Genesis of Tertiary Akcakis,la vein-type Pb-Zn-Cu mineralisation (Central Anatolia, Turkey): Evidence from fluid inclusion and O, H, S, Pb-isotope compositions

The Akcakis,la Pb-Zn-Cu vein type deposit is one of the active mining deposits located in the Akdagmadeni (Yozgat) metallogenic province in Turkey. The sulfide vein deposit, trending E-W, is hosted by calcschist of the Akcakis,la and Topaktas, formations of Akdagmadeni metamorphites, which are intruded by the Central Anatolian granitoids and overlain by sedimentary and Tertiary volcanic rocks. Microthermometric measurements indicate that the Pb-Zn-Cu deposit formed by hydrothermal fluids containing dissolved CaCl2, MgCl2 and NaCl. A mixing of fluids with greatly varying salinities and temperatures is shown by the wide range of calculated salinity (0.2-10.4%) and temperature (170-400 degrees C) values. Isotope ratios of oxygen (& delta;18OH2O =-5.09 to +4.71%o) and hydrogen (& delta;D =-67%o and-82%o) suggest that water in hydrothermal fluid might be either mixing of meteoric and magmatic waters or meteoric water that oxygen isotope composition was modified by fluid-rock interaction. Sulphide minerals exhibit & delta;34S values ranging from 5.51%o to 8.40%o, which assume a magmatic sulphur source modified by assimilation of upper crustal material (possibly the host metamorphites). In galena from the studied Akcakis,la Pb-Zn-Cu deposit ratios of 206Pb/204Pb (18.783-18.821),207Pb/204Pb (15.654-15.700) and 208Pb/204Pb (38.874-39.039) suggest a mixture of lead sources from orogenic-upper crust materials. We assume that hydrothermal fluids dissolved the sulphur from the intruded granitoids and the lead from the host metamorphites. The galena Pb model ages values point out two different ore forming ages; suggesting initial formation in upper Cretaceous (87 Ma) and highly reworking in Eocene-Oligocene (23 and 39 Ma).