U-234/U-238 signatures associated with uranium ore bodies: part 2 Manyingee

The Manyingee ore body is a roll-front U ore body located at depth in the Cretaceous sandstone sediments of a Proterozoic palaeo valley. It is located in a confined aquifer. The aquifer is recharged 4 km upstream by the Ashburton River. Groundwater samples were collected at and up to 4.7 km downstream of the ore body. The ground water U-234/U-238 activity ratios (AR) were elevated to 1.86 in the vicinity of the ore body and then declined to 1.06 over the 4.7 km transect. The elevated U-234/U-238 ARs are attributed to selective leaching of U-234 sites by oxidising waters, with a recoil as a necessary precursor to produce activated U-234 sites. Direct ejection into another phase following a recoil is considered to be a minor contributor to U-234 U-238 disequilibrium in this environment. The profile is considered to be typical of the U-234/U-238 AR profile at and down gradient of the redox front of a U ore body. © 2013, Elsevier Ltd