Geological and tectonic influence on water–soil–radon relationship in Mandi–Manali area,Himachal Himalaya

Radon measurements in soil and groundwater (springs, thermal springs and handpumps) were made in a variety of lithological units including major thrusts between Mandi and Manali in Himachal Himalaya. Analysis of radon data in light of lithological controls and influence of deep-seated thrusts has been made to elucidate the causative factors for anomalous emanation of radon. The lithological types include banded gneisses, schists, quartzite, granite, phyllites, volcanics and mylonites. The low-grade metasedimentries of Shali and Dharamsala generally show low and narrow range of radon concentration in water (5.6–13.4 Bq/l) as well as in soil (1.8–3.2 kBq/m³) except for the samples related to thrusts. On the other hand, sheared and deformed rocks of Chail and Jutogh show moderate radon content (average 5.03 kBq/m³, range 2.9–11.1 kBq/m³) in soil. However, the groundwater radon concentration shows wide variation in different types of sources (2.1–80.8 Bq/l). The quartzite and volcanic rocks of Rampur formation in this area present as a window separated by Chail thrust. Radon emanations on these rock types are relatively high (6.3–68.1 Bq/l in water and 5.5–15.9 kBq/m³ in soil) and are exceptionally high in samples that are related to uranium mineralization, deep-seated thrusts and hot springs (13.5–653.5 Bq/l). It is generally observed that anomalous high radon content is associated with mineralization, deeper source and tectonic discontinuities. Whereas it is obvious that subsurface radioactive mineralization would facilitate enhanced radon production, however, thrust plains provide easy pathways for escape of gases from the deeper sources. Shallow and deep sources of the groundwater have contrasting radon content particularly in the deformed and metamorphosed rocks of Jutogh and Chail. Shallow groundwater sources, mainly handpumps, have lower radon concentration due to limited superficial water circulation, whereas deeper sources, mainly perennial springs, show higher radon content because of larger opportunity for water–rock interaction.     

Isotope hydrochemical approach to understand fluoride release into groundwaters of Ilkal area,Bagalkot District,Karnataka, India

Isotope and hydrochemical investigations have been carried out in the Ilkal area of Karnataka, India, in order to determine the source and mechanism of fluoride release into groundwaters and to understand groundwater hydrochemistry. Agriculture, granite quarrying and rock-polishing industries are the main occupations in this area. Closepet granite, Peninsular gneiss and Dharwar schists are the major geological formations. Results show that the fluoride concentration in groundwater is 0.3–6.5 mg/L and it is found to increase from recharge area to discharge area. Fluoride variability is found to be influenced by the geology of the area and depth wise correlation was not observed. Water samples are unsaturated with respect to fluorite, indicating the possibility of further increase in fluoride in groundwater. Positive correlations between fluoride with sodium and bicarbonate in groundwater show that high fluoride content and alkaline sodic characteristics are the result of dissolution of fluoride bearing minerals, possibly derived from weathered granite and gneiss. A positive correlation between fluoride and δ¹⁸O, and the presence of high tritium in fluoride-contaminated groundwater, point to contribution from surface waters, contaminated by anthropogenic activities. Dumping of rock wastes that are rich in fluoride into the streams by the rock-polishing industries plays a significant role in contaminating groundwater.     

Geochemistry of granites and metasediments of the urban area of Vila Real (northern Portugal) and correlative radon risk

Radon concentration was evaluated in dwellings of the urban area of Vila Real (Northern Portugal). The area is mainly composed of Hercynian granites and Cambrian metasediments, and CR-39 passive detectors (n = 112) were used for the purpose. The results obtained in winter conditions suggest that the most productive geological unit is the Hercynian granite G1 (geometric mean of 364 Bq/m³), while Cambrian metasediments of the Douro Group show the lowest average indoor radon concentration (236 Bq/m³). The geological, geochemical and radiological data obtained suggest that the most effective control on the radon concentrations of the area is related with the uranium content of the rocks; indeed, the highest contents were observed in granite G1 (21 ppm) and the lowest in the metasediments (3 ppm). This is also confirmed by the results obtained for groundwater, where granites present the highest concentrations of dissolved radon (up to 938 Bq/l), uranium (5–18 ppb) and gross α activities (0.47–0.92 Bq/l). No important radiometric anomalies were found in relation with geological structures such as faults, veins and contacts, but a moderate increase of the uranium content can occur locally in such structures. Petrographic observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals (apatite, zircon, monazite, xenotime), which reduces radon emanation. Notwithstanding, due to the high U contents granites show a significant potential to induce indoor radon concentrations in dwellings in excess of the recommended value of 400 Bq/m³. Overall, we can conclude that the region of Vila Real presents a moderate to high radon risk in dwellings and groundwater.     

Determination of the radiation dose due to radon ingestion and inhalation

The distribution of radon in ground and surface water samples in Sankey Tank and Mallathahalli Lake areas was determined using Durridge RAD-7 analyzer with RAD H₂O accessory. The radiation dose received by an individual falling under different age groups (viz., 3 months; 1, 5, 10, 15 years and adult) depending upon their average annual water consumption rate was attempted. The mean radon activity in surface water of Sankey Tank and Mallathahalli Lake was 7.24 ± 1.48 and 11.43 ± 1.11 Bq/L, respectively. The average radon activities ranged from 11.6 ± 1.7 to 381.2 ± 2.0 Bq/L and 1.50 ± 0.83 to 18.9 ± 1.59 Bq/L, respectively, in 12 groundwater samples each around Sankey Tank and Mallathahalli Lake areas. Majority of the measured groundwater samples (viz., 100 % in Sankey Tank area and 75 % in Mallathahalli Lake area) showed mean radon values above the EPA’s maximum contaminant level of 11.1 Bq/L and only 66.67 % of samples in Sankey Tank area showed radon above the WHO and EU’s reference level of 100 Bq/L. The overall radiation dose due to radon emanating from water in the study area was increasing with increase in age and water consumption rates, but significantly lower than UNSCEAR and WHO recommended limit of 1 mSv/year except for few groundwater samples in Sankey Tank area (i.e., 0.92, 0.99 and 1.39 mSv/year). The radiation dose rate received by bronchial epithelium via inhalation was very high compared to that by stomach walls via ingestion.     

Radon in groundwater in Tumkur district of Karnataka with special reference to sampling sensitivity

Radon is a naturally occurring colourless and odourless radioactive gas that is soluble in water and is the main source of radioactivity of groundwater. Use of radon contaminated groundwater increased the radon levels in the air, especially in poorly ventilated houses, which is hazardous to health. Ingestion of such water for quite long period may lead to stomach cancer. The drinking water standards proposed by the Bureau of Indian Standards (BIS) exclude the permissible concentration of radon in drinking water. The US Environmental Protection Agency (USEPA) in 1991 proposed a Maximum Concentration Level (MCL) of 11.1 Bq/l for public water supply. The water samples from the bore wells in Tumkur district of Karnataka show radon concentrations in the range of 5 to 250 Bq/l. Ninety percentages of the samples show radon levels above the permissible limit as per USEPA. The spatial variation and geological control over radon concentration in groundwater in the area and sampling sensitivity are discussed here. The study was conducted during March 2012.     

Geology and geochemistry of metabasalts of Shimoga schist belt,Dharwar Craton: implications for the late Archean basin development

The late Archaean Shimoga schist belt in the Western Dharwar Craton, with its huge dimensions and varied lithological associations of different age groups, is an ideal terrane to study Archean crustal evolution. The rock types in this belt are divided into Bababudhan Group and Chitradurga Group. The Bababudhan Group is dominated by mafic volcanic rocks followed by shallow marine sedimentary rocks while the Chitradurga Group is dominated by greywackes, pillowed basalts, and deep marine sedimentary rocks with occasional felsic volcanics. The Nb/Th and Nb/La ratios of the studied metabasalts of the Bababudhan Group indicate crustal contamination. They were extruded onto the vast Peninsular Gneisses through the rifting of the basement gneiss. The Nb/Yb ratios of high-magnesium basalts and tholeiitic basalts of Chitradurga Group suggest the enrichment of their source magma. Based on the flat primitive mantle-normalized multi-element plot with negative Nb anomalies and Th/Ta-La/Yb ratios, the high-magnesium basalts and tholeiitic basalts are considered to have erupted in an oceanic plateau setting with minor crustal contamination. The high-magnesium basalts and tholeiitic basalts formed two different pulses of same magma type, in which the first pulse of magma gave rise to high-magnesium basalts which were derived from deep mantle sources and underwent minor crustal contamination en route to the surface, while the second pulse of magma gave rise to tholeiitic basalts formed at similar depths to that of high-magnesium basalts and escaped crustal contamination. The associated lithological units found with the studied metavolcanic rock types of Bababudan and Chitradurga Groups of Dharwar Supergroup of rocks in Shimoga schist belt of Western Dharwar Craton confirm the mixed-mode basin development with a transition from shallow marine to deep marine settings.     

The geology of Goa Group: Revisited

The supracrustals that constitute the Goa Group of Gokul et al. (1985) can be divided into two lithostratigraphic sequences namely the Barcem Group and the Ponda Group. The former comprises predominantly greenstones (metabasalts) and rests on a basement of the 3300–3400 Ma Anmode Ghat trodhjemite gneiss with a crudely developed quartz-pebble conglomerate at the base, and shows lithological similarities with the lower part of the Bababudan Group. The younger sequence is dominated by clastics, and is assigned to a new stratigraphic group formally termed the Ponda Group which is equivalent to the Chitradurga Group of the Dharwar Supergroup. This group rests on a basement of the 2700–2900 Ma Chandranath granite gneiss with a distinct unconformity marked by a polymict, granite-clast metaconglomerate. The conglomerate displays many similarities with the Talya conglomerate that occurs at the base of the Chitradurga Group. It is overlain by a psamolitic sequence which is followed in ascending order by the chemogenic sediments that host the BIF and by the deep water turbidite sequence (argillite-graywacke association) with intercalations of mafic volcanics. The supracrustal sequence is intruded by the Bondla layered mafic-ultramafic complex along a major shear zone (NW-SE) that largely controls the course of the northwesterly flowing tributary of River Mandovi. The late intrusive, Canacona potassic granite marks the culmination of the sedimentation in the Shimoga-Goa basin.     

Radon in Himalayan springs: a geohydrological control

 This paper presents the results of radon measurements in springs of the Himalayan region by using radon emanometry technique. The radon was measured in different springs, draining from different geohydrological setups, and from stream water in order to find the geohydrological control over radon concentration in groundwater emanating in the form of spring. The radon values were found to vary from 0.4 Bq/l to 887 Bq/l, being observed lowest for a turbulent stream and highest for the spring. The radon values were recorded highest in the springs draining through gneiss, granite, mylonite, etc. Radon concentrations have been related with four spring types viz. fracture-joint related spring, fault-lineament related spring, fluvial related spring and colluvial related spring, showing geohydrological characteristics of the rocks through which they are emanating. The high radon concentration in fracture-joint and fault-lineament spring is related to increased ratio of rock surface area to water volume and uranium mineralisation in the shear zones present in the close vicinity of fault and thrust. The low concentration of radon in fluvial and colluvial springs is possibly because of high transmissivity and turbulent flow within such deposits leading to natural de-emanation of gases. Received: 6 January 1998 · Accepted 11 May 1999     

Impact of geohydrology and neotectonic activity on radon concentration in groundwater of intermontane Doon Valley, Outer Himalaya, India

 Radon concentration was measured in 133 water samples from tubewells, handpumps, dug wells and springs of the Doon Valley, Outer Himalaya, India. The observed radon values were found to vary from 10 to 154 Bq/l whereas radium in selected water samples varied from 0.11 to 0.75 Bq/l. Three different clusters of high radon values were observed in the north-western, central and south-eastern parts of the Doon Valley. These clusters were found to be associated with tectonics (thrust/fault) and associated uranium mineralization in the area. In general, radon concentration in groundwater was found to be positively correlated with the depth of the wells, whereas no significant correlation was observed between radon concentration in groundwater and the water temperature, pH value, conductivity and altitude of the water samples. An attempt has also been made to determine the nature and extent of aquifers in the Doon Valley on radon concentration in groundwater. The variation in radon concentration within the groundwater of the study area was found to be controlled by the neotectonic activity and geohydrological processes that occur in the area. The impact of these activities on radon concentration in groundwater are discussed. Received: 17 September 1999 · Accepted: 11 April 2000     

Measurement of Radon Concentration in Drinking Water in Bhiwani District of Haryana

This investigation aims to evaluate the concentration of dissolved radon in drinking water and to assess the associated radiation doses for infants, children and adults in Bhiwani district of Haryana The radon concentrations were measured in 82 drinking water samples collected from 32 villages/towns in the Bhiwani district. The measurements were performed by RAD7, an electronic radon detector manufactured by Durridge Company Inc. The mean radon concentration ranged between 1.3 ± 0.4 and 13.4 ± 2.2 Bq l^-1. The mean radon concentrations from two locations exceeded the maximum contamination level (MCL) of 11 Bq l^-1 recommended by United States Environmental Protection Agency. The total annual effective doses due to ingestion and inhalation of radon in drinking water varied from 10.1 to 104.4 μSv y^-1 for infants, 5.8 to 59.6 μSv y^-1 for children and 6.6 to 67.7 μSv y^-1 for adults and the average values were found to be 46.3, 26.5 and 30.1 μSv y^-1, respectively.     

Spatial distribution mapping and radiological hazard assessment of groundwater and soil gas radon in Ekiti State,Southwest Nigeria

Groundwater constitutes the major source of utility water in Ekiti State with the majority of the population depending on groundwater for drinking and other household uses. Soil in the area is commonly used as a component of building materials, which may produce radon in the indoor environment. Excessive concentrations of radon in water and soil can cause radiological health risks to human as witnessed by the increased cases of lung cancer among non-smokers in Nigeria, which may be traceable to the ingestion and inhalation ²²²Rn in drinking water and indoor air. In the present study, comparative in situ measurements of radon in groundwater and soil gas were carried out at one hundred selected locations across the Ekiti State in southwest Nigeria, using a RAD7 radon detector to generate a radon distribution map and to estimate radiation hazards due to radon. The concentrations of radon in groundwater ranged from 0.9 to 472 Bq L^?1 with a mean of 34.7?±?4.4 Bq L^?1, while those of soil gas ranged from 0.1 to 315 kBq L^?1 with a mean of 38.9?±?1.4 kBq L^?1. The total annual effective dose due to inhalation and ingestion of radon in groundwater amounted to 94.7 µSv year^?1, which is lower than the reference dose of 100 µSv year^?1 recommended by the World Health Organization (WHO). The radon map generated for groundwater and soil gas identified three distinct areas with radon levels ranging from low to high. The results of this study show that some locations (Emure, Gbonyin, Ijero and Ikole) show mean total annual effective doses which are higher than the recommended limit. It can then be inferred that the groundwater samples pose significant radiological hazards to the population and that the noticed increase in lung cancer cases may be attributed to the consumption of groundwater in the area.     

Timing and geochemistry of potassic magmatism in the eastern part of the Svecofennian domain,NW Ladoga Lake Region,Russian Karelia

The Puutsaari intrusion is a potassium-rich magmatic complex in the eastern part of the Svecofennian domain close to the Archaean border. The intrusion is generally undeformed in contrast to 1880–1875 Ma-old country rock tonalitic migmatites and diatectites. The main rock types are: (1) mafic rocks of a gabbro–norite–diorite–quartz monzodiorite series; (2) quartz diorite–tonalite–granodiorite; and (3) coarse-grained microcline granite. The three rock-types intruded coevally forming a peculiar three-component mingling system. The mafic rocks, enriched in K, P, Ba, Sr and LREE, have marked shoshonitic affinities (K₂O=1.97–5.40, K₂O/Na₂O=0.6–2.37). On a regional scale they demonstrate transitional geochemistry between less enriched syn-orogenic 1880 Ma-old gabbro–tonalite complexes and strongly enriched 1800 Ma post-collisional shoshonitic intrusions. The microcline granite as well as the tonalite–granodiorite rocks are geochemically similar to crustal anatectic granitoids of the NW Ladoga Lake area. The three rock groups do not form a single trend on Harker-type diagrams and are unlikely to be related by fractional crystallisation or mixing. Zircons from the Puutsaari microcline granite and from the mafic rock series have been dated by ion-microprobe (NORDSIM) at 1868.2±5.9 and 1869±7.7 Ma, respectively. Most zircons recovered from a granite sample had zoned or homogeneous cores and unzoned fractured rims. No statistically significant variation of zircon core and rim ages from the granite was established in the course of this study. Zircons from the mafic rock are unzoned. It is suggested that the mafic rocks at Puutsaari were derived from an enriched mantle shortly after the main Svecofennian collisional event and the roughly 1.88 Ga regional metamorphic culmination. The emplacement of the mafic melt caused anatectic melting of various crustal protoliths and produced coeval granitic and tonalitic compositions.     

Anomalous concentrations of radionuclides in the groundwater of Ede area,southwestern Nigeria: a direct impact of geology

An assessment of the groundwater in areas underlain by pegmatite in Ede, southwestern Nigeria was carried out to determine the concentration of Potassium-40 (⁴⁰K), Uranium-238 (²³⁸U) and Thorium-232 (²³²Th) radionuclides. In the earlier work, it was established that zircons in these pegmatites have suffered a high degree of metamictization that has enhanced continuous loss of some radionuclides since the time of emplacement of the pegmatite host rock to the present. The aim of this work is to determine whether or not there is corresponding increase in the concentration of radionuclides in groundwater in the study area. Fifteen groundwater samples were collected from both hand dug wells and boreholes in the area. Ten samples were from Ede town, two samples each from nearby communities of Iddo and Ekuro and one from Iwoye, where the bedrocks were not pegmatites. All the 15 samples were analyzed with the Sodium Iodide scintillator (NaI [Tl]) detector at the Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Nigeria. The results showed varying concentrations of the radionuclides in the water samples. Activity concentrations of Potassium-40 (⁴⁰K) indicated an average value of 17.149 Bq/L for samples from Ede, 9.265 Bq/L for Iddo, 6.6 Bq/L for Ekuro, while Iwoye has a value of 21.21 Bq/L. The Uranium-238 (²³⁸U) series had an average value of 13.64 Bq/L for Ede, 13.49 Bq/L for Ekuro, 11.685 Bq/L for Iddo and 12.04 Bq/L for the lone sample from Iwoye. Thorium-232 (²³²Th) series had an average value of 11.182 Bq/L for Ede, while average values of 7.79 Bq/L and 9.025 Bq/L, respectively, were recorded for Iddo and Ekuro and 12.25 Bq/L for Iwoye. The annual effective dose level of ⁴⁰K is generally below the World Health Organization (WHO) recommended dosage of 0.1 mSv/y except for three locations, while those of ²³⁸U and ²³²Th are in excess of the standard values. The high radionuclides in the groundwater in the study area were not due to anthropogenic sources but directly due to geological processes which release the radioisotopes from rocks after weathering, continuous loss from metamict minerals and natural lateral mobility from regions of radionuclides’ release to other areas. There is thus the need to carry out systematic studies of the radionuclides concentrations on regional scale in the area which could lead to investigating on both short- and long-term health effects on organic species in these areas, and development of purification systems before utilizing water from the areas for domestic and industrial purposes.     

北京广东典型地区室内氡气浓度与地质背景关系

为了解不同地质背景条件室内氡浓度水平,采用脉冲电离室测氡仪AlphaGUARD测量了北京广东不同地质背景典型测点的室内氡浓度,同时对广东某一测点进行了长期的室内氡监测。测量和研究结果表明：地表岩性是影响室内氡浓度高低的重要因素之一。地处花岗岩地区的建筑物内氡浓度高于其他岩性地区的室内氡浓度,广东室内氡水平明显高于北京地区,广东北京花岗岩地区的平均室内氡浓度分别为69.98 Bq/m^3和43.97 Bq/m^3,第四系覆盖地区的平均室内氡浓度分别为43.60 Bq/m^3和35.74 Bq/m^3。民用住宅卧室内的室内氡浓度略高于公共建筑物办公室内的室内氡浓度。因此,结合地质背景研究室内氡的水平与分布对指导开展室内氡调查中确定抽样方案、选择测点及进行区域尺度室内氡评价有重要的实用价值。     

The influence of geological factors on radon risk in groundwater and dwellings in the region of Amarante (Northern Portugal)

The region of Amarante (Northern Portugal) is composed of Hercynian tardi-tectonics granites and Paleozoic metasediments. Petrographic observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals such as apatite, zircon, monazite, uraninite, thorite and thorianite. The geological, geochemical and radiological data obtained suggest that the radon concentrations in dwellings of the studied area are mainly related with the uranium content of the rocks. Indeed, the highest contents were observed in granite AT2 of Padronelo (18.2 ppm) and the granite AT1 of Telões (10.3 ppm), with metasediments showing much lower uranium contents of 1.6 ppm; radon concentrations were evaluated in dwellings, using CR-39 passive detectors, and the results obtained in winter conditions suggest that the most productive geological units are the granites AT2 and AT1, with geometric means of 430 and 220 Bq/m³, respectively, while the metasediments show the lowest value of 85 Bq/m³. Some moderate radiometric anomalies, where uranium contents can double typical background values, were found in relation with specific fault systems of the region affecting granitic rocks, thus increasing radon risk; this is an indication of uranium mobility, likely resulting from the leaching of primary mineral supports as uraninite. Groundwater radionuclide contents show a wide range of results, with the highest activities related with granitic lithologies: 2,295 Bq/l for radon, 0.83 Bq/l for gross α and 0.71 Bq/l for gross β, presenting metasediments much lower values, in good agreement with other results obtained. Absorbed dose measured with gamma spectrometers in direct contact with the rocks is directly related with the uranium contents of the rocks, and thus works as a fast proxy for radon risk. It is concluded that radon risk is moderate to high in the granitic areas of the Amarante region and low in the metasediments of the same region.     

Lead isotope evidence for recent uranium mobility in geological formations of Brazil: implications for radioactive waste disposal

Lead–lead isotope data from whole rock samples are used to investigate the recent (last few million years) mobility of U and Th. The method is based on the comparison of the calculated present day U and Th concentrations required to yield the Pb isotope composition in the samples with the actual present day concentrations of U and Th obtained by direct measurement. The geological formations studied include the Neoproterozoic carbonate sediments of the Bambuı́ Group, Archean/Paleoproterozoic granite–greenstone terrain of the Contendas–Mirante Complex and a Proterozoic ortho-gneisses hosting U deposit in Lagoa Real. All these formations are in the São Francisco Craton, Brazil. The data show high U mobility in the carbonate sediments and in the deformed ortho-gneisses set in a ductile shear zone. Infiltration of groundwater through fault zones seems to have facilitated the U mobility. The Pb isotope approach is a useful technique complementing U-series disequilibrium studies and may be included for site characterization studies for radioactive waste disposal.     

引绰济辽工程文得根引水隧洞放射性调查评价

对长约70 km引水工程洞线上进行的地面伽马能谱测量、陆地伽马剂量率测量、土壤氡浓度测量、岩石表面氡析出率测量以及钻孔岩芯样品的放射性元素U、Ra、Th、K含量分析的综合放射性地质调查,并对获得的测量数据进行分析研究。结果表明,测区引水沿线地质体放射性核素当量含量平均值为：U 1.56×10-6,Th 14.12×10-6,K 2.16×10-2;钻孔岩芯放射性元素分析含量平均值为：U 32.34 Bq/kg,Ra 35.68 Bq/kg,Th 35.29 Bq/kg,K 865.65 Bq/kg。陆地伽马剂量率为90.42 nGy/h;土壤氡浓度平均值为4 272.1 Bq/m3;岩石表面析出率平均值为4.01×10-2 Bq/m2·s。根据测量结果,利用内照射和外照射辐射剂量计算了对施工人员造成的辐照剂量为0.759 mSv,低于国家对公众的剂量限值1 mSv/a,表明引水工程输水隧洞的施工在安全辐射范围内。     

江西金山金矿田矿山辐射调查

对金山金矿田的金山金矿、花桥金矿区露天水源天然铀、氡,居民区和井下作业人员γ外照射有效剂量等进行调查的结果表明：金山、西蒋矿区露天水源天然铀、氡浓度均小于限值0.05 m g/L和37.00 Bq/L,空气氡浓度为0.008~0.013 Bq/L.居民和井下作业人员γ外照射年有效剂量均小于1 m s和5 m s.矿区放射性均在国家规定的环境评价指标限制之内,对矿山的人身和环境无影响.     

Mafic and ultramafic magmatism and associated mineralization in the Dharwar craton,southern India

Evidence of mafic and ultramafic magmatism exists in many parts of the Dharwar craton which is divided into two blocks, the West Dharwar Craton (WDC) and the East Dharwar Craton (EDC). The mafic-ultramafic rocks occur in supracrustal/greenstone belts and in numerous enclaves and slivers in the WDC. The oldest recorded maficultramafic rocks, which are mainly komatiitic in nature, are preserved in the Sargur Group which is more than 3.3–3.4 Ga old, the youngest being manifested by 63–76 Ma old mafic dyke magmatism, possibly related to Deccan volcanism. In the Sargur Group, ultramafics rocks greatly dominate over mafic lithological units. Both extrusive and intrusive varieties, the latter in the form of differentiated layered complexes, occur. Mafic volcanics exists in all the greenstone belts of the eastern block and in the Bababudan and Western Ghats belts of the western block. In addition to the Sargur Group where stratigraphic sequences are unclear, mafic magmatism is recorded in three different formations of the Bababudan Group and two sub-divisions of the Shimoga and Chitradurga Groups where basaltic flows are conspicuous. In the well studied greenstone belts of Kolar and Hutti in the EDC, three to four different Formations of mafic volcanic rocks have been mapped. Isotopic dating has indicated that while mafic magmatism in the greenstone belts of the EDC covers only a short time span of between 2.65 to 2.75 Ga, those in the Dharwar Supergroup of the WDC cover a much longer time span from 3.35 to 2.5 Ga. Mafic dyke magmatism has taken place repeatedly from 2.45 Ga to about 1.0 Ga, but, the peak of emplacement was between 1.8 and 1.4 Ga when the densely developed swarms on the western and south western portions of the Cuddapah Basin and in the central part of Karnataka, were intruded. Emplacement of potassic ultramafic magma in the form of kimberlite-lamproite which is confined to the EDC, is a later magmatic event that took place between 1.4 Ga and 0.8 Ga. From a mineralization perspective, mafic magmatism of the supracrustal groups of the WDC and the greenstone belts of the EDC are the most important. V-Ti-magnetite bands constitute the most common deposit type recorded in the mafic-ultramafic complexes of the Sargur Group with commercially exploitable chromite deposits occurring in a number of belts. PGE mineralization of possible commercial value has so far been recorded in a single mafic-ultramafic complex, while copper-nickel mineralization occurs at certain localities in the Sargur and Chitradurga Groups. Gold mineralization hosted by mafic (occasionally ultramafic) rocks has been noted in many of the old workings located in supracrustal groups of rocks in the WDC and in the greenstone belts of EDC. Economically exploitable mineralization, however, occurs mainly in the greenstone belts of the Kolar, Ramagiri-Penkacherla and Hutti-Maski and along the eastern margin of the Chitradurga belt, where it is associated with a major N-S striking thrust zone separating the WDC from the EDC. Gold deposits of the eastern greenstone belts are comparable to those of the younger greenstone belts of Canada, Zimbabwe and Australia where the mineralization is associated with quartz carbonate veins often in iron-rich metabasic rocks. The gold was emplaced as hydrothermal fluids, derived from early komatiitic and tholeiitic magmas, and injected into suitable dilatent structures. The other common type of mineralization associated with the ultramafic rocks of the Sargur Group and supracrustal belts, particularly of the WDC, are asbestos and soapstone, related to autometamorphism/metasomatism. Ruby/sapphire deposits occur in places at the contacts of ultramafic rocks with the Peninsular Gneiss, and are related to contact metamorphism and metasomatism. Mineable magnesite deposits related to low-temperature hydrothermal/lateritic alteration exist in the zone of weathering, particularly in the more olivine-rich rocks. Recent spurt in diamond exploration is offering promise of discovering economically workable diamondiferous kimberlite/lamproite intrusions in the EDC.     

Geological and geochemical factors affecting radon concentrations in dwellings located on permeable glacial sediments—a case study from Kinsarvik,Norway

In 1996–1997, indoor radon values of more than 40,000 Bq/m³ and large seasonal and geographical variations in indoor air radon were reported from a residential area located on a highly permeable ice-marginal deposit. Geochemical analyses of bedrock, groundwater and sediments and comparisons between indoor radon values and soil radon values indicate that the indoor radon concentrations in this area are strongly affected by subterranean airflows caused by temperature differences between soil air and atmospheric air. The airflows concentrate the radon-laden soil air towards the topographic highest part of the deposit in winter and towards the topographic lowest part in summer. In areas where subterranean airflows are likely to occur, radon measurements performed both in summer and in winter provide the best estimate of annual average indoor radon concentrations, and assessments of indoor radon concentrations based on single soil gas measurements are not recommended.