Genesis of host rock in the Tamusu Mudstone pre-selected area in Northwest China for high-level radioactive waste geological disposal purposes

Mudstone characterized by typical structures and mineral assemblages in the Tamusu Mudstone pre-selected area, in Inner Mongolia, Northwest China, has been selected as a potential host rock for China’s high-level radioactive waste (HLW) repository purpose. Based on indications of petrological and geochemical characteristics, hydrothermal sedimentary geneses of host rock are well discussed from the perspectives of hydrothermal sedimentary structures, sedimentary environments, and the hydrothermal sedimentary model. The results show that host rocks have the characteristics of low-temperature "white smoke" hydrothermal sedimentary rocks. The rocks developed in a dry, anaerobic and reducing saline lake environment with transient oxidation and dry–wet evolution. The 100–120 Ma tectonic activity in the Altun fault may have been the main factor controlling the process of hydrothermal exhalative, which provided the migration pathway for water–rock reactions and contributed to the formation of typical structures and mineral assemblages. The hydrothermal sedimentary rock is a new kind of argillaceous rock that serves as a potential host rock, and will provide new insights into suitability evaluations of mudstone properties to promote the site screening of the Tamusu Mudstone pre-selected area for China’s HLW disposal purpose.