Geochemical perspectives of the rare earth elements and yttrium in some Permian and Paleogene coals of India: A review

Abstract

The increasing demand and utilization of rare earth elements (REE or REY, if yttrium is included) in numerous sectors have led to the consideration of secondary resources for their recovery. The worldwide research has been focused on coal beds that may have potential recovery of REE or REY. Despite India's extensive coal reserves, the complex geochemistry of REE in its coalfields remains underexplored, with only a few basins being investigated. This paper reviews existing literature on the enrichment types, modes of occurrence, and anomalies of REE in Indian coal measures. Key findings indicate the presence of REY-bearing minerals such as xenotime, rhabdophane, mixed layer smectite/illite, etc., in Gondwana and Paleogene coals along with a high fractionation of LREE (light REE). Coals from Satupalli, Hura, Meghalaya, and Jharia show strong potential for the REY extraction. The Upper Continental Crust (UCC)-normalized REE patterns of the coal deposits illustrate variations in their distribution types. Satupalli coals exhibit an heavy-type distribution, Hura coals display light- and medium-type distribution patterns, Sohagpur coals show light-type pattern, while Assam coals have an heavy-type distribution pattern. The modes of occurrence of the REE in Indian coals are primarily influenced by the input of detrital minerals in erosional areas. The Paleogene coals have experienced marine-influenced environments; however, few of them exhibit distinctive depositional settings as well. Limited coal samples from Meghalaya and Raniganj show substantial REE enrichment. This study highlights the dissimilar characteristics in REE distribution patterns across India's coalfields, each with disparate geological settings, which need supplementary research work to establish their precise modes of occurrence and incorporation mechanisms into the peat depositional environment.