Rajendrakumar Budihal^1,, Ganapathi Pujar¹

The laterite deposits of Swarnagadde plateau occurs in Uttar Kannada district of Karnataka state, forming low altitude flat topped laterite hills and plateaus adjoining part of Central Western Ghats, in the western continental margin of India. In this study, using geochemical techniques for calculation of relative weathering (SiO₂ content), CIA and correlation coefficients, the effective factors in mobilization and redistribution of major and trace elements during lateritization processes across selected profile were considered. According to the Al₂O₃-Fe₂O₃-SiO₂ ternary diagram of Schellmann [1] the limit of kaolinization on the tri-plot for the protolith of Swarnagadde plateau profile (granite/gneiss rock) is determined to occur at 68.22% SiO₂ and gradual change from SiO₂-rich to Fe₂O₃-rich to Al₂O₃-rich compositions and of increasing degree of lateritization. The laterite samples were highly weathered with chemical index of alteration ca.98.92%, nearly complete loss of Na, Ca, Mg and K in the ferruginous zone. Fe mainly occurred as goethite, hematite, while Al mainly occurred as secondary clay minerals (kaolinite) and gibbsite below the ferruginous zone. On the basis of mineralogy and geochemistry, these deposits are grouped as aluminous laterites, ferruginous laterites and lithomargic clay. The major, trace elements and mineralogical characteristics of laterites, these were formed in situ by the alteration of parent rocks of granite/granitic gneiss compositions. The correlation coefficient patterns of several major and trace elements and their preferential enrichment have suggested that there is an influence of precursor rock on the distribution of trace elements. Significant depletion of base cations and Si, coupled with enrichment of Fe and Al, reveal that intense leaching of cations, kaolinization, desilication and ferruginization took place in lateritic deposits during weathering and lateritization.

Swarnagadde, laterite, weathering, cations, aluminous