Title: Chemical geothermometers and mineral equilibria of some hot waters in Yugoslavia

Abstract

Geochemistry is a relatively young branch of hydrochemistry which is applied in each step of geothermal research and is also one of the less expensive investigation
methods. The main goal of geochemistry in surface exploration is predicting of subsurface temperatures. In later stages monitoring of chemical changes in the
reservoirs and solving scaling and corrosion problems are common. Yugoslavia is situated within an active tectonic and seismic belt known as the Alpic-KavkazHimalayan belt and in its territory there are found about 300 hot occurences both springs and wells with temperatures of 20-111 'C. The geothermal energy in this country is used in health spas, for greenhouse farming and heating. This report deals with chemical data from a part of Yugoslavian hot waters belonging to rwo tectonic units, the Vardar zone and the Serbo-macedonian mass. The main geological and tectonical features of the Vardar zone are ophiolites, melange and flysch sediments and young magmatic rocks of Quaternary age. The Tertiary grabens covered by young sediments are found in this zone. The Vardar zone is a very active tectonic and seismic zone. The Serbo-macedonian mass represents an older tectonic unit where rocks from Precambrian to Quaternary age are spread. This unit is not as active as the Vardar zone but some seismic areas are found, mostly related to regional faults.
In the report 52 chemical analysis from hot springs or wells are taken into consideration. The samples belong to rwo republics, Serbia and Macedonia. In Serbia
the waters are mainly of Na-HCOJ or Na-Cl type but in Macedonia the waters show complex compositions. The waters are mainly Ca-Mg-Na-HCOJ or Na-HCOJ type.
Chemical geothermometry, mixing models and mineral equilibria were used to interpret the samples. Waters of Na-CI type often show mineral equilibria but
bicarbonate waters often show disturbed equilibria. Waters with extremely high magnesium are often very difficult in interpretation. In Serbia, reservoir temperatures
in the range of 120-140"C were obtained for a few samples and in Macedonia the highest predicted temperature is in Bansko, 110-I1S'C.