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

S. V. G. Krishna Rao ¹, Samit Bhattacharyya ¹, K. J. Sarma ¹

Affiliations
1 Geological Survey of India, Himayatnagar, Hyderabad 500029, IN

Abstract

Manganese silicate-carbonate protore (queluzite) and a rare manganese olivine (knebelite) are being reported for the first time from India. The protore is comparable to the 'Queluzite Type' and occurs as conformable bands in close association with manganese ore body as well as different members of the Khondalite Group of rocks. So far, the knebelite is reported to occur in association with other manganese minerals, particularly in iron-manganese ore deposits and their associated skarns. It is surmised that the protore represents metamorphic equivalent of carbonate-silica-bearing manganiferous sediments.

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M. Ramakrishnan ¹, Samit Bhattacharyya ²

Affiliations
1 Geological Survey of India, Gujarat Circle, Ashram Road, Ahmedabad 380014, IN
2 Geological Survey of India, OME and MG Wing, 4, Chowringhee Lane, Calcutta 700 016, IN

Abstract

Granophyric rocks produced at the contact of post-Dharwar dolerite dykes in the host gneisses and granites of Peninsular Gneissic Complex stand out conspicuously at the weathered dyke margins in the vicinity of Hole Narsipur, Karnataka. The degree of development of granophyric texture is variable, and with its progressive increase, there is a shift in the host rock composition from granodiorite to alkali granite. Since there is no possibility of addition of potash from the dolerite to the granodiorite (the reverse is commonly the case) to cause this potash enrichment in host rocks, the origin of granophyres in the contact zones is attributed to partial melting rather than metasomatism or assimilation. This view is consistent with experimental evidence that partial melting of sodie gneisses (tonalites, trondjhemites and even granodiorites) results in the production of more potassic rocks like adamellites and alkali granites. The production of granophyres in the present case is, therefore, taken as a textural evidence for the partial melting of quartzofeldspathic gneisses. Similar phenomena are observed at the contact of Skaergaard intrusion of Greenland and Newer Dolerite of Singhbhum in eastern India.

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Samit Bhattacharyya ¹

Affiliations
1 OME & MG Wins, Geological Survey of India, 85, Prince Anwar Shah Road, Calcutta 700033, IN

Abstract

Pyroxferroite, (Fe, Mn, Ca) SiO₃, the rare manganiferous pyroxenoid, has been identified in manganese silicate - carbonate rock from the Vizianagaram manganese belt, Andhra Pradesh. Optical data and chemistry of the mineral have been presented and is compared to other occurrences.

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Samit Bhattacharyya ¹

Affiliations
1 Geological Survey of India, Calcutta 700 033, IN

Abstract

The manganese silicate-carbonate rock or manganese protore occurring asa conformable band within Khondalite Group of rocks, represents metamorphosed impure manganiferous sediments comprising manganese carbonate admixed with silica and clay. This manganese protore differs from gondite as well as kodurite and resembles queluzite and hence this protore is equated with the queluzite type. The significance of the presence of knebelite (manganese olivine) in the protore as an indicator of an original carbonate-bearing sediment has been discussed. Besides, mineralogy and chemistry of the various constituent minerals of the prot ore have been presented.

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Samit Bhattacharyya ¹, Ranadhir Sengupta ¹, Manas Chakraborty ²

Affiliations
1 OP:East Coast-I, Marine Wing, GSI. 9 & 10/1, Raja S.C. Mullick Rd, Calcutta-32, IN
2 Chemical Laboratory, Marine Wing, GSI, 63, N.S.C. Bose Rd, Calcutta-40, IN

Abstract

Elemental chemistry of ilmenite has been determined with a view to studying the applicability of the parameter in determination of provenance of the placer minerals. While the values of Mn/Mg ratio conform to the already determined provenance of the east coast occurrence, the west coast ilmenites have lower values for this ratio suggesting a basic rock dominated provenance rather than chamockite/khondalite/migmatitic source. Present study recommends a fresh look at provenance study of the west coast placers vis-a-vis examination of applicability of Mn/Mg values of ilmenite in relation to the provenance.

Keywords

Geochemistry, Sedimentology, Ilmenite, Provenance Studies.

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Samit Bhattacharyya ¹, Birendra K. Mohapatra ², Bibhuranjan Nayak ³

Affiliations
1 Geological Survey of India, Marine Wing, DK-6, Salt Lake, Kolkata - 700 091, IN
2 Regional Research Laboratory, Bhubaneswar - 751 013, IN
3 National Metallurgical Laboratory, Jamshedpur - 831 007, IN

Abstract

No Abstract.

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