La distribution globale des principaux eléments métalliques dans l'ecorce terrestre des continents

Abstract

1. 1.The concentrations of the metals in the crust are very irregularly distributed and form regions with immense reserves (CuMo in the Cordillera and the Andes, AuU in the Witwatersrand and others). 2. 2.The conditions of preconcentrations are of different types: endogene, exogene or metamorphogene. The initial material of the endogene deposits is often of exogene or metamorphogene origin and, to the contrary, the source of exogene or metamorphogene concentrations can be the destruction of endogene concentrations. The circulation of the elements in the natural processes occur in that way. 3. 3.The size and the associations of the metal-concentrations depend on the type of the structure, the intensity of the stages of its development and age of the structure. The geotectonic position of the region in a shield or a folded belt, or an area of activization is also a decisive parameter. 4. 4.The shield structures contain more frequently metamorphogene concentrations of Fe, Mn and AuU. Two different types of concentrations are recognized in the folded belts: (a) the internal zones with moderately acid granitoids and basic-ultrabasic intrusions with Cr, Fe, Ti, Pt, CuMo, PbZn, Au, Ag and Hg mineralizations; (b) the external zones with acid granitoids and Sn, W, Mo, U, PbZn, Au and Sb mineralizations. The areas of activization are accompanied by alkaline-ultrabasic intrusions, and in connection with them, by great concentrations of carbonatites (Nb, Ta, Zr, REE), but also of PbZn, Au, U, HgSb and fluorine. 5. 5.The different metals have a definite distribution in times the Precambrian structures in Fe, Au, U, Ni, Pt-oides, Ti; the Paleozoic structures in Cr, Pt, Cu, Sn; the Cimmerian in Sn, W, Au, Sb and the Alpine are remarkable rich in Cu and Mo, Ag, Hg, Mn (the last of sedimentary type).