The Hazinemagara (Gumushane) Pb-Zn deposit is located in the southern part of the Eastern Pontides Orogenic Belt in northeastern Turkey. It occurs as irregularly shaped ore bodies with breccia fill structure within the intraformational breccia or brecciated horizons of limestone in the Upper Jurassic-Lower Cretaceous Berdiga Formation. The dominant ore minerals are pyrite, sphalerite, galena, and tetrahedrite, and the major gangue minerals are calcite, quartz, and barite. Microthermometric investigations of the fluid inclusions show that the ore-forming fluids contain CaCl2 and MgCl2 in addition to NaCl. The salinity of the fluid ranges from 1.7% to 9.2% with an average of 5.7% (wt.% NaCl equivalent) (n - 93). The homogenization temperature of the fluid ranges from 160.0 to 386.0 degrees C with an average of 263.5 degrees C (n = 98). The plots of the delta D values of water trapped in fluid inclusions hosted by barite and quartz (in the range of 92 parts per thousand to 81 parts per thousand) and the delta O-18 values calculated for water in equilibrium with these minerals (4.1 parts per thousand to 18.5 parts per thousand) are closer to the magmatic range than any other water sources and suggest the presence of magmatic water in hydrothermal fluid with some modifications by interaction with fluid from surrounding sedimentary rocks. The sulfur isotope composition of sulfide minerals (in the range of -7.8 parts per thousand(VCDT) to +5.4 parts per thousand(VCDT) avg.: -2.0 parts per thousand; n = 13) indicates a magmatic source for sulfur. It is concluded that the magmatic water derived from deep-seated Eocene plutonic rocks (Kackar Granitoids-I and -II) possibly carried metals and the sulfur derived from the source magma or leached from magmatic rocks on the pathway along the fault zones and precipitated mainly within voids between limestone fragments in intraformational breccia horizons of the Berdiga Formation. The Berdiga Formation is observed in large areas within the Eastern Pontide region and the intraformational breccia horizons could provide large stratabound ore potential.