• C Mahadevan

      Articles written in Proceedings – Section A

    • X-ray studies of peaty lignites and anthracitic coals

      C Mahadevan

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    • Monazite in the beach sands of Vizagapatam district

      C Mahadevan A Sriramadas

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      The beach sands of the Vizagapatam coast between Yarada village and Rushikonda, covering a distance of about ten miles have been taken up for detailed study by sedimentary petrographic methods. Six representative samples from the collection, three of white sands and three of black sands, were subjected to mechanical, heavy mineral, and magnetic separation and the products thus obtained gravimetrically and optically estimated. It is found that of the heavy mineral suite, magnetites are most abundant, followed by monazite, garnet, sillimanite, zircon and ilmenite. At least about 2% of the black sand concentrate consists of monazite. Excluding +60 mesh material, monazite is found to be 8% of the bulk of black sands. Though the white sands invariably yield monazite, their quantity is proportionately insignificant. Further investigations are in progress.

    • Optically positive cordierite from the khondalites of Pachipenta, Vizagapatam District

      C Mahadevan Gopalakrishna Sastry

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      An optically positive cordierite from the khondalites in Pachipenta of Vizagapatam District was chemically analysed and its optical properties determined. It has a hardness of 7·5 and Sp. Gr. 2·71 and its 2V as determined by Fedorov’s Stage is 74°. In contrast to the negative optical sign of a normal cordierite, this cordierite gives a positive optical sign. The tentative suggestion put forward by Krishnan and others that the optically positive character of cordierites is probably due to the ratio of MgO to FeO does not find support from the present studies. As shown by Winchell it appears that there is no close correspondence between chemical composition and optical characters in cordierites. The possibilities of traces of alkalies contributing to the change in optical sign as suggested by Folinsbee, is worth consideration but must await the availability of analyses giving these constituents.

    • Petrological studies of rocks of Borabudur, Java

      C Mahadevan N Sathapathi

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    • Distribution of radioactivity in the rocks of South India - Part IV. Fluorine-bearing granites of podili-kanigiri area and associated rocks

      C Mahadevan A V R Sastry

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      The study on the distribution of radioactivity in granites and associated rocks, with relevant geological and chemical data confirm that:

      the metasomatically formed granites will have higher radioactivity than the normal batholithic type of granites,

      granitisation will enhance the radioactivity of the country rocks, and

      radioactivity increases with the increase in the feldspathisation of the country rocks.

      The study on the distribution of radioactivity in rocks will be of great use in suggesting the petrogenetic history of the rocks.

    • Studies of copper minerals in old workings for copper in Yenambail, Khamman District, Andhra Pradesh

      K Kameswara Rao C Mahadevan

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      The old workings for copper about 2 miles north of Yenambail (Long. 80° 41′, Lat. 17° 41′) in Khammam District were first reported by C. Mahadevan in 1943, while in Hyderabad Geological Survey and later were taken up for detailed prospecting in summer, 1957, by the staff and students of the Geology and Geophysics Departments of the Andhra University. The work was sponsored by the Government of Andhra Pradesh.

      The formations in this area consist of hornblende schists, phyllites, magnesian limestones and quartzites, striking N.E.-S.W. to N.N.E.-S.S.W., dipping towards west, with concordant intrusions of quartz veins. Some of the quartz veins carry the copper minerals—chalcopyrite, chalcocite and covellite along with other sulphide minerals like pyrite and arsenopyrite. Malachite, azurite and cuprite are conspicuous as thin films and coatings on the surfaces of quartzites and silicified limestones. The ore minerals have been studied both in the field and the laboratory and the results are briefly recorded. The textures are due to replacement and colloform zoning. The paragenetic sequence of the minerals is arsenopyrite, pyrite, chalcopyrite, covellite and chalcocite. Chalcopyrite, pyrite and arsenopyrite are considered to be hypogene and covellite and chalcocite are of supergene origin.

    • Studies on lead-zinc mineralization in Karempudi area, Guntur District, Andhra Pradesh

      K Kameswara Rao C Mahadevan

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      The geological formations near Karempudi area in Guntur District of Andhra Pradesh (Lat. 16° 20′ and 16° 26′; Long. 79° 38′ 40″ and 79° 45′) consist of slaty shales of Cumbum, Irlakonda quartzites, Kolumnala slates and shales with intercalations of siliceous dolomitic limestones and Sreesailam quartzites of Krishna Series, forming a perfect conformable sequence, all the formations striking N.E.-S.W. and dipping on average 25° S.E. The Srisailam quartzites are overlaid unconformably by Palnad limestones (Narjis) of Jammalamadugu stage of Kurnool Series with a constant dip of 8–12° in the same direction.

      The Krishna Series were subjected to local but intense structural disturbances resulting in an overfold. Subsequent to the overfolding, lead mineralization has taken place in dolomitic limestones. The lead-zinc minerals of Karempudi consist of Galena, Sphalerite, Jamesonite, Tetrahedrite as primary minerals, and Anglesite as secondary mineral; there is association of chalcopyrite with Sphalerite. The textures are due to replacement and unmixing (?). The paragenetic sequence of the minerals is established to be sphalerite, chalcopyrite, galena, jamesonite, tetrahedrite and anglesite.

      Correlation of field to laboratory studies revealed that the minerals are of hydrothermal (hypogene) origin. The structural and lithological favourability and controlling of the mineralisation are also explained. Anglesite owes its origin to the oxidation of galena due to air-water processes. The mineralization is surmised to have taken place in Pre-Palnads and Post-Krishna times.

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