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 of 5 documented deposits of potassium-magnesium salts were estimated at above 688 million tonnes, anticipated sub-economic resources at almost 19 million tonnes, whereas economic resources – at more than 2.7 million tonnes (Table 1). The sulfate (polyhalite) salt deposits of the Bay of Puck (Table 2) form the bulk of these resources. The deposits of the Bay of Puck area are of the sulfate (polyhalite) salt type, with polyhalite 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. The K2O content ranges from 7.7% to 13.7% in that depth interval. 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 and new resources calculations are needed in the future.
Small accumulations of potassium-magnesium salts (almost 72 million tonnes of anticipated economic resources and 2.7 million tonnes of economic resources) were identified along the eastern margin of the Kłodawa salt pillow, where salts of the potassium chloride type (carnalite and sylvine) occur in rocks of the Younger Potash unit, steeply inclined (at the angle of 70o) and folded and locally squeezed and crumple. The chloride salts are strongly contaminated with the clay matter and sulfates. Mean contents of K2O and MgO are 8.5% and 8.1%, respectively. 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. In the next years, this part of the salt deposit became abandoned. Nowadays, there is no potassium and magnesium salt exploitation carried out.
Potassium salt deposits are documented to the depth of 1,200 m within beds, while in salt domes it is the depth of documentation. 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 3 years (the Bay of Puck area).
Anticipated economic resources of potassium-magnesium salts in Poland increased by more than 19 million tonnes in comparison with 2016 due to the recalculation of Kłodawa 1 deposit resources.
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).
Prepared by: Grzegorz Czapowski