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

C. Anjaneya Sastry ¹, J. S. R. Krishna Rao ¹

Affiliations
1 Department of Geology, Andhra University, Waltair, IN

Abstract

Samples of iron ore from Kemmangundi (Mysore), Ongole (A. P.) and Salem (Tamilnadu) are investigated by ore microscopic, X-ray and spectrographic methods, and the results are presented.

Under the ore microscope, primary relict magnetite and secondary hematite are observed in ores of Kemmangundi. Magnetite is primary and hematite is secondary in ores from Ongole and Salem. X-ray study of Ongole and Salem ores does not indicate the presence of maghemite, and it is concluded that original magnetite is oxidized to hematite. The trace elements in ores of Kemmangundi are mainly Al and Ti, which are typical of residual hydrolysate sediments. There is depletion of elements like Si, Ca and Mg due to solution and leaching. The ores from Ongole and Salem are deficient in elements like Mn, Ni, Ti, Co, Cr, and V (Ferride group of elements), which feature is characteristic of metasediments.

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R. Dhana Raju ¹, J. S. R. Krishna Rao ¹

Affiliations
1 Department of Geology, Andhra University, Waltair, IN

Abstract

Though much work has been done on the manganese ore deposits of Koduru, Devada, Duvvam and Garividi, no attempt has been made so far to study the powder form occurring as thin beds Intercalated with the primary ore bands. Therefore, an attempt is made in the present paper to know the source of the manganese powder, its depositional environment, mineral constituents and textural features. For this purpose, the manganese powder from Devada was subjected to magnetic separation, and the magnetic and non-magnetic parts were analysed by size analysis, ore microscopic and X-ray studies.

The following are some of the Significant conclusions arrived at from this investigation (1) From the size analysis it is shown that the source of the manganese powder is very near and almost in situ, and the powder was formed due to crushing from the primary bedded ores. (2) The elongation and roundness studies show that most of the grams are not spherical, the average length is about 1.4 to 1.7 times the average width; and this also indicates a near source for the manganese powder. (3) The magnetic part consists of vredenburgite, magnetite and hematite with little pyrolusite, while the non-magnetic part comprises pyrolusite, psilomelane, hematite, hollandite, braunite, bixbyite, geothite and limonite. (4) A new mineral, quenselite (PbMnO₂(OH)) is reported for the first time from this area. (5) The magnetic susceptibility of different powder fractions is correlated with the amount of the sum of vredenburgite and magnetite; of these, coarse fractions contammg much vredenburglte are having high magnetic susceptibilies.

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B. Satyanarayana ¹, J. S. R. Krishna Rao ¹

Affiliations
1 Department of Geology, Andhra University, Waltair, IN

Abstract

No Abstract.

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J. S. R. Krishna Rao ¹, R. Dhana Raju ¹

Affiliations
1 Department of Geology, Andhra University, Waltair, IN

Abstract

Lead-Copper deposits in dolomites, cherty dolomites, quartzites, and calcareous quartzites occur at Bandalamottu, Dhukonda, and Nallakonda of Agnigundala area. The mineralization is mainly controlled by stratigraphic and lithologic features. Galena, sphalerite and pyrite are the dominant ore minerals in dolomites, while chalcopyrite and bornite are dominant in quartzites. Linnaeite, covellite, chalcocite, and bravoite are accessories. In addition to these, X-ray patterns show the presence of violarite, cobaltite, niccolite, stibnite, meneghinite, sternbergite, penroseite, and cuprobismutite. Malachite and azurite are the liberation products of chalcopyrite and bornite during oxidation.

The field and mineralogical associations, textural, petrographic and petrochemical features show that Pb, Zn, and Fe sulphides represent a primary sedimentary genesis, subsequently metamorphosed and recrystallized, while copper mineralization is due to later hydrothermal activity. The presence of linnaeite and bravoite indicates low temperature of the order of 300°C and below, low pressure, and low oxidation for the ore formation.

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J. S. R. Krishna Rao ¹, R. Dhana Raju ²

Affiliations
1 Department of Geology, Andhra University, Waltair, IN
2 Atomic Minerals Division, Dept. of Atomic Energy, Hyderabad, IN

Abstract

Potassium feldspars from the granitic and related rocks occurring in Hyderabad, Salem, Mysore and Waltair areas were subjected to X-ray diffraction studies, both in their natural state and after heating to 1050°C for 8 hrs. The triclinicity (Δ) value in the natural samples varies from 0.98 to 0.74, indicating more or less complete ordered Al/Si distribution, whereas in the heated samples it varies from 0.76 to 0.0, showing increasing disorder with heating. The % Or for these samples as well as for the K-feldspars of Chipurupalle-Razam area was estimated using d-_̅201 following different methods. The % Or obtained from the equations of Wright (1968) very closely agrees with the value obtained from reliable chemical analysis.

Quantitative estimation of the Al contents in the four tetrahedral sites (T₁O, T₁m, T₂O and T₂m), following the method of Stewart and Ribbe (1969), shows that in orthoclase the Al content is equally distributed between T₁O and T₁m sites, whereas in intermediate and maximum microcline A1 is concentrated more in T₁O site than in T₁m site. Based on the triclinicity values, the K-feldspars from the Chipurupalle-Razam area belong to the high structural state followed by those from Salem, Waltair, Hyderabad, and Mysore areas with low structural states, and the differences in the structural state may be related to the differences in the P-T conditions prevaling at the time of K-feldspar formation in these areas.

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