Laterites above ultramafic complexes in Brazil and the Philippines consist of in-situ (autochthonous) and partly transported (semi-autochthonous) horizons. Enrichment and distribution of minor and trace elements in the laterites are controlled by weathering processes and the morphology of the peridotite massifs. Mn and Co migrate towards the base of doline-like depressions of the peridotite karst where they precipitate in the ferruginous horizon above the saprolite, due to rising pH and concentration of the solution. Mass balance calculations reveal absolute enrichment of Mn and Co and depletion of Zn and Cr. Semi-autochthonous laterites represent a mixture of Fe-Cr-rich limonitic material derived from ultramafic rocks and Al-Si-Ti-Zr-rich kaolinitic material derived from sialic rocks. They may reveal unusually high contents of A1203, SiO2, TiO2 and Zr, thus camouflaging the underlying ultramafic bedrock. During and after deposition of semi-autochthonous laterites, acidic leaching under humid (sub-) tropical climate leads to the mobilization of REES from the weathering products of sialic rocks. Subsequent migration and precipitation of REES together with Mn at the base of depressions result in concentrations of predominantly Ce which under favourable conditions exceed 0.5 wt.%. High proportions of sialic weathering material in laterites can be expected in geological settings where ultramafic and sialic rocks occur in close spatial association. Enrichment of REES in weathering profiles above ultramafics is favoured by the abundance of weathering material from REErich alkaline rocks like those of the Alkaline Complex of Jacupiranga, Brazil.

In humid coastal regions and in areas of accentuated relief of SE-Bahia, Brazil, weathering of alkaline rocks resulted in the formation of kaolinitic and lateritic weathering mantles. Under subhumid conditions in the inland region of Bahia, less mature sandy-clayey soil have developed. Rare Earth Element (REE) distribution in the weathering profiles has been investigated in order to establish relationships between climatic and morphological parameters and the enrichment and fractionation of REE. Under tropical humid climate and intensive drainage conditions, REE fractionation is enhanced. Ce is absolutely enriched in laterite layers while the Heavy REE are retained in the saprolite. Moderate drainage due to high groundwater tables lead to minor fractionation and enrichment of REE. Restricted drainage conditions in subhumid climatic zones hamper liberation of REE from primary minerals and impede enrichment and fractionation of these elements. REE distribution is also controlled by polyphase evolution of the weathering mantle: the positive Ce anomalies in laterite layers are related to stable mineral phases like Mn oxides, which have developed in roots of weathering during former, less humid weathering cycles. The REE fractionation patterns correspond to the drainage conditions which prevailed during the formation of the weathering products. Thus they may represent a valuable tool for the reconstruction of landscape evolution and the investigation of the paleoenvironment.

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