Gypsum and anhydrite
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 hydration of anhydrite. 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 within 15 deposits amount as of the end of 2018 to above 255 million tonnes (the resources have decreased by about 0.4% since 2017) and the resources of 4 exploited deposits - at 83.3 million tonnes (decreased by about 1.3% in comparison with 2017; Table 1). Economic resources (equal above 67 million tonnes) have decreased by 1.09 million tonnes (1.6%) since 2017, whereas anticipated sub-economic resources have not changed..
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 Borków-Chwałowice and Leszcze.
Documented deposits of Zechstein sulfates (mainly anhydrites and secondary gypsum – originated from the anhydrites gypsification in the zones of aggressive groundwater infliltration) 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 beds occur at the depth below 180 m, their thickness varies from 2 m to 34 m and the CaSO4.2H2O ranges from 10.2% to 92.4%. Moreover, estimated resources of non-exploited gypsum and anhydrite deposits 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.
Table 1 shows resources and the state of development and exploration of gypsum and anhydrite in Poland.
The output of gypsum and anhydrite decreased by 66 thousand tonnes (about 6%) and amounted to 1.042 million tonnes in 2018. It contained: 913.83 thousand tonnes of gypsum from 3 deposits – the drop by 8% and 128.05 thousand tonnes of anhydrite from 2 deposits – the growth by 12.7% in comparison with 2017. It should be emphasized that during the exploitation of anhydrite the losses were still significant (about 103% of the output). They are caused by the exploitation system and therefore by the lack of possibilities of including particular resources parts to losses. In case of gypsum losses account for about 1.5% of the output. 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 1989-2018.
Prepared by: Grzegorz Czapowski