General information and occurrence
Gypsum (CaSO4.2H2O) is a product of sea water evaporation in a temperatures lower than those necessary for the precipitation of anhydrite (CaSO4). Gypsum may originate also in the result of the anhydrite hydration. Alabaster is a fine-grained variety of gypsum. Finer kinds of alabaster are used mainly as an ornamental and decorative stone and by sculptors.
Fired gypsum is one of the most common and ancient mortar of buildings. At present, it is widely used in the production of various building materials and prefabricates. It is also used in the production of moulds for the ceramic industry and is added to Portland cement as a component preventing cement flash setting. Some amounts of gypsum are used in the paint, lacquer and varnish industries and its especially pure varieties – in the surgery and dental clinics. Clear colorless gypsum crystals (selenite) were used to make optical instruments. Anhydrite is currently added to Portland cement and in the production of self-leveling floors.
In Poland, deposits of calcium sulfates (gypsum and anhydrite) are associated with saline (halite and potassium-magnesium salts) series of the evaporate formations of the Miocene and Zechstein. Their anticipated economic resources, beyond the protective pillars, documented in 15 deposits amount in 2021 to almost 259 million tonnes (it means that the resources increased by about 2.5% in comparison with 2020) and the resources of 4 exploited deposits – amount to almost 87 million tonnes (increased by more than 7.6% in comparison with 2020; Table 1). Economic resources (equal 64.1 million tonnes) decreased by 1.15 million tonnes (about 1.8%) since 2020, whereas anticipated sub-economic resources have not changed.
The Miocene gypsum deposits of the economic importance are located mainly along the northern margin of the Carpathian Foredeep, especially in the Nida valey. In these areas gypsum forms a thick, extensive bed, gently inclined and slightly disturbed tectonically. The gypsum bed crops out at the surface or is covered with a sedimentary blanket a few to over a dozen meters thick. The deposit series is from 3 m to 46 m thick and is characterized by fairly uniform of the mineral raw material and content of CaSO4.2H2O ranging from 85% to 95%. Deposits exploited in this region include the Borków-Chwałowice and Leszcze deposits.
Documented deposits of Zechstein sulfates (mainly anhydrites and secondary gypsum – originated from the anhydrites gypsification in the zones of aggressive groundwater infiltration) from the Lower Silesian region are characterized by markedly more complex geological conditions (strong tectonic disturbances) and a variability in a quality of mineral raw material. Two deposits are exploited in that region: Nowy Ląd and Nowy Ląd-Pole Radłówka (Table 2). The sulfates series occurs at the depth between 25 m and 400 m, their thickness varies from 1.7 m to 50.3 m and the CaSO4∙2H2O content ranges from 56% to 95.3%. Moreover, estimated resources of non-exploited gypsum and anhydrite which are associated with copper ores of the Lubin-Głogów Copper Area and made accessible by mining works of the copper mines are estimated – for their shallower occurring parts – at 57 billion tonnes.
In an accordance with domestic regulations, gypsum deposits are explored down to the depth of 50 m and those of anhydrite – down to 400 m. The minimum thickness accepted for gypsum deposits is 2 m and for those of anhydrite – 5 m. The accepted minimum content of usable components equals from 60% for anhydrite to 80% for gypsum, with the maximum ratio of thickness of cap rock to that of the deposit is 0.5 in the case of gypsum deposits.
The location of gypsum and anhydryte deposits in Poland is presented on the map.
Resources and output
Table 1 shows resources and the state of development and exploration of gypsum and anhydrite in Poland.
The output of gypsum and anhydrite increased in 2021 by 66 thousand tonnes (6.2%) in comparison with the previous year and amounted to 1.123 million tonnes. It contained: 999.88 thousand tonnes of gypsum from 3 deposits (the growth by 8.4% comparing with 2020), and 123.38 thousand tonnes of anhydrite from 2 deposits (the drop by 8.8% comparing with 2020). It should be emphasized that during the exploitation of anhydrite the exploitation losses – in contrast to the minor losses in the case of gypsum (about 0.8% of the output) – were much bigger (about 113% of the output) to the exploited amount. Such significant losses are caused by the exploitation system (the altitudinal zonation of the resources output) and therefore by the lack of possibilities of including particular resources parts to losses. Still, the residual gypsum emerging in the process of fumes desulfurization is used.
The figure given below show changes in domestic resources and production of gypsum and anhydrite in Poland in the years 1989-2021.
The prognostic resources of gypsum and anhydrite are assessed to be equal 483,985.52 million tonnes, whereas the prospective resources to be equal 91,740.46 million tonnes*.