Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Sinan Akiska, Gökhan Demirela, Sönmez İ. Sayili

Geology, mineralogy and the Pb, S isotope study of the Kalkım Pb-Zn ± Cu deposits, Biga Peninsula, NW Turkey

Journal of Geosciences, volume 58 (2013), issue 4, 379 - 396

DOI: http://doi.org/10.3190/jgeosci.154

Three main Pb-Zn ± Cu deposits (Handeresi, Bağırkaçdere, and Fırıncıkdere) occur south of Kalkım in the southeastern part of the Biga Peninsula (NW Turkey). Massive and disseminated Pb-Zn mineralization consists of ore veins in fault zones and replacement bodies in carbonate layers in metamorphic rocks. Garnet (~Ad₆₄Gr₃₆), pyroxene (~Di₃₀Hd₄₅Jo₂₅), epidote and rare tremolite-actinolite are found as gangue minerals in ore zones. The garnets often show oscillatory zoning and correspond to grossular, andradite and grandite in composition. The pyroxene minerals are manganiferous hedenbergite, johannsenite and diopside. The Mn/Fe ratios of the pyroxene range between 0.3 and 0.9 (mean 0.5). Such compositions of the garnet and pyroxene and gangue assemblages are typical of distal Pb-Zn skarns. The ore minerals are pyrite, sphalerite, chalcopyrite, galena, magnetite, hematite, and arsenopyrite.
The mean lead isotopic values for galena are ²⁰⁶Pb/²⁰⁴Pb ~ 18.760, ²⁰⁷Pb/²⁰⁴Pb ~ 15.689, and ²⁰⁸Pb/²⁰⁴Pb ~ 38.935. The comparison of these isotope data with the host-rock samples (graphite schist, andesite and granodiorite) indicates that part of lead could have been leached from the schists. The δ³⁴S_VCDT values for galena, sphalerite, and chalcopyrite are -1.1 to +1.5 ‰ (mean: -0.2 ‰), 0.7 to +2. 1 ‰ (mean: +0.7 ‰), and -0.6 to +1.5 ‰ (mean: +0.4 ‰), respectively. Lead isotope data and δ³⁴S_VCDT ratios close to 0 ‰ indicate the formation of ores by magmatic processes.
Taken together, the Oligo-Miocene magmatism in the area is taken responsible for the polymetallic mineralization. However, the metamorphic rocks and their protoliths may have contributed part of the lead.