東濃ウラン鉱床でのナチュラルアナログ研究からみた古水理地質研究の役割

抄録

Paleohydrogeological study is a method to clarify the state of hydrogeological and geological environments from the past to the present.
In the Tono uranium deposit, most of the uranium has been preserved in the deposit since formation, even though the deposit has been subjected to the effects of several cycles of uplift, erosion and subsidence since its formation about 10 million years ago. Such long-term uranium fixation results from the preservation of a favorable geological environment. At present, redox, pH and PC02 are estimated to control the uranium solubility and groundwater-rock-microbe interactions are important to the redox buffer system.
In order to enhance confidence in the demonstration of long-term safety of a geological disposal system for high-level radioactive waste in a geologically active area such as the Japanese Islands, it is necessary to understand how geological phenomena such as uplift and erosion have affected deep geological environments and how such multiple phenomena have influenced the hydrogeological and geological systems. To contribute the studies of the Tono uranium deposit to paleohydrogeology, it is important to determine any long-term changes and to evaluate the stability of the geological environments. Because the deep geological environment is affected by many factors such as groundwater flow, microbes, water-rock interaction and so on, a paleohydrogeological approach is essential to know the state of ancient, deep geological environments which might influence the preservation or mobilization of uranium.