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Kantharaja D.C.,Karnatak University | Kantharaja D.C.,Guyana Geology and Mines Commission | Lakkundi T.K.,Karnatak University | Basavanna M.,Karnatak University | Manjappa S.,Kuvempu University
Environmental Earth Sciences | Year: 2012

Hydrogeochemical investigations with emphasis on groundwater fluoride concentrations were carried out in the Shivani watershed area, Karnataka, South India. This drought-prone watershed is characterised by poor groundwater potential and is composed of different lithounits like gneisses, migmatites, tonalites, mafics-ultramafics, conglomerates and quartzites. Analysis of spatial variation of groundwater fluoride concentration through the use of GIS technology software platforms like ArcView 3.2a and MapInfo Professional 8.5 has enabled the identification of low-fluoride and high-fluoride areas within the watershed. Geochemical data indicates that 38% of groundwater samples have excessive fluoride concentration which poses a health risk to the population of the area. Correlation studies indicate that higher groundwater alkalinity activates leaching of fluoride resulting in elevated concentrations of fluoride. No other significant geochemical interrelationship could be identified between fluoride and rest of the physico-chemical parameters owing to the lack of any significant correlation coefficients. This holds good in the case of both low-fluoride (<1.5 mg/L) and high-fluoride (>1.5 mg/L) groundwaters of the watershed. However, differential or non-uniform type (positive or negative) of coefficient of correlation is observed between fluoride at different levels and other physico-chemical parameters. Among the different lithounits of the study area, gneisses house comparatively more number of high-fluoride groundwaters. Fluoride-bearing minerals biotite, hornblende and apatite are the probable natural sources of groundwater fluoride. © 2011 Springer-Verlag.

Nadeau S.,Guyana Geology and Mines Commission | Chen W.,State Key Laboratory of Mineral Deposit Research | Reece J.,Guyana Geology and Mines Commission | Lachhman D.,Guyana Geology and Mines Commission | And 5 more authors.
Brazilian Journal of Geology | Year: 2013

A Hadean zircon xenocryst with a U-Pb zircon age of 4,219 ±19 Ma, along with several zircon xenocrysts of Archean age (ca. 2,510 to 3,811 Ma) were found in a rock of the Paleoproterozoic Iwokrama Formation, which includes felsic volcanics and co-magmatic granitic intrusions. It demonstrates the existence of an underlying "Lost Hadean Crust", representing the oldest crustal component of the Guiana Shield. Detrital zircons of late Archean age, up to 2,700 Ma, are also present in the high-grade rocks of the Kanuku Complex, located to the south, and may be derived from the same Hadean-Archean crustal block.

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