Lead and Sulfur Isotope Studies of the Koru (Canakkale, Turkey) Lead-Zinc Deposits

Abstract

Koru (Canakkale) barite-bearing lead-zinc deposits are typical examples of the lead-zinc deposits occurring in the Tertiary volcanic rocks which crop out in the Biga Peninsula. Volcanic rocks around the investigated deposits are distinguished as Eocene Akcaalan andesite, Oligocene Adadagi pyroclastics, Miocene Dededag dacite and Plio-Quaternary Karaomerler basalt. The investigated deposits are hosted by Adadagi pyroclastics and show two different mineralization styles such as stockwork ore veinlets in the upper parts and ore veins along the fault zones in WNW-ESE direction, in the lower parts. Sphalerite, galena, pyrite, chalcopyrite, quartz, barite and calcite are the main minerals and they are accompanied by small amounts of fahlore (tennantite), marcasite, covellite and bornite. Sulfur isotope studies show that the delta(34)S values of sphalerite, galena and barite change in the range of -1.9 to -0.1 (average -1.2) parts per thousand(VCDT), -5.2 to -3.0 (average -3.9) parts per thousand(VCDT) and +14.9 to +17.3 (average +16.5) parts per thousand(VCDT), respectively. There are two different ranges of delta(34)S values of H(2)S in equilibrium with barite (+5.5 to +7.9 parts per thousand) and sulfide minerals (-2.1 to -0.5 parts per thousand), indicating that the sulfur in sulfide minerals and barite derived from different sources. The similarity of the delta 34S values of barite to those of precipitated sulfate minerals in sediments or SO(4)(=) ions dissolved in sea water of Late Tertiary suggests that the sulfur in barite was derived from the precipitated sulfate minerals or SO(4)(=) ions dissolved in pore water in surrounding volcano-sedimentary units. On the other hand, proximity of the delta(34)S values of sphalerite, galena and H(2)S (in equilibrium with these two minerals) to 0 parts per thousand points to a genetic relation of the sulfur with the volcanic components of the surrounding volcano-sedimentary units. Lead isotope data are close to those of a model orogenic reservoir and are very different from a mantle-related reservoir. Calculated Pb-isotope model ages for these deposits (from 70 to 1 Ma) are in accordance with the possible geological age of the mineralization (post Oligocene) and indicate that the lead in galena was derived from the surrounding Eocene - Quaternary volcanic and volcano-sedimentary units. These data, along with the results of previous studies related to trace element and REE abundances and O- and H-isotope compositions, suggest that the Pb, Zn, Cu and S in sulfide minerals were leached from the volcanic components of the volcano-sedimentary units, while the Ba and S in barite were leached from the precipitated sulfate minerals or SO(4)(=) ions dissolved in pore water in surrounding volcano-sedimentary units by deep circulation of meteoric water.