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K. S. Anantha Murthy ¹

Affiliations
1 Dept. of Applied Geology, Kuvempu University, Shimoga - 577203, IN

Abstract

No Abstract.

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T. C. Devaraju ¹, K. S. Anantha Murthy ¹

Affiliations
1 Department of Geology, Karnatak University, Dharwar - 580003, IN

Abstract

Barytes occurs as small, subeconomic, discontinuous lenses and bands interstratified with sericite and fuchsite-bearing quartzite. The mineral has 2V_z=34°, nβ=1.632 and (γ - α)=0.095. There is a close similarity in the powder X-ray data obtained for three samples of the mineral and between these and the ASTM values for BaSO₄. The deposit bears evidence of sedimentary origin; both biochemical processes and volcanic exhalations are inferred to have contributed to the formation of the deposit. The deposit perhaps constitutes the terminal phase of a volcanic cycle.

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T. C. Devaraju ¹, K. S. Anantha Murthy ¹, N. M. Udayashankar ¹

Affiliations
1 Department of Geology, Karnatak University, Dharwad-580003, IN

Abstract

The 'bauxite' of Shivaganga is actually an aluminous clay deposit containing essentially a mixture of halloysite and kaolinite.

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T. C. Devaraju ¹, K. S. Anantha Murthy ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 580 003, IN

Abstract

Mineralogy of ferroan ankerite with the composition (Fe, Mn)_0.67 (Mg)_0.38 (Ca)_0.93 C₂O₆ is discussed with the aid of X-ray, DTA, and chemical data. The mineral typically occurs in the iron-enriched carbonate bands, which are either closely associated or enclosed within the iron formation. Available evidence suggests syngenetic chemical sedimentary origin for the mineral.

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T. C. Devaraju ¹, K. S. Anantha Murthy ²

Affiliations
1 Department of Studies in Geology, Karnataka University, Dharwad 580003, IN
2 Department of Geology, Bangalore University, Bangalore 560056, IN

Abstract

Carbonates of the Chiknayakanhalli (CN halli) area include (i) dolomite, (ii) limestone, (iii) ankerite and (iv) calc-schist. Of these, dolomite is the most widely developed rock. chemically the CN halli carbonates cover a wide range from almost pure calcite and dolomite-ankerite to Mg-limestone, shaly limestone and cherty limestone/dolomite/ankerite. In their trace element content, the rocks are typically much depleted in comparison with carbonatites. Available evidence indicates overall primary chemical sedimentary deposition of the carbonates in a barred basin with a gradual rise in salinity, pH, temperature and Mg:Ca ratio of the environment. Evidence of dolomitization is limited to the border zones between limestone and dolomite and there is no recognizable indication of organic activity.

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B. Mahabaleswar ¹, K. S. Anantha Murthy ¹, M. Basavanna ²

Affiliations
1 Department of Geology, Bangalore University, Bangalore, IN
2 Depat1ment of Geology, Karnataka University, Dharwad, IN

Abstract

Through a consideration of major element chemistry it is inferred that the orthopyroxenes and clinopyroxenes of the iron formations are ferrohypersthene and ferroaugite respectively, whereas the garnets belong to pyralspite series. The opx and garnets are rich in Mn content, which may be due to bulk composition of the host rock and oxygen fugacity. The P-T estimates give values of 7.5 to 8 Kbars and 607°C to 657°C.

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T. C. Devaraju ¹, K. S. Anantha Murthy ², S. D. Khanadali ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 580003, IN
2 Department of Geology, Bangalore University, Jnanabharati, Bangalore 560056, IN

Abstract

The iron-formation of the Chiknayakanhalli (CN Halli) greenstone belt constitutes the youngest lithological unit of the late Archaean supracrustal geosynclinal sequence (3 to 2.4 b.y. old) which unconformably overlies the older (3 b.y.) granitic gneisses. They are consistently located in the core parts of the synclinal fold structures and occur over-lying either carbonates or chlorite schists. There are four main sedimentary facies, viz., oxide - (OF), mixed oxide-silicate - (MOSF), mixed oxide.silicate·carbonate-(MOSCF), . and carbonate-facies-(CF) constituting the iron-formation, All the facies types are strongly banded on metre to micron scale and frequently show small to large scale fold structures of both depositional and tectonic origin. While the lighter bands account for 43 to 57 per cent of the rocks and contain either silica (chert to quartz) and lor silicate (grunerite), the dark bands are chiefly made up of hematite, magnetite and goethite in OF, magnetite in MOSF, siderite and magnetite in MOSCF and ankerite-ferroan ankerite in CP. Although some of hematite and goethite could be interpreted as secondary after magnetite, a good proportion of these and the bulk of magnetite are syngenetic sedimentary. Grunerite appears to have been derived by the metamorphism of the precursor minnesotaite. The striking simplicity in chemical composition and distinctly low minor and trace element contents .are in accordance with the formation of eN Halli Iron-Formation through the process of inorganic chemical deposition. The carbonates underlying the iron-formation show upward iron enrichment and the iron-formation is interpreted as terminal phases of chemical sedimentary carbonate deposition in an essentially 'quiet' and' closed' environment.

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