REE and Y enrichment in peralkaline felsic rocks of the Siwana region, Rajasthan, Northwestern India

In the modern world, rare earth elements (REE) and yttrium (Y) dominate the development of high-end electronic equipment and green energy technologies. The global economic deposits of REE and Y are primarily associated with alkaline and peralkaline igneous rocks. The REE deposit of the Siwana ring complex, Rajasthan, India, is entirely composed of peralkaline igneous rocks. This complex is made up of REE and Y enriched (both LREE and HREE) peralkaline granite, rhyolite and its younger felsic intrusives such as rhyolite, micro- granite, aplite and felsite dykes. We present a study of the REE and Y potential of granites, volcanic rocks and felsic dykes from 17 quarries in the Siwana area. Monazite, zircon and apatite were the primary (magmatic) REE-bearing phases identified under a micro- scope. The late/post-magmatic replacement in granite is evident as coarsening of perthite lamellae, pseudomorphic replacement of alkali feldspar grains by aegirine, replacement of a enigmatite by aegirine, etc. The granites, volcanic rocks and dykes show significant enrichment of REE + Y and other trace elements (Sn, Hf and U). A total of 20 rock samples were analysed using inductively coupled plasma mass spectrometry, which indicated significant REE + Y values ranging between 1061.22 and 9088.62 ppm, with an average of 2361.89 ppm. This includes LREE (707.42–5743.83 ppm, avg. 2080.40 ppm) and HREE (135.77–1422.23 ppm, avg. 402.41 ppm) Hf up to 425.55 ppm. Totally five samples from a soil profile were also analysed, yielding REE + Y values between 223.39 and 3175.75 ppm, with an average of 1714.51 ppm. The ion adsorption clay horizon developed within the soil profile showed a maximum REE + Y value of 3175.75 ppm. (author)