Distribution of U, Th, and K in granites of the Aue and Eibenstock Massifs, Erzgebirge, Germany

Samples from mine working and drill holes were used to study the distribution of U, Th, and K in the Aue granitic massif over a vertical extent of nearly 2.5 km and in some granites of the Eibenstock massif down to a depth of 250 m from their gently dipping roof. In the inner zones of the granites, at a depth of 1-1.5 km below the present-day surface, the original content of U and Th is 35-40 ppm, and the U/Th ratio in the unaltered granites is close to unity. Toward the surface, the granites become increasingly oxidized (as indicated by the Fe oxidation coefficient), the primary distribution of the radiogenic elements is disturbed (according to fission-track studies), and the abundances of U and Th decrease sharply. For example, in the Aue massif, the average U content decrease nearly eightfold upward, and the Th content decreases nearly sevenfold. Enormous amounts of U and Th - hundreds and thousands of tons - were leached from the granite of the Aue dome. 23 refs.; 7 figs.; 5 tabs