Аннотация:Sangaredi bauxite district conditionally distinguished by us occurs in the left bank area of the upper and middle Kogon River, the northwestern Guinea. Its bauxite-bearing weathering mantle was mainly formed after the Faro Formation (mudstones and siltstones with interlayers of fine-grained quartz sandstone), as well as after the Mesozoic trap association (dolerites and konga-diabases).
Generic bauxite-bearing weathering profile on the parent rocks consists of the following horizons (upsection): clays (polymineralic and kaolinitic), ferruginous laterites (transition zone), bauxites, and cuirass (occasional).
Zoning of the lateritic weathering profile has resulted from the infiltration metasomatism and physical-chemical conditions of different sections of the profile, and therefore, each subjacent horizon is considered as the initial substratum after which its superjacent horizon formed. When comparing absolute abundances (concentration values calculated on isovolumetric base) one can better study the behavior, input, and output of chemical elements with the zoning. Such a study was made for 55 chemical elements, using values of concentration ratio (Rc): for each element the value was calculated as absolute abundance ratio of superjacent to subjacent zone.
Polymineralic clays, when compared with their protoliths, demonstrate output to inertness of all elements except for Cd, Te, Cs, La, Ce, Pr, Nd, Hf, Th, U, W, Sn, Tl, Pb, Zr, Nb, Sb, Bi, and Ga accumulated to various grades. Superjacent kaolinite clays usually also show output of chemical elements, except for Al2O3, TiO2, W, Ag, Sn, Bi, and Ga. Ferruginous laterites are characterized by a very intense absolute accumulation of iron along with accumulation of Al2O3, V, Cr, Mo, Sb, Hf, Bi, Th, Cd, W, and Zn. Group of the elements accumulated in the transition zone includes Li, Be, Sc, Ni, Cu, Zn, Sr, Cd, REE, Ta, Tl, and Pb. When compared with subjacent ferruginous laterites the bauxite horizon shows accumulation of Al2O3, Nb, Hf, Sr, Cd, Sn, Pb, Bi, and U. Superjacent cuirass demonstrates accumulation of Fe2O3, Rb, Mo, Cd, Sb, Te, U, Sc, V, Cr, Cu, Li, Be, and Th.
Thus, changes in physical-chemical conditions of the weathering profile and the redistribution of large volumes of rock-forming components are accompanied by the redistribution (often bidirectional) of minor elements.
Keywords: Sangaredi, bauxite-bearing weatherin profile, behavior trace elements.
