Hydrothermal alteration modelling of Kaletaş-Söğütağil-Akpınar (Gümüşhane) regions

Kaletaş-Söğütağıl-Akpınar (Gümüşhane) alteration areas are situated in southern zone of Eastern Pontide Tectonic Unit. The Early-Mid Eocene age Alibaba Formation, which is comprised of andesitic-basalt and its pyroclastics, forms the basement rocks of the study area. This unit is cut by Mid-Eocene aged Kaletaş Granitoid body composed of monzogranite, granodiorite and quartz-monzodiorite. It is determined that the volcanics have andesitic and basaltic composition and own calc-alkaline character; and so they were derived from same or similar mantle source. It is also defined that Kaletaş Granitoid has calc-alkaline and metaluminous character; and hence according to tectonic setting they are of I-Type volcanic arc granites. The alterations developed within Alibaba Formation are related to fractures having strikes of NW-SE and approximately E-W directions. Limonitization, hematitization, chloritization, argillitization and silicification are the most characteristic alteration types According to the calculations of MINSQ method, quartz, K-feldspar, sericite ± kaoline are the dominant alteration minerals in ore-carrying alteration zone; whereas albite is determined as the dominant alteration mineral in propylitic zone, along with epidote, Fe-chlorite and Mg-chlorite. Based on relative mass change calculations, it is determined that there is an increase in K, Pb, Mo and Au elements, but decreases observed in Ca, Na, Fe, Mg, Cu and As elements of mineralization zone. According to the results of net mass change calculations, enrichment is observed only in K, Pb, Mo and Au elements. The calculated oxygen isotope values changes between 5.6 and 10.0 ‰, and that of hydrogen ranges in 61- 71 ‰; and according to these data it can be said that fluids formed the mineralization is made of mixing of magmatic and meteoric waters.