Mineralogy of the Boom Clay in the Essen-1 borehole

In the current belgian concept of the geological disposal of high-level radioactive waste, the Boom Clay plays a crucial role as an ultimate barrier against radionuclide migration in the far field. The mineralogical composition of the Boom Clay was studied in detail in the outcrop areas and in the Mol-1 borehole in the frame of clay barrier characterization. However, the BoomClay lateral variability was identified as an important uncertainty. The Essen-1 borehole located in the north-western region of the Campine basin provided a unique opportunity to compare already existing mineralogical data of Boom Clay from Mol site to newly generated data of the Essen site. The lateral variability of Boom Clay is an important issue with respect to safety and feasibility case 1. In this study we show that the mineralogy of the Boom Clay in the Essen-1 borehole is comparable to that of the Boom Clay at the reference site Mol. At both locations, the Boom Clay is composed of quartz, K-feldspar, Na-pagioclase, pyrite, carbonates and clay minerals, namely kaolinite, mica, mixed-layered I-S and chlorite. Although the mineralogy is comparable at both areas from qualitative point of view, the variations in the quantitative mineralogical composition cannot be excluded.