Articles written in Journal of Earth System Science

    • REE mineral chemistry and the nature of REE mineralization: A study from felsite dykes of Phulan area, Siwana Ring Complex, Rajasthan, India


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      Neo-Proterozoic Siwana Ring Complex (SRC) comprises per alkaline rocks of Malani Igneous Suite,viz., rhyolite, granite, and late phase microgranite and felsite dykes. Phulan area, lying at the north-easternmargin of SRC exposes a small body of rhyolite (<$1.0 \rm{km}^{2}$) containing feldspar + quartz + aegirine + rebeckite and is cut by dykes of felsite. These felsite dykes have a general NNW–SSE trend andvary from 60–200 m long and 0.10–2.50 m wide. These dykes are composed of quartz, alkali feldspar,aegirine and opaques. These felsite dykes were sampled and analyzed using inductively coupled plasmamethods. Of special significance is the enrichment of trace elements and rare earth elements (REE) in thefelsite dykes. These include up to 1.17% Ce, 0.6% La, 0.8% Y, 0.12% Dy, 169.25 ppm U, 571 ppm Th,1385 ppm Nb, 9944 ppm Zr. These dykes are peralkaline in nature and show negative europium (Eu)anomaly. In this study, the authors attempted to characterize REE bearing phases of the felsite dykes ofPhulan area, SRC with respect to their geneiss. REE bearing phases identified in felsite dykes aremonazite, bastnaesite, parisite, eudiyalite, allanite, perreierite and tritomite. Monazite, perreierite,allanite and tritomite are mostly found to be of magmatic in origin whereas bastnaesite, parasite andeudiyalytes occur both as magmatic and as well as of hydrothermal types. Magmatic REE minerals aremostly formed during crystallization of REE rich magma. In felsite dykes, Zr/Hf ratio varies from 23 to 31and Nd/Ta ratio ranges from 7 to 44. These two ratios are positively correlated and indicators ofhydrothermal fluid influx.

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