Trace elemental signatures and mineral chemistry of clays associated with the alteration halos of the Paleoproterozoic U mineralization in Bijawars of the Sonrai Basin, Central India

Abstract

Paleoproterozoic Bijawars of the Sonrai basin consists of (a) Sonrai (mostly carbonate carbonaceous shale and phosphatic breccia) and (b) Solda Formations (commonly chloritic and ferruginous shale) with well-developed clay-organo-rich facies, often marked with hydrothermal activities. Previous studies revealed abundance order of kaolinite > chlorite > illite > smectite; and kaolinite > illite > chlorite in clay (0.2–2.0 µm) fractions separated from the Sonrai and Solda Formations, respectively. To understand atomic substitutions and trace elemental concentrations, clay minerals were analyzed by fusion ICP-MS and SEM–EDS. PAAS normalized data plots show U, Th, Rb, Ba, Pb Sr, and large-ion lithophiles enrichment, whereas, Bandai sandstone and Rohini carbonate clays show HREE enrichment with asymmetrical patterns, similar to those reported from the well-established McArthur River, Cigar Lake, and Sue UTUD of Canada. For Rohni carbonate, chondrite-normalized REE data plots revealed M shape REE patterns, ascribed to Gd–Tb–Dy–Ho tetrad effect and anomalous Y, Zr, and Hf concentrations. Owing to HREE incorporation in the clay inter-layers, linear and flattened REE trends were noticed. Flat REE patterns associated with the highly altered chlorite and illite represent negative Eu anomaly related to the dilational nature of the uraninite structure and is suggestive of anoxic conditions.