[en] Geochemical and geochronological analyses of samples of surficial Acre Basin sediments and fossils indicates an extensive fluvial-lacustrine system, occupying this region, desiccated slowly during the last glacial cycle (LGC). This research documents direct evidence for aridity in western Amazonia during the LGC and is important in establishing boundary conditions for LGC climate models as well as in correlating marine and continental (LGC) climate conditions. (author)

[en] By treating typical Elliot Lake uranium mine effluents with calcite and potassium phosphate solutions (300 ppm) radium leach levels have been reduced to below 0.1 pCi/L. Mine tailing permeabilities can be reduced by use of appropriate clay additives, in particular thin bentonite layers

[en] At present uranium mill tailings at Elliot Lake are treated by sulfate precipitation of uranium, thorium and radium under strongly alkaline conditions. As the pyrite in the tailings is oxidized, however, the radioactive elements are solubilized, giving rise to doubts about the long-term effectiveness of such treatment. It is suggested that phosphates may prove useful in immobilizing uranium, thorium, and particularly radium, since apatite is highly resistant to weathering. (LL)

[en] The geochemistry of natural phosphates of the apatite group indicates that these minerals have a high capacity for retention of uranium and its daughter products. ESCA spectroscopy shows that U and Ba (cf. Ra) are strongly absorbed on apatite. Large, reactive surfaces of apatite have been created by partial replacement of calcite and gypsum by phosphate solutions at the 300 ppm level. The same replacement has been achieved in impermeable calcite-rich, glacial tills. When typical waste effluents from a uranium mine are treated with such active phosphatic materials, radium-leach values are reduced to levels below 0.1 pCi/L, values in the range of ocean waters and high-quality fresh water

[en] The Pelotas batholith is composed predominantly of a Cambrian multi-intrusive granitic complex (Dom Feliciano Granitic Suite) associated to rhyolitic dike swarms and small basic plutons. The Piratini Gneisses (Late Riphean -Vendian) correspond to calcalkaline dioritic-tonalitic-granodioritic orthogneisses with chemical features of pre-collisional granitoids related to oceanic crust subduction (B-subduction) under an active continental margin. The Pinheiro Machado Granitoids (Vendian) are alkali-calcic granodiorite-monzogranites with Caledonian-type characteristics, but appear to also correspond to pre-collisional granitoids as a latter and more mature phase in the evolution of the magmatic arc. The Dom Feliciano Granitic Suite (Cambrian) is subdivided into porphyritic and equigranular facies, with predominance of monzogranites and syenogranites, respectively, with alkali-calcic late-orogenic characteristics. While the Rb/Sr isotopic data is consistent with the proposed evolution, the Nd model ages range from 2.0 - 1.2 Ga. This may reflect episodes of Sm/Nd fractionation within a lithospheric mantle instead of the accretion age of the granitoids. These apparent ages, which are also obtained in Parana and Karroo continental basalts, probably indicate coupled evolution of the continental crust and lithospheric mantle. In the suggested model, the Piratini Gneisses were orginated by differentiation of basic magmas formed by partial melting of lithospheric mantle, induced by dehydration of subducted oceanic crust, while the more mature arc granitoids had increasing crustal contamination or mingling-mixing with crustal melts and finally, in the late-and post-orogenic stages, partial melting of continental crust predominates. (author)