Groundwater in Palnad sub-basin is alkaline in nature and Na + -Cl --HCO 3 type around Macherla-Karempudi area in Guntur district, Andhra Pradesh. Total dissolved solids (TDS) show strong positive correlation with Cl -, Na + , Ca 2+ and Mg 2+ , and positive correlation with SO 4 2-, K + and HCO 3 -. Calcareous Narji Formation is the dominant aquifer lithology, and water-rock interaction controls the groundwater chemistry of the area. Chloro-alkaline indices (CAI) are positive at Miriyala, Adigopula, Mutukuru, Macherla and Durgi suggesting replacement of Na + and K + ions from water by Mg ++ and Ca ++ ions from country rock through base exchange reactions. Negative CAI values are recorded at Terala, Rayavaram and Nehrunagar, which indicate exchange of Na + and K + from the rock as cation-anion exchange reaction (chloro-alkaline disequilibrium).TDS range from 91 to 7100 ppm (Avg. 835 ppm) and exceed the prescribed limit of drinking water around Mutukuru, Durgi, Rayavaram, Khambampadu and Ammanizamalmadaka areas. Scanty rainfall and insufficient groundwater recharge are the prime factors responsible for high salinity in the area. Fluoride content ranges from <1 to 3.8 ppm and contaminated areas were identified around Macherla (1 sq km; 3.8ppm), Mandadi (1 sq km, 2.1ppm) and Adigopula (2 sq km, <1 to 3.7 ppm). The % Na + content varies from 17 to 85 with the mean value of 57, and eighty (80) samples showed higher %Na + in comparison to the prescribed limit of 60 for irrigation water. Sodium Adsorption Ratio (SAR) and % Na + in relation to total salt concentration indicate that groundwater (51%) mostly falls under doubtful to poor quality for irrigation purpose. Groundwater of Adigopula village is fluoride contaminated and remedial measures are suggested to improve the water quality.
Relationship of hydro-uranium anomalies (2-649 ppb) vis-à-vis underlying uranium ore body has been attempted based on seventy nine water samples collected from the exploratory boreholes on the northern periphery of Srisailam sub basin, Nalgonda district, A.P. Water table is hosted in the granitoid aquifer which underlies the cover rocks of Srisailam Formation. TDS (total dissolved salt) range from 123 to 1088 ppm (x -= 329 ppm) and analyzed >500 ppm in eight samples. Water samples show a strong positive correlation of TDS with Cl -(r=0.90), Na + (r=0.82), Mg (r=0.80) and a moderate positive correlation with Sr (r=0.48) and Ca (r=0.70). Low value (<0.4) of Normalised Magnesium (NMg) indicates that host rock aquifer has not undergone chloritisation. Accumulate contour plan of uranium ore body shows NW-SE trend and coincides with the hydro-uranium contour. Correlation sections of ore body display true as well as false hydro-uranium anomalies in N-S and E-W profiles. Hydro-uranium anomalies owe their origin to uranium cations, dissolved from the mineralized horizon in to groundwater. Hydro-geochemical orientation survey carried out at Chitrial plateau may be applied regionally in the Srisailam sub basin as an effective tool to explore the concealed unconformity type uranium mineralization below Srisailam Formation.
This article describes a survey using low-frequency electromagnetics (VLF-EM) over an unconformity-related uranium mineralization in the northern part of India's Cuddapah Basin. The uranium occurs in granite close to the contact between basement granite and Srisailam sediments. The uranium mineralization is controlled by the basement fractures containing rich concentrations of coffinite and pitchblende. The basement granite is Palaeoproterozoic age.
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