Geochemical/isotopic evolution of Pb–Zn deposits in the Central and Eastern Taurides, Turkey (original) (raw)

2010, International Geology Review

The Central and Eastern Taurides contain numerous carbonate-hosted Pb-Zn deposits, mainly in Devonian and Permian dolomitized reefal-stramatolitic limestones, and in massive Jurassic limestones. We present and compare new fluid inclusion and isotopic data from these ore deposits, and propose for the first time a Mississippi Valley-type (MVT) mode of origin for them. Fluid inclusion studies reveal that the ore fluids were highly saline (13-26% NaCl equiv.), chloride-rich (CaCl 2) brines, and have average homogenization temperatures of 112°C, 174.5°C, and 211°C for the Celal Dag, Delikkaya, and Ayrakl0 deposits, respectively. Furthermore, the d 34 S values of carbonate-hosted Pb-Zn deposits in the Central and Eastern Taurides vary between-5.4‰ and +13.70‰. This indicates a possible source of sulphur from both organic compounds and crustal materials. In contrast, stable sulphur isotope data (average d 34 S-0.15‰) for the Çad0rkaya deposit, which is related to a late Eocene-Oligocene (?) granodioritic intrusion, indicates a magmatic source. The lead isotope ratios of galena for all investigated deposits are heterogeneous. In particular, with the exception of the Suçat0 district, all deposits in the Eastern (Delikkaya, Ayrakl0, Denizovas0, Çad0rkaya) and Central (Katranbas0, Küçüksu) Taurides have high radiogenic lead isotope values (206 Pb/ 204 Pb between 19.058 and 18.622; 207 Pb/ 204 Pb between 16.058 and 15.568; and 208 Pb/ 204 Pb between 39.869 and 38.748), typical of the upper continental crust and orogenic belts. Fluid inclusion, stable sulphur, and radiogenic lead isotope studies indicate that carbonate-hosted metal deposits in the Eastern (except for the Çad0rkaya deposit) and the Central Taurides are similar to MVT Pb-Zn deposits described elsewhere. The primary MVT deposits are associated with the Late Cretaceous-Palaeocene closure of the Tethyan Ocean, and formed during the transition from an extensional to a compressional regime. Palaeogene nappes that typically limit the exposure of ore bodies indicate a pre-Palaeocene age of ore formation. Host rock lithology, ore mineralogy, fluid inclusion, and sulphur+ lead isotope data indicate that the metals were most probably leached from a crustal source such as clastic rocks or a crystalline massif, and transported by chloride-rich hydrothermal solutions to the site of deposition. Localization of the ore deposits on autochthonous basement highs indicates long-term basinal fluid migration, characteristic of MVT depositional processes. The primary MVT ores were oxidized in the Miocene, resulting in deposition of Zn-carbonate and Pb-sulphatecarbonate during karstification. The ores underwent multiple cycles of oxidation and, in places, were re-deposited to form clastic deposits. Modified deposits resemble the 'wall-rock replacement' and the 'residual and karst fill' of non-sulphide zinc deposits and are predominantly composed of smithsonite.