Characteristics and evolution of groundwater flow and uranium behavior in granitic mountains, Southwest Japan

Nohara, Tsuyoshi   ; Takesue, Norito ; Endo, Kaito*; Sato, Haruo*

In order to understand the characteristics and evolution of groundwater flow and uranium behavior in the granitic mountains, existing information was organized, and a field survey was conducted on the Ningyo-toge uranium deposits. Existing borehole data for the main aquifers were organized and divided into high permeable layers and low permeable layers. Field investigations revealed that the high permeable layers were continuously distributed from the north side of the southern slope to the basin where the uranium deposits were distributed, and the low permeable layers were distributed immediately below the high permeable layer. Uranium was estimated to be transported by groundwater from the granitic rocks, and then reduced by carbon materials in the basin, resulting in the accumulation of uranium. Based on these findings, a conceptual model of groundwater flow is discussed that considers the heterogeneity of regional groundwater flow and topographic evolution.