Control of the distribution of Mn, Co, Zn, Zr, Ti and REEs during the evolution of lateritic covers above ultramafic complexes

Abstract

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.

Geochemical characterization of the largest upland lake of the Brazilian Amazonia: Impact of provenance and processes

“…12) shows high positive loading of most of the trace elements, REEs, Al, K, and Ti in Group 1, while these elements are poorly correlated with Fe (Group 2) and TOC (Group 3). Strong positive correlation of most of the trace and REEs with Al 2 O 3 and TiO 2 in Group 1 indicates they are likely scavenged by aluminosilicate minerals (Marker et al, 1991). Based on the distribution of Al 2 O 3 , these elements are likely enriched in LTI1, mainly in the central part of the lake, towards the eastern border.…”

Lateritization process of peridotites in Siruka, Choiseul, Solomon Islands

“…Relative to chromium, practical application of Equation 1 illustrate apparent removal of most major and trace element in amounts ex-ceeding~80% of the original concentration in the parent body prior to weathering (Table 4). Enrichment and distribution of minor and trace elements in the laterites are often controlled by weathering processes and morphology of the peridotite massifs (Marker et al, 1991).…”

L’or, le zircon et la tourmaline : Traceurs de l’origine des materiaux des profils lateritiques d’afrique

“…Pour de nombreux auteurs dont Jolliff et al (1986), la tourmalinite est associée à des intrusions granitiques; elle peut aussi se former par métamorphisme de dépôts de tourmaline. Fieremans et Paepe (1982) (Trescases, 1975;Golightly, 1981;Schellmann, 1989;Freidrich et al, 1990;Marker et al, 1991). La base, autochtone, est issue de l'altération de la roche sous-jacente; alors que la partie sommitale semiautochtone est un mélange de produits ferrugineux issus M. OUANGRAWA Figure 10: Diffractogramme de rayon X de la tourmalinite de la roche ultrabasique et de minéraux provenant des roches acides.…”