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

T. C. Devaraju ¹, S. D. Khanadali ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwar, IN

Abstract

Analysis of 34 bauxite-laterite and 11 precursor granitic gneiss samples, from Paduvari plateau, fer alkali and alkaline earth elements has revealed: (1) the strong depletion of laterites/bauxites in Ca, Na, K, Sr, Li and Rb, with a reduction in Ca by 124 times, Na and K by 55 times, Sr by 38 times, Li and Rb by 7½-8 times, (2) low mobility of Mg and Be to result in a depletion of only 2½ times, (3) the lack of significant or systematic variation in the content of these elements in the laterite-bauxite profile and (4) the retention of Na: K and Li : Rb ratios of the precursor gneiss in the laterite/ bauxite. The study substantiates the general observation that alkali and alkaline earth elements with their low ionic potential (except Be) are thoroughly leached during lateritization.

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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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S. D. Khanadali , T. C. Devaraju ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 3, IN

Abstract

The different litho-units of the weathering profile of Paduvan Plateau show clear gradation contacts and contain relics of nearly all the minerals which are native to the underlying granitic gneiss. Mineralogically, the latent profile is dominated by gibbsite with kaolinite compared to lithomarge and goethite-hematite in the ferruginous laterite horizons. There is evidence of development of gibbsite both by the direct alteration of feldspar of the precursor rock and by the desilication of kaolinite. Four stages of transformation represented by altered gneiss, lithomarge, laterite and aluminous laterite bauxite are maintained in the weathering profile. As compared with the basalt derived laterite profiles, the Paduvari occurrence is characterised by relatively strong depletion of soda and potash and enrichment of ferrides. The field, petrographic mineralogical and geochemical data provide enough evidence of formation of Paduvan laterite profile by the in-situ chemical weathering of the underlying granitic gneiss and the aluminous laterite-bauxite by the 'in-situ chemical reworking' of laterite.

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S. D. Khanadali ¹, T. C. Devaraju ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 580003, IN

Abstract

The laterite-bauxite profile of Paduvari plateau, which bears evidence of having been derived by the in-situ chemical weathering of essentially early Precambrian granodiorite-tonalite gneisses, shows: (1) The overall predominance of gibbsite in the entire profile except in the lithomarge zone, (2) the abundance of kaolinite in the lithomarge zone and enrichment of goethite/hematite in the ferruginous laterite crust, (3) the general downward increase of kaolinite and upward increase of gibbsite, (4) the consistent occurrence of allophane, in minor amounts, in the entire profile, (5) evidence of formation of gibbsite both by direct alteration of feldspars of the precursor rock aqd by desilication of kaolinite, (6) occurrence of nearly all the minerals, which were present in the precursor rock, as resistant relics, (7) occurrence of zircon of the same shape and size as those in the precursor rock, and (8) the high crystallinity and the more common tight framework-type of microtexture of bauxites and aluminous laterites suggesting the formation of these deposits under extremely good leaching conditions, high above the water table.

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K. R. Jayaraj ¹, S. D. Khanadali ¹, T. C. Devaraju ¹, B. Spiering ²

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 580 003, IN
2 Mineralogisch-Petrologisches Institut, Universitat Bonn, Poppelsdorfer Schlos, 5300 Bonn 1, DE

Abstract

Hogbomite is of widespread occurrence as an accessory and minor mineral in the V-Ti-Fe ore deposits of Ubrani, Tavarekere, Masanikere, Magyatahalli and Devaranarsipur in Shimoga district and Mulemane in Uttar Kannada district. Both primary and secondary hogbomite are found. The mineral shows considerable variation in chemistry. The analytical data indicate that hogbomite structure is relatively more open than that of coexisting magnetite/ilmenite and can admit a variety of substitutions.

Keywords

Hogbomite, Electron Microprobe Analysis, Iron Ore Deposits, Karnataka.

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T. C. Devaraju ¹, T. T. Alapieti ², A. A. Halkoaho ², K. A. Jayaraj ¹, S. D. Khanadali ¹

Affiliations
1 Dept of Studies in Geology, Karnatak University, Dharwad 580 003, IN
2 Dept of Geology, University of Oulu, Linnanmaa, SF 905 070, Oulu, FI

Abstract

No Abstract.

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