Petrographical, mineralogical, and geochemical characteristics of the Palaeocene lateritic bauxite deposits of Kachchh Basin, Western India

Abstract

Petrographical, mineralogical, and geochemical characteristics of a blanket‐type lateritic bauxite deposit, bordering the Deccan basalt in Kachchh, are investigated to interpret the parent rock, lateritization processes, and palaeogeographical position of the basin. The presence of partly weathered vesicular basalt at the base of the succession along with partly preserved plagioclase, augite, and hornblende in petrographical observations suggests the in situ nature of these bauxites. X‐ray diffraction analysis reveals gibbsite as the major bauxitic mineral associated with kaolinite, goethite, titanium‐rich anatase, calcite, haematite, and quartz as subconstituents. The presence of gibbsite, kaolinite, and goethite in the majority suggests that warm and humid climatic conditions prevailed during the lateritic bauxite formation. SEM‐EDS analysis shows that most of the gibbsites are mesocrystalline with particle sizes 50–200 μm that coexists with microcrystalline goethite, kaolinite, rutile, and haematite. These deposits are classified as bauxite, ferruginous bauxite, and laterite, based on chemical composition. The high CIA values (86.6–98.1%) suggest their formation under high run‐off and water‐logged conditions similar to that which prevails in the equatorial region. The Zr–Cr–Ga ternary plot testifies to the mafic composition of the parent rock. The major oxides and chondrite‐normalized trace and REEs behaviours, (La/Sm)N ratio (~5.77), and Eu anomaly of these lateritic bauxites suggest that they (bauxites) were formed in situ by the intensive leaching and alteration of the basaltic parent rock, and the process of bauxitization followed the path of deferruginization and destruction of kaolinite. The development of a lateritic regolith over the Deccan basalt was possible during Palaeocene time when the Indian Plate was in complete isolation and the Kachchh region was positioned near the equator in the Southern Hemisphere.