Abstract

A chemical study of the laterite profile developed over basalts in the Hazaridadar plateau in Madhya Pradesh, India, is presented, based on data obtained from intensive exploration. In ascending order the profile consists of lithomarge (saprolite), laterite, and bauxite with laterite.The formation of the profile essentially involves desilication and hydration. In absolute terms there is no major gain or loss in TiO 2 and Al 2 O 3 . Judging from the chemical character of the different zones, the profile has been evolved by gradual in situ weathering of basic rocks under favorable conditions.It is postulated that the profile has been developed in three distinct stages. First, formation of lithomarge (by partial desilication and hydration) has been followed next by the formation of a laterite horizon with a fixed composition in terms of Al 2 O 3 + Fe 2 O 3 . Desilication is more or less complete in this stage. Finally, differential leaching of Al 2 O 3 and Fe 2 O 3 and the downward migration of the latter have resulted in the formation of a zone of bauxite within the laterite at the top and another of laterite at the bottom, the latter showing evidence of deposition of secondary Fe 2 O 3 . Zones favoring free movement of water in the top levels of the laterite are suggested as favorable horizons for enrichment in Al 2 O 3 .

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