Geochemical behavior of uranium series nuclides (238U, 234U, 226Ra, 222Rn) around the Tono uranium mine, Gifu Prefecture, central Japan

Uranium series nuclides such as 238U, 234U, 226Ra and 222Rn, were measured in the groundwaters and surface waters around the Tono uranium mine and their geochemical behaviors and hydrogeochemical implications were investigated. 238U contents in the groundwaters were low because the groundwater was reducing and its pH was high. 226Ra contents were higher than the equilibrium amounts of 238U, which suggests that radium is easy to move than uranium. 222Rn was abundant in the groundwaters from several hundreds times to several ten thousands times than its precursor 226Ra, which inferred that much amount of radon was supplied by the rocks and ore body through micro paths. 234U/238U activity ratios of some groundwaters were high (about 6). It may be because the water is reducing and uranium is leached from the clay minerals that adsorb uranium relatively weakly. The waters from the Sublevel gallery of the Tono mine were low in radon content and 222Rn/226Ra activity ratios, which suggests that the water originated not in the deep groundwater, but in the shallow groundwater. (author)