Apatite-hosted REE mineralization in the Eastern Ghats Mobile Belt: A future prospect for REE

Abstract

The growing need of rare earth elements in different sectors of the modern-day world has led to their increasing demand, which is in accordance with their limited supply. In such a scenario, investigations related to search for potential zones of rare earths have become the need of the hour. In one such investigation, undertaken by Geological Survey of India, the authors report profuse intrusion of the apatite veins into the syenite-pyroxenite suite in the eastern part of the Eastern Ghats Mobile Belt (EGMB) in Nayagarh area of eastern Odisha. These apatite veins are anomalously rich in REEs, particularly LREEs, which on average ranges between 37,000 to 53,000 ppm. Rare earths and apatite are generally directly proportional, where apatites tend to carry sufficient REE budget, depending on the phosphorous fugacity and other ambient conditions inducing their genesis. The major-oxide chemistry of apatite veins indicates that apatites in the study area can be divided into two types based on SiO₂ wt.% and their inverse relationship with P₂O₅ and CaO wt.%. Mineral chemistry data shows overall SiO₂ depletion, with dominance of CaO, followed by P₂O₅. Apatite veins, as per mineral chemistry, contain numerous veinlets (identified microscopically), where one type is REE-bearing and another type is REE-free. The REE-bearing phases are rich in Ce, Nd, La and Pr and are represented by allanite, monazite, and bastnaesite. Thorite and zircon are prevalent. Earlier instances of apatite intrusions into granulite have been reported from parts of south India. On the contrary, in this area, the intrusion is typically restricted to the younger intrusive units of the EGMB, represented by syenite-pyroxenite suite. The intrusives also show moderately high values of REEs. In this paper, an attempt has been made to characterize the apatite veins and the syenite-pyroxenite suite, they have intruded, in respect to their mineralogy and tectonics and to elucidate the potentiality of the area in terms of future REE exploration.