Abstarct: The Cheshmeh Taji copper deposit is situated approximately 150 km southwest of Shahroud and 22 km northwest of Toroud, forming a critical part of the Torud–Chah Shirin volcanic-intrusive belt within Semnan Province, which lies on the northern margin of the Central Iranian Microcontinent. This belt is characterized by intense Eocene to Miocene magmatic and volcanic activity, with multiple mineralizations tied to subduction and the development of a back-arc extensional basin. The host rocks for the mineralization comprise andesitic, basaltic-andesitic lavas, pyroclastic units (tuffs and agglomerates), and diabaxse dikes, all exhibiting a calc-alkaline to alkaline nature, having formed in a sub-marine, shallow volcanic arc setting. The mineralization is epigenetic and occurs as vein-veinlet stockworks, open-space fillings, massive lenses, and disseminations along faults and fractures, evolving through primary (hypogene) and secondary (supergene) stages. Primary minerals include pyrite, chalcopyrite, chalcocite, and bornite, which were subsequently altered by weathering and oxidation to form high-grade secondary minerals such as secondary chalcocite, covellite, digenite, cuprite, native copper, malachite, and chrysocolla. Extensive iron oxides and hydroxides (hematite, magnetite, goethite, and limonite) mark a significant zone of oxidation. Petrographic analysis identifies multiple hydrothermal alteration assemblages, including chloritic, carbonatic, argillic, propylitic, and silicic types, with the main alterations being chloritic (pre- and syn-mineralization) and carbonatic. Propylitic alteration forms a broad halo, while argillic alteration is late-stage and confined to the upper parts. Geochemical analysis of the volcanic rocks confirms an active magmatic arc setting, characterized by enrichment in LILEs (e.g., K, Th, Sr) and depletion in HFSEs (e.g., Nb, Ti), consistent with magma derivation from a mantle wedge affected by subduction-related fluids. Magmatic differentiation involved fractional crystallization of minerals like plagioclase, supported by the decrease in MgO and CaO with increasing silica and the presence of a negative Europium (Eu) anomaly. Statistical data confirm a strong positive correlation between copper and sulfur, validating the sulfidic nature of the ore. Fluid inclusion studies on the Cheshmeh Taji deposit show that mineralization occurred from two-phase liquid-vapor inclusions with homogenization temperatures ranging from 155C to 219 C and salinities of 2 to 17.7 wt% NaCl equivalent, suggesting a near-surface origin (estimated depth 350m and pressure <50 bar) where fluid mixing was the primary depositional mechanism. baxsed on the integration of its tectonic environment, host rock type, stratabound nature, mineralogy, mextal content (Cu dominant), and alteration patterns, the Cheshmeh Taji deposit is classified as a Manto-type copper deposit in the northern Central Iranian Zone.