Chemical character and structure of uraniferous bitumens (Vrchlabi, Czech Republic)

Black shales from the Permian rocks at Vrchlabi in the Krkonos'e Piedmont Basin (Czech Republic) contain bi-tumens with uraninite grain inclusions and bulk uranium concentrations up to 4.8 wt%, determined by instru-mental neutron activation analysis. The carbonaceous matter in the bitumens has been characterised by gas chromatography/mass spectrometry, attenuated total reflection Fourier transform infrared spectroscopy, scan-ning electron microscopy, and stable carbon isotopic composition. Progressive radiolytic alteration was docu-mented by changes in the chemical composition and structure of both bulk samples and on the microscale. Condensation of aromatic structures, increase in content of oxygenated compounds, and enrichment in C-13 were documented in the uranium-rich bulk samples. Micro-ATR-FTIR area mapping throughout the bright halos around uraninite inclusions revealed detailed structural changes, particularly a decrease in aliphatic bond in-tensities and an increase in the aromaticity of the structures close to the inclusions. A radiolytic alteration pathway has been suggested assuming a complex of reactions between organic matter and uranyl containing hydrothermal solutions, and oxidation by OH radicals produced in radiolysis of water. The organic matter transformations observed in the uraniferous bitumen correspond to the coalification processes, changing the bitumen composition from type I to type III and IV kerogens. Detailed characterisation of the radiation-induced chemical and structural changes in the naturally occurring uraniferous bitumens will contribute to the general understanding of the nature and behaviour of organic matter in other uraniferous environments or in the radioactive waste repositories.

Automated summary

This study analyzed uranium-rich bitumens from the Permian rocks in Vrchlabi, Czech Republic, and found that the inclusion of uraninite grain can lead to chemical and structural changes in the organic matter. This research is important for understanding the nature and behavior of organic matter in other uraniferous environments or in radioactive waste repositories.