Sulphur- and lead-isotope geochemistry of the Arapucandere lead-zinc-copper deposit, Biga Peninsula, northwest Turkey

Abstract

The Arapucandere Pb-Zn-Cu ore body is a typical vein-type lead-zinc deposit of the Biga Peninsula, and is currently being mined for lead and zinc. In the study area, Permian-Triassic metamorphic rocks, Triassic metaclastic and metabasic rocks, Oligocene-Miocene granitoids, Miocene volcanic rocks, and Quaternary terrigenous sediments crop out. The ore deposits developed as Pb-Zn-Cu-bearing veins along faults in Triassic metasandstone and metadiabase. Microscopic studies reveal that the veins contain galena, sphalerite, chalcopyrite, pyrite, marcasite, covellite, and specular hematite as ore minerals, and quartz, calcite, and barite as gangue minerals. Analysed sulphur-isotope compositions (34SVCDT) of galena, sphalerite, and chalcopyrite range from -5.9 to -1.9 parts per thousand (average-3.4 parts per thousand), from -5.5 to -1.7 parts per thousand (average -4.2 parts per thousand), and from -3.5 to -0.9 parts per thousand (average -2.6 parts per thousand), respectively; that of H2S in the hydrothermal fluid was in the calculated range of -5.8 to +0.1 parts per thousand (average -2.5 parts per thousand). These isotopic values suggest that magmatic sulphur dominates in sulphides, mixed with minor, isotopically light sulphur. Because no contemporaneous magmatic activity is associated with mineralization, it may be assumed that sulphur was leached from the surrounding Triassic units, mainly from metabasic, partly from metaclastic rocks. Lead-isotope studies indicate a model age of 114-63Ma for the lead reservoir, in accord with possible sulphur-bearing local source rocks. Thus, the sulphur and lead deposited in the studied ore veins were probably leached from Triassic metabasic and metaclastic rocks some time during the Early Cretaceous to the Palaeocene.