Implications of heavy mineral assemblage to sediment recycling, rare earth element budget and provenance of Kaimur sandstones, Vindhyan Supergroup, Son Valley

The heavy mineral assemblage (HMA) of sandstones belonging to Mesoproterozoic Kaimur Group in the eastern Son valley, Central India, was investigated. The present communication is aimed at assessing mineralogical maturity, quantifying the contribution of heavy fraction to the bulk rock and its REE budget, sediment recycling and provenance. The transparent heavies record a relative decreasing trend upwards from 63 to 36.4% and on the contrary, opaque heavies show gradual increasing trend upwards from 36.4 to 65.4%. Tourmaline in the transparent heavy fraction reveals an overall decreasing trend of 59-22.8%. Whereas, zircon registers an increasing trend of 3.3-9.5% stratigraphically upwards. The contribution of opaque detrital clasts of ferruginous material composed of hematite and magnetite increases in the Upper Kaimur Sandstone. Tourmaline and zircon grains are characterised by etched, pitted and grooved surfaces. Zircon is also present as tiny inclusion within tourmaline and zircon itself. Heavy fraction of Upper Kaimur sandstone from the lower stratigraphic horizon exhibit lower Sigma REE as compared to higher levels. The heavy fraction exhibit LREE/HREE < 1 as compared to bulk rock which has 8-10 times higher ratio. Heavy fraction exhibits enrichment in HREE and [Gd/Yb](N) = 0.36-0.43, stratigraphically upwards, which is consistent with increasing Zr values suggesting zircon to be the major contributor to the REE budget of Upper Kaimur Sandstones. The percentage contribution of the zircon to the REE budget of bulk rock could have been similar to 50-60%. ZTR index (99-100) reveals mineralogically mature nature of Kaimur sandstones. Dominance of zircon amongst the heavies and Th/Sc vs. Zr/Sc plot shows the eAect of zircon addition and sediment recycling. The plausible explanation for dominance of opaque minerals in HMA in the Upper Kaimur reCects their contribution from Paleoproterozoic metasedimentary rocks of Mahakoshal Group. HMA of Kaimur sandstones suggests derivation from granitic source. Nb/Yb vs. U/Yb diagram indicates that zircon was derived from magmatic arc source, which is in conformity with inference that Bundelkhand Granite Complex and Chhotanagpur Granite complex dominantly contributed to the Lower and Upper Kaimur Groups, respectively.

Automated summary

This study investigated the heavy mineral assemblage of sandstones from the Kaimur Group in the eastern Son valley, Central India. The results showed a decreasing trend in the transparent heavies and an increasing trend in the opaque heavies. The transparent heavies exhibited a decreasing trend in tourmaline content and an increasing trend in zircon content. The heavy fraction of the Upper Kaimur sandstone showed enrichment in heavy rare earth elements and suggested zircon as the major contributor to the REE budget.