Sulphur and lead isotope geochemistry of the Dursunbey (Balıkesir) lead–zinc deposit

Abstract

The Biga Peninsula (northwest Anatolia) hosts several Pb–Zn occurrences, and the Dursunbey Pb–Zn deposit is one such important Pb–Zn province of Turkey.The basement rocks in the study area comprise metamorphic rocks of the Menderes Massif (Simav Metamorphites, Sarıcasu Formation, and Budağan Limestone) and ophiolitic units of the İzmir-Ankara Suture Zone, known as the Dağardı Mélange. These units were intruded by the Miocene Alaçam granite. Cover units start with the Early Miocene Yeniköy Formation (comprising alternating sandstone, claystone, marl, and clayey limestone, and tuff additives) and are terminated by Civanadağ tuffs, Akdağ volcanics, and the Toklargölü Formation, consisting of unattached grains and alluvium deposits.Mineralisation that is trending along N50°W 30–35°NE occurs between the Alaçam Granite and the carbonate rocks of the Menderes Massif Metamorphites. Microscopic analysis revealed that the mineralisation contains chalcopyrite, pyrite, sphalerite, galena, fahlerz (tetrahedrite, tennantite), pyrrhotite, pyrargyrite-proustite, magnetite, and haematite as major ore minerals.The δ34S values range from 2.4 to 4.1‰ in pyrite (n = 2, mean = 3.25‰), from 1.7 to 3.4‰ in chalcopyrite (n = 4, mean = 2.8‰), 2.2–3.5‰ in sphalerite (n = 6, mean = 3.05‰), but from only 0.2–1.8‰ (n = 8, mean = 1.12‰) in galena. The low δ34S values of the sulphide minerals (varying over a narrow range) may indicate that sulphur in the ore-depositing solutions had a magmatic origin.The Pb isotope ratios of galena ranged from 18.729 to 18.742 for 206Pb/204Pb, 15.589 to 15.606 for 207Pb/204Pb, and 38.589 to 38.647 for 208Pb/204Pb. In one sphalerite sample, these ratios were measured as 18.738, 15.614, and 38.648, respectively.The Pb isotope model ages are between −90 and −45, which are consistent with those of J-type lead. In 207Pb/204Pb–206Pb/204Pb and 208Pb/204Pb–206Pb/204Pb diagrams, such ages plot below the average Pb-isotope crustal growth curve, indicating that lead in the studied mineralisation had an orogenic source.