Evolutionary Model of the Sepid Sarve Manto Type Copper Mineralization, Doruneh Fault Volcanic Plutonic Belt (NW Bardeskan, Central Iran): An Integrated Geological, Geochem-ical, Fluid Inclusion and Stable O–S Isotope Study

The Sepid-Sarve copper deposit is part of an Eocene volcano-sedimentary sequence located in the southern Sabzevar Zone. The copper mineralization occurs at the con-tact between pyroclastic and lava units with various limestone layers (including marly, Nummulitic, sandy, and clastic limestones). The ore minerals consist of mala-chite, azurite, chalcocite, digenite, cuprite, tenorite, covellite, and occasionally native copper. The associated hydrothermal fluids show moderate to high salinities, ranging from 3.08 to 13.38 wt.% NaCl equivalent, with homogenization temperatures between 90 and 356°C, indicating fluid mixing during ore formation. Chalcocite is rarely ac-companied by quartz, suggesting low silica content in the ore-forming fluids. The δ³⁴S values of sulfide samples from the Sepid-Sarve deposit range from −24.2‰ to −2.7‰, while δ³⁴S values of hydrothermal H₂S range from −24.4‰ to −2.7‰. The δ¹⁸O values of hydrothermal fluids associated with mineralization fall within the range of basaltic rocks, meteoric waters, and sedimentary rocks. Geochemical variations in major and trace elements suggest the involvement of continental crustal contamination in the magmatic evolution. The studied volcanic rocks fall within the calc-alkaline to sho-shonitic fields, formed in a continental arc setting, and are derived from an enriched mantle source influenced by subduction-related fluids. These rocks are characterized by HREE depletion, moderate LREE enrichment, and a weak negative Eu anomaly. Based on the results, the Sepid-Sarve deposit is classified as a stratabound (man-to-type) copper sulfide deposit, formed in a volcano-sedimentary setting associated with a subduction-related magmatic arc environment.