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Suryanarayana Rao, C.
- Occurrence of Andalusite in a Quartz Vein Near Mallegowdanahalli, Bangalore District, Mysore State
Authors
1 Department of Atomic Energy, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 9, No 2 (1968), Pagination: 159-163Abstract
Andalusite occurs in a quartz "Vein intrusive into ultrabasic rocks altered to tremolite-actinolite schists, on a low mound about half a mile to the SE of Mallegowdanahalli, Doddaballapur Taluk, Bangalore District, Mysore State and about 35 miles to the NNW of Bangalore. Andalusite is formed along the margins of the quartz vein as a result of reaction between the quartz and alumina-rich magmatic vapours, following the intrusion of the quartz vein, in the presence of magnesia and lime available in the surrounding ultra basic schists. Corundum has formed in the final stages of the pneumatolytic activity and is deposited in the fracture planes of andalusite. Continued activity by potash-rich hydrothermal solutions at the closing phases of the magmatic processes has partly transformed the andalusite and corundum into dumortierite, muscovite and pyrophyllite.
- Radioactive Carbonatites of Pakkanadu and Mulakkadu, Salem District, Tamil Nadu
Authors
1 Atomic Minerals Division, Department of Atomic Energy, Hyderabad, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 2 (1978), Pagination: 53-63Abstract
Precambrian carbonatites associated with pyroxenites occur as discontinuous lenticular bodies intruding the syenites west of Pakkanadu (11°40'15'': 77°50'1'') and Mulakkadu (11°44'3'' : 77°50'2''). They strike northeast to southwest with easterly dips and have been emplaced along a major northeasterly trending deep crustal fault zone. Large outcrops of serpentinised dunites carrying accessory chromite, cut by asbestos and magnesite veins are also found along the same fault zone to the east and northeast of Pakkanadu.
The carbonatites are of the pure calcite-rich sovite type, with biotitic and ankeritic variants. Apatite, magnetite, allanite, barite, monazite, zircon and cerianite, are the accessory minerals.
Spectrographic analysis has revealed Ba, Sr, Ce and La in major amounts (more than 10,000 ppm) and Th, Nb, P, Zr, Y and Sc in minor amounts (< 10,000 ppm). Spectrographic data suggest that the carbonatite-pyroxenite complex is Ce-La rich.
Niobium is not found in economic concentrations. The general radioactivity recorded by the carbonatite-pyroxenites ranges from 5 to 20 x BG. Representative whole rock samples assay from 0.02% to 0.054% eU3O8 (Carbonatites) and 0.02% to 0.06% eU3O8 (pyroxenites). Allanites assay from 0.35% to 0.4% eU3O8 with chemical U3O8 values from 0.007% to 0.034%, thereby indicating the predominance of thorium over uranium. Monazite is mostly concentrated in the biotite-rich portions of the carbonatites to the west of Pakkanadu, whereas allanites predominate in the pyroxenites west of Mulakkadu.