Geothermal areas of Czechoslovakia

Geothermal areas of Czechoslovakia

Geotherraics (i97o) - SPECIALISSUE :2 U. N. Symposiumon the Developmentand Utilizationof GeothermalResources,Pisa I97O. Vol. 2, Part 2 Geothermal Ar...

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Geotherraics (i97o) - SPECIALISSUE :2

U. N. Symposiumon the Developmentand Utilizationof GeothermalResources,Pisa I97O. Vol. 2, Part 2

Geothermal Areas of Czechoslovakia S. KLfR *

ABSTRACT Czechoslovakia is characterized by a complicated geological structure. Its western part is built up of a horst called the Bohemian Massif and the eastern part belongs to the Alpine-Balkanian arch of the Carpathian system with the West Carpathians reaching the territory of Czechoslovakia. Geothermal areas are found in both geological units. The main thermal areas in Czechoslovakia are confined to the Kru[n~ Holy graben in the Bohemian Massif and to a fault system along the River V~lh in the West Carpathians. The location, geological situation and thermal capacity of the springs at the localities of Carlsbad, Sokolov, Teplice, Piettany, Sklenn6 Teplice and Bansk~/ Stiavnica are described, in addition to the methods of using thermal energy. In conclusion, the project of investigation in the Sokolov area is characterized, and the results of application of the thermal pumping at Turt~ianske Teplice are stated. Introduction

The geological structure of Czechoslovakia was discussed at the XXIII International Geological Congress held in Prague in 1968. The participants had the opportunity to study its characteristics personally both during pre-Congress excursions and from Congress papers. The whole territory of Bohemia and most of Moravia consists of the Bohemian Massif, which contacts the Kru~n~ Hory crystalline complex on the northwestern frontiers of Bohemia. This tectonic contact is distinctly seen especially on account of a large graben filled with sediments of Tertiary age and economically important deposits of brown coal, kaolin and other non-mineral resources. The area covered by the Kru~n6 Hory graben as a whole represents a thermal area. In the last few years detailed studies were made in its western part (with the world-famous Karlovy Vary Spring having excellent therapeutic effects at a temperature of 73°C) and still further to the west, in the central part of the Sokolov Basin, again with a high thermal capacity. The other portions of the Kru~n6 Hory graben are not as important as the two mentioned above. The eastern part of Moravia and Slovakia are ranged on the Alpine-Balkanian System, specifically to the arch of the West Carpathians. Geothermal areas are mostly confined to the area of late faults; these form ascending routes for thermal siphons, in the sense of L. MORET (1946), having infiltration borders on easily-permeable limestones and dolomites. The thermal waters do not descend to great depths but their springs as a rule are of high yields. The warmest thermal water in the West * Geoindustria, 32 u. Pr6honu, Praha 7, Czechoslovakia.

Carpathians is that at Piegtany, with a temperature of 67°C; it is also well known in the world because of its balneotherapeutic effects in combination with a dissolved solids content of the Pie~tany mud. Its high temperature is due to a fault system along the Vfih River at the border of the Vienna Basin. Another promising area is that of late igneous rocks, and it will be discussed. The other thermal areas in the West Carpathians are of subordinate importance only. Karlovy Vary (Carlsbad)

Spring area

According to records preserved, the Carlsbad area has been known for more than 600 years and its thermal capacity as well as carbon dioxide and dissolved solids contents have effectively been used therapeutically since the Middle Ages. Hvdrogeologically, this is a spring overcharged with carbon dioxide of the alkaline Glauber salty water type with a dissolved solid content amounting to about 6400 mg/kg. The spring temperature is as much as 73°C, whereas its branches attain lower temperatures. The ascending central part is confined to the crossing of the obliquely-running Carlsbad fault with the north-south trending Carlsbad fault (Figure 1 showing a tectonic diagram of the Carlsbad Sprin~ area), the two faults of great importance in the Nejdek-Eibenstock granite massif. The tectonic diagram also shows the other directions of granite tectonics, particularly that trending east-west and in places running conformably to a marginal fault of the Kru~n6 H o ~ graben on the south, the Oh~e fault. Drillin~ work done in the last few years indicates that this fault is impermeabile. This is why the east-west trending granite tectonics are regarded as particularly-significant, in a wider areal unit even forming the ascending central part of the basalt of the Doupov Mountains. The infiltration area is located in the area of the Nejdek-Eibenstock granite massif south of Carlsbad. The dissolved solid content and temperature of the spring suggest that the descending path is slow and attains a depth of about 2000 metres. The carbon dioxide inflow is regarded as being connected with the tectonic boundary of the basalt of the Doupov Mountains. The infiltravious investigations emphasized the tectonics in the basin filling of Tertiary age; new drillings, however, indicate that there is not a direct hydraulic contact. The Carlsbad area is separated from the central part of the 1055

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Fro. 1. -- Tectonic diagram showing the Cartsbad Spring area (trom maps by Academicians V. Zoffn~K,P. SA~'RU~..K,]. VJ~:I, and I. ZIKMUNDcompiled and supplemented by S. KLIR1 9 6 9 ) . 1 ~ . " , i . .~ ~- . - ' ~ ' . ~ ~ " i 1 - granite of Nejdek.Eibenstock pluton, 2 - Kru[n~ Hory crystalline complex, 3 - basin filling of Tertiary age, 4 . Ohre fault, marginal, impermeable, 5 . Carlsbad fault, running obliquely, 6 - Cadsbad fault, trending north-south, 7 . Chodov fault, 8 . fault tectonics of the basin filling, according to mining and drilling, especially during the quarrying of kaolin, 9 - other faults in Nejdek-Eibenstock pluton, I0 - Carlsbad Spring.

Sokolov Basin (lying further to the west, by the Chodov fault). The temperature of the Carlsbad Spring reaches 73°C; at a utilizable temperature of 68°C and a yield of 33 l/sec, the spring heat utilization is 7,840,800 keal × hour 1. The yield is mostly used for balneological purposes and to a lesser degree for heating, as in highpotential heat exchangers. Plans have also been made to enlarge heating of the spa buildings, using the same technique. Central

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Sokolov

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Thermal waters in the basal horizon of the central part of the Sokolov Basin were established when mine waters rushed into mining works of the lower coal seam in about 1900. Their location was gradually verified by drilling. The central part of the Sokolov Basin in the Kru~n6 Hory graben is limited by two marginal faults 1056

with northwest and southeast trends (see Figure 2 showing a tectonic diagram of the central part of the Sokolov Basin), the Svatava fault on the southwest and the Chodov fault on the northeast. In this central part, in the basin filling, two structurally significant faults are situated m the Grasset and Nov~ Sedlo faults. I1 may be inferred from their trend that these are rejuvenated early structural lines. Granites and a crystalline complex come into tectonic contact on the Alberov fault. It is the crossing of the Grasset, Nov~ Sedlo and Alberov faults that makes an important ascending central part for carbon dioxide from beneath the basin. The thermal horizon is restricted to a basal clastic complex of the basin filling, the so-called Star~ Sedlo formation. Hydrogeologically the lower coal seam is also included here. The interlying seams, upper coal seam and overlying claystones arc poorly permeable for water. This applies particularly to the voleano-detrital interlying seams forming an impermeable top of the thermal horizon.

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FIG. 2. - - Tectonic diagram showing central part o/ the Sokolov Basin (from maps by Academicians V. ZOUBEK, V. HOMOLA, Z. HOKR, I. GEBOO$tV, 1. HOLU~.C, O. MICHALEK, A. P A Z D ~ , P. ~A~rRUC~K, I. VZCL compiled and supplemented by S. KLIR 1969). 1 - granite of Ne.idek-Eibenstoek pluton, 2 . Kru~n6 Horv and Cisarsky crystalline complexes, 3 - basin filling of Tertiary age, 4 - marginal faults of Sokolov Basin, 5 - Svatava fault, limiting the central part of the basin on the southwest, 6 - Chodov fault, limiting the central part of the basin on the northeast, 7 - structurally less important Grasset and Nov6 Sedlo faults, longitudinal in basin filling, 8 - Alberov fault in the central part of the basin; tectonic contact of granite with crystalline complex, 9 - fault tectonics of basin filling, according to mining and drilling especially during coal mining. 10 - megafolds (anticlines and synclines), 11 - schistosity

The temperature of the basal horizon attains 35 °C; with the utilizable temperature of 30°C and yield of 89 1/see, the spring heat utilization is 9,612,000 kcal×hour I. According to chemical composition, this thermal water is of the natrium-bicarbonate type. The highest dissolved solid content has been found to be about 8000 mg/kg, and the carbon dioxide content indicates a mineral water. In view of the protection of mining works, about 30 litres are being pumped continuously from the upper coal seam. The use of the thermal content depends on the preparation, development and working of this upper seam. It is planned that in the future the water will be used directly for thermal baths and the heating of hothouses for decorative plants. Investigation is being made to determine safe workable bases; the efficiency of the heat spring cannot be known until the data are evaluated. It may be expected

that, owing to a high dissolved solid content, the water will be employed in local balneology for mining workers. Teplice

thermal

area

The Teplice thermal area is situated at the northeastern border of the Kru~n6 Hory basin. Infiltration, circulation and ascending routes of the Teplice thermal water are confined to a large body of the Permian porphyry. The thermal spring has received world-wide attention, forming the basis of the extensive thermal spa, with famous therapeutic effects and remarkable balneology. Hydrochemically, this is a plain thermal water devoid of carbon dioxide, having a temperature of about 42°C. With the utilizable temperature of 37°C and a yield of 34 litres/sec, the spring heat utilization is 4,528,800 kcal × hour x. 1057

At present prospection is in progress in this area, including one well drilled to great depths. The purpose of this well is to find a thermal water of standard chemical properties and a higher temperature at a depth of about 600 metres, and to enlarge the spring basis of the spa. Geological and related technical works are made under the auspices of the biggest surveying corporation in Czechoslovakia, GEOINDUSTRIA, Prague.

In spite of the fact that this area does not now represent an important central part, it should be noted that it is very promising, as is attested by almost every well recording the existence of thermal waters underlying the neovolcanic rocks. If systematically concentrated here, investigation would no doubt discover new efficient springs. The realization of this depends on real requirements which are, however, small with respect both to curative and tourist aspects.

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Piestany thermal area

At Pie~tany, the characteristics of the thermal siphon in the West Carpathians are less clearly visible owing to a fault system along the River Vfih. These faults are responsible for a subsidence in the western part of the area into depth. In addition, they affected sedimentation in the gulf of the Tertiary sea. The extraordinary tectonic structure caused deeper circulation. higher dissolved solid content, and higher temperature in the Pie~tany Spring, which has a high yield and similar chemical composition to the other low-temperature waters of the West Carpathians. Hydrochemically, the Pie~tany thermal water is that of the hydrogen sulphide gypsum type reaching as much as 67°C, with a watershed on the adjacent slopes of Inovec. With a spring temperature of 67°C, the utilizable temperature is 62°C representing, at a yield of 35 litres/sec, the spring heat utilization of 7,812,000 kcal × hour 1. The Pie[tany thermal water is used for balneological purposes, its curative effect being multiplied by thermal mud. It is also employed, although to a lesser extent, in heating of the spa buildings (with the use of heat exchangers). The heat loss exceeds the required optimum value, and therefore it is not possible to expect further exploitation. Recently the protection of the springs has been solved theoretically with respect to excessive loss; unfortunately the project has not yet been realized. Thermal waters in neovolcanic rocks of the West Carpathians

Late igneous rocks of the West Carpathians form the core of the Carpathian arch. The thermal waters are mostly restricted to the underlying rocks composed of limestones and dolomites. These are exploited mainly locally in small spas of subordinate importance only. Neither attains the high values which the spring yields. Of them, the best known thermal water is that at Sklenn~ Teplice, yielding 3.5 litres/sec at a temperature of 53 °C (so-called gypsum water), and that coming from the Franti[ek mine at Bansk~i ~tiavnica yielding 17 litres/sec at a temperature of 48°C.

1058

Exploitation and exploration

The principal thermal areas of Czecoslovakia are used for balneotherapeutic purposes. Most of them are known all over the world and therefore visited (Carlsbad, Teplice). The greater amount of the thermal water is for direct balneology, and the smaller amount having favourable temperature supplies heat to spa buildings using heat exchangers (Carlsbad, Pie[tany). At the locality of Pie~tany, thermal mud is also used for balneological purposes. The present investigation is concentrated in the central part of the Sokolov Basin. The method of exploiting the thermal horizon cannot be determined until mining plans as regards the brown coal seam are decided. Another very promising area is that underlying neovolcanic rocks of the West Carpathians; however, no work has been done here yet. In exploiting the heat content of a low-potential spring at the local Turc~iansk~ Teplice spa, ]. PRIBIL (1962) was fully successful employing a thermal pump. In the case of one spring, the heat content (from 45°C to 35°C) was used, for heating a group of the spa buildings. The equipment of the whole thermal pump, and especially the compressor, were manufactured by the well-known Czech specialized firm CKD Chocefi. This method proved especially useful in the heating of spa rooms, particularly with regard to the living environment, light ashes and smoke removal, and air purity. Thermal water springs used for spa purposes are discussed in greater detail in the Hydrogeology of Czechoslovakia, Part II. This paper was written by the outstanding Czechoslovak hydrogeologist O. HYmE, who died in 1968 and who devoted his whole life to the hydrogeology of mineral and thermal waters. His excellent work is here warmly acknowledged. REFERENCES H ~ E O. 1963 -- Hydrogeologi¢CSSR. Part 2, Mineralnf vody. Praha.

MORE'I"L. 1946 -- Les sources thermominerales. Paris. PRIBIL J. 1962 -- Thermo~erpadlo v Tur~ianskych Teplicfch Bratislava.