Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

D. Bhattacharya ¹, Madhuparna Roy ¹, Dhirendra Kumar ², Pawan Misra ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, NR, New Delhi - 110 066, IN
2 Flat No. B-170, Kendnya Vihar, Sector-51, Noida, IN

Abstract

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.

Keywords

Jungel Valley, Caibonate Lamprophyre, Mahakoshal Greenstone Belt, Uttar Pradesh.

Full Text

     

Jyotsna Chhabra ¹, Dhirendra Kumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, New Delhi - 110066, IN

Abstract

Textural, mineralogical and chemical features of radioactive biotites from the melanosomes and leucosomes of migmatites in Chhotanagpur Gneiss at Kudri Hills are described. Biotite from melanosome is usually large and contains profuse inclusions of zircon, allanite, uranothorite and uraninite, as compared to thc biotite from leucosome. The melanosome biotite also shows contrasting microtextures, viz., presence of Fe-Ti oxide granules along cleavages and as rims around the flakes, as well as sieve texture as compared to leucosome biotite. The FeO(t)/MgO value in melanosome biotite varies from 5.0 to 5.3, whereas it is 5.9 to 6.5 in leucosome biotite. Structural formulae of biotite, calculated on the basis of 24 (0, OH, CI, F), show that the 12-coordinated cations of X-group do not reach the ideal figure of 2 in either case. The octahedral sites occupied by Y-group cations have a wide range in leucosome biotite in contrast to the very narrow range in melanosome biotite.

Anomalous concentration of rare and radioactive elements, viz., U (up to 1200 ppm), Th (up to 656 ppm), Zr (up to 31076 ppm), Ce (up to 1576 ppm), Nb (up to 193 ppm) and Y (up to 2053 ppm) in melanosome biotite seems to result from its favourable crystal structure, conducive physico-chemical attributes and stability at high temperature of amphibolite facies. The most important feature of melanosome biotite is the presence of inclusions of radioactive minerals like uraninite, uranothorite, allanite and zircon.

Keywords

Mineralogy, Radioactive biotite, Migmatite, Leucosome, Melanosome, Sonbhadra District, Uttar Pradesh.

Full Text