THE MOBILITY OF THE REE, U AND TH IN GEOLOGICAL ENVIRONMENTS IN IDAHOAND THEIR RELEVANCE TO RADIOACTIVE-WASTE DISPOSAL

Investigation of natural analogues of radioactive waste disposal envir onments in eastern central Idaho generally reveals minimal mobility of the elements Th, U and REE. The mineral allanite, containing Th and R EE, is altered by hydrothermal solutions, but these elements are retai ned in secondary phases. The contents of U, Th and REE in present-day thermal waters in the area are low (ng l(-1) range). However, the appa rent high mobility of Th and REE during the formation of the Lemhi Pas s Th-REE deposits indicates that conditions may exist where REE and ac tinides can be mobilized by aqueous fluids in the Earth's crust.