The chemistry of some Brazilian soils: Element mobility during intense weathering

Abstract

Chemical data for 56 elements in soils from three regions of Brazil (Bahia, Amazon, Goias) indicate that intense chemical weathering leads to a product soil essentially in the system, SiO~--AI20 ~ --F%O3--H~O. The major minerals of the leached soils are quartz, kaoli nite, gibbsite, goethite and hematite. Trace elements show a wide range of behaviour from those which are enriched as for some bio-important elements (B, C1, Mo, Se, Sn, I) and refractory metals (Sc, Zr, Nb, Gd, Tm, Th) to the majority which are severely leached. Trace-element behaviour appears to be largely controlled by the dominant clay or AI303--SiO 2 minerals, or the degree of weathering. Consideration of the chemistry of lateritic soils and groundwaters indicates that the development of deep lateritic profiles requires times in the order of tens of millions of years in a very stable continental setting.