The major and trace element content in hydrothermal pyrite was analyzed, as the most abundant sulfide mineral associated with quartz veins, to reveal ore-forming processes in the Mamuniyeh deposite, central Urumieh-Dokhtar Magmatic Arc. The Co–Ni–As signatures in pyrite is closely linked to the genetic model and geological processes of the deposits. Cobalt, nickel, and arsenic data from the Mamuniyeh pyrites indicate a predominance towards the cobalt region, consistent with hydrothermal and epithermal magmatic ore deposits. Data shows fluid evolution from primary magmatic water to later meteoric waters, with magmatic water dominating the early stages and meteoric waters added later. The reduction in arsenic content in pyrites, due to the mixing of the ore-forming fluid with oxygen-rich meteoric waters, leads to an increase in arsenic concentration in the system. Under oxidizing conditions, arsenic with an oxidation state of As¹⁻ substitutes for sulfur, and in combination with Fe²⁺, it incorporates into the pyrite structure as As³⁺ and As⁵⁺. Vertical zoning of elements in epithermal systems suggests that most Mamuniyeh samples exhibit characteristics of the middle part of the mineralization system and somewhat deeper zones. Copper contents in the Mamuniyeh pyrites, up to 1.1 wt.%, indicate pyrite can act as a significant copper absorber. Nickel contents in the Mamuniyeh pyrites (up to 0.34 wt.%) are higher than continental crust nickel, indicating a mantle origin of them. Variations in Ni/Co ratios in pyrite for classifying hydrothermal deposit origins show a dominant range between 1 and 10, consistent with magmatic-hydrothermal origin, likely formed by fluid-rock interactions between magmatic-hydrothermal fluids and volcanic host rocks. Introduction Pyrite as the most common sulfide mineral in the Earth's crust, widely exists in magmatic-hydrothermal systems (Reich et al., 2013; Deditius et al., 2014; Dubosq et al., 2018). The rare element content in pyrite can reflect the conditions of the mineralizing fluid, such as temperature, pH, and oxygen fugacity, as well as the mechanisms of element formation and deposition during fluid evolution and ore formation (Agangi et al., 2014; Sykora et al., 2018). Pyrite commonly plays a vital role in determining the distribution of rare elements and heavy metals in these systems and can effectively control the distribution of economically valuable elements such as silver, arsenic, gold, and heavy metals (Large et al., 2009; Cook et al., 2013; Agangi et al., 2014). Given pyrite's ubiquity and its capacity to host many rare elements (e.g., Co, Ni, Cu, As, Se, Ag, Sb, Te, Pb, Bi, and Au), its chemistry has been successfully used to trace the physicochemical evolution of hydrothermal fluids and to reveal formation processes in various mineral deposits (e.g., Carlin-type gold, Cline, 2001; Large et al., 2009; epithermal gold, Deditius et al., 2008; Kouhestani et al., 2017; orogenic gold, Wu et al., 2019; volcanogenic massive sulfide, Martin et al., 2022; porphyry copper (gold), Reich et al., 2013, Keith et al., 2022). The aim of this studyis to analyze chemistry of pyrite in the low-sulfidation epithermal copper mineralization system in southern Mamuniyeh. The findings will enhance the understanding of the epithermal mineralization processes and magmatic evolution in this region. The results provide insights into the fluid evolution and ore formation processes within the epithermal system, contributing to a broader understanding of mineral deposit formation. Geology and Petrography Mamuniyeh epithermal system includes significant rock outcrops composed of intrusive rocks such as gabbro, diorite, and monzodiorite, along with a series of acidic to basic volcanic rocks. These include andesite tuff, pyroxene andesite-andesite porphyry, dacite-rhyodacite tuff, acidic lava, basaltic andesite, diabase, and basalt-diabase (Goudarzi et al., 2024a). According to the 1:100,000 scale geological map of Zaviyeh (Amidi et al., 2004), the volcanic and pyroclastic units are of Eocene age, while the intrusive units likely intruded during the Oligocene to Early Miocene periods. Geochemical characteristics show that these magmatic series are calc-alkaline, significantly influenced by mantle metasomatism (Rezaei Kahkhaei et al., 2014). Features like LILE enrichment over HFSE, negative Nb and Ti anomalies, and highly positive lead anomalies indicate calc-alkaline magmatism associated with a subduction zone, with crustal contamination during the ascent of the parent magma in this region (Goudarzi et al., 2024a). Mineralization and Mineralography The main copper mineralization in the Mamuniyeh epithermal system features veins and veinlets aligned with regional structures. Primary mineralization includes quartz with sulfide minerals like chalcopyrite, pyrite, and bornite, and oxide minerals such as specularite. Pyrite, the most abundant sulfide, appears in two generations. The first generation consists of framboidal and semi-euhedral pyrite, which can be fine- to coarse-grained and sometimes altered to hematite and goethite (Goudarzi et al., 2024c). The second-generation forms vein and veinlet fillings and occasionally include inclusions within chalcopyrite. Pyrite occurs in various assemblages: quartz + pyrite (Qz+Py); quartz + chalcopyrite + pyrite (Qz+Ccp+Py); quartz + specular hematite + pyrite (Qz+Py+Hem); and quartz + chalcopyrite + specular hematite ± pyrite ± bornite (Qz+Ccp+Hem±Py±Bn), found in replacement, breccia, disseminated, and colloform textures. Vein/Veinlet Pyrite Quartz + Pyrite (Qz+Py): Oldest veins, 1-20 mm thick, with coarse, euhedral pyrite grains Quartz + Chalcopyrite + Pyrite (Qz+Ccp+Py): Veins contain chalcopyrite (50%), pyrite (30%), and quartz (20%), 1 mm to 5 cm thick Quartz + Chalcopyrite + Specular Hematite ± Pyrite ± Bornite (Qz+Ccp+Hem±Py±Bor): Most common, 0.5-5 cm thick, with chalcopyrite (40%), specular hematite (30%), pyrite (10%), bornite (5%), and quartz (15%) Quartz + Specular Hematite + Pyrite (Qz+Py+Hem): Veins, 0.5-10 cm thick, contain specular hematite (60%), pyrite (10%), and quartz (20%) Other types of Pyrite mineralization Disseminated type: Euhedral to anhedral pyrite crystals spread within intrusive and volcanic rocks and quartz veins Colloform type: Rapid, low-temperature quartz deposition in shallow epithermal systems, forming alternating ore-bearing and ore-free bands Crustiform type: Periodic temperature fluctuations and fluid changes during boiling, forming colloform banding with iron oxides, hematite, pyrite, and secondary copper minerals Hydrothermal Breccia Mineralization: Hydraulic fracturing from fluid pressure increases, creating breccia with ore mineral fragments like pyrite, indicative of boiling processes Research Methodology After thorough field examinations of surface outcrops and drill cores, 70 polished sections from mineralized zones and veins containing sulfide and oxide minerals were collected for ore and mineralogical studies. Suitable sulfide samples from 8 polished sections were re-examined using an electron microscope and BSE images. Following carbon coating, the samples were analysed using a CAMECA SX Five Electron Microprobe equipped with a field emission cathode and energy-dispersive X-ray (EDX) system. This setup, with a 20 kV accelerating potential, 25 nA probe current, and 60 µm beam diameter, enabled rapid semi-quantitative elemental analysis in the Department of Lithospheric Research laboratory at the University of Vienna. Results and Discussion EPMA analysis on 58 points in pyrite shows no gold presence and very low silver concentration, up to 0.05 wt.%. Maximum concentrations of elements measured are arsenic (0.20 wt.%), lead (0.26 wt.%), copper (0.95 wt.%), antimony (0.23 wt.%), tin (0.04 wt.%), zinc (0.018 wt.%), nickel (0.34 wt.%), and cobalt (1.12 wt.%). Strong element correlations in pyrite include tin with zinc, arsenic with lead, manganese with zinc, and manganese with silver. BSE images show pyrite in oxide-sulfide veins as individual grains, often with chalcopyrite at the edges or as inclusions within chalcopyrite. Element variation diagrams for the Mamuniyeh pyrites indicate no significant changes in iron and sulfur with increasing arsenic. Cobalt content increases, while copper decreases with more iron. Cobalt and nickel show a stable relationship. Copper increases with zinc, while silver decreases with increasing arsenic and antimony but increases with tin. Previous studies indicate that the composition of trace elements in sulfides is controlled by the physicochemical conditions of hydrothermal fluids, such as temperature, pH, and redox conditions, revealing ore-forming processes in hydrothermal environments (Reich et al., 2013; Large et al., 2014; Gregory et al., 2016; Sykora et al., 2018; Saravanan Chinnasamy et al., 2021). For example, Te content in pyrite is mainly influenced by oxygen fugacity and pH, whereas As and Se are likely controlled by temperature (Huston et al., 1995; Deditius et al., 2008; Keith et al., 2018). The Co–Ni–As ratio in pyrite correlates closely with the deposit's genetic model and geological processes (Loftus-Hills and Solomon, 1967; Yan et al., 2012). Co, Ni, and As data plots for the Mamuniyeh pyrites indicate samples skewed towards the cobalt region, typical of magmatic-hydrothermal and epithermal deposits (Yan et al., 2012; Niu et al., 2016) (Fig. 7A). S-As substitution degree in pyrite is a temperature indicator, showing arsenic enrichment at lower temperatures (Kusebauch et al., 2018). Co and Ni are mantle-derived elements; Ni is usually concentrated in early-stage magmatic minerals, decreasing gradually with magmatic evolution, while Co increases (Kusebauch et al., 2018; Niu et al., 2016). Arsenic content depends on meteoric and magmatic water ratios, with higher arsenic content indicating a meteoric water role. If magmatic water predominates, samples plot towards Co; with meteoric water dominance, samples plot closer to arsenic (Yan et al., 2012). The plotted data suggests fluid evolution from initial magmatic water to later meteoric water. Reduction of arsenic content in pyrites, due to the mixing of hydrothermal vein fluid with high-oxygen-fugacity meteoric water, may increase arsenic content. Under oxidizing conditions, arsenic content decreases as arsenic replaces S in the pyrite structure (Cook and Chryssoulis, 1990; Liang et al., 2013). Geochemical studies have shown vertical zoning in epithermal systems (Boyle, 1979), with As, Sb, Hg, Ba, and Ag dominant in the upper parts; Cu, Pb, Zn, and Bi in the middle parts; and Co, Ni, Ti, and Cr in deeper parts. Mamuniyeh's system mainly shows middle to deep characteristics. Studies indicate that copper can significantly incorporate into pyrite's structure, sometimes reaching notable weight percentages (Einaudi, 1968; Clark, 1970; Pacevski et al., 2008). In Mamuniyeh, copper concentrations in pyrite reach up to 1.1 wt.%, showing pyrite as a substantial copper host. Due to large ionic size, lead rarely enters pyrite's lattice and typically deposits as galena (Huerta-Diaz and Morse, 1992; Koglin et al., 2010). Pyrite can also trap elements like silver, antimony, and tin when remobilized, though their contents in the Mamuniyeh pyrites are minimal (0.05 wt.%, 0.02 wt.%, and 0.002 wt.%, respectively). Nickel, easily incorporated into pyrite, remains even during recrystallization (Huerta-Diaz and Morse, 1992). High nickel content in the Mamuniyeh pyrites (0.34 wt.%) suggests a mafic-ultramafic mantle source (Palme and O'Neill, 2003; Zhao et al., 2011), exceeding continental crust levels (Rudnick and Gao, 2014). Nickel’s solubility limit is around 10 mol% NiS2 in pyrite while cobalt can fully mix into pyrite at temperatures above 700 °C (Abraitis et al., 2004), making Co concentration in pyrite a useful geothermometer (Zhao et al., 2011). Co/Ni ratios in pyrite, unaffected by slight differences in Co and Ni affinities for chloride ligands, reflect hydrothermal deposit conditions (Bralia et al., 1979; Bajwah et al., 1987). In Mamuniyeh, Co/Ni ratios between 1 and 10 indicate a magmatic-hydrothermal origin (Reich et al., 2016), consistent with previously defined characteristics.

The low-sulfidation epithermal copper mineralization in the Mamouniyeh area occurs as silica-sulfide-oxide veins hosted by monzonitic, gabbroic intrusions, and andesite. Magnetite and titanomagnetite are the primary hypogene oxide ore minerals in this system, present as titanomagnetite in intrusions and mainly as magnetite in silica veins. The chemical composition of Mamouniyeh magnetites in the FeO-Fe2O3-TiO2 system indicates a tendency towards wüstite (FeO). Increased Al2O3 and TiO2 content in silica vein magnetites compared to monzonitic intrusions is characteristic of hydrothermal magnetites. The decreased Cr2O3 and V2O3 content in re-equilibrated silica vein magnetites suggests their formation at higher oxygen fugacity than monzonitic titanomagnetites. The Al+Mn vs. Ti+V diagram shows that intrusive titanomagnetites formed at temperatures above 500°C, while silica vein magnetites formed at 200-300°C. The temperature drops in the system, influenced by atmospheric fluid mixing during hydrothermal fluid intrusion, led to magnetite deposition in silica veins at lower temperatures. The Ti vs. Mg+Al+Si diagram indicates the crystallization of intrusive titanomagnetites under conditions of limited hydrothermal fluid-wall rock interaction. An increase in oxygen fugacity from the parent magma towards the mineralized veins is observed, with intrusive magnetites forming at higher temperatures and lower ƒO2. ntroduction Iron oxides are present in many magmatic-hydrothermal mineral deposits, either as primary minerals (e.g., IOCG deposits and banded iron formations) or as secondary minerals (e.g., massive sulphide deposits). The chemical composition of magnetite provides insights into the characteristics of ore-forming fluids during magmatic or hydrothermal processes. Unique features of magnetite, such as its formation under various geological conditions and its ability to host numerous trace elements, have led to its use as an important petrogenetic indicator in recent years. This study investigates the composition of magnetite - titanomagnetite as the main hypogene oxide minerals associated with the low-sulfidation epithermal copper mineralization system in southern Mamuniyeh, within the central part of the Urumieh-Dokhtar magmatic arc (UDMA). The findings offer a better understanding of the evolution of the epithermal mineralization system and magmatic evolution in this area for the first-time using magnetite-titanomagnetite compositions. Despite numerous signs of ancient mining, mineral indices, and copper-gold-silver deposits associated with Eocene magmatism in this region, it has received less attention from researchers compared to other areas of the UDMA. Petrography, Mineralogy and Mineralization The study area features a series of intrusive and volcanic rocks ranging from acidic to basic, including andesite tuff, pyroxene andesite-porphyritic andesite, dacitic-rhyodacitic tuff, acidic lava, basaltic andesite, diabase, gabbro, diorite, monzonite, granodiorite, monzodiorite, and basalt-diabase. Geochemical characteristics show calc-alkaline magmatism related to a subduction zone, with crustal contamination during magma ascent (Goudarzi et al., 2024a). Copper mineralization appears as veins, primarily aligned NW and N40W. Six main types of veins/veinlets exist: quartz + pyrite (Qz+Py); quartz + chalcopyrite + pyrite (Qz+Ccp+Py); quartz + chalcopyrite (Qz+Ccp); quartz + specular hematite + pyrite (Qz+Py+Hem); quartz + chalcopyrite + specular hematite ± pyrite ± bornite (Qz+Ccp+Hem±Py±Bor), and quartz + secondary copper minerals, with magnetite ± titanomagnetite as minor accessory minerals (Fig. 2). During main mineralization, quartz formed with sulfides like chalcopyrite, pyrite, and bornite, and oxides like magnetite-titanomagnetite and specularite (Goudarzi et al., 2024c). In the supergene stage, chalcocite, covellite, minor native copper, and limited magnetite were observed. The oxidation stage saw minerals like malachite, cuprite, azurite, chrysocolla, hematite, goethite, and limonite forming. Syngenetic iron oxide ores include magnetite, titanomagnetite, specular hematite, and ilmenite exsolution lamellae. Magnetite and titanomagnetite, as primary hypogene oxide ores, are found in hypabyssal monzodioritic bodies and silica veins, sometimes associated with copper sulfides. Magnetite occurs as scattered grains, while titanomagnetite forms micro-grains in mineralized veins. Some titanomagnetite crystals intergrow with ilmenite, and hematite blades form during final cooling stages. The transformation of magnetite to hematite due to Fe2+ leaching in acidic environments results in martitic textures. The association of iron and titanium oxides suggests non-equilibrium conditions. Replacement of magnetite and titanomagnetite by hematite indicates alteration under higher oxygen fugacity, likely due to weathering or hydrothermal alteration (Klein, 2005; Makvandi et al., 2016; Riegler et al., 2014). Research methodology After detailed field examinations, 70 polished sections from various ore-bearing sections and veins were prepared for mineralogical studies. The study of oxide minerals in 8 polished sections was conducted using an electronic microscope and SEM-BSE analyses. The samples were analyzed using the CAMECA SX Five Electron Microprobe at the University of Vienna. The analysis was performed on 48 points of primary titanomagnetite-magnetite in intrusive units and 45 points of magnetite associated with mineralized veins. Results and discussion The results show that the FeO and TiO2 contents vary significantly. In intrusive rocks Fe2O3 ranges from 60 to 80 wt.% and TiO2 from 0 to 16.57 wt.%. In mineralized veins Fe2O3 ranges from 80.6 to 91.4 wt.% and TiO2 from 0 to 0.12 wt.%. Al2O3 and TiO2 contents decrease towards siliceous veins, indicating minimal spinel formation, characteristic of hydrothermal magnetites. Fe2O3 in intrusive masses correlates with Cr2O3 and V2O3, whereas in mineralized veins it correlates with MnO and Cr2O3. TiO2 in intrusive masses correlates with Al2O3, V2O3, and MnO, but not in mineralized veins. SiO2 content is generally less than 1 wt.%. Variation diagrams show that in intrusive samples, Al, Cr, and V oxides increase with TiO2, while Fe and Mg decrease. In mineralized veins, Al and Fe oxides decrease with TiO2, while Cr increases slightly, and V, Mn, and Mg initially increase then decrease. Chemical Composition Titanomagnetite (TixFe3-xO4) is a significant Fe-Ti phase in orthomagmatic rocks and oxide deposits (Spencer and Lindsley, 1981). It can undergo reduction or oxidation (O’Reilly, 1984), forming ilmenite lamellae or intergrowths (Saito et al., 2004). Ideal titanomagnetite forms through deuteric oxidation along the magnetite-ulvospinel line. Mamouniyeh titanomagnetites trend towards wüstite (FeO) (Fig. 9). Martitic hematites indicate final oxidation stages with decreasing temperature and increasing oxygen fugacity (Mondal and Baidya, 2015). With rising temperatures, titanomagnetite separates into ulvospinel and magnetite, forming a Widmanstätten texture (Mondal and Baidya, 2015). Ilmenite forms upon cooling and ulvospinel instability, reacting with oxygen and TiO2. Thick ilmenite blades are formed under advanced oxidation conditions and thin ilmenite blades are formed under early oxidation conditions. Martitization intensity varies, with high oxygen fugacity leading to heavily martitized crystals. Hematite lamellae in ilmenites may result from final oxidation and cooling. Petrographic analysis shows disrupted cubic structures in titanomagnetite, with thin lamellae forming due to oxidation and titanium enrichment, and thicker lamellae forming under advanced oxidation (Pasteris, 1985). Origin Comparing magnetite-titanomagnetites from intrusive rocks and mineralized zones reveals element redistribution during iron oxide transformation. Intrusive bodies are enriched in Ti, Al, and V, while mineralized veins are depleted. Higher V and Cr in magnetite from intrusive bodies align with the mafic nature of host rocks (Curtis, 1964). Reduced Cr and V in mineralized veins indicate high oxygen fugacity during formation. In Mamuniyeh, vanadium oxide content in titanomagnetites of intrusive rocks ranges from 0.016 to 1.28 wt.% (average 0.88 wt.%) and in magnetites of mineralized veins from 0.012 to 0.39 wt.% (average 0.12 wt.%). Vanadium content in magnetite reflects oxygen fugacity conditions of the environment, with higher oxygen fugacity leading to less vanadium in magnetite (Canil and Lacourse, 2020). V3+ incorporates into magnetite under low oxygen fugacity, while V5+ is incompatible with iron oxide structures at higher oxygen fugacity. Titanium content in magnetite is temperature dependent, with higher crystallization temperatures resulting in higher titanium contents (Tian et al., 2021). Magnetite appears in primary, secondary replacement, and solid solution forms. Primary magnetite shows no elemental substitution in fractures. Hematite replaces magnetite in fractures, starting from cracks and spreading across the crystal. Magnetite forms solid solutions with ilmenite, indicating limited Ti solubility at low temperatures. In tholeiitic magma, high-temperature liquidus minerals form first, while in calc-alkaline magma, elevated oxygen fugacity leads to earlier crystallization of iron oxide minerals (Mason and Moore, 1966). As magma approaches the surface, increased oxygen fugacity results in fine-grained magnetite and titanomagnetite crystals, with titanomagnetite forming first, followed by magnetite and ilmenite (Wechsler et al., 1984). In Mamuniyeh samples, ilmenite as a solid solution with magnetite indicates similar formation conditions. The V/Ti ratio in magmatic magnetite is generally 1 (Dupuis and Beaudoin, 2011). Vanadium is mobile in low-temperature hydrothermal fluids, while Ti is immobile (Oliver et al., 2004). A V/Ti vs. Fe diagram is used to study re-equilibration in magnetite (Wen et al., 2017). EPMA analysis shows magmatic magnetite in intrusive rocks and re-equilibrated magnetite in mineralized veins, indicating hydrothermal fluid influence during crystallization and re-equilibration. Temperature and Oxygen Fugacity Titanomagnetites formed in high-temperature intrusive bodies, while magnetites in siliceous veins formed at moderate temperatures (200-300°C), consistent with fluid inclusion data in quartz veins. This indicates a temperature decrease due to atmospheric equilibrated meteoric fluid mixing during hydrothermal fluid intrusion and magnetite deposition at lower temperatures. The Ti vs. Mg+Al+Si diagram shows that titanomagnetites in Mamunieh intrusions crystallized under limited hydrothermal fluid-wall rock reaction, while magnetites formed under extensive reaction conditions. Petrographic evidence shows primary magnetites in intrusive bodies have a magmatic origin, partially replacing primary crystallized sulfides and silicates. A Ti vs. V diagram distinguishes hydrothermal from magmatic magnetites, showing clear separation between titanomagnetite-magnetite crystals in intrusive bodies and mineralized veins. Magnetites from semi-deep rocks are found at temperatures above 500°C, while those from siliceous veins are at 200-300°C. Sun et al. (2017) showed magnetite in the early retrograde stage has high levels of cobalt, vanadium, titanium, aluminium, and manganese, indicating low oxygen pressure (ƒO2) and high temperature. High TiO2 and V2O3 levels in intrusive magnetites indicate high temperature and relatively low ƒO2 magma. According to Toplis and Corgne (2002), increased vanadium in magnetite indicates reduced oxygen fugacity. Wang et al. (2018) showed changes in vanadium content reflect changes in fluid oxygen fugacity during metallogenic processes. V2O3 oxide content indicates increasing oxygen fugacity from the parent magma to mineralized veins, with higher oxygen fugacity in siliceous veins. It appears crustal contamination occurred with decreasing temperature, evolving magnetite composition from porphyry to skarn-porphyry type.