Évaluation de la mobilité des métaux dans les sédiments fluviaux du bassin de la Vire (Normandie,France) par extractions simples ou séquentielles

This work compares the quantities of labile metals removed from the Vire River (Normandy) sediments by a sequential extraction procedure to those liberated by single leaches (Mg(NO₃)₂, HCl and EDTA). Compared to the other extractions, Mg(NO₃)₂ underestimated the mobility results. The sequential procedure was the most aggressive, except for Ca and Pb. The hypothetic correlation between quantities of an element removed by single leaches and its fractionation in the sediment according to the sequential procedure was not satisfying. Finally, it should be underlined that enrichments of Cd, Pb and Zn were noticed in the Vire sediments. To cite this article: L. Leleyter, F. Baraud, C. R. Geoscience 337 (2005).     

Geochronological framework of the Quadrilátero Ferrífero, with emphasis on the age of gold mineralization hosted in Archean greenstone belts

Archean terrains of the Quadrilátero Ferrífero comprise a greenstone belt association surrounded by granitoid–gneiss complexes, mainly composed of banded TTG gneisses whose igneous protoliths are older than 2900 Ma. This early continental crust was affected by three granitic magmatic episodes during the Neoarchean: ca. 2780 to 2760 Ma; 2720 to 2700 Ma; and 2600 Ma. Dating of felsic volcanic and volcaniclastic rocks defines a felsic magmatic event within the greenstone belt association around 2772 Ma, contemporaneous with emplacement of several of the granitic plutons and constrains a major magmatic and tectonic event in the Quadrilátero Ferrífero. Lead isotopic studies of lode–gold deposits indicate that the main mineralization episode occurred at about 2800 to 2700 Ma.Proterozoic evolution of the Quadrilátero Ferrífero comprises deposition of a continental-margin succession hosting thick, Lake Superior-type banded iron formations, at ca. 2500 to 2400 Ma, followed by deposition of syn-orogenic successions after 2120 Ma. The latter is related to the Transamazonian Orogeny. The western part of the Quadrilátero Ferrífero was also affected by the Brasiliano Orogeny (600 to 560 Ma).