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

T. S. Giritharan ¹, V. Rajamani ¹

Affiliations
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi -110 067, IN

Abstract

The Hutti-Maski schist belt in the eastern Dharwar craton consists predominantly of mafic metavolcanics metamorphosed to amphibolite facies. The amphibolites are tholeiitic in composition with higher abundances of iron and with flat to LREE enriched rare earth patterns. Modelling of major and trace elements suggests that the tholeiitic protoliths were formed from melt enriched mantle sources by different extents of partial melting at pressures -25 kbars. The most common mafic metavolcanics in the three auriferous schist belts of eastern Dharwar craton such as the Kolar. the Ramngiri and the Hutti belts are high-iron tholeiites with LREE enriched rare earth patterns. The gold mineralization in the form of quartz-carbonate veins in the three belts is commonly hosted in high irontholeiitic protoliths. The process of formation of Fe-rich tholeiites. their metamorphism to amphibolites and their subsequent emplacement along terrane boundaries could have provided a favourable geochemical environment for gold mineralization.

Keywords

Geochemistry, Metabasalts, Petrogenesis, Gold, Hutti-Maski Belt, Karnataka.

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J. Sahoo ¹, T. S. Giritharan ², S. Balakrishnan ², V. Rajamani ³

Affiliations
1 Department of Earth Sciences, IIT Roorkee, Roorkee - 247 667, IN
2 Department of Earth Sciences, Pondicherry University, Pondicherry- 605 014, IN
3 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi - 110067, IN

Abstract

The Banded Gneissic Complex (BGC) occurring around Masuda consists of granitoids, migmatized mica schist, calc-gneiss and amphibolites. The amphibolites (few cm to tens of metre wide) are co-folded with the granitoid and calc- gneisses. The ortho-amphibolites are classified into high-Mg and tholeiitic amphibolites and they have distinct chondrite normalized Rare Earth Element (REE) patterns and Ce/Nd ratios. Modeling of their geochemical data suggests that magmas representing the high-Mg amphibolites were derived by low extents of partial melting of mantle sources more Fe-enriched than lherzolite whereas magmas representing the tholeiitic amphibolites were derived by low-extents of partial melting of sources formed by mixing of high-Mg magmas with lherzolite. The composition of this source is similar to the komatiites. The tholeiitic amphibolites have geochemical and petrogenetic characteristics of the basalts formed in island arcs. They are different from that of amphibolites found in the basal part of Aravalli Supergroup and mafic enclaves found within the BGC occurring east of Nathdwara and Udaipur.

Keywords

Geochemistry, Petrogenesis, Amphibolites, Banded Gneissic Complex, Aravalli Craton, Rajasthan.

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