Abstract: The Madayi clay deposit consists of a thick sequence of residual white kaolinitic clay underlying the sedimentary Warkallai Formation, which includes gray carbonaceous kaolinitic clays, lignite, ferruginous kaolinitic clays, laterite and bauxite with ferricretes. The conditions of clay genesis and the economic significance of the major residual kaolin seam have been investigated. The raw clay and <2 µm fractions were subjected to X-ray diffraction (XRD), chemical analysis, differential thermal analysis (DTA), Fourier transform infrared (FTIR) spectroscopic and scanning electron microscopic (SEM) studies. The firing behavior of the <45 µm fraction of the major residual clay sequence (L), was investigated systematically to determine the potential industrial use of this kaolin.
Geochemical and morphological studies of different strata indicate the following conditions for clay formation: (1) intense lateritized weathering conditions for kaolinization of the residual white clay from parent quartzo-felspathic mica-gneiss; (2) reducing environment for the gray carbonaceous layers; and (3) oxidizing environment for the uppermost hematite-rich ferruginous clay. Pyrite/marcasite enriched detrital gray carbonaceous clay shows two distinct environments for in situ kaolinite crystallization: (1) within plant fossils influenced by the high organic content and FeS2 leaching; and (2) precipitation from solution.
Incomplete kaolinization of white residual clay is evident from the presence of pyrophyllite, muscovite with lenticular cleavage void and a lower percentage of fines (<2 µm). The plant fossils from the uppermost portion of residual clay show pyrite mineralization. The Hinckley Index, FTIR and rare earth analysis point towards diverse geochemical environments of deposition and technological evaluation indicates its suitability for application in the ceramics industry.