International Geology Review, Vol. 50, 2008, p. 848–862. DOI: 10.2747/0020-6814.50.9.848 Copyright © 2008 by Bellwether Publishing, Ltd. All rights reserved. 0020-6814/08/1018/848-15 $25.00 848 Fluid Inclusion and Stable Isotope Characteristics of the Arapuçandere Pb-Zn-Cu Deposits, Northwest Turkey GÜLCAN BOZKAYA, 1 AHMET GÖKÇE Cumhuriyet University, Department of Geological Engineering, 58140 Sivas, Turkey AND NATHALIE V. GRASSINEAU Royal Holloway University of London, Department of Geology, Egham, United Kingdom Abstract The Arapuçandere Pb-Zn-Cu ores are typical examples of vein-type lead-zinc deposits in the Biga Peninsula. Permian–Triassic metamorphic, Triassic metaclastic 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 as ore minerals, with quartz, calcite, and barite as gangue minerals. Based on macro- and micro-petrographic 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°C) during stages of sulfide precipitation. In contrast, the salinity (avg. 27.1% NaCl equiv.) increased and the temperature (avg. 240.2°C) decreased during crystallization of the quartz. Finally, the salin- ity 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 (δ 18 O = –7.5 to –1.7‰, and δD = –90 to –55‰) indicate the presence of meteoric water modified slightly by fluid-rock interaction. A geologic and genetic relation between ore veins and Oligo-Miocene granitoids and Miocene volcanic rocks appears to be lacking. The ore and host-rock relations suggest only a post-Triassic age for the mineralization. Pb-isotope model ages suggest a pre-Eocene age for the mineralization, which predated Oligo-Miocene granitoid emplacement and Miocene volcanic activity. We conclude that the Pb-Zn-Cu veins in the study area formed by deeply circulating meteoric water. The metals and sulfur were leached from the surrounding pre-Eocene units and deposited along fault zones. Introduction PB-ZN-CU deposits are widespread in the Biga Pen- insula. Some of the deposits hosted by metamorphic rocks are pre-metamorphic in occurrence, and thus bear the effects of regional recrystallization. How- ever, most are vein-type deposits hosted by various rock types, including Paleozoic metamorphic rocks, Permo-Triassic clastic and calcareous rocks, and Tertiary volcanic rocks. In recent years, the first two authors of the pres- ent paper began carrying out detailed geological, ore-petrographic, fluid inclusion, and stable- and Pb-isotopic studies on various deposits of the Biga Peninsula in order to identify similarities and differ- ences among deposits in different units of varying lithology and age—e.g., Koru (Bozkaya, 2001; Bozkaya and Gökce, 2001, 2002, 2006), Balcilar (Bozkaya, 2003, Bozkaya and Gökce, 2007), Kumarlar (Bozkaya and Çelik, 2007). These previ- ous studies showed that the S-isotopic compositions and fluid-related characteristics of these deposits differ in accordance with age and host lithology, and that the genesis of the various deposit types needs to be studied separately. The present study focuses on the microthermo- metric and isotopic characteristics of the fluids trapped in fluid inclusions within quartz in order to elucidate the origin of the mineralizing hydrother- mal solutions in the Arapuçandere Pb-Zn-Cu depos- its, and the genesis of this and similar deposits in the region. The Arapuçandere Pb-Zn-Cu deposits, located in the northwestern part of the Yenice district of 1 Corresponding author; email: gbozkaya@cumhuriyet.edu.tr