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

G. S. Roonwal ¹, S. K. Srivastava ¹

Affiliations
1 Department of Geology, University of Delhi, Delhi 110 007, IN

Abstract

The clay fraction of the sediments contain illite, chlorite, kaolinite, montmorillonite and iron-smectite with minor amounts of goethite. The siliceous sediments contain both montmorillonite and iron-smectite, while the calcareous sediments show only montmorillonite. This suggests that montmorillonite is formed by the alterations of ridge basalts, palagonite and volcanic glass. Iron-smectite is probably formed during low temperature diagenesis by the chemical combination of iron and silicon. High biogenic sedimentation in the calcareous sediments inhibited the formation of iron-smectite.

Keywords

Clay Mineralogy, Pelagic Sediments, Indian Ocean.

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D. C. Banerjee ¹, K. V. G. Krishna ¹, G. V. G. K. Murthy ¹, S. K. Srivastava ¹, R. P. Sinha ¹

Affiliations
1 Atomic Minerals Division, Dept. of Atomic Energy, Begumpet, Hyderabad-500016, IN

Abstract

Spodumene bearing rare metal pegmatites are reported mostly from Karnataka in contrast to lepidolite and amblygonite bearing pegmatites described from major mica-fields of India. Tantalite (Ta₂O₅ 50-70%) rich pegmatites intruding the Sargur metasediments of Nagamangala schist belt near Marlagalla- Allapatna are also rich in spodumene (10-15% by vol.) as well as beryl (10.6-11.4% BeO). Light green spodumene (Li₂O 6.55-7.35%) occurs randomly as prismatic crystals a few cm to 30 cm in length. Under the microscope, symplectic intergrowth between spodumene and quartz along the contact with albite and replacement of spodumene by quartz and muscovite are noticed. The 'd' spacings and intensities obtained from the X-ray diffraction patterns match well with the published values for Alphaspodumene from Pala San Diego County, California, U.S.A. Some variations observed in the intensities ofinterplanar spacings could be due to preferred orientations exhibited by the mineral. When heated to 1000° C for 3 hours, the Alpha-spodumene transformed to Beta- spodumene.

Chemically these spodumenes are "high iron non-chromian" types (FeO+Fe₂O₃ 1.17 to 1.29%, Cr47- 87 ppm). While Mn content is high (1237-1826 ppm), other trace elements such as V, Cu, Co, Pb and Be are less than 10 ppm, Cs 39-98 ppm and Sn 19-28 ppm. Sn values are considerably low as compared to specimens reported from elsewhere, possibly because these pagmatites are devoid of cassiterite. Mineralogical assemeblage ofspodumene-tnntalite-pollucite in these pegmatites places them in "LCT (Lithium-Caesium-Tantalum) family" of rare element pegmatites as per classification of Cerny. Petromineralogical and geochronological studies of Allapatna granites have been undertaken which will throw furthur light on the geochemistry and paragenesis of these pagmatites. Few hundred tonnes of spodumene are expected to be recovered commercially from shallow depths alone along with tantalites and beryl.

Keywords

Spodumene, Symplectic Texture, Pegmatites, Petrology, Kamataka.

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P. Nageswar Rao ¹, Prakash Kumar ¹, S. K. Srivastava ¹, R. M. Sinha ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN

Abstract

No Abstract.

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S. K. Srivastava ¹, P. K. Kothari ¹, Sandeep Hamilton ¹, Amit Majumdar ¹

Affiliations
1 Department of Atomic Energy, Shillong, IN

Abstract

No Abstract.

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S. K. Srivastava ¹, N. Pandey ²

Affiliations
1 Department of Geology, Nagaland University, Kohima - 797 002, IN
2 Department of Earth Science, Assam University, Silchar - 788 011, IN

Abstract

Provenance of the Oligocene Barail sandstones has been ascertained by means of petrographic and heavy mineral studies. Petrography reveals an abundance of angular to sub-rounded monocrystalline, non-undulatory quartz followed by lithic fragments. The overall composition of sandstones matches with those of sublith-arenites. The heavy mineral suite of Barail sandstones displays rounded to sub-rounded as well as euhedral/angular grains of iron oxide, zircon, tourmaline, rutile, kyanite, sillimanite and staurolite in decreasing order of abundance. Petrography coupled with heavy mineral suite suggests for a mixed provenance dominated by a sedimentary source of recycled orogenic provenance in a foreland basin setup.

Keywords

Petrography, Heavy Minerals, Provenance, Barail Group, Nagaland.

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