Bentonites and bentonitic clays
Primary bentonites are produced in result of weathering of extrusive and pyroclastic rocks and usually display parent rock structure. In turn, bentonite clays originate due to redeposition of bentonite material and often yield fairly large admixture of foreign mineral components. Bentonite clays which form a weathering mantle developed on the Jawor-Męcinka and Krzeniów basalts were explored as mineral deposits accompanying those of basalts.
Rocks rich in smectite group minerals have some common features such as: ability to swell, their susceptibility to the dispersion of water, their easy absorption of cations and organic substances from water solutions. Therefore, these rocks are utilized for example in the foundry, drilling and ceramic industries.
In Poland typical bentonites, i.e. containing more than 75% montmorillonite, occur very seldom. More common are bentonite clays, such as:
- bentonite weathering cover of basalts in Lower Silesia,
- bentonite clays in Upper Silesia,
- bentonite clays of southern fringes in the Holy Cross Mountains,
- bentonite clays in the Carpathian Mts.
In 2015, anticipated economic resources amounted to 2,884 thousand tonnes. There were two deposits with exploitation concession approved – Jawor-Męcinka and Krzeniów (Dolnośląskie Voivodeship). The output of bentonites mantle rock (accompanying raw material) of basalt tuff is carried out only in Krzeniów deposit. Production of bentonites amounted to 450 tonnes in 2015.
Table 1 shows the current state of identification and management of resources of bentonites and bentonite clays in Poland.
At present, the only active bentonite mine is that in Krzeniów where accumulations of bentonite clays form a deposit accompanying that of basalts (table 2).
Prepared by: Dariusz Brzeziński