Products: Table Salt.
Lifetime: 13th century, continuously until 2007
Owner: Żupy krakowskie Salt Mines.
Overview: Just a few kilometres south of Cracow, in southern Poland, the scenery changes abruptly from the fluvial plain of the Vistula river, mantled by tills and loess deposits of the Pleistocene glaciation, to a boldly undulating topography representing the outermost thrust sheet of the Carpathian mountains. These northern foothills of the Carpathians are known in Poland as the Beskid Mountains. The Carpathian thrust front can be traced from Upper Silesia through Cracow and Przemysl in southern Poland as far as the Ukraine and Romania. At several places along the thrust front, salt deposits have been found, which have been mined over many centuries. One of the best known mines is located at Wieliczka, 15 km south-east of Cracow. The mine is a popular tourist location, but it also illustrates some spectacular geological features.
The Wielicka Salt Mine is the oldest continuously operating industrial venture in Poland, having started production in 1290 when it was acquired by King Przemislav II. Salt was a royal monopoly and in the 14th and 15th centuries it contributed one-third of the entire royal income. The revenue obtained from salt was used to build the royal castle on the Wawel hill in Cracow and the walls which surround the city, and paid the salaries of the professors at Cracow University. By 1380 the salt mine employed 200 men and for centuries was the largest industrial concern in Poland. By the 20th century the work force had risen to 1600. The salt was originally dug by hand, and many of the galleries still bear the marks of the miners’ picks. Production in the 18th century was around 30 000 tonnes per year, and peak production was reached during the decade beginning in 1964 when it reached 256 000 tonnes per year.
In 2010 it was successfully proposed that the nearby historic Bochnia Salt Mine (Poland's oldest salt mine) be added to the list of UNESCO World Heritage sites. The two sister salt mines now appear together in the UNESCO list of World Heritage Sites as the "Wieliczka and Bochnia Royal Salt Mines". In 2013 the UNESCO World Heritage Site was expanded by the addition of the Żupny Castle.
Geology & Mineralization: In the Wieliczka–Bochnia area the Middle Miocene (Badenian) salt-bearing formation consists of terrigenous, argillaceous and clastic sediments at the bottom (the Skawina Beds), an evaporite series (the Wieliczka Beds), and marly clays, siltstones and sandstones of the Chodenice Beds at the top (Garlicki, 1968, 1979).
|Geological sketch of the Wieliczka-Bochnia area.|
1 - platform Mesozoic sediments; 2 – Bochnia and Wieliczka salt deposits; 3 - Flysch Carpathian border; 4 - extent of folded Miocene sediments.
The Wieliczka salt deposits are extremely complex as they are involved in the Carpathian thrust belt. The salt is Tortonian (late Miocene) in age (about 10 million years old) and accumulated in a lake adjacent to the active thrust front. The salt-bearing formation unconformably overlies Carboniferous rocks in Upper Silesia, but in the Cracow area Jurassic and Cretaceous flysch deposits are present beneath the unconformity. The Tortonian sequence comprises over 1000 m of evaporites, siltstones and claystones with the main salt horizon towards the base. The salt section varies from 100 m to 300 m in thickness but frequently exhibits much greater thicknesses due to overthrusting and concentration in fold axes. At Wieliczka, two major subdivisions can be recognized, a lower stratified unit beneath the thrust plane, which represents the remains of the autochthonous salt flat, and an upper, much more chaotic, unit which represents part of the salt flat which was thrust over the lower unit during the mid-Tortonian tectonism. This has produced an extremely complex melange in the upper unit with salt concentrated in irregular bodies ranging in size from very small to about 20 000 m3. This explains the isolated nature of the worked caverns and the large areas of barren ground separating the main caverns (Fig. 2). The deepest salt deposits at Wieliczka are the stratified autochthonous deposits which represent the central and northern part of the original salt pan. The lower unit includes the ‘Green Salt’ with a total salt thickness of 10.8 m in four seams. The salt is coarsely crystalline with crystals up to several centimetres in size. The roof of the Crystal Chamber contains spectacular examples of large euhedral salt crystals .The green colour is attributed to the presence of small amounts of clay minerals. This salt is believed to have crystallized slowly in the deepest part of the lake in water depths of 400–500 m. Overlying the ‘Green Salt’ is a thin unit of clays containing anhydrite and the so-called ‘Shaft Salt’. The ‘Shaft Salt’ is a relatively pure salt with a characteristic straw-yellow colour, and is believed to have formed in the quietest part of the lake. The uppermost salt formation at Wieliczka is known as the ‘Spiza Salt’. It reaches 40 m in thickness and contains impurities of silt, clay and organic debris. It is generally finely crystalline and is believed to have crystallized quickly. It passes gradually upwards into saliferous sandstones.
Natural and historic heritage of the Bochnia salt mine (South Poland)
Janusz WIEWIÓRKA, Krzysztof DUDEK2, Józef CHARKOT Małgorzata GONERA
Don Hallet The Wieliczka Salt Mine