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 the production of various building materials and prefabricates. It is also used in the 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 2016 at more than 257 million tonnes (decreased by 0.4 % since 2015) and the resources of four exploited deposits - at 85.65 million tonnes (table 1). Economic resources decreased by 39.2 million tonnes, whereas anticipated sub-economic resources have not changed since 2015.

Miocene gypsum deposits of economic importance are situated mainly along the 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 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 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 the 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.

Table 1. Gypsum and anhydrite - million tonnes

The geological resources decreased in 2016 as a result of the exploitation by 1.11 million tonnes despite a small resources growth (above 32 thousand tonnes in Leszcze deposit and about 5.5 thousand tonnes in Nowy Ląd deposit due to the Belter geological exploration).

The output of gypsum and anhydrite increased by 25 thousand tonnes and amounted to 1.043 million tonnes in 2016. It contained: gypsum from three deposits – 898.42 thousand tonnes (increased by 1.8%) and anhydrite from two deposits – 136.71 thousand tonnes (increased by about 0.5% in comparison with 2015). It should be emphasized that during the anhydrite exploitation the losses where much bigger (by about 109.4%) than the output. Such significant losses where caused by the exploitation system 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 1989-2016.

Table 2. List of gypsum and anhydrite deposits - thousand tonnes

Prepared by: Grzegorz Czapowski