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Sarbajna, Chanchal
- Mineralogical and Chemical Characteristics of Complexly-Zoned Columbite-Tantalite from the Rare Metal Pegmatites of Southern Karnataka
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 56, No 5 (2000), Pagination: 557-571Abstract
Detailed mineralogical and chemical studies by EPMA on the Nb-Ta minerals from the rare metal pegmatites of southern Karnataka have revealed wide compositional variations, and the presence of some new minerals like tapiolite and microlite, hitherto unreported from these pegmatites. Back scattered electron (BSE) images have indicated complex zoning patterns such as oscillatory, patchy and/or their combinations, associated with replacement of columbite-tantalite by microlite, manifested by the variations of Nb2O5, Ta2O5, FeO and MnO. Such features, although known from a few rare meral pegmatites of the world, are being recorded here for the first time in India. Oscillatory zones in columbite-tantalites are manifested as alternating dark and light grey coloured bands, of which darker bands are Nb-rich (30-300 μM thick) and lighter bands are Ta-rich (125-450 μm thick). The wider zones may, in turn, consist of a group of very fine sub-zones (1-50 μm) of slightly varying composition: Patchy zoned crystals exhibit corroded remnants of early formed columbite-tantalite (with 39.73-44.02% Ta2O5), surrounded by later formed zones which are enriched in Ta2O5 (up to 50.99 %) in columbite-tantalite leading to the formation of microlite containing up to 73.4% Ta2O5. The zoning of the columbite-tantalites has been attributed to periodic changes in the composition of the major components such as Nb, Ta, Fe and Mn in the pegmatite fluid system, apparently influenced by the late stage fractionation of volatiles. This ultimately generated fluids rich in Ta and Na, resulting in resorption and replacement with patchy zoning of early formed, zoned columbite-tantalites.Keywords
Columbite-Tantalite, Rare Metal Pegmatite, Zoning, Ore Mineralogy, Southern Karnataka.- Mineralogy and Geochemistry of Alkali Beryl from the Rare Metal Bearing Pegmatites of Marlagalla-Allapatna, Mandya District, Karnataka
Abstract Views :237 |
PDF Views:2
Authors
Chanchal Sarbajna
1,
R. P. Sinha
1,
P. Krishnamurthy
1,
K. V. G. Krishna
2,
R. Viswanathan
1,
D. C. Banerjee
1
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Nagarbhavi, Bangalore - 560072, IN
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Nagarbhavi, Bangalore - 560072, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 54, No 6 (1999), Pagination: 599-608Abstract
White coloured alkali beryl from the pegmatites of Mariagalla-Allapatna in Mandya district, Karnataka contains distinctly higher alkali elements (Na, Li, Rb, Ca) and relatively low beryllium oxide (c. 11 % BeO) compared to normal beryl. Beryl occurs mostly between graphic intermediate zone and quartz core in the complexly zoned, spodumene-bearing Li-Cs-Ta (LCT) type pegmatites in this area. The average value (n = 7) for alkali beryl from this area are Na2O 1.26%, Li2O 0.6%, Cs2O, 0.74%, K2O 0.07 and Rb2O 0.08%. Cs content in some of the beryls are higher than Na and hence such beryls may be termed as a new Na-Li-Cs type X-ray powder diffraction data for the beryl (ao = 9.2765-9.339 Å, co = 9.2079-9.2487 Å) reveal differences in crystal structure with respect to normal beryls from Royalstone, Massachusetts, USA (ao = 9.215Å, co = 9.192Å) and compares well with the reported alkali beryl from Arizona, USA (ao = 9.30Å, co = 9.20Å) Their refractive index (Nω) ranges from 1.588 to 1.592 and the specific gravity varies from 2.74 to 2.79.Keywords
Economic Geology, Geochemistry, Mineralogy, Rare Metal Pegmatites, Beryl, Marlagalla, Karnataka.- The Fertile Granite at Allapatna, Mandya District, Karnataka : A Possible Parent to Rare Metal Pegmatites of Southern Karnataka
Abstract Views :204 |
PDF Views:1
Authors
Affiliations
1 Atomic Minerals Division, Hyderabad - 500 016, IN
1 Atomic Minerals Division, Hyderabad - 500 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 47, No 1 (1996), Pagination: 95-98Abstract
The Allapatna granite has been found to be a low-calcic (CaO-0.85%), peraluminous (A/C+N+K ratio = 1.04) and potassic type (K2O=4.75%), enriched in Rb(362), Ga(25), Cs(3), Nb( 19), U(l3), Ta(18), Th(38), Pb(55) and strongly depleted in Ba(333). Such abundances together with low K/Rb ( 118.9), Ba/Rb (0.92) and Th/U (2.92), and high Rb/Sr (3.45) ratios than normal granite indicate their highly fractionated and fertile character and strongly suggests that the Li-Cs-Ta (LeT) rich rare metal bearing pegmatites of Marlagalla and nearby areas may have been derived from such a parental granitic magma.Keywords
Granite, Pegmatites, Rare Metals, Allapatna, Karnataka.- Late Archaean Granitoid With a Ring Structure Around Chandra, Mandya District, Karnataka
Abstract Views :208 |
PDF Views:2
Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Hyderabad-500 016, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Hyderabad-500 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 54, No 4 (1999), Pagination: 411-414Abstract
A ring-like structure is defined by a late Archaean granite around Chandra. It is a fertile granite with a parental status akin to the rare metal pegmatite-hosted deposits of Li-Be-Nb and Ta around Allapatna-Marlagalla. This observation has important implications for new exploration targets for rare metal pegmatites in southern Karnataka and also geological evolution of the terrain as a whole.Keywords
Petrology, Ring Structure, Fertile Granite, Karnataka.- Tantalum in Tin Slag-A Report from Bastar Pegmatite Belt
Abstract Views :204 |
PDF Views:132
Authors
Affiliations
1 Flat B-203, Block-B, United Ave Apts,South End, 7-1-29, Ameerpet, Hyderabad - 500 016, IN
2 Department of Atomic Energy, Atomic Minerals Directorate for Exploration and Research, West Block-7, R K Puram, New Delhi - 110 066, IN
1 Flat B-203, Block-B, United Ave Apts,South End, 7-1-29, Ameerpet, Hyderabad - 500 016, IN
2 Department of Atomic Energy, Atomic Minerals Directorate for Exploration and Research, West Block-7, R K Puram, New Delhi - 110 066, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 3 (2005), Pagination: 372-372Abstract
No Abstract.- Geology, Geochemistry and Genesis of Rare Metal Bearing Granitic Pegmatites from Parts of Southern Karnataka
Abstract Views :183 |
PDF Views:118
Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN