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Cave of the Krkonoše National Park: cave fill and speleogenesis
Bosák, Pavel ; Tásler, R. ; Šťastný, Martin ; Hercman, H. ; Mikysek, Petr ; Pruner, Petr ; Kdýr, Šimon ; Matoušková, Šárka ; Rohovec, Jan
Sub-/vertical phreatic channels dominate in original cave morphologies together with ceiling half-channels, scallops and ceiling cupolas. Infiltration cave sediments are composed of lutitic component with some coarser authochthonous admixture. Sediments were locally re-distributed by intensive drip from open fissures. According to clay and heavy minerals, the primary source was in weathering products of crystalline rocks, mature and immature or polycyclic mixed in different proportions. No allogenic sediments were detected. Speleothem dating indicates, that caves were filled and exhumed several times, partially or fully. Normal polarization of samples proved the deposition within the Brunhes Chron (<773 kyr). Speleothems and rare paleontological remains date clastic sediments to >400 kyr. Speleothems crystallized mostly during interglacials, but also in cold and extremely cold periods in glacials (MIS 2, MIS 6c to 6a, MIS 8b, MIS 10c to 11a). Tectonical near-surface rock fissuration and corrosion substantially contributed to cave re-shaping by rock falls. Cryogenic processes modified the morphology of cave walls and damaged speleothems. Mostly ascending speleogenesis took part in substantial depths under the surface without any link to the present morphology. Present near-surface position of most of caves reflects the gradual uplift during younger tectonic phases and incision of river systems.
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New data on the origin of the Fe-Cu-As skarn deposit at Obří důl, West Sudetes, Bohemian Massif
Pašava, J. ; Veselovský, F. ; Dobeš, P. ; Erban, V. ; Pour, O. ; Žák, Karel ; Ackerman, Lukáš ; Haluzová, Eva ; Creaser, R. ; Tásler, R.
The Obří důl Fe-Cu-As sulfide deposit is hosted in metamorphosed lenses of marble, calc-silicate rocks and skarns. The deposit is located up to a few hundred meters away from the contact of the large, late-orogenic Variscan Krkonoše-Jizera Plutonic Complex (KJPC). Mineralogical and fluid inclusion studies of the Gustavská ore lens show that the main sulfide stage, dominated by pyrrhotite, chalcopyrite and arsenopyrite, originated from water-rich hydrothermal fluids with salinities up to 8 wt.% NaCl eq. at temperatures ranging from 324 to 358°C.These fluids replaced mainly the carbonate-rich lithologies. The 34S values indicate a magmatic source of sulfur and Re/Os dating of molybdenite are consistent with simultaneous formation of the main sulfide stage ore and the KJPC.
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