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Singh, Yamuna; Bagora, Sanjay; Jain, P.K.; Pandit, P.S.C.; Mishra, K.S., E-mail: yamunasingh2002@yahoo.co.uk2010
AbstractAbstract
[en] The Archaean gneisses and metasedimentary rocks of the Bengpal Group form the oldest lithounits in the Kawadgaon Challanpara area. These are intruded by the Palaeoproterozoic granitoids (2497 Ma) and related pegmatoids. The granitoids display textural and mineralogical gradations in their aureoles. The average concentrations of some critical elements in the granitoids are 288 ppm Rb, 90 ppm Sr, and 597 ppm Ba, whereas, the average concentrations of these elements in the pegmatoids are 421 ppm Rb, 47 ppm Sr, and 321 ppm Ba. The granitoids have average Ba/Rb ratios of 2.1 and Rb/Sr ratios of 3.2, whereas, the pegmatoids have lower average Ba/Rb ratios of 0.76 and higher Rb/Sr ratios of 9.0. The data indicate anomalously low Ba/Rb and high Rb/Sr ratios for the investigated felsic bodies, as against similar ratios for the 'average' low Ca-granite (Ba/Rb = 2.35 and Rb/Sr = 1.7). Furthermore, a similar trend is also revealed by the Ba/Rb and Rb/Sr ratios of the investigated coexisting granitoids-pegmatoids, when compared with similar ratios for the granite formed from highly 'evolved' melt (Ba/Rb = <0.25 and Rb/Sr = >5.0). The data, therefore, reveal that the investigated coexisting granitoids-pegmatoids belong to the category of 'evolved' granitoids-pegmatoids, even though certain granite samples fall under the category of normal granitoids. It thus suggests that a major part of the investigated granitoids formed from the evolved melts, and the coexisting pegmatoids formed from still more evolved melts. Such evolved granitoids-pegmatoids are known for hosting rare-metals. Accordingly, the investigated granitoids and associated pegmatoids appear suitable for hosting economic concentrations of rare-metals. Interestingly, the pegmatoids, genetically related to the investigated granitoids, are known to carry concentrations of rare-metals (Be, Nb, Ta) and some rare-earths (La, Ce, Y). Therefore, the investigated granitoids and pegmatoids, including their soils/gravels, should be targeted for locating hitherto undiscovered concentrations of rare-metals in and around the Kawadgaon-Challanpara area. (author)
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Source
International symposium on carbon management and climate change and the role of applied geochemistry in mineral exploration; Hyderabad (India); 25-27 Nov 2009; 17 refs., 5 figs., 3 tabs.
Record Type
Journal Article
Literature Type
Conference
Journal
Journal of Applied Geochemistry; ISSN 0972-1967;
; v. 12(3); p. 447-456

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