HYDROCHEMISTRY OF WATERS OF VOLCANIC ROCKS: THE CASE OF THE VOLCANOSEDIMENTARY ROCKS OF THRACE, GREECE C. PETALAS1,∗,N.LAMBRAKIS2 and E. ZAGGANA3 1Laboratory of Ecological Engineering and Technology, Department of Environmental Engineering, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi, Greece; 2University of Patras, Department of Geology, Laboratory of Hydrogeology, 26500 Patras, e-mail:
[email protected]; 3Hellenic Centre for Marine Research (HCMR), Institute of Oceanography, Athens-Sounio Avenue, 19 013 Anavyssos, Greece, e-mail address:
[email protected] (∗author for correspondence, e-mail:
[email protected], Tel: +30-541-0-79385, Fax: +30-541-0-79385) (Received 21 February 2005; accepted 2 September 2005) Abstract. This work is referred to the characterization of the environmental hydrochemistry in the broader Sapes area – Thrace region, on the basis of physico-chemical properties of surface and groundwaters occurring in the volcanosedimentary formations of this area, where gold mining activ- ities are planned to operate. Volcanic rocks are considerably altered where they are in contact with hydrothermal solutions. Aquifers are formed within these formations. Surface and ground waters are strongly metalliferous and their hydrochemical facies present similar but complex water types. Cer- tain characteristic chemical types are the following: Ca-Mg-HCO3-SO4, Ca-Mg-SO4-HCO3. Ca-SO4, Ca-Mg-SO4. Ca-Na-Cl-HCO3, Na-Cl. A small majority of the water samples present the following − 2− − order of anion dominance HCO3 > SO4 > Cl . Calcium is the dominant cation. Bicarbonates and sulfate ions are the dominant anions. The order of dominance for the heavy metals in surface and ground waters is as follows: Fe > Mn > Zn > Ni > Cu.