Rock salt
Polish rock salt deposits are related to two 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 to Wieliczka and Bochnia and further eastwards up to the Poland-Ukraine border and running along and close to the present-day 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 Miocene rock salt deposits are estimated to be over 4.36 billion tonnes, accounting currently for about 4.8% of 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. The Wieliczka mine was included on the UNESCO World Heritage list in 1978. Nowadays the Wieliczka and Bochnia mines 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 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 Monocline. Anticipated economic resources of these deposits (beyond protective pillars) are estimated at about 26.15 billion tonnes, which accounts for above 28.9% 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 in the south-east. Deposits of rock salt and potassium-magnesium salt were explored and documented in a number of the shallowest of these structures. Documented anticipated economic resources (beyond protective pillars) of deposits related to the salt structures are estimated at almost 59.84 billion tonnes, which accounts for 66.2% of domestic salt resources. Exploitation of the latter deposits gives 100% of the current domestic salt production (table 2). 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 – rock salt Bądzów deposit).
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 geological objects, especially advantageous for the construction of underground facilities for a storage of crude oil, natural gas and fuels - such as already operating Mogilno II (gas), Góra (fuels) and put into operation in 2014 Kosakowo storage with the active capacity of 4 storage caverns being equal 119 million m3 (within Mechelinki deposit).
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 bedded rock-salt deposits in Germany, or mines located in 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.
Anticipated economic resources of rock salt (beyond protective pillars) in 2018 amounted to over 90.35 billion tonnes, increasing by more than 5.07 million tonnes (about 5.95% of domestic resources) in the relation to the previous year. It was due to the re-assessment of the salt resources for the Lubień salt dome. Anticipated sub-economic resources remained unchanged. Economic resources dropped by 67.77 million tonnes (3.4% of domestic resources) due to the 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 2018 the total domestic output of rock salt amounted to 4,125 thousand tonnes (decreasing by 11.5% in comparison with the previous year), including 2,817 thousand tonnes coming from a solution mining method (Góra and Mogilno I mines – accounting for 68.3% of domestic production, decreasing by about 12.9% year to year, despite the lack of exploitation from Mogilno II deposit). Moreover, 552 thousand tonnes of crushed salt were exploited from Kłodawa 1 deposit (about 13.4% of the domestic production, 5.5% less than in 2017) and from Bądzów deposit (made available in the end of 2013) there was 325 thousand tonnes extracted (about 7.9% of the domestic production, increasing by 44.4% year to year).
There was also the production coming from the copper ores Sieroszowice mine where 33.3 thousand tonnes of rock salt as the accompanying raw material above cooper ores deposit Sieroszowice were exploited.
The production (in the form of brine) from Mechelinki deposit amounted to 432 thousand tonnes (about 10.5% of the domestic production, decreased by almost 29.1% in comparison with 2017) – the brine was dumped to the Bay of Puck.
In 2018 Przedsiębiorstwo Gospodarki Wodnej i Rekultywacji Spółka Akcyjna (in Polish) – the former name: Dębieńsko Desalination Plant Ltd., recovered 67,006 tonnes of evaporated salt from the treatment of brines and salty water from Upper Silesian coal mines. The production increased in relation to the previous year by 6.9% in comparison with the previous year when 62,673 tonnes were obtained.
The figure given below shows changes in resources and production of rock salt in Poland in the years 1989-2018.
Prepared by: Grzegorz Czapowski
Table 1. Rock salt - million tonnes