Evciler granitine (Kazdağ, Kuzeybatı Anadolu) bağlı gelişen skarn alterasyon zonlarının mineralojik ve petrografik incelemesi

The purpose of this study is determination of the petrographic features, geology and alteration-mineralization style of the Evciler district with the aid of analytical data obtained by the electron probe microanalyses of the skarn mineral assemblage of Evciler, and establishment of the results of a stable isotope study of the skarnforming minerals at the Evciler location. This study also draws attention to the similarities of this occurrence with the other skarns of the world, some of which are well known for their ore potential. The skarn zones in the study area are both calcic exoskarn and endoskarn and have an oxidized mineralogy dominated by garnet, clinopyroxene, epidote, amphibole and chlorite. Skarn at Evciler contain up to 80 percent sulfides (pyrrothite, pyrite, and chalcopyrite) and massive pyrrothite-bearing mineralization body replaces prograde skarn and marble. The garnet-pyroxene skarn represent early skarn formation (prograde stage) and are composed of the anhydrous minerals, predominantly pyroxene with garnet. Epidote-amphibole skarn represent late skarnforming phases (retrograde stage) and replace early mineral assemblages. Microprobe analyses indicate that clinopyroxene has diopside-rich, whereas garnet composition has andradite-rich composition (typical for Au-Cu, Fe sulfide associations). Stable isotope compositions of skarn minerals from Evciler indicates that garnetpyroxene skarn was produced by predominantly magmatic fluids during initial skarn forming metasomatism in the study area and amphibole-epidote rich skarn was formed by magmatic water mixed with meteoric water. We concluded that the isotopic evolution of the hydrothermal fluid can be accounted for by circulation of 2 meteoric water through a convention system heated by the Evciler granitoid, causing exchange of oxygen isotopes with the granitoid and country rock, and possibly involving some admixture of magmatic water. Keywords. Skarn, geochemistry, stable isotope, Evciler, Kazdağ, Northwestern Anatolia.