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Kaolinites, Laterites and Bauxites |
Department of Geology, The University, Manchester M13 9PL
The 23 samples studied represent a complete vertical profile, 11 m thick, from topsoil to bedrock. Multiple bedrock samples were collected to obtain good estimates of bedrock variability and bulk composition. Nineteen of the 22 major and trace elements studied fall into five behavioural groups within each of which all element pairs show strong positive correlations: (1) Al, Ti, V, Nb and Zr are very highly enriched (factors 20–65 relative to bedrock) in horizon B; (2) Fe, Cr, Sc, Cu and Ce are also strongly enriched (factors 4–40) in horizon B, but show slightly greater enrichment (factors 10–50) in horizon C; (3) Ni, Y, La, Nd and Zn are characterized by concentrations (enrichment factors 8–90) in horizon C of 5–10 times their levels in horizon B; (4) Mn and Co are intermediate between (2) and (3); (5) Si and Mg are strongly depleted in all soil horizons. A mass-balance model, based on quantitative Ti retention, gives relative wt% losses over the profile as a whole of MgO 99.5, Na2O 99.3, CaO 98.5, SiO2 98.3, K2O 96, NiO 91, CoO 89, MnO 88, Cr2O3 83, Fe2O3 79, Sc 78, Zn 75, La 69, Ce 65, Al 59, V 57, Nb 40, Nd 19, Y 12, TiO2 0. Zr and Cu show ca. 10% relative gains, indicating stronger retention than Ti. In situ leaching of an estimated serpentinite thickness in excess of 200 m is required to produce 11 m of residual laterite.
