Caracterización geoquímica de los sedimentos de la red de drenaje del Rio Garona en la Val d'Aran (Catalunya, España).

Abstract

A geochemical survey of stream sediments from the Garona River was performed in order to define the main regional lithogeochemical units and, based on this geochemical exploration study, to establish the reference levels of some chemical elements in the upper Garona River basin. The analysis of the lower grainsize fraction (˂180 μm) by HR-ICP-MS of 33 stream sediment samples allowed us establish reference levels for 48 elements. We have also studied the leachates of the sediments to model the environmentally available geochemical fraction. The trace elements with the lowest reference level, ranging between 10 and 50 mg/kg, are Th, Pr, Ga, Y, Ni, Pb, As, Cu, Zr, Li, Cr, Nd, La, and V. Instead, Zn, Rb, Sr, Ce and Ba show concentrations higher than 50 mg/kg. Some enrichments were observed in the streams sediments according to the three main litogeochemical units defined; the Maladeta-Marimanya granitoids (higher concentrations of Y, Th, Pb and U), the metasediments of an extensive area of the basin (enrichments in Pb, Sr and Sn), and the black shales (in Cu, U, Sr, Ni, Zn, V, Sb and Mo) which are present in local areas of the basin.