This post is part of the GeoConnect³d blog.
Introduction
The Pannonian Basin covers approximately 20% of the territory of Bosnia and Herzegovina. There are several sub-basins within this regional basin; one of them is the Tuzla Basin, which is located in the NE part of country. Numerous mineral raw materials have been discovered and used in the Tuzla Basin, but salt and coal are in the first place. The city of Tuzla was formed and developed due to the exploitation of salt.
The subject of this blog is the rock salt deposit Tuzla, which is located in city of Tuzla (Figure 1). This deposit has been exploited in the past, and the exploitation was finished in 2006 due to the negative consequences for the space and life of people in the central parts of the city. Namely, the long-term overexploitation of the salt deposit (primarily in the exploitation field Trnovac – Hukalo) has led to a ground subsidence problem, causing great damage to residential and commercial buildings, as well as transport infrastructure.
History of exploitation of rock salt and salt water in Tuzla
Archaeological research demonstrates that salt was exploited in Tuzla during the Neolithic period, as evidenced by the remains of a Neolithic settlement and salt extraction vessels from this period (5.000-4.500 B.C.) in the center of Tuzla (on today’s Salt Square is marked the place of salt exploitation).
During the period of Ottoman rule in Bosnia, salt water was exploited in Gornja and Donja Tuzla. Name of Tuzla derives from that period; comes from the Turkish word “tuz” which means salt. It is known that in Ottoman period, dug wells were made in places of natural springs (the first was constructed in 1476). One such well with depth of 60 m existed on today’s Salt Square in the center of Tuzla, where salt water was exploited and salt extracted in process of evaporation by boiling salt water in cauldrons. According to Jovanović and Vujović (1976) about 2.500 kg/day of salt was obtained on location Salt Square, and in the same time in Gornja Tuzla ca 300 kg/day.
Modern exploitation of salt in Tuzla by pumping thermomineral groundwater from deep wells began in 1880 during the period of Austro-Hungarian rule in Bosnia and Herzegovina when the first industrial facilities for salt water processing were built in the wider area of Tuzla (Jovanović and Vujović, 1976). The first chemical analysis of salt water was performed by the Austrian researcher E. Ludwig in 1887, when he analyzed the water from well no. 5 and 6 in Tuzla (Ludwig, 1893). These wells were 379 and 367 m deep (Katzer, 1919).
Parallel with the exploitation of salt water in the exploitation field Trnovac-Hukalo, the underground mining exploitation of salt in the exploitation field Tušanj began in 1967.
A new salt deposit in the Tuzla area was found in 1973 by drilling the well DS-3 in the village Tetima (Municipality of Tuzla), what was followed by detailed research and exploitation continues up today. Rock salt deposit Tetima is located about 10 km northeast from the salt deposit Tuzla.
Except in salt production, thermomineral salt water is used for therapeutic purposes in the Tuzla Spa. Jovanović B. (1940) writes: “In 1912 is constructed a beautiful spa in Tuzla with tubs and inhalatorium. The healing properties of salt water are especially effective for rheumatism, sciatica, gynecological diseases, respiratory problems, etc. Respiratory diseases are treated in the inhalatorium with dispersed salt water”. In 1936 the spa was extended with two large indoor and one outdoor swimming pool.
Geological and hydrogeological characteristics of rock salt deposit Tuzla
More detailed information on the geology of Tuzla basin and salt deposit have been provided by several authors: Katzer 1903; Soklić 1959, 1964, 1982; Jovanović and Vujović, 1976; Stevanović 1977; Čičić 2002; Jovanović 1980; Vrabac 1999; Ferhadbegović 2003; Hrvatović 2006. The hydrogeology of the salt deposit in Tuzla area was studied by Luković 1952; Patrlje 1956; Miletović 1980; Baturić 1961; Đurić 1987, 1988; Hadžihrustić, Oruč et al. 2006 and others.
The rock salt deposit Tuzla was formed within Miocene sediments (according to numerous earlier researchers it is Upper Burdigalian and Helvetian, while geologists of recent times the deposit classify as Carpathian or Lower Badenian) where clay marls are dominant, but in some places it is dolomitic and bituminous marls. Gypsum and anhydrite also follow salt layers (Fig. 2). Within this rock complex, which is called the “trakasta serija” (or “salt formation” according to Hrvatović, 2006), five layers of salt are distinguished by depth; they are separated by marls. Tortonian “Schlir” (marls, sandstones and conglomerates) and alluvial sediments occur in the roof of the “trakasta serija”, while the bottom sediments represent “red series” with red sandstones, conglomerates, clays and marls (Lower Miocene).
The rock salt deposit Tuzla is almost entirely lying inside the Trnovac-Tušanj syncline structure, and has Dinaric direction (NW-SE).
Legend: 1-Alluvial sediments, 2-Tortonian (marls, clays, sandstones, conglomerates), 3-Upper Burdigalian and Helvetian (“trakasta serija”), 4- pelite, tuff, 5-rock salt; in the lower layers is Glauber’s salt, 6- anhydrite
The depth to the salt body and the thickness of the layers varies spatially; the depth to the salt is 150 to 500 m from the surface of the terrain, while the thickness of the salt layers is 20-100 m, where the thickest layers are in the central part of the syncline (Jovanović and Vujović M 1976).
The entire “trakasta serija”, including the salt layers, has low water permeability, while the roof sediments (Schlir) are impermeable. The alluvium of the rivers Jala and Solina, which in some places lie directly on the “trakasta serija”, are very permeable and water-bearing aquifers with fresh waters.
The rock salt deposit Tuzla was exploited on two exploitation fields: 1) Trnovac-Hukalo and 2) Tušanj. The salt exploitation in the Trnovac-Hukalo area was carried out by salt water pumping from wells, while in the Tušanj area exploitation was done by underground mining methods.
The main groundwater accumulation is formed in the zone of the first salt layer and these waters have less mineralization in relation to deeper horizons (Jovanović P. et al., 1971). The groundwater in the alluvial sands and gravels is hydraulically connected with that accumulation. The main groundwater accumulation is recharged by infiltration atmospheric precipitation into permeable rocks and from alluvial aquifer of rivers Jala and Solina.
Pumped waters from wells have high mineralization up to 300 g/l and temperature of 24 – 27°C, Cl–Na type.
Intensive pumping of groundwater has led to dissolving soluble rocks (halite, gypsum and anhydrite) resulting in the formation of caverns and cavities that collapsed over time, devastating the terrain in the central part of the city of Tuzla. Many residential buildings, roads and exploitation wells were destroyed, the terrain in the area of today’s artificial lakes was swamped, and because of these facts a controlled stopping of exploitation had to be done, so exploitation of salt in the city of Tuzla was finished in 2006.
Artificial salt lakes “Pannonica” in the function of reducing the devastation of space
Extraction of salt by pumping thermomineral water on wells in Tuzla caused the subsidence and deformation of terrain in the urban part of Tuzla (up to 12 m in period 1947-1991); maximal subsidence of 1100 mm during one year was recorded in 1983 (Taletović N. et al. 2014). According to the same authors the results of the subsidence were the relocation of 15.000 inhabitants and destruction of 2.700 housing units and approximately 200.000 m2 of production facilities, educational, health, cultural and sport objects.
The terrain was mostly rehabilitated after the end of the exploitation of the salt deposit Tuzla. Demolished and damaged buildings were renovated where the terrain was estimated as stable, but even now in the city center destroyed and unrepaired buildings can be seen (Figure 3).
In an area where the terrain was difficult and economically unacceptable to turn into safe for construction, as a measure to mitigate the consequences of subsidence of terrain and devastation of space, three artificial salt lakes with gravel beaches were made; these lakes that have a common name “Pannonian lakes” or “Pannonca” are used in summer times for recreation (Figure 4). Other accompanying facilities, attractive for tourists, were also built, such the Archeological park (Neolithic settlement), the Salt Museum, etc: https://panonikasojenice.ba/en/home/
Lakes’ water is a combination of fresh water (delivered by pipeline from the artificial lake Modrac) and brine of high concentration (300-350 g/l) from wells of Tetima salt deposit. The share of salt water in the total water volume is about 30 %. Bottom of lakes is covered with geosynthetic and natural materials (gravel and sand), so their coast looks like a sea beach. The complex of Pannonian lakes has a total area of 75.000 m2, the length of the coast 1.000 m, and the area of the gravelly part of the beach is 22.000 m2.
After the finishing of the salt extraction at deposit Tuzla, greater exploitation of the Tetima salt deposit, which is located in sparsely populated area, was activated. The exploitation at deposit Tetima is performed by artificial leaching of salt bodies in deep wells, so the devastation of the area of Tetima is not expected.
Natalija Samardžić
FZZG – Geological Survey of Federation of Bosnia and Herzegovina
References
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Hadžihrustić I., Oruč E. et al. (2006): Supplementary mining project for stopping pumping of salt water at the Trnovac-Hukalo exploitation field, Unpublished document, Mining Institute, Tuzla.
Hrvatović H. (2006): Geological guidebook through Bosnia and Herzegovina, Separate Monograph of Herald Geological, 25, Sarajevo, 1-165.
Katzer F. (1919): To knowledge of mineral springs of Bosnia. State museum herald in Bosnia and Herzegovina, Sarajevo.
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Vrabac S., Ferhatbegović Z., Đulović I., Bijedić Dž. (2008): The associations of microforaminifera in the roof sediments of the salt formation and their application during the drilling of the borehole B-84 in the rock salt deposit Tetima, Herald geological, 37, Geological survey of Federation of Bosnia and Herzegovina, Sarajevo.
Vrabac S., Ćorić S. (2008): Revision of the “Carpathian” of the Tuzla Basin with review to the stratigraphic position of the salt formation, Herald geological, 37, Geological survey of Federation of Bosnia and Herzegovina, Sarajevo.
Taletović N., Isabegović J., Avdić A., Šabović A. (2014): Results of geodetic observations at characteristic subsidence zone in salt deposit Tuzla analysed through 3D models in post exploitation period, e-Zbornik no. 8, Mining Institute Tuzla, Tuzla.
https://e-zbornik.gf.sum.ba/images/radovi//e_zbornik_08_06.pdf
Websites:
https://www.bljesak.info/lifestyle/putujte-s-nama/tuzla-pa-se-hvali-da-se-mlijekom-hrani/314100