Disappearing lignite seam in the Tomisławice opencast (Konin Basin, central Poland) – the case study based on field and borehole data

This geological study is devoted to an interesting cognitive issue regarding a large mining problem. A narrow, so-called 'lignite-free' zone occurs in the Tomisławice opencast in central Poland. This surprising disappearance of an exploited lignite seam posed a threat to the proper operation of a nearby Pątnów lignite-fired power plant. Therefore, the Konin Lignite Mine carried out geological studies into the 'lignite-free' area, as designated in the field. During the investigation, it turned out that, in the 'lignite-free' zone, there was, in fact, a continuous lignite seam, but it was at least 11 m lower than the surrounding part of the 'Tomisławice' deposit. This phenomenon can be explained in two ways. First, it could result from greater peat-to-lignite compaction in the zone where the lignite seam is at least twice thicker. Secondly, the zonal lowering of the lignite seam could be caused by post-depositional tectonics, most likely of Quaternary age. The latter hypothesis seems more probable at the current stage of research. Regardless of the reasons for such a large hypsometric lowering of the exploited lignite seam, it is lost to the Konin Lignite Mine. Its extraction is technically possible but would involve lowering the mine water table in the cone depression by at least 11 m. Leaving aside the formal and legal aspects, such action would be too costly and, therefore, lignite from the examined 'lignite-free' zone will remain as mining losses in the Tomisławice deposit.