by Georgi NAUMOV, Dr. Sc. (Geol. & Mineral.), Vernadsky State Museum of Geology, Russian Academy of Sciences Uranium is our planet's heaviest natural element. Still, it is active enough in migrating-both on the earth's surface and in the earth's crust (true, with some exceptions here and there). Why is that? And what is the mechanism of the migration process? An answer to these questions may clarify a good deal in our understanding of the travel of heavy elements in the bowels of the earth and also enable an insight into how uranium deposits are formed. Uranium is rather widespread on the terrestrial surface: the mean content of this chemical element is by a factor of 102 higher than, say, in meteorites. Besides, space studies show that the surface shells of the other terrestrial planets are uranium-rich too. Within the earth shell uranium accounts for 2.5*10^-4 percent of the overall mass of rock. And even though the occurrence of uranium there exceeds that of tungsten and molybdenum, bismuth and gold, it is but very seldom found in large accumulations as essential mineral - for the most part, uranium occurs in association with other, nonuranium natural compounds. But how do uranium accumulations come into being? Physicists attacked this problem toward the close of the Second World War when developing a nuclear weapon. Yet much earlier, in 1910, Academician Vladimir Vernadsky wrote thus: "Radioactivity phenomena open to us atomic energy sources millions of times as high as the power sources that have been pictured in the human mind." And he warned, "Man will be in for a great future if he understands that and does not use his work and his intelligence toward self- destruction." Now where is uranium to be sought? Relevant research was launched back in the 1940s so as to learn more about the chemical behavior of elements under various natural conditions. A GEOCHEMIST'S VIEW Two valent states of uranium, U4+ and U6+, starkly different in their behavior, ha ... Читать далее