GEOCHEMISTRY OF THERMAL WATERS AND ITS RELATION TO THE VOLCANISM IN THE KIZILCAHAMAM (ANKARA) AREA, TURKEY

Thermal waters issuing through the Tertiary aged volcanics in the Kizi lcahamam (Ankara) area are all alkali-bicarbonate waters with temperat ures ranging from 28-degrees-C to 86-degrees-C. The waters from the to wn center (MTA-1 and KHD-1 drilling wells, Big Bath and Small Bath) ha ve the highest temperature and an intermediate TDS content, in compari son to the waters sampled from the localities outside the town center (Mineral Water Spring and Sey Bath). The Mineral Water Spring is chara cterized by the lowest temperature and the highest TDS content. The wa ters from the Sey Bath have an intermediate temperature and the lowest TDS content. The variations in the temperature and the chemical compo sition of the waters can be accounted for by a combination of processe s including mixing between cold-shallow and hot-deep waters, boiling e ither before or after mixing, steam heating and conductive cooling. Th e chemical geothermometers, silica-enthalpy and enthalpy-chloride mixi ng models suggest a reservoir temperature of 124-190-degrees-C for the Kizilcahamam region, and a maximum of 71 % deep, hot component for th e thermal waters. Within the framework of water-rock interaction, the volume of volcanic rocks necessary to supply the annual water output h as been estimated as 16.5 x 10(6) m3 a-1; the volume of the volcanic r ocks necessary to supply the annual chemical output of the thermal wat ers has been estimated, on the basis of cation contents, as 16,785 m3 a-1. This suggests that, for the thermal waters to obtain their chemic al composition, only 0.1 % of the volcanics is required to have underg one leaching. As this amount is rather low, the waters seem to have ob tained their cation contents almost totally from the volcanics nearby. On the other hand, the bicarbonate enrichment in the Kizilcahamam wat ers points to the fact that groundwaters dissolve CO2 arising, probabl y, from a magmatic body solidifying at depth, which can also account f or the heat source of the Kizilcahamam geothermal system.