Episodic ferricretization of the Deccan Laterites (India): Inferences from ore microscopy, mineral magnetic and XRD spectroscopic studies

Studies based on sampling a ~40 m thick profile comprising the basalt protolith, saprolitic horizon and various levels of ferricretization in the Deccan upland lateritic sequence of the western Maharashtra (India), indicated episodic nature of lateritization. Mineral magnetism precisely demarcated the ferrimagnetic to anti-ferromagnetic (fm/afm) boundary at the base followed by various stages of lateritic developments in the upper horizons. The fm/afm boundary can be traced in field using magnetic susceptibility and therefore provide a datum for laterite base-level mapping. Ore microscopy details the inter-association and paragenesis of amorphous and crystalline varieties of iron oxide minerals (hematite, limonite, goethite) that are further modified by allochthonous inputs and changes in porosity. The lowermost horizons show silcretization, while the XRD studies record sporadic kaolinitic occurrence throughout the profile with gibbsite appearing in the upper part of the profile. Combination of mineral magnetic and ore microscopic observations depict frequent lateral inputs possibly during periods of heavy precipitation arresting and further reclaiming the process of lateritization to produce large composite thicknesses of the Deccan lateritic sequence without matured lateritization.