Geochemistry of a ferruginous bauxite profile from southeast Venezuela

For the geochemical characterization of an in-situ-formed ferruginous bauxite profile over a diabase from the southeast of Venezuela, 27 samples were quantitatively analyzed for Al, Si, Ti, Fe, H2O+, Na, Sc, Cr, Mn, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Zr, Sb, Cs, Ba, La, Ce, Nd, Sm, Eu, Tb, Dy, Ho, Tm, Yb, Lu, Hf, W, Ta, Th and U. The minerals determined by X-ray diffraction were gibbsite, kaolinite, goethite and hematite. Calculations of the gains and losses during the lateritisation were made under the assumption that Ti is immobile. They showed that Fe was generally enriched while Si was nearly completely depleted. Al exhibited losses in the uppermost part of the profile and in its middle part. The remaining main constituents of the source diabase Na, K, Mg and Ca were quite leached. The concentration ratios ClateriteCdiabase revealed that Al, Ti, Fe, Ni, Ta, Th and U were enriched by a factor of 2–2.8. The elements Sc, Cr, Ga, Zr and Hf were concentrated by a factor <2 while all other elements were lixiviated. The chondrite-normalized rare-earth element (REE) distribution patterns presented partly more or less pronounced-negative Eu anomalies and in part pronounced-positive Ce anomalies. Similarities in the behaviour of the elements during the laterite formation were established by the linear correlation coefficients employing log-transformed concentration data. Additionally, the following correlation coefficients with non-parametric characteristics were employed: the rank correlation and the correlation score. The latter pointed to a close affinity between AlNi, TiGa, TiSr, TiHf, TiTa, NiSr, GaSr, GaHf, SrHf, ZrHf, ZrTa, SmHo, SmYb, HfTa and HfTh. Positive associations were ascertained by the rank correlation coefficients between the element pairs TiZr, SmEu, SmDy, SmHo, SmYb, EuDy, EuHo, DyHo and DyYb while AlFe, AlZn, FeCu and DyHf were negatively correlated. According to the linear correlation coefficients the elements SmEu, SmHo, SmYb, EuHo and DyHo are evidently positively correlated. AlFe and CrCu are clearly negatively related with one another. All three evaluation methods established close relations among the intermediate REE. Both non-parametric correlation coefficient matrices presented also distinct relationships among bauxitophilic elements.