Connecting fracture filling geochemistry and migration paths in deep granitoid rocks from the Bukov Underground research facility (URF)

The predictability of transport pathways in potential host rock formations for deep geological disposal of nuclear waste is crucial, as it helps to understand contaminant mobility and importantly, retention processes and the mechanistical understanding causing these reactions. This is currently being investigated at the BUKOV Underground Research Facility in the Czech Republic. In the recent study by Kuva et al. 2025, transport pathways were intensively analyzed using a drill core sample, with extraction approved by SÚRAO (Radioactive Waste Repository Authority).

Their analysis revealed that the core was overprinted by a complex network of fractures and veins, and the surrounding rock exhibited noticable variations in porosity. Revisiting those samples, this study focuses on the trace element enrichment within multiple carbonate infills to better understand the genesis and retention capacity of these migration paths. Trace element analysis was conducted using µXRF and LA-ICP-MS. Cluster analysis enabled the identification of several precipitation events. Comparisons of selected areas using SEM-CL and SEM-EBSD demonstrated that, in these samples, carbonate trace element incorporation is primarily influenced by fluctuations in the initial solution composition.

By comparing our findings with the characteristics of the fracture network, we traced some of the investigated transport paths, allowing us to connect geochemical observations with the structure of migration pathways.

References:

Kuva, Jukka; Jooshaki, Mohammad; Jolis, Ester; Sammaljärvi, Juuso; Siitari-Kauppi, Marja; Jankovský, Filip et al. (2025): Characterizing heterogeneous rocks in 3D with a multimodal deep learning approach – Implications for transport simulations. In: Tomography of Materials and Structures 7, S. 100055. DOI:10.1016/j.tmater.2025.100055.