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

G. R. Narayan Das ¹, T. N. Parthasarathy ¹, P. C. Taneja ¹, N. V. A. S. Perumal ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, West Block No. VII, R. K. Puram, New Delhi 110022, IN

Abstract

Uranium mineralisation as Uraninite vein filling is seen in joints and fractures in the quartzites exposed within an eroded cover of crystallines, tectonically thrust from east and NE in Kulu-Banjar area of Himachal Pradesh. Analysis of the joints suggests a tensional origin and can be related to the three main folding events identified from the fold structure in the quartzites. It is believed that the mineralisation is essentially under low temperature-pressure conditions as there is a remarkable absence of large scale wallrock alteration.

U-Pb dating of six Uraninite samples reveals two distinct episodes of mineralisation at 1200 m.y. and 700 m.y. confirming the Precambrian age of Uranium mineralisation, and associated metasediments.

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T. N. Parthasarathy ¹

Affiliations
1 Atomic Minerals Division, Hyderabad 500016, IN

Abstract

Fluvial conglomerates, separating two flysch sequences have been identified at several places in Middle Andaman island. These conglomerates are characterised by poorly sorted, polymictic, well-rounded to sub-rounded pebbles, and consist of black cherty quartzite, vein quartz, slaty phyllite, andesite-basalt, reddish jasper, limestone, serpentinite and tuffaceous rocks. The linear continuity of the conglomerate is broken and its thickness much affected by structural deformation.

The conglomerates appear to have been initially deposited as lags on steep slopes and later resedimented in deep waters of the basin. It is implied thereby that the Middle Andaman conglomerate represents unconformable unit separating two sequences of flysch beds, and marking a period of tectonic uplift. It is suggested that the uplift of the source area followed the deposition of the older flysch sequence and perhaps the basalt andesitic volcanism also. Such an uplift may be linked with the oft-suggested subduction of Indian Ocean plate along Indo-Burma-Andaman-Nicobar-Sunda arc boundary.

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K. V. Ramana Murthy ¹, Y. S. Manjunath ¹, G. V. G. K. Murthy ¹, M. A. Nayeem ¹, T. N. Parthasarathy ¹

Affiliations
1 Atomic Minerals Diivision, Begumpet, Hyderabad - 500 016, IN

Abstract

Brannerite occurs as subrounded to subangular grains (0.05mm to 20mm) in marble, quartzite, carbonate rock, quartz biotite schist and albitite, and in soils derived from these lithounits of Ajabgarh Group of metasediments around Kachera dam-Ladikabas area of Sikar district, Rajasthan. It alters to rutile along the margins and fractures. The analysis shows 30.6-36.9% UO₃, 0.9 to 3.2% UO₂, 33.40% TiO₂ and 3.4% total (REE)₂O₃.

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T. N. Parthasarathy ¹, P. Rajasekharan ¹, Y. S. Manjunath ¹, S. N. Chaturvedi ¹, A. Bose ¹

Affiliations
1 Atomic Minerals Division, Hyderabad-500 016, IN

Abstract

Ultramafic-mafic rocks of komatiitic affinity are reported from the Kerali area of Abujhmar basin in Bastar Craton, Madhya Pradesh. These rocks, occurring below the Gundul sandstone member of the Middle Proterozoic Abujhmar group, are composed of peridotitic komatiites, pyroxenitic komatiites and basaltic komatiites, besides tholeiites and microgabbro emplaced into them as dykes. Petrographically, olivine and pyroxene occur both as major phenocrysts, and as microphenocrysts, with the groundmass made up of interstitial glass. Normatively, these rocks are both olivine and hypersthene normative. Petrochemical data plots on discriminant ternary diagrams such as AFM, Jensen Cation plot, MgO-CaO-AI₂O₃ diagram, indicate their close similarity to the komatiitic trends shown by the type area rocks from the Munro Township area, Canada and Yilgarn Block of West Australia very much paralleling the trend of Barbertonland komatiites. Trace element data involving Ti, Y, Zr and V plots also points out that these rocks fall in the kornatiitic field as against the tholeiitic field. Tectonic environment discriminant diagram involving the plots of these ultramafic-mafic rocks indicates the possibility of deep passive or 'failed' (?) rift in the region through which these ultramatic-mafic rocks of komatiitic affinity might have been emplaced.

Keywords

Ultramafic Rocks, Komatiite, Petrochemistry, Abujhmar Basin, Bastar Craton, Madhya Pradesh.

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