Current Science

R. P. Nagar ¹, M. M. Korakoppa ¹

Affiliations
1 National Centre for Excellence in Geoscience Research (NCEGR), Geological Survey of India, 40th Cross, Eshwar Nagar, Bangalore 560 070, IN

Abstract

Magmatic epidote (mEp) in calc-alkaline, high-Mg granite is distinguished on the basis of euhedral crystals with allanite core and embayed contact, 'pistacite' components (25-32) and very low TiO₂ (<0.02%) content. Non-magmatic epidote occurs in association with biotite and chlorite, amphibole, magnetite and titanite and contains either <0.2% TiO₂ or <25% Ps. Consideration of stability of magmatic epidote under different fO₂ and dissolution characteristic against quartzofeldspathic material suggest that these granitoids are emplaced at a faster rate to low-pressure upper crustal region under high fO₂ condition by dyking.

Keywords

High-Mg Granitoids, Kolar, Oxygen Fugacity, Pistacite.

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K. R. Randive ¹, J. Vijaya Kumar ¹, M. M. Korakoppa ², M. K. Sahu ¹

Affiliations
1 Post Graduate Department of Geology, RTM Nagpur University, Nagpur 440 001, IN
2 National Centre of Excellence in Geoscience Research (NCEGR), Geological Survey of India, Bengaluru 560 070, IN

Abstract

Among the magmatic rocks, carbonatites are known to possess the highest concentration of rare earth elements (ΣREE = 72-15,515 ppm), and they have the best REE mineral resourses. Rare earth deposits in igneous rocks have been grouped into five distinct categories differing in the provenance and evolution of magma and in the rock types hosting mineralization, viz.: (i) carbonatites, (ii) peralkaline silica-undersaturated rocks, (iii) peralkaline granites and pegmatites, (iv) pegmatites associated with sub- to metaluminous granites, and (v) Fe oxide- phosphate deposits. Occurrence of REE minerals in rocks other than those mentioned above, especially mafic and ultramafic rocks is scantily documented; only recently, they were looked upon as hosts of REE-mineralization.

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