Hydrothermal alteration and gold potential assessment of eocene-age volcanites in Canca-Aktutan and Lerikoy (Yitirmez)-Dolek Regions (Gumushane-NE Turkey)

Canca – Aktutan and Leriköy (Yitirmez) – Dölek (Gümüşhane, NE Turkey) alteration areas are located in southern zone of the Eastern Pontide Tectonic Unit. In Canca-Aktutan alteration areas the late Cretaceous aged Kermutdere Formation and the Eocene aged Alibaba Formation are found; whereas the Eocene age Alibaba Formation and late Eocene age Dölek Granitoidic rocks are common in alteration areas of Leriköy (Yitirmez) – Dölek. The Alibaba Formation consists of andesite, basalt and their pyroclasts. Eocene age volcanics fall in andesite and andesite/basalt fields in chemical diagrams plotted as SiO2 versus Na2O+K2O and Nb/Y versus Zr/TiO2 x 0.0001, have calc-alkaline character and it is determined that they are located in medium to high - potassium areas. The plagioclases observed in volcanic rocks of Eocene age Alibaba Formation are defined as andezine (An39-69) and labrador (An29-34); hornblends are edenit (Mg#: 0.66-0.79) and Fe-Ti oxide minerals are magnetite (Fe#:0.995-0.93) in composition. The alterations developed in the Eocene Alibaba Formation are associated with fault zones having NW-SE and about D-B directions. Limonitization, hematitization, chloritization, clayification and silicification are the most characteristic types of alteration. Kaolen, illite and chlorite were determined as clay mineral paragenesis in the fields, and the amount of illite and kaolin increase as it is approached to the alteration center. According to MINSQ method, quartz, ± kaolene ± Fe-chlorite are determined in ore-bearing alteration zone of Canca-Aktutan; and Mg-chlorite ± sericite, beside albite the dominant alteration mineral of propylitic zone. On the other hand, in mineralized alteration zone of Leriköy (Yitirmez)-Dölek quartz ± kaolene and in propylitic zone Mg-chlorite ± epidote are identified, beside the dominant alteration mineral albite. According to the relative to net mass change calculations, enrichment of Au, As and Pb elements are seen in ore zone of Canca-Aktutan alteration area. However, in ore zone of Leriköy (Yitirmez)-Dölek alteration area Au and Mo elements enrichment are assigned. Homogenization temperatures from fluid inclusions are measured for quartz between 142 and 344°C. The ore-forming fluids having 0.2-1.9 % wt. NaCl equivalent salinity and 0.75-0.94 g/cm3 density in NaCl±KCl±MgCl2-H2O system point out that the mineralization occurred in epithermal system. When the data obtained are evaluated all together, it is clear that the potential gold mineralizations in the alteration area are of epithermal type and their formation is related to granitic magma.