The Arapucandere Pb-Zn-Cu ores are typical examples of vein-type lead-zinc deposits in the Biga Peninsula. Permian-Triassic metamorphic, Triassic metabasic and metabasic rocks, Oligocene-Miocene granitoids, Miocene volcanic rocks, and Quaternary terrestrial sediments crop out in the study area. The veins occupy fault zones in Triassic metasandstone (meta-arkose and subarkose) and metadiabase, and contain galena, sphalerite, chalcopyrite, pyrite, marcasite, covel-lite and specular hematite ore minerals, with quartz, calcite, and barite as gangue minerals. Based on macro- and micro-pretrographic investigations, sulfide minerals formed in the earliest stage of mineralization, and were followed by quartz and calcite crystallization. Fluid inclusion studies showed that salinity (avg. 18.3%) was low, but that temperature was relatively high (avg. 301.4 degrees C) during stages of sulfide precipitation. In contrast, the salinity (avg. 27.1% NaCl equiv.) increased and the temperature (avg. 240.2 degrees C) decreased during crystallization of the quartz. Finally, the salinity and temperature of the fluid gradually declined through the later episode of mineralization when the primary and secondary inclusions in calcite formed. Isotopic compositions of the aqueous fluid (delta O-18 = -7.5 to -1.7%(0,) and delta D = -90 to -55 parts per thousand) indicate the presence of meteoric of meteoric water modified slightly by fluid-rock interaction.