A Note on Carbonate Rock with Igneous Affinity from Jungel Valley, Sonbhadra District, Uttar Pradesh, Central India

The Lower Proterozotc (1800-2400 Ma) Jungel Valley mafic-ultramatic complex (JVMUC) is an integral pait of Mahakoshal greenstone belt in district Sonbhadra. The complex is known for its diversity of locks like alkali olivine basalt, kimbeihte and ultramalic lamprophyre. In addition to these, a carbonate rich rock having igneous affinity is being reported for the first time from this complex High CaO, CO₂, Sr and Ce with low SiO,, A1₂O₈ and TiO₂ characterise this rock. However, these rocks are not significantly enriched in incompatible elements and REE, implying that these may have possibly formed by partial melting of a depleted mantle at shallow depth. The geochemical characters combined with association of mantle derived rocks, presence of high level of carbonate in the lamprophyre and absence of sedimentary limestone in the area point towards an igneous origin, probably as a residual concentrate of a differentiated Kimberlite-Ultramahc lamprophyre sequence Sr isotope data, which fall well within the range of reported carbonatites of India, suggest moderate crustal contamination. The mafic-ultramafic suite together with the carbonate rocks developed in Son-Naimada nit zone are interpreted to be coeval with the intrusive syenite pluton, alkali gabbio and lamprophyres of the adjoining areas and is related to the development of Mahakoshal greenstone belt.