Ceramic clays are generally represented by sedimentary clays of a marine or lacustrine origin and with minerals of the kaolinite and illite group as the major rock-forming components. The clays, also known as kaolinite rocks, are raw materials for the production of whiteware ceramics. From the technology process point of view, the fired products may be assigned to whiteware or stoneware. For the production of porcelite and faiance, there are used whiteware ceramic clays, characterized by: - the 60% of whiteness when fired at the temperature of 1,200°C; - the high bending strength after drying - minimum of 0.6 MPa. In turn, stoneware ceramic clays are characterized by a worse witheness degree, but they obtained a high bending strength, a large mechanical and chemical resistance and a low level of water absorption when fired – maximum of 5%.
Whiteware ceramic clays
Whiteware ceramic clays deposits occur only in Dolnośląskie Voivodeship. There are two types of deposits. First of them are the Upper Cretaceous kaolinite clays forming interlayers in sandstones and are represented by Bolko II and Ocice deposits. The second type are poorly coherent sandstones of kaolinite binder represented by Janina I, Janina-Zachód and Nowe Jaroszowice deposits. The usable fraction is separated from these rocks by the water-washing and the obtained concentrate contains about 30% of kaolinite clay.
The ceramic clays deposits occurrence in Poland is presented on the map.
Table 1 shows the current state of the exploration and development of the above discussed deposits.
As of 31.12.2020 the anticipated economic resources of whiteware ceramic clays (faiance and porcelite) amounted to 60.39 million tonnes and decreased by 0.17 million tonnes (it means by 0.28%) in comparison with the previous year. The drop was the result of the exploitation and losses. Similarly to the previous years, Janina I deposit was the only whiteware ceramic clays deposit exploited in Poland – the output amounted to 161.92 thousand tonnes of the sandstones of kaolinite binder, that is by 40.77 thousand tonnes less than in 2019 (the drop by 20.11%). The economic resources of the raw material as of 31.12.2020 were equal 0.73 million tonnes and decreased by 0.17 million tonnes in comparison with the previous year – due to the exploitation and losses. List of deposits is presented in Table 2.
The figure given below shows changes in domestic resources and production of whiteware ceramic clays in Poland in the years 1989-2020.
Stoneware ceramic clays
Stoneware ceramic clays occur mainly in the Lower Silesian region and central parts of the country (Świętokrzyskie and Dolnośląskie Voivodeships). Couple of deposits are located in Mazowieckie Voivodeship, while single ones in Łódzkie and Śląskie Voivodeships.
As of the end of 2020, the anticipated economic resources of stoneware ceramic clays amounted to 77.79 million tonnes and decreased in comparison with the previous year by 0.96 million tonnes (1.22%). The resources drop resulted from: - crossing out two deposits from “The balance…”: Borkowice II (-0.56 million tonnes) and Borkowice-Radestów 1 (-0.04 million tonnes); - the exploitation and losses.
The anticipated economic resources within exploited deposits amounted to 7.10 million tonnes which accounted for 9.13% of the total anticipated economic resources. Almost all of these resources were covered by the detailed exploration (A+B, C1 categories), only in Baranów deposit remained 3 thousand tonnes of resources explored in C2 category. The economic resources decreased by 0.90 million tonnes (21.58%) as a result of the crossing out Borkowice II deposit from “The balance…” (-0.56 million tonnes), the exploitation and losses. They amounted to 3.27 million tonnes and accounted for 46.06% of the anticipated economic resources of the exploited deposits.
Table 3 shows the current state of exploration and development of these deposits.
In 2020, the exploitation of stoneware ceramic clays was carried out from three deposits. The total output was equal 229.24 thousand tonnes and dropped by 11.22% (28.96 thousand tonnes) in comparison with 2019. The significant output increase was recorded for Zebrzydowa Zachód deposit (by 13.80 thousand tonnes, that is by 7.42%), whereas there was a slight growth noted for Baranów deposit (by 0.04 thousand tonnes, that is 0.30%). The exploitation level from Rozwady 1 deposit dropped by 4.80 thousand tonnes (23.08%). The negative output balance was also caused by the crossing out Borkowice-Radestów 1 deposit from “The balance…” – the output volume from this deposit was equal 38 thousand tonnes in 2019. List of deposits is presented in Table 4.
The figure given below shows changes in domestic resources and production of stoneware ceramic clays in Poland in the years 1989-2020.
In The balance of prospective mineral resources of Poland the assessment of resources prospective for ceramic clays in Poland was updated*. The main criteria, adopted for determining the whiteware and stoneware ceramic clays deposits were: the deposit thickness (minimum of 2 m) and the overburden to the deposit thickness ratio (N/Z maximum of 2), in addition the raw material qualitative parameters: the clay minerals content (minimum of 40%), CaCO3 content (maximum of 2%) and the grains >2 mm content (maximum of 1%). Taking into account also such parameters as: the whiteness after firing, the bending strength or the water absorption after firing, the prognostic resources of whiteware and stoneware ceramic clays were assessed to be equal, respectively 127.20 million tonnes (within 3 areas in Dolnośląskie Voivodeship) and 230.41 million tonnes (within 9 areas: 2 in Świętokrzyskie Voivodeship and 7 in Dolnośląskie Voivodeship).
Prepared by: Marcin Tymiński
* Galos K., 2020 - Iły biało wypalające się (white-firing clay, ball clay), kamionkowe (stoneware clay, ceramic clay) i ogniotrwałe (refractory clay, flint clay). In: Bilans perspektywicznych zasobów kopalin Polski wg stanu na 31.12.2018 r. (eds. Szamałek K., Szuflicki M., Mizerski W.): 335-329. PIG-PIB, Warszawa [in Polish].