Isotope and chemical assessment of geothermal potential of Kos Island, Greece

The island of Kos is located in the southern part of the Aegean volcanic ar e. Between 1991 and 1993, water and gas samples were collected from cold an d thermal springs and from several water drill-holes. The maximum surface t emperature of 45 degrees C is associated with Fokas spring water, which con sists of a seawater modified by interaction with sedimentary rocks in the N W parr of the island. Two distinct groundwater circulations develop in the sedimentary and volcanic rocks; these are meteoric waters dominated by HCO3 ions that have ions formed by interaction with the calcite present in the rocks as primary or secondary mineral. Addition of CO2 from an external sou rce to the groundwaters locally leads to the formation of aggressive waters and a water-rock interaction characterised by the leaching of CaSO4 and pa rtial attainment of mineral/fluid equilibrium. The gas compositions suggest the presence, at depth, of a CO2-producing high-temperature system in its waning stage. an the basis of chemical solute geothermometry, temperatures higher than 110 degrees C appear unlikely at relatively shallow depths. (C) 1999 CNR. Published by Elsevier Science Ltd. All rights reserved.