Modeling of hydrothermal alterations in the kermut (Tekke-Gümüşhane) area

Kermut (Gümüşhane, NE Turkey) alteration field is located in southern zone of Eastern Pontide Tectonic Unit. In Kermut area, from older to younger, Dogger-Malm Lower Cretaceous age Berdiga Formation, Upper Cretaceous age Kermutdere Formation and Eocene age Alibaba Formation are found. Berdiga Formation is composed of, in places massive and in some layered, a stack consisting of sandy limestone at the base, and crystallized limestones at the top. The subunits of yellow coloured sandy limestone, red coloured limestone and turbidite like stack intermitted marl, clay stone and sandstone interlayered with tuffite compose Kermutdere Formation, from lower to the top orderly. Alibaba Formation is consisting of andesite, basalts and their pyroclastics. Basalts and andesites are mostly found as in forms of pillow lavas, round and lava flow shapes. It is determined that the Eocene age volcanics have calc-alkaline character and are plotted in andesite and andesite/basalts areas and placed in medium-high K fields, based on chemical naming diagrams of SiO2 versus Na2O+K2O and Nb/Y versus Zr/TiO2*0.0001. It is defined that the volcanic rocks are composed of plagioclase, clinopyroxene, hornblende and magnetite mineral phases. In trace element changing diagrams normalized according to the MORB, the analyzed samples have showed and enrichment in terms of LILE (High Ion Radius Litophile Elements (Sr, K, Rb ve Ba), Th and Ce concentrations, while an impoverishment of Nb and Ta in terms of HSFE (High Strength Field Elements like Zr, Ti and Y). The REE distributions values of examined volcanics, normalized according to the Kondrite, shows, in general, similarity to each other. This situation points out that the rocks composing of Kermutdere area volcanics are originated from same or similar mantle source. The alterations subject to this study are developed and related to andesites found within Eocene age Alibaba Formation. The alterations seen in the study area are observed in general around the NE-SW and about E-W trending fractures. Within the area of fracture zones, the alteration types observed in the andesites hosting the mineralization are in general as follow: limonitization, hematitization, argillitization and silicification. In the sampling profile based on the MINSQ method as alteration mineralogy quartz, K-feldspar, sericite ± kaolin is determined in potassik alteration zone. In the propylitic zone, epidote, Fe-chlorite, Mg-chlorite are defined in addition to the dominant alteration mineral albite. According to the slope values calculated isocone method; mass loss in the propylitic zone (m=1.16) and mass gain in the potassic zone (m=0.60). Based on the proportional (%) and net (g/100g) mass change calculations prepared for the whole, an increase in the amounts of K and Si (major elements) and Cu, Pb, Au, As and Ag (ore elements) were observed. On the other hand, a proportional decrease in the amounts of Na, Ca, Fe, Mg elements were determined.. It is calculated that a mass loss of % 12.28 have occurred in the mass of the rocks sampled along a profile perpendicular to the fracture line. When the all data obtained from mass changes calculations made were evaluated; due to the high correlations between the elements carried by ore-forming fluids and to be enriched in similar zones, it is concluded that mineralizations in the region are occurred in the same phase. Keywords: Hydrothermal alteration, Kermut, Mass loss, Mass gain, MINSQ,