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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K. Gopalan ¹, J. R. Trivedi ¹, M. N. Balasubrahmanyan ², S. K. Ray ³, C. Anjaneya Sastry ⁴

Affiliations
1 Physical Research Laboratory, Ahmedabad 380009, IN
2 Geological Survey of India, 29, Jawaharlal Nehru Road, Calcutta 700 016, IN
3 Geological Survey of India, Bhutan Circle, Samchi, BT
4 Geological Survey of India, Geochronology and Isotope Geology Division, 29, Jawaharlal Nehru Road, Calcutta 700016, IN

Abstract

Rubidium and strontium determinations are reported for the Udaipur and Saladipura granites from the Khetri copper belt. The whole-rock data define a Rb-Sr isochron corresponding to an age of 1480 ± 40 m.y. and initial Sr ratio of 0.7131 ± 0.006. This age is older than previously believed, but consistent with the generally high age of post-Delhi intrusive rocks so far dated in the region. Biotites associated with these rocks give younger ages around 700 m.y, This indicates mobilisation of Sr isotopes in a later metamorphic event. It is significant that this secondary event is almost synchronous with the intrusion of granites to the west and south of the Aravalli mountains.

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