The Chah-Musa porphyry-epithermal copper system in the Toroud-Chah Shirin magmatic zone, NE Iran

The Chah-Musa copper deposit, located within the Cenozoic Toroud-Chah Shirin (TCSH) magmatic arc in northeastern Iran, represents an example of porphyry-epithermal mineralization in the region. This study aims to investigate the local geology, mineralogical and geochemical characteristics, wall-rock alteration, fluid inclusion properties, and geological context of the Chah-Musa deposit. The deposit is hosted by a subvolcanic diorite porphyry intrusion that intruded into Eocene volcano-sedimentary sequences consisting of volcanic breccia, agglomerate, and red tuffaceous rocks. Mineralization occurs in two main forms: (1) Cu-bearing stockwork veins (V1–V3) hosted within the porphyry body and (2) epithermal Cu–Ba veins (V4) controlled by fault structures. Wall-rock alteration includes a central potassic core, flanked by phyllic and peripheral propylitic zones. Geochemical analyses of the host intrusion confirm its calc-alkaline and adakitic nature. Stockwork mineralization includes three vein types: V1 (Qz+Kfs+Cpy+Bn+Mag), V2 (Qz±Kfs±Anh+Cpy+Py), and V3 (Qz+Py+Cpy); with V1 and V2 veins associated with potassic alteration, while V3 is linked to the phyllic alteration stage. A second mineralization style (V4) features Qz+Cal+Brt+Adu+Bn+Sph+Gn+Py+Cpy. Supergene alteration is expressed by chalcocite, covellite, and malachite. Fluid inclusion microthermometry reveals homogenization temperatures and salinities of 120–484°C and 3.1–58.6 wt.% NaCl eq. in V2 veins, 118–365°C and 2.6–18.1 wt.% NaCl eq. in V3 veins, and 165–239°C and 7.2–10.5 wt.% NaCl eq. in V4 veins. These data, combined with paragenetic and mineralogical features, indicate a porphyry-style system overprinted by intermediate-sulfidation epithermal mineralization, later modified by supergene enrichment. In summary, the Chah-Musa deposit documents a prolonged magmatic-hydrothermal evolution that reflects fluid and metal transport processes within an evolving porphyry-epithermal system, thereby contributing valuable insights into the metallogenic potential of the TCSH arc.