Lateritization cycles and their relation to the formation and quality of kaolin deposits in south Kerala, India

Laterite occurs extensively over the crystalline and sedimentary rocks in the midland and lowland areas of south Kerala, India. Two lateritization cycles are identified in this area. Large, good-quality kaolin deposits, composed mostly of kaolinite, are characteristic of the sedimentary sequence in south Kerala. These deposits were formed on deposition of the weathering materials of the khondalites towards the first cycle of lateritization. After deposition and uplift of the sedimentary rocks, another lateritization cycle affected these, as well as the khondalites during pre-Quaternary times with the formation of a planation surface at 25–125 m above sea level having thick laterite profiles. The laterite profiles over the kaolin deposits show higher concentration of Fe-oxides (mostly in the form of hematite) and titania, compared to their concentration in the kaolins. Higher contents of Cr and Ni are also characteristic of the laterite over kaolin deposits. Recrystallization of the kaolinite, appearance of Al, Fe and Si amorphous phases in the kaolin clays and partial removal of Fe and Ti from them are attributed to the second lateritization cycle.