Gypsum and anhydrite
Gypsum (CaSO4.2H2O) is a product of evaporation of sea water in temperatures lower than those necessary for 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 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 production of various building materials and prefabricates. It is also used in production of moulds for 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 surgery and dental clinics. Clear colorless gypsum crystals (selenite) were used to make optical instruments. Anhydrite is currently added to Portland cement and in 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 evaporite formations of the Miocene and Zechstein. Their resources in 15 major deposits were estimated in 2015 at more than 258 million tonnes (decreased by 0.5% since 2014) and the resources of five exploited deposits - at more than 126 million tonnes (table 1). Economic resources decreased by 1.4 million tonnes, whereas anticipated subeconomic resources have not changed since 2014.
Miocene gypsum deposits of economic importance are situated mainly along northern margin of the Carpathian Foredeep, especially in the Nida Basin. 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 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 from the Lower Silesian region are characterized by markedly more complex geological conditions (strong tectonic disturbances) and variability in quality of mineral raw material. These are mainly deposits of anhydrites and secondary gypsum formed in result of gypsification of anhydrite in zones of infiltration of aggressive groundwater. Three deposits are exploited in that region: Lubichów (in November 2015 there was a decision made to finish the exploitation), Nowy Ląd and Nowy Ląd-Pole Radłówka (table 2). The deposits occur at the depth of 25 m to 400 m, their thickness changes from 1.7 m to 50.3 m and content of CaSO4.2H2O ranges from 56.0% to 95.3%. Moreover, resources of shallow-seated parts 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 at 57 billion tonnes.
In 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 60% for anhydrite and 80% for gypsum and the maximum ratio of thickness of cap rock to that of the deposit is 0.5 in the case of gypsum deposits.
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.
Production of gypsum and anhydrite amounted to slightly above one million tonnes in 2015 (including 882.37 thousand tonnes of gypsum from 3 deposits – 2.5% drop and 136.08 thousand tonnes of anhydrite also from 3 deposits – 7.7% drop) and decreased in comparison with 2014 by 4.1% (Table 2). It should be emphasized that during anhydrite exploitation the losses were almost three times bigger than the output, whereas it was only 8% of the output in the case of gypsum. Such losses are caused by the exploitation system.
The figure given below show changes in domestic resources and production of gypsum and anhydrite in Poland in the years 1989-2015.
Prepared by: Grzegorz Czapowski