Turkish Journal of Earth Sciences




Koru (Çanakkale) 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 Akçaalan andesite, Oligocene Adadağı pyroclastics, Miocene Dededağ dacite and Plio-Quaternary Karaömerler basalt. The investigated deposits are hosted by Adadağı 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) ^o/_{oo VCDT}, -5.2 to -3.0 (average -3.9) ^o/_{oo VCDT}, and +14.9 to +17.3 (average +16.5) ^o/_{oo VCDT}, respectively. There are two different ranges of \delta^{34}S values of H_2S in equilibrium with barite (+5.5 to +7.9 ^o/_{oo}) and sulfide minerals (-2.1 to -0.5 ^o/_{oo}), indicating that the sulfur in sulfide minerals and barite derived from different sources. The similarity of the \delta^{34}S 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_2S (in equilibrium with these two minerals) to 0 ‰ 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.

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