> An<sub>68</sub> to Ab<sub>58</sub> An<sub>42</sub> and are andesine-labradorite type. Clinopyroxene and orthopyroxene have diopside-like augite and enstatite composition, respectively. The crystallization temperature for clinopyroxene and orthopyroxene were about 1175 and 1200 °C respectively and the pressure was 2 to 5 kb. The geochemical data of whole rocks show that the andesitic lavas of Shourestan have high potassium calc-alkaline nature and the amount of Mg# in them varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. These rocks show signs of differentiation including LREE/HREE ((La/Yb)<sub>N</sub>) from 9.95 to 12.42, LREE/MREE ((La/Sm)<sub>N</sub>) from 3.53 to 6.55, MREE/HREE ((Sm/Yb)<sub>N</sub>) from 1.89 to 2.99. High ratios of Zr/Nb (9.81-22.10), Th/Nb (0.68-1.79), Th/Ta (7.29-24), and Nb/Ta (9.69-15.66) along with the pattern of LIL elements, support the possibility of different degrees of crustal contamination-assimilation of magma during its ascent to the earth's surface. The studied rocks have low ratios of Ce/Y (2.44-3.48), (Tb/Yb)<sub>N</sub> (1.17-1.39), Sm/Yb (1.92-2.78), and relatively flat MREE-HREE pattern that confirms the melting of the subcontinental lithospheric mantle in the field of spinel stability and at a depth of fewer than 75 kilometers.<br /> <br /><strong>Discussion</strong><br />Petrographic studies show that the volcanic rocks of the Shourestan area have pyroxene-andesite composition. After plagioclase, pyroxene is the most abundant mineral in Shourestan andesitic lavas. The values of Mg# in clinopyroxene and orthopyroxene are 72-78 and 71-77, respectively. High values of Mg# in pyroxenes indicate the role of mantle components in the magma source. Based on the chemistry of clinopyroxene, andesitic lavas of the Shourestan area have sub-alkaline nature and are located in the field of volcanic arc basalts. The anorthite content of plagioclases in andesitic lavas of Shourestan (52-66%) and Mg# of clinopyroxenes (72-78) indicate the low amount of water during the formation of these minerals from primary magma. The formation temperature of investigated clinopyroxene and orthopyroxene was about 1200 °C and the calculated pressure at the time of their crystallization was determined 2 to 5 kb. The volcanic rocks of Shourestan were located in the range of andesite with high potassium calc-alkaline nature. The amount of Mg# in these rocks varies from 40.97 to 60.97, which indicates the role of mantle components in their formation. The presence of negative Ti, Nb, and P anomalies in trace element diagrams of the studied samples, confirms the formation of these rocks in subduction zones. Relatively low values of Yb<sub>N</sub> in the samples (8.42 to 10.05 ppm) indicate low amounts of garnet in the source. Geochemical characteristics of the Shourestan andesitic rocks such as K<sub>2</sub>O/P<sub>2</sub>O<sub>5</sub> ratio >2 along with high Al<sub>2</sub>O<sub>3</sub> and Th enrichment can be related to crustal contamination or magma formation from a heterogeneous metasomatized mantle source. In addition, Th/Ta (7.29-24), Nb/Ta (9.69-15.66) and Ta/La (0.02-0.05) ratios also indicate different degrees of the crustal contamination-assimilation of magma during the ascent to the surface of the earth. Based on various element ratios, the Shourestan andesitic lavas originated from a subcontinental lithospheric mantle that evolved during subduction. The geochemical characteristics of the investigated rocks, such as the high ratio of LILE/HFSE and LREE/HREE, as well as the different tectonic discriminant diagrams, confirm active continental margin tectonic setting.https://econg.um.ac.ir/article_43649_9803e26d116626ca5391f455cf2ecfb4.pdf