| Abstract |
Bulgaria is a small country situated within the Balkan Peninsula. The country is quite rich of geothermal resources. There are more than 700 explored springs with temperature up to 103oC in about 140 sites. The Erma Reka geothermal system belongs to the most interesting and prospective in Bulgaria and Balkan Peninsula with respect to reservoir conditions. A big geothermal anomaly, the widest and unique for the country, was discovered during the geological and hydrogeological investigations of non-ferrous metals in the region of Erma Reka and Allamovtsi village during the period 1955-1956. It is a result of combination of various factors: geological structures, tectonic faults, paleo- and neo-tectonic lifting up of the massif, thermal characteristics of the rocks, etc. To clarify this anomaly, 60 deep structural hydrogeological drillings were made to a depth of more than 1500m. As a result of the investigation, it was established that a thick marble horizon exists in the region of Erma Reka and Malka rivers over an area of about 30 sq.km from elevation +100 m down to elevation -2000m. The upper part of the marble horizon is about 40 m thick and is strongly cavernous. The marbles can be said to be unevenly enkarsted. Several drillings found vertical failures 500 m to 1250 m deep, filled with thermo-mineral water of about 90?C temperature. The hot water in the region has a permanent piezometric level at elevation +490m. On the Bulgarian territory, there are no surface expressions of hydrothermal activity, such as hot springs and altered rock, while on the territory of neighbor Greece, the geothermal water overflows at elevation +430 m into the Elidze river bed, with a temperature of 60-70?C. Careful study of the Erma Reka geothermal system is a key for proper exploitation and planned wide activity. It makes an excellent subject of many further researches for sustainable use of geothermal water resources in the cross-border region and utilization of the thermomineral waters in Bulgaria in the flow rates, which will not cause negative impact on the Greek side. The work carried out in the Erma reka geothermal system consisted of geological and hydrogeological mapping, geophysical investigations and water sampling of thermal springs, located on Greek territory, and wells for geochemical analysis. Silica and cation geothermometers were applied to predict possible subsurface temperatures. The equilibrium state of thermal waters was studied by means of log Q/K diagrams and Na-K-Mg triangular diagram. It was found that water with temperature 100-150oC could be obtained by drilling. |