Potassium-magnesium salt

In Poland, the distribution of potassium-magnesium salts appears to be limited by the extent of the Zechstein salt formation. Together with rock salt they form two separate lithostratigraphic units – the Older and Younger Potash units of the Zechstein. The units are traceable in the Polish Lowlands where they were recorded in countless drillings as well as several salt structures in central Poland and layers in the south-western part of the Fore-Sudetic Monocline.

Anticipated economic resources (beyond protective pillars) of 5 documented deposits of potassium-magnesium salts are estimated at above 686 million tonnes, anticipated sub-economic resources at almost 19 million tonnes (Table 1) and the bulk of these resources are formed by the four sulfate (polyhalite) salt deposits of the Bay of Puck (Table 2). In these deposits polyhalite is occurring in the form of early diagenetic minerals developed in anhydrite layers which underlay, intercalate and overlay the oldest rock salt bed of the Zechstein. Polyhalite inclusions are present as irregularly disseminated nests and aggregate intergrowths in a depth interval from 740 m to 900 m, where the K₂O content ranges from 7.7% to 13.7%. The deposits situated along the rim of the Bay of Puck rock salt deposit were covered by a preliminary exploration in the years 1964-1971. Their anticipated economic resources were estimated in a C₁ category at more than 597 million tonnes assuming a regular distribution of a polyhalite mineralization. The subsequent explorations demonstrated that the mineralization process was more complex than it was previously assumed and new resources calculations are needed in the future.

Small accumulations of potassium-magnesium salts (>89 million tonnes of anticipated economic resources) were identified along the eastern margin of the Kłodawa salt pillow (within the documented in the central part of the pillow deposit Kłodawa 1), where salts of the potassium chloride type (carnalite with a small addition of sylvine) and magnesium salts (kieserite) occur in rocks of the Younger Potash unit, steeply inclined (at the angle of 70^o) and folded and locally squeezed and crumple. The chloride salts and magnesium salts are strongly contaminated with the clay matter and rock salt. The mean content of K₂O is of 8.5% and MgO of 8.1%. The potassium salt accumulations are of a minimal economic interest due to a high variability in thickness of the strata (from a few to 50 m) and problems in the processing of the raw material. The salts were exploited temporarily till the year 2000 when 1,400 tonnes were mined. Nowadays, there is no potassium and magnesium salt exploitation carried out.

Potassium-magnesium salts according to the parameters that define a deposit are documented to the depth of 1,200 m (within beds, while in salt domes it is the depth of a deposit documentation process). The 2 m thickness is accepted as the minimum, providing that the weighted average K₂O content in the deposit is not lower than 8%. Since 2012 there has been more interest demonstrated by the national and foreign companies in Polish potassium and magnesium salt occurrences and deposits especially located in the Bay of Puck area. These deposits need to be explored more precisely and resources have to be recalculated together with the assessment of the exploitation worthwhileness. There have been 2 concessions for the searching and exploration of the raw material issued in the last couple of years in the Bay of Puck area (the concession for Polski Potas company was taken back in 2015, whereas the concession for the KGHM Polish Copper Combine S.A. is still in force).

Anticipated economic resources of potassium-magnesium salts in Poland decreased by 2.81 million tonnes in comparison with 2017, whereas the anticipated sub-economic resources have not changed. These changes were the result of re-documentation and re-classification of the resources within the Kłodawa salt pillow where anticipated economic resources amounted to 89.1 million tonnes (dropped by 2.81 million tonnes)) and economic resources amounted to 3.46 million tonnes (grew by 0.7 million tonnes (26.6%)) (Table 2).

Potassium–magnesium salt deposits in Poland are presented on the map.

Table 1 shows resources and the current state of exploration and development of potassium-magnesium salts. The data refer to exploitable resources (that is except of those remaining in safety pillars).

Table 1. Potassium-magnesium salt - million tonnes

Table 2. List of potassium-magnesium salt deposits - thousand tonnes

Prepared by: Grzegorz Czapowski