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Rock salt

General information and occurrence

Polish rock salt deposits are related to 2 main halite formations: of the Miocene and Zechstein age.

The earliest explored and developed in Poland, were deposits of the Miocene formation which are situated in a belt extending from the Silesian region through Wieliczka and Bochnia towns and further eastwards up to the eastern Polish border and running along and close to the frontal overthrust of the Carpathian Mts. on their Foredeep. The exploitation of these deposits ended in 1996 when the salt mining was phased out in the Wieliczka mine. The documented anticipated economic resources of the Miocene rock salt deposits (excluding protective pillars) are estimated to be over 4.36 billion tonnes (the deposits: Rybnik-Żory-Orzesze, Siedlec-Moszczenica, Wieliczka, Wojnicz), accounting currently for about 3.8% of the domestic resources. However, a geological structure of these deposits is very complex due to an intense folding (the majority are folded and folded-bedded deposits, except for Rybnik-Żary-Orzesze deposit which is a bedded deposit in a tectonic trough). That complexity of the geological structure along with a markedly varying salt quality and high risks of water flooding and methane inflow to mining works were the reasons why further mining of these deposits became practically uneconomic. Nowadays, the historical mines (Wieliczka and Bochnia) are great tourist attractions and recreation centers.

The Zechstein halite formation is at present the major source of mined salt in Poland. The salt-bearing series are distributed throughout two-thirds of the country area, mainly in the Polish Lowlands. In the Late Permian these areas were occupied by the evaporitic epicontinental basin which was the place of a salt sediments accumulation with the total thickness of over 1,000 m. Bedded rock salt accumulations were documented down to 1,000 m depth in the marginal parts of the basin and in the Łeba Elevation and the Fore-Sudetic zone (the deposits: Bądzów, Łeba, Mechelinki, Sieroszowice and Zatoka Pucka). The anticipated economic resources of these deposits (excluding protective pillars) are estimated at nearly 26.14 billion tonnes, which accounts for more than 23.2% of domestic salt resources. In turn, in an axial part of the basin (central Poland) the salt-bearing series are buried at depths up to 7 km, locally rising almost to the surface in salt dome- and pillow-like structures. The salt structures occur in a belt stretching from Wolin in the northwest to the vicinities of Bełchatów town in the south-east. Deposits of the rock salt and potassium-magnesium salt were explored and documented in a number of the shallowest of these structures. The documented anticipated economic resources (excluding protective pillars) of deposits related to the Zechstein salt structures (deposits from the following Voivodeships: Kujawsko-Pomorskie, Łódzkie and Wielkopolskie) are equal more than 81.9 billion tonnes, which accounts for about 73% of the domestic salt resources. The exploitation of the latter deposits gives 100% of the current domestic salt production (table 2). The bedded rock-salt deposits have been also documented in the bed of the oldest rock salt – in the overburden of the copper ore deposits in the Fore-Sudetic Monocline (e.g. the rock salt deposit within the copper ore deposit Sieroszowice and forming its part – documented in 2013 – the rock salt Bądzów deposit).

The bedded rock-salt deposits are being documented down to the depth of 1,200 m, providing that the deposit series (including partings) is at least 30 m thick and the minimum weighted mean of NaCl in the deposit series and partings equals at least 80%. In accordance with the Polish regulations, salt deposits related to the dome and pillow salt structures are explored down to 1,400 m, providing that the distance between top surface of salt deposits and salt mirror (a protective shelf) is not smaller than 150 m. The remaining requirements are the same as in the case of the bedded deposits. At present, the salt deposits increasingly begin to be treated as the geological objects, especially advantageous for the construction of underground facilities for a storage of crude oil, natural gas and fuels (e.g. already operating the Mogilno II (gas) and Góra (fuels) facilities and put into operation in 2014 the Kosakowo storage (gas) with the active capacity of ten storage caverns being equal 299.8 million m3).

In the world, the salt domes are also being used as the safe disposal underground sites for wastes – e.g. Asse and Morsleben domes and Herfa-Neurode and Heilbronn mines in the bedded rock-salt deposits in Germany, or mines located in the bedded potassium and rock salt deposits in the area of Regina (southern Saskatchewan) in Canada. In recent years, in Alberta Province (Canada) the crude oil recovered from so-called bituminous sand is stored, whereas the exploitation wastes are being disposed in caverns within Devonian salt formations: Lotsberg and Prairie. Optionally, the caverns leached in the rock salt are also being used for the hydrogen storage as part of the zero-emission energy – currently, there are 3 such facilities functioning in the United States (Clemens Dome, Moss, Bluff and Spindetop) and 1 in the United Kingdom (Teeside), whereas in the Netherlands and France 2 pilot facilities are operating*.

Resources and output

The anticipated economic resources of rock salt (excluding protective pillars) in 2022 amounted to nearly 112.42 billion tonnes, increasing by almost 11 million tonnes in the relation to the previous year (due to the new assessment of resources in the Kłodawa 1 deposit – in a new geological documentation with recalculated resources (supplement No 3), the growth by 42.7 million tonnes), whereas the anticipated sub-economic resources remained unchanged. The economic resources increased by more than 44 million tonnes (nearly 2.4% of the domestic resources) due to the new assessment of resources in the Mogilno I deposit (supplement No 4 to the deposit development plan), in spite of the ongoing exploitation.

Rock salt deposits in Poland are presented on the map.

Table 1 shows resources and the current state of exploration and development of domestic rock salt deposits. Data refer to resources excluding those within protective pillars.

In 2022, the total domestic output of rock salt amounted to 3,883 thousand tonnes, including 2,879 thousand tonnes coming from a solution mining method (the Góra and Mogilno I mines – more than 74% of the domestic production). Moreover, 796 thousand tonnes of crushed salt were obtained from the Kłodawa 1 deposit (about 20.5% of the domestic production) and from the Bądzów deposit – 209 thousand tonnes (about 5.4% of the domestic production).

In the copper ores Sieroszowice mine there were 49,288 tonnes of rock salt as the accompanying raw material above the copper ores deposit Sieroszowice exploited (the drop by nearly 43.5% since 2021).

In the Mechelinki and Mogilno II deposits the exploitation of rock salt was not carried out in 2022.

In 2022, Przedsiębiorstwo Gospodarki Wodnej i Rekultywacji Spółka Akcyjna – the former name: Dębieńsko Desalination Plant Ltd., recovered 66,203 tonnes of evaporated salt from the treatment of brines and salty water from the hard coal mines. The production decreased by 2.1% in comparison with the previous year.

The figure given below shows changes in resources and production of rock salt in Poland in the years 1989-2022.

Output corrected for 2016-2021 period.

The foreseen (prospective and prognostic) resources of rock salt in Poland, assessed to the depth of 2 km, amount to almost 4,060 billion tonnes, including over 4,050 billion tonnes of the Permian salts and 6.9 billion tonnes of the Miocene salts**.

Prepared by: Grzegorz Czapowski

* https://unece.org/sites/default/files/2021-04/09_Serge_van_Gessel-Hydrogen_Storage_and_UNFC-UNECE_RM_Week-2021.pdf.

** Czapowski G., Bukowski K., Mazurek S., 2020 - Sól kamienna (rock salt, salt, halites), sole potasowo-magnezowe (potash salts, potassium salts, potassium-magnessium salts). In: Bilans perspektywicznych zasobów kopalin Polski wg stanu na 31.12.2018 r. (eds. Szamałek K., Szuflicki M., Mizerski W.): 218-232. PIG-PIB, Warszawa [in Polish].