The copper deposits of the Ergani-Maden area, in the Taurus Mountains of southeastern Turkey, have been a major source of copper for more than 4,000 years. The area is underlain by gently dipping mudstones interlayered with mafic volcanic rocks and lenticular beds of limestone, mainly of Eocene age. The layered rocks were intruded and slightly metamorphosed by large masses of gabbro and related mafic rocks that are now largely serpentinized. The copper deposits are in an east-trending belt about 20 km long, near the center of which is the town of Maden. A broad geochemical anomaly extends north-northwest and south-southeast from this belt, its axis passing near Maden. Near the mines the main igneous mass has a gently dipping roof and steep sides. Around and south of Maden, where the mass has barely been unroofed, are many roof pendants and remnants of sedimentary and volcanic material. One of these contains the largest mine in the area--the Ana Yatak. The largest deposit, the Aria Yatak ore body, occurs in a canoe-shaped pendant of mudstone that occupies atrough about 1 km long and 1/2 km wide in the top of the intrusive. The present vertical extent is about 170 meters. In the central and western parts of the trough the mudstone is chloritized and partly replaced by ore minerals. The main ore body is about 550 X 300 X 50 m in maximum dimensions. It consists mainly of pyrite and chalcopyrite, and locally it contains abundant magnetite or pyrrhotite. The gangue consists predominantly of chlorite, smaller amounts of quartz, and very minor amounts of calcite and barite. The massive sulfide ore body is underlain by "impregnation ore" in which veinlets and irregular small masses of sulfides are embedded in chloritized mudstone. A zone rich in supergene chalcocite, corellite, and bornite lies between the sulfide mass and the well-developed gossan in many places, and this was extensively mined in ancient times. The Mihrap Dagi mine, about 1 km northwest of the Aria Yatak deposit, is also near a contact between the intrusive and the sedimentary rock. It too contains a massive sulfide ore body accompanied by chloritized rock, but it contains little "impregnation ore." In the Ergani-Maden area, ore deposition followed a long history of sedimentation, lithification, faulting, intrusion of mafic igneous rocks, serpentinization, and further faulting, and was part of a broad-scale introduction of metal into the sedimentary, extrusive, and intrusive rocks. Thus it is epigenetic. The major ore bodies are fracturecontrolled replacement masses. Adularia which occurs in veins a few hundred meters south of the main sulfide ore bodies is inferred to have formed contemporaneously with the sulfide and shows a potassium-argon age of 31.5 +/- 0.8 m.y. If this inference is correcthe deposits formed during middle Oligocene or slightly later.