Study On Clay Formation Of Upper Bayingebi Formation In Tamusu Candidate Area—High-level Radioactive Waste Disposal Repository

Clay rock is one of the important host rocks for high-level radioactive waste(HLW) geological disposal repository. The clay rocks of Upper Bayingebi formation in Tamusu candidate area have been studies in this paper, including the studies of field geological investigation, clay rock thin section identification, X-ray diffraction analysis, scanning electron microscope analysis, chemical composition analysis and others. In addition to the studies on gnenral geological conditions in Tamusu candidate area, systematic studies mainly focused on the mineralogical and chemical compositions, the macro-and micro-structural characteristics of clay rocks of Upper Bayingebi formation. The results of this study and the preliminary evaluation on clay rocks indicated that the clay rocks in clay rocks of Upper Bayingebi formation in Tamusu candidate area is suitable as the host rocks for HLW geological disposal repository. The research in this paper shows that:(1) The main clay formation of upper part of lower Cretaceous Bayingobi formation in Tamusu candidate area, Bayingebi basin, Inner Mongolia is composited of mudstone and shale with the thickness of more than 200 m and the embedded depth of more than 500 m. The highly compacted mudstone presents gray, dark gray with a small amount of silt.(2) The mineral compositions of the mudstone in the study area are as follows: kaolinite, illite, zeolite, dolomite, feldspar, pyrite and clastic minerals, etc..(3) The results of scanning microscope identification indicate that the mudstone is dominated by lamellar kaolinite and silk thread form illite with poor intergranular pores. It’s also visible by kaolinite filling in the intergranular pores.(4) U, Th and Sr are relatively enriched in mudstone. And the concentration of rare earth elements is higher than the average contents of North American shale. The geochemical characters of mudstone implied the source rock mainly from the granite in northern Zong Sinai – Shazara uplift mixed with the sedimentary rocks and mafic rocks. The mudstone was precipitated and compacted in a reduced environment.(5) The highly compacted structure, lower porosity and water permeability of the mudstone in study area are favorable for preventing the migration of nuclides. And the clay minerals with the strong adsorption characters such as kaolinite, illite, zeolite are also positive to decrease the migration and diffusion capacity in mudstone. The results of mineralogical and geochemical studies and the preliminary evaluation on mudstone show that the clay formation of Upper Bayingebi formation in Tamusu candidate area is favorable as the host rocks for HLW geological disposal repository.