The Chah-Bagh gold occurrence is located in Muteh mining district, in the central part of the Sanandaj-Sirjan zone. Gold mineralization occurs in ductile to ductile-brittle shear zones and is comparable with orogenic gold deposits. Silicification and sulfidization are the most important hydrothermal alteration features in the inner parts of altered shear zones and coincide most closely with the ore-bearing zones. Principal ore minerals are pyrite, chalcopyrite, arsenopyrite and native silver. Silver commonly occurs both as native Ag grains (ca. 5 µm in diameter) intimately associated with siliceous gangue and as invisible silver within sulfides. The maximum concentration of invisible silver occurs in chalcopyrite. Although native gold was not identified in the siliceous gangue and in the sulfide minerals and their alteration products, electron microprobe analyses confirmed the occurrence of invisible gold within sulfides. Two phases of gold mineralization occurred in the Chah-Bagh area: 1- invisible gold within coarse-grained sulfides (pyrite and chalcopyrite); 2- invisible gold (the main phase) within fine-grained sulfides (pyrite and chalcopyrite). Evidently, the precipitation of gold was an integral part of the hydrothermal alteration system and was associated with sulfide minerals. Although electron microprobe analyses of auriferous sulfide indicated the presence of gold in sufficient quantities to explain the bulk gold concentrations, native gold has not been detected in our polished sections.