Littva, J., Bella, P., Gaál, Ľ. & Herich, P., 2025: Geological setting and origin of Blue Cave with blue and green carbonate speleothems (Central Slovakia) [Geologické pomery a vznik Modrej jaskyne s modrými a zelenými sintrovými útvarmi (stredné Slovensko)]. Mineralia Slovaca, 57, 1, 5 – 38.
DOI: https://doi.org/10.56623/ms.2025.57.1.2
Abstract: Blue to green carbonate speleothems are a principal feature of Blue Cave, located in the northeastern part of the Nízke Tatry Mountains. The copper, colouring the speleothems, was thought to originate from the Permian volcanics neighbouring the Middle Triassic carbonates hosting the cave. Tracing sparse mentions about the Pb-Zn-(Cu) ores in the carbonates, we identified previously overlooked studies, that studied of the mineralisation in surprising detail. Based on the data from these works, remapping of the area, and by examining the geology and geomorphology of the Blue Cave, we conclude the following. 1) The Hronic Unit near the Blue Cave forms two nappes, and the carbonates hosting the cave are involved in the structurally imbricated zone at the top of the lower nappe. 2) The imbricated thrusts predispose the Pb-Zn-(Cu) sulphide mineralisation in the carbonates, while secondary azurite and malachite follow younger NE-SW and NW-SE fractures. 3) This mineralisation, rather than the volcanics, provided copper for the coloured speleothems, formed along NW-SE fractures. 4) The dissolution of carbonates by the sulphide oxidation might have created the precursor porosity for later cave formation. 5) The Blue Cave formed in three stages. In Stage I – likely in the Middle Pleistocene – the cave formed below the water table, underneath the stream terrace levelled by the surface stream. During the later valley incision and formation of lower-lying stream terraces in Stage II, the cave was modified by episodic floodwaters. As they bear floodmarks, the coloured speleothems formed mostly during this stage. The bedded and fractured bedrock that predisposed the solution also contributed to the cave’s remodelling by collapse during Stage III.
Key words: Hronic Unit, Pb-Zn ores, copper minerals, blue and green speleothems, speleogenesis, phreatic morphologies