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. The saturation index of waters regard- ing minerals is low. Computer simulation indicates that calcite and dolomite are common minerals in all water samples which are saturated in respect to quartz and argillaceous-siliceous minerals. The most pronounced property of waters is their acidic character. The high metal concentrations are related to water with low pH. Sulfide minerals control the low pH values of waters which is an important control factor for the evolution of the water chemical composition. The abundance of sulfates is attributed to the dissolution of the minerals pyrite (FeS2) and alunite (KAl3(SO4)2(OH)6. The water–mineral interactions are responsible for the chemical composition of waters. Water qual- ity problems can be successfully handled by the use factor analysis. 17 chemical parameters can be substituted by five factors which successfully represent the hydrochemical processes as well as their geographic distribution. Volcanic rocks in the study area have the potential to produce acid drainage. Keywords: Acid water, groundwater, hydrochemistry, saline water, volcanic rocks 1. Introduction Recently, environmental problems caused by acid drainage, are evident in many parts of the world. In the last few years, these problems have been intensely studied Water, Air, and Soil Pollution (2006) 169: 375–394 C Springer 2006 376 C. PETALAS ET AL. in order to minimize their adverse effect on the environment. The pollution of surface and ground waters by acid mine drainage cause serious damage to ecosys- tems. The occurrence of acid waters is related to the solution of sulfide compounds, such as sulfides, in water. Such compounds are very common in volcanic rocks and are originated as metallic deposits precipitated from hydrothermal fluids. Gold is usually found along with these minerals, in exploitable amounts, in relation to advanced argilic alteration in the andesitic rocks with silica and chalcedony bod- ies. Fluid inclusion data suggests an epithermal system for the ore forming-fluid (Lattanzi et al., 1991; Ruggieri, 1993). Usually, the utilization of the aforemen- tioned compounds creates metal-reach metallurgical wastes, which causes serious environmental problems when they are leached by rain or surface waters. One of the most characteristic examples is the case of Sardinia, where after some decades of production of Pb, Zn, Ag, Cu, Sb, and Ba minerals, enormous volumes of met- allurgical wastes caused serious problems of quality degradation on surface and ground waters (Cidu et al., 1997). Also, in Tuscany, the metallurgical wastes orig- inated from the utilization of metal-reach sulfide compounds of Hg, Sb and Fe, created acid mine drainage that has caused serious environmental problems (Ben- venuti et al., 1997). Similar problems occur in South Korea, where the wastes of poly-metallic mines produce W, Mo, Fe, Sn, Cu, Mb, Zn and Au, Ag which are considered responsible for introducing heavy metals to the environment (Lee et al., 2001; Lee, 2003). In Greece, the intense utilization of silver-bearing galena during the period 3000 B.C.to1989 in the historical mining area of Lavrion, Attica, caused the accumulation of vast volumes of metallurgical wastes wich are considered to be responsible for the degradation of the environment (Marinos and Petrascheck, 1956; Konofagos, 1980; Kontopoulos et al., 1995). Stavrakis et al., (1994) and Kontopou- los et al., 1995 mention that the soils of the pit-area, but also in the surrounding area show high concentrations of Pb, Zn, Sb, Cu, Hg, Cd, As, Fe and Mn. Chronopoulos and Chronopoulou-Sereli, (1986) measured high concentrations of Pb, Zn, Cu, Fe and Mn in vegetable fibres. Alexakis and Kelepertsis (1998), and Stamatis et al. (2001) attribute the high metal concentrations in ground water to the geological environment. The presence of sulfide minerals has been postulated in the broader Sapes area (Thrace) – northeastern Greece. These minerals occur in volcanic rocks and hy- drothermal fluids. This study was set up to characterize the environmental hydrochemistry and heavy metal contamination in the broader Sapes area, on the basis of physico- chemical properties of surface and groundwaters occurring in volcanosedimen- tary formations of this area. The results of the study will help identify rocks which have the potential to produce acid drainage. This work aims also to pre- vent the groundwaters and streams from further pollution in the future, taking into account that intense gold mining activities are planned to operate in the study area in the near future. Figure 1 shows the location map of the study area. HYDROCHEMISTRY OF WATERS OF VOLCANIC ROCKS 377 Figure 1. Principal geologic units and structural features in the study area. Water sampling points and stream systems are also shown. (Modified from the geological map 1:200000 of the Institute of Geological and Mineral Exploration, Greece). 378 C. PETALAS ET AL. 2. Geology of the Study Area The study area belongs geotectonically to the Rhodope massif located at the south- ern boundary of Xanthi – Komotini basin which was formed during the tertiary upon the metamorphic rocks of Rhodope massif and the Perirhodopic unit. According to Jacobshagen (1978) the formation of the tertiary basins in the broader area was a result of the orogenetic phase of Eocene time. The broader Komotini-area, east of Komotini city, is made up by the following geotectonic units: a) The pre-alpine bedrock of the Rhodope massif, b) The perirhodopic belt (Makri and Drimou-Melia unit of Mesozoic era) and c) the tertiary basins related to taphrogenic tectonism of North Aegean (Middle to Upper Eocene – Pliocene), (Mposkos et al., 1988). Prin- cipal geologic units, a geologic cross section, structural features as well as water sampling points and streamline network in the study area are shown in Figure 1. Rocks of Tertiary age present in the study area are intensely altered and un- conformably overly the metamorphic bedrock (Makri unit). According to Mposkos et al. (1988) Makri unit is part or tectonic remnant of the Peri-Rhodopic belt which is geotectonically related to the Mesozoic geosyncline of Tethys. Makri unit is made up by the overlying metavolcanosedimentary series or greenschist series and the underlying metasedimentary series, which mainly is made up by marbles and calcitic phyllites. The geologic structure of the broader area is characterized by the presence of synclinal and antisynclinal structures of many kilometers long. The direction of their axes ranges from 40 to 50◦NE. Generally, folds are vertical-symmetrical without inclination of the axial surface (Mposkos et al., 1988). Subvolcanic and intrusive rocks display linear development following tertiary fault zones. Clastic sediments and volcanic rocks were deposited within the study area during a period characterized by intensive synsedimentary – intrusive activity. Pyroxene andesites and amphibole – biotite andesites, subvolcanic rocks (of rhyo-dakeitic composi- tion) and plutonic rocks are dominant in the study area. According to Michael et al., (1989a, 1989b), Arikas (1981), Arikas et al. (1993) and Michael et al., (1995), pyroclastics and lavas in the Rhodope massif locally display paragenesis originated from hydrothermal alteration, usually related genetically to basic metal deposits. Neogene formations are mainly made up by argillaceous-siliceous minerals. In Thrace, lavas, pyroclastics and igneous intrusions are sufficiently altered by hy- drothermal fluids related to sulfer metalliferous deposits (Sideris, 1975; Arikas, 1981; Katirtzoglou, 1986). The petrochemical analysis of volcanic rocks indicates that they are mineralogically characterized as calc-alkali rocks, namely as basaltic andesites, andesites and dacites (Sideris et al., 1991). According