D. Sengupta

Radiogenic heavy minerals in Chhatrapur beach placer deposit of Orissa, southeastern coast of India

The beach placer deposit at Chhatrapur coast of Orissa state, southeastern coast of India, has a significant concentration of radiogenic heavy minerals. The average activity concentrations of radioactive elements such as 232Th, 238U and 40K were measured by gamma ray spectrometry using a HPGe detector, and found to be 2650±50, 400±30 and 120±30 Bq/kg, respectively, for the bulk sand samples. The activity concentrations in monazite and zircon sands are found to be 305,000±2000 and 2000±150 Bq/kg for the 232Th and 21,500±300 and 3450±250 Bq/kg for the 238U. Electron probe microanalysis results of monazite sands show the average ThO2 and UO3 concentrations to be 10.42 wt.%, and 0.32 wt.%, respectively. The major contributors for the enhanced level of radioactivity are monazite and zircon sands. These heavy mineral sands were derived from the nearby source areas such as Eastern Ghats Group of rocks.

Geophysical anomalies associated with uranium mineralization from Beldih mine, South Purulia Shear Zone, India

Beldih mine at the central part of the South Purulia Shear Zone (SPSZ) has been reported with low grade uranium-bearing formation within quartz-magnetite-apatite host in kaolinized formation. Therefore, the present integrated geophysical study with gravity, magnetic, radiometric, very low frequency electromagnetic (VLF) and gradient resistivity profiling methods around the known mineralized zones aimed at identifying the exact geophysical signatures and lateral extent of these uranium mineralization bands. The closely spaced gravity-magnetic contours over the low to high anomaly transition zones of Bouguer, reduced-to-pole magnetic, and trend surface separated residual gravity-magnetic anomaly maps indicate the possibility of high altered zone(s) along NW-SE direction at the central part of the study area. High current density plots of VLF method and the low resistive zones in gradient resistivity study depict the coincidence with low gravity, moderately high magnetic and low resistivity anomalies at the same locations. Moderate high radioactive zones have also been observed over these locations. This also suggests the existence of radioactive mineralization over this region. Along profile P2, drilled borehole data revealed the presence of uranium mineralization at a depth of ∼100 m. The vertical projection of this mineralization band also identified as low gravity, low resistivity and high magnetic anomaly zone. Thus, the application of integrated geophysical techniques supported by geological information successfully recognized the nature of geophysical signatures associated with the uranium mineralization of this region. This enhances the scope of further integrated geophysical investigations in the unexplored regions of SPSZ.

Radon exhalation and radiometric prospecting on rocks associated with Cu-U mineralizations in the Singhbhum shear zone, Bihar.

The Singhbhum thrust belt is a 200 km long arcuate orogenic belt in Bihar, eastern India. The huge mineral resources, viz. copper, uranium, magnetite, apatite and molybdenite, etc., make it significant from an economic as well as a geological point of view. The belt hosts three types of mineralization: sulphides of copper and other metals, uranium oxides and apatite-magnetite. Several distinct geological episodes are responsible for the evolution of mineralization and the thrust zone itself. Extensive and reliable radiometric prospecting and assaying have been carried out by us for the past 5 years from Dhobani in the east to Turamdih in the west of the Singhbhum shear zone. The present work indicates uranium mineralization in the Pathargora-Rakha area presently being mined for copper and also within areas in the vicinity of Bhatin. Studies on radon emanation have also been undertaken in some parts of the shear zone which indicate reasonably high radon emanation of the soils and rocks studied. This suggests the need for regular monitoring and suitable controls on the mine environment (air quality) and its vicinity. Radon emanation studies coupled with gamma-ray spectrometry and the subsequent modelling of the radiometric and radon measurements will help in the application of radon as a geophysical tracer in exploration of radioactive ore bodies and in radon risk assessment as well as in delineating active and passive faults and even in petroleum exploration.

Seasonal levels of radon and thoron in the dwellings along southern coastal Orissa, Eastern India

Inhalation of radon ((222)Rn) and thoron ((220)Rn) are a major source of natural radiation exposure. Indoor radon-thoron study has been carried out in some dwellings of Ganjam district, southern coastal Orissa, India using LR-115 type II plastic track detectors. Seasonal variation of indoor radon and thoron shows high values in winter and low values in both summer and rainy. The inhalation dose lies in the range of 0-0.06muSvh(-1) and is not high from those found elsewhere in India.

Spatial distribution of gamma radiation levels in surface soils from Jaduguda uranium mineralization zone, Jharkhand, India, using γ-ray spectrometry, and determination of outdoor dose to the population.

The concentrations of natural radionuclides in surface soil samples around selected villages of Jaduguda were investigated and compared with the radioactivity level in the region. Concentrations of 238U, 232Th, and 40K were determined by a gamma ray spectrometer using the HPGe detector with 50% relative efficiency, and the radiation dose to the local population was estimated. The average estimated activity concentrations of 238U, 232Th, and 40K in the surface soil were 53.8, 44.2 and 464.2 Bq kg−1 respectively. The average absorbed dose rate in the study area was estimated to be 72.5 nGy h-1, where as the annual effective dose to the population was 0.09 mSv y-1. A correlation analysis was made between measured dose rate and individual radionuclides, in order to delineate the contribution of the respective nuclides towards dose rate. The radio-elemental concentrations of uranium, thorium and potassium estimated for the soils, in the study area, indicated the enrichment of uranium series nuclide. The results of the present study were subsequently compared with international and national recommended values.

Economically viable rare earth element deposits along beach placers of Andhra Pradesh, eastern coast of India

A comprehensive study was carried out in order to determine the radioelement and rare earth element (REE) concentrations in beach placer deposits at selected locations along the eastern coast of Andhra Pradesh in India. This was done to evaluate the economic value of these deposits. The findings of this study suggest that high Th and low K concentrations delineate the prospective regions having REE deposits. The beach placers, in general, can be characterized by high thorium and moderate uranium concentrations. The concentrations of REEs vary in the following order: Ce > La> Nd > Pr > Sm > Gd > Dy. Rapid in situ thorium prospectivity coupled with laboratory-based techniques like ICP-MS, as proposed in this study, would help in the identification of prospective REE sources along the coastal placers. The development of indigenous resources of light rare earth elements (LREEs), medium rare earth elements (MREEs), and heavy rare earth elements (HREEs) would decrease the dependence on imports, which have a strategic hold on the production and supply of the REEs, globally.

Estimation of 238U, 232Th and 40K concentrations in rock and soil samples around South Purulia Shear Zone, India

The first few measurements for low level gamma ray spectrometry for the delineation of U and Th along South Purulia Shear Zone (SPSZ) are reported. Estimation of 238U, 232Th and 40K concentrations in widely dispersed rock and soil samples around SPSZ has been undertaken using HPGe detector having relative efficiency of 50%. The maximum concentration among all the samples studied is observed in the sample close to the Beldih region, SPSZ. An attempt has been made to study the variation in the concentration of these rock and soil samples with respect to location from the shear zone. Central part of the shear zone is found to contain higher concentration of radionuclides than the samples from the periphery. This proves that intensity of shearing controls the activity of radionuclides in a sample, apart from alteration, metamorphism, weathering, etc. A comparison of radionuclide activities of soil samples in study area with other studies worldwide is reported.

Ambient gamma radiation levels (indoor and outdoor) in the villages around Jaduguda (India) using card-based CaSO4: Dy TL dosemeters

A systematic study of the gamma radiation levels (indoor and outdoor) in the villages surrounding the uranium-enriched regions around Jaduguda, India has been undertaken by monitoring selected dwellings in six villages. Each dwelling unit was monitored for a total duration of 1 y. The gamma radiation measurements were carried out using card-based CaSO(4): Dy thermoluminescent dosemeters. The estimated average annual gamma dose values for indoor and outdoor were 980 and 924 (µGy y(-1)), respectively, for the entire region studied. The maximum indoor and outdoor gamma doses experienced in North Dungridih and South Dungridih villages were 1305 and 1223 (µGy y(-1)), respectively. The minimum indoor and outdoor gamma dose values observed in Chatikocha village were 624 and 696 (µGy y(-1)), respectively. Seasonal variation of the indoor gamma values was not observed during the year; however, a small variation was seen with the type of building materials used for construction purposes. A statistical analysis was attempted to characterise the distribution of terrestrial gamma radiation obtained in the study area. The average quarterly indoor gamma values for spring, summer, monsoon and winter seasons as prevalent in the regions were 267±71, 262±54, 213±91, 238±66 (µGy 90 d(-1)), respectively. The annual effective doses to the local population residing in the selected dwelling units were estimated to be 0.6 and 0.1 (mSv y(-1)) for indoor and outdoor, respectively, using an occupancy factor of 0.8 and 0.2.

Heavy Metal and Radionuclide Contaminant Migration in the Vicinity of Thermal Power Plants: Monitoring, Remediation, and Utilization

Environmental pollution has been an important issue particularly in a period which is witnessing a rapid industrial growth. The major sources of heavy metal and radionuclide pollution in urban areas are anthropogenic which includes the fossil, coal combustion, etc. Coal, one of the most abundantly found materials in nature, has trace quantities of primordial radionuclides, 238U, 232Th, and 40K. Thus, combustion of coals in thermal power plants (TPPs) is one of the major sources of environmental pollution enhancing the natural radiation in the vicinity of TPPs. Fly ash, the main residue from the combustion of pulverized bituminous or sub-bituminous coal (lignite), is directly disposed of in large ponds in the nearby areas of TPPs. This problem is of particular significance in India, which utilizes coals of very high ash content (approximately 40–55 %). Background knowledge, i.e., monitoring of the origin, chemistry, and risks of toxic heavy metals (Pb, Cr, As, Zn, Cd, Cu, Hg, and Ni) and radionuclides in contaminated soils, is necessary for the selection of appropriate remedial options. For this purpose, soil, ash, and coal samples were collected from the nearly areas of TPPs. In order to validate the fact of heavy metal and radionuclide contaminant migration in the vicinity of TPPs, several geophysical, radiochemical, and trace element analysis tests were carried out. Lack of proper insulation at the bottom of the ash disposal ponds enhances the chances of groundwater contamination. The direct current (dc) resistivity survey, employing Schlumberger configuration, was undertaken to identify the local subsurface and to estimate the depth of contamination around ash ponds near a thermal power plant in Eastern India. A continuous conductive zone with resistivity <5 Ωm was identified throughout the studied region at a depth of about 2–10 m indicating the presence of water with higher ionic concentration. The study was also supported by the radiometric geophysical measurements indicating the presence of radionuclides in the vicinity of ash ponds. Groundwater samples have also been collected from the tube wells located near the ash ponds and analyzed for pH, TDS and trace elements. Results of the chemical analysis show high values of TDS and high concentration of the toxics. The studies on the geochemistry of the ash ponds have shown that the ashes are characterized by high concentration of As, Pb, Cu, Ni, Fe, Zn, Cr, Co, and Mn all of which exceeded the crustal abundance by a factor of 3–5. The high concentration of the toxics (As, Al, Li, Zn, Ag, Sb, Si, Mo, Ba, Rb, Se, Pb) in the water samples implies significant input from the ash pile due to leaching. This increases the TDS values of the water. Radiochemical characterization of coal, ash, and soil samples was done based on Radium equivalent activity, dose rate, and hazard index. The activity concentration variations infer to the high radioactivity in the vicinity of the ash ponds up to a radius of 500 m and indicate a decreasing trend beyond 500 m. In general, the radioactivity of the nearby area showed three to four times higher values than the prescribed limit, and the hazard index was estimated as unity. In order to mitigate the associated risks, make the land resource available for agricultural production, enhance food security, and scale down land tenure problems, remediation of contaminated soil is necessary. Immobilization, soil washing, and phytoremediation are one of the best technologies for cleaning up of contaminated soils but have been mostly demonstrated in developed countries. Such technologies need high recommendation for field applicability and commercialization in the countries (developing) where agriculture, urbanization, and industrialization are causing environmental degradation. The utilization of contaminated soil is also discussed. Rare earth elements, heavy metal, and radionuclides, which are of economical importance, can be extracted from the contaminated soil and the remainder can be utilized in filling voids and reclamation of the mining lands.

Electrofacies Analysis of Well Log Data Using Data Mining Algorithm: A Case Study

The unsupervised data mining methods help to extract the hidden patterns within a large multidimensional dataset of subsurface well log measurements. The well logs are continuous measurements of some parameters related to the physical properties of the rocks in subsurface with respect to depth. Log data are used by oil and gas industries to understand the lithology of the formation, and to detect potential hydrocarbon-bearing zones if any. The present study has utilized principal component analysis (PCA) to consider the contribution of each of the well logs, and to reduce the dimensionality of the multivariate logs. The first four principal components from PCA, which define around 90% variance of the dataset, were utilized for clustering using k-means clustering technique. The elbow method was employed and the optimum number of clusters was obtained to be four for the present dataset. The obtained clusters were interpreted to determine the electrofacies associated with each of the clusters. The electrofacies reflect the lithology and the potential hydrocarbon-bearing zones, in the study area.