Geochemical study of laterites of the Jamnagar district, Gujarat, India: Implications on parent rock, mineralogy and tectonics

The laterite deposits occur in a linear stretch along the northern Arabian Sea coast in the Jamnagar and Porbandar districts of, Gujarat state, India. These deposits are characterised by presence of gibbsite, kaoline, calcite, quartz, anatase, natroalunite, goethite and hematite, and relicts of mafic minerals and plagioclase. On the basis of petro-mineralogy and geochemistry, these deposits are grouped as aluminous laterites (Fe2O3 – 1.45–3.84%, Av. 3.13, Al2O3 – 39.31–57.24, Av. 45.80) and laterites (Fe2O3 – 9.84–32.21, Av. 25.13%, Al2O3 – 34.74–49.59, Av. 41.27). The major, trace and REE characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic/andesitic composition, and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation. The correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements.The Jamnagar laterite deposits occur as capping over the Deccan Trap basaltic lava flows and pyroclasic deposits. Lateritisation prevailed during Palaeocene age when India was separated from the Seychelles and passing over the equator. During this time climate, morphology and drainage conditions were favourable for lateritisation that result in the formation of Jamnagar and other laterite deposits within the Deccan Province. Flood basaltic provinces of Deccan, Columbia, North Australia and Hawaii appear good location for hosting laterite deposits due to their wide areal extent, small geological time span and uniform chemical composition. However, comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate, morphology and drainage are equally important factors for facilitating lateritisation.

► Pyroclastic rocks were parent material for the laterite deposits of Jamnagar.
► Mineralogical influences govern distribution of trace and REE during lateritisation.
► Laterites formed during passage of Indian plate over equator.
► Flood basaltic provinces and laterite deposits?