Element mobility in crystalline rock around open fractures at Palmottu

Rock specimens adjacent to two conducting fractures at a depth of about 205 m from the Palmottu uranium deposit, a natural analogue study site for radionuclide migration, Southern Finland, were studied in order to obtain information on element mobility. The drill core was sawn in such a way that a series of specimens perpendicular to the water conducting fracture were obtained for each of the fractures. Concentration profiles for a number of elements were determined. Uranium series disequilibrium studies as well as petrographic studies and porosity determinations were also performed. In spite of closeness of fractures (only 67 apart) they were different in character. Hardly any mobilization was observed for the lower fracture but for the upper fracture several elements had been mobilized, while many remained immobile. Elements such as Na, Ca, Al, Si and u were enriched adjacent to the upper fracture. At the same time Fe, Sc, Co, S and Cu remained immobile. Elemental concentration data provided also for the alteration depth about 25 mm. The conditions have been reducing for very long times