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

N. V. A. S. Perumal ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Hyderabad, IN

Abstract

Geological mapping of a 300 sq km area forming part of the Eastern Ghats, east of Chipurupalle, supplemented by modal analyses, optical petrographic data, and chemical analyses of seven whole-rock samples and a garnet, show that (1) basic charnockites of the area represent igneous rocks of noritic composition metamorphosed to granulite facies, and (2) some rocks of the area that resemble intermediate charnockites are metamorphosed hybrid rocks derived from assimilative reaction between basic magma and pelitic sedimentary rocks.

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C. Suryanarayana Rao ¹, G. R. Narayan Das ¹, B. Krishnaiah Setty ¹, N. V. A. S. Perumal ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Hyderabad, IN

Abstract

Precambrian carbonatites associated with pyroxenites occur as discontinuous lenticular bodies intruding the syenites west of Pakkanadu (11°40'15'': 77°50'1'') and Mulakkadu (11°44'3'' : 77°50'2''). They strike northeast to southwest with easterly dips and have been emplaced along a major northeasterly trending deep crustal fault zone. Large outcrops of serpentinised dunites carrying accessory chromite, cut by asbestos and magnesite veins are also found along the same fault zone to the east and northeast of Pakkanadu.

The carbonatites are of the pure calcite-rich sovite type, with biotitic and ankeritic variants. Apatite, magnetite, allanite, barite, monazite, zircon and cerianite, are the accessory minerals.

Spectrographic analysis has revealed Ba, Sr, Ce and La in major amounts (more than 10,000 ppm) and Th, Nb, P, Zr, Y and Sc in minor amounts (< 10,000 ppm). Spectrographic data suggest that the carbonatite-pyroxenite complex is Ce-La rich.

Niobium is not found in economic concentrations. The general radioactivity recorded by the carbonatite-pyroxenites ranges from 5 to 20 x BG. Representative whole rock samples assay from 0.02% to 0.054% _eU₃O₈ (Carbonatites) and 0.02% to 0.06% _eU₃O₈ (pyroxenites). Allanites assay from 0.35% to 0.4% _eU₃O₈ with chemical U₃O₈ values from 0.007% to 0.034%, thereby indicating the predominance of thorium over uranium. Monazite is mostly concentrated in the biotite-rich portions of the carbonatites to the west of Pakkanadu, whereas allanites predominate in the pyroxenites west of Mulakkadu.

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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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N. V. A. S. Perumal ¹

Affiliations
1 Department of Atomic Energy, Hyderabad, IN

Abstract

No Abstract.

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