Natural Mineral Analogues from a Hydrothermally Altered Granite

Summary

Uranium, thorium and R.E.E. concentrations and distribution from a deep drill hole within the Coles Bay granite are being investigated using fission-track micromapping and electron microprobe analytical techniques, amongst others, in an attempt to provide a natural analogue of potential far field radionuclide movement. For example, uranium occurs in three mineralogical locales: 1. as background in quartz, fresh biotite and feldspars; 2. in resistate accessory minerals which contribute the greatest concentration of uranium, and 3. as minerals formed during hydrothermal alteration. Alteration minerals are dominated by Fe carbonates and oxides and Ti oxides (? anatase and secondary sphene), with chlorite and clays (phengite and sericite). The fission track distribution is mostly non-uniform and may be affected by further alteration indicating the dominant mechanism for fixation of uranium as adsorption and ionic exchange. These minerals are found replacing biotite or infilling fractures throughout the rock. Of these distributions, uranium associated with secondary minerals provides the most appropriate far-field analogue. Preliminary leach tests indicate preferential adsorption of 239-Pu from 239-Pu doped SYNROC onto these secondary alteration phases.