Superimposed ore formation and hydrothermal alteration at the Kirazlı porphyry-epithermal deposit, Biga Peninsula, NW Türkiye

The Kirazlı deposit, located at the center of the Biga Peninsula, is one of the superimposed high-sulfidation (HS) epithermal Au-Ag and porphyry Cu systems in Türkiye. Ore formation and hydrothermal alteration at the Kirazlı were developed in 4 stages from oldest to youngest: (a) porphyry Cu, (b) re-opening base metal, (c) quartz-molybdenite, and (d) HS epithermal Au-Ag. Superimposed features of hydrothermal alteration are recognized in QEMSCAN mineral maps, suggesting progressive overprinting by an epithermal-related alteration on a porphyry Cu-style alteration. The sulfur isotopic compositions of the porphyry Cu and HS epithermal Au-Ag stages range from – 0.3 to + 3.7 ‰, and from −1.9 to + 0.1 ‰, respectively. Although magmatic input is observed in the generation of both deposits, the compositional gap and much lower δ³⁴S values of the HS epithermal Au-Ag ore body are attributed to different hydrothermal fluids that overprinted the earlier porphyry Cu system. The coexistence of multiphase highly saline fluid inclusions with vapor-rich inclusions indicates boiling during early porphyry Cu mineralization. The low-temperature and low-salinity fluid inclusion assemblages trapped in a later stage indicate overprinting hydrothermal activity. Hydrogen and oxygen isotopic compositions of illite and muscovite from the phyllic and argillic alteration zones indicate that the ore-bearing fluids at the Kirazlı consist of a magmatic and meteoric fluid mixture, with a dominant magmatic component during the porphyry event. A K-Ar age of illite from late argillic alteration is ca. 26 Ma, suggesting that hydrothermal activity at Kirazlı continued after the formation of the HS epithermal deposit.