Airborne Gamma-ray Survey Research Articles

Using of airborne gamma-ray spectrometric data to the exposure of potassic alteration -recognition of alteration relates to gold mineralization

It is well known that many mineral deposits are related to hydrothermal processes, especially auriferous deposits. In this research paper, we show how to distinguish areas that have experienced hydrothermal activity, by construing airborne gamma-ray spectrometry data, especially potassium. An indirect application of aerial gamma-ray spectrometry technique is used to detect possible minerals deposits.In this region, an airborne gamma ray survey (K, eU and eTh) was carried out, based on irregular K, “F” parameter -, and Th-normalized of the K and eU anomalies. This work exhibits the mapping of hydrothermal regions possibly showing gold mineralization and the pointing out of new geological portions for this sequence, establishing prospective criteria for regional mineral exploration.We can suggest a new exploratory target, the area that is located next to Jabal Al-Ardiya (white colour on ternary map), which is characterized by high values of F-parameter, KD%, and K/eTh. Besides, enriched areas are found scattered in the north-eastern side of the study area. As result, the airborne gamma ray spectromertic data, might be used for estimation of prospective Gold Ore zones associated with the potassium alteration."

Advantages of Gamma-Radiometric and Spectrometric Low-Altitude Geophysical Surveys by Unmanned Aerial Systems with Small Scintillation Detectors

Unmanned aerial systems (UAS) for airborne gamma-ray surveys in radioecological and geological research are being increasingly used, since they provide radiation safety for personnel and high survey performance. Improvement of detection modules is one of the main directions in which UAS-gamma is developing. Semiconductor detectors are used increasingly as they have a small mass and are convenient for light unmanned aerial vehicles (UAVs). Simultaneously, in our opinion, the potential of traditional scintillation detectors is not exhausted because they are cheaper and more affordable. Radiometric and spectrometric detection modules based on scintillation detectors can even be created at home. The main disadvantage of scintillation detectors is the need for large crystals with significant mass to obtain high data quality. Traditional aerial gamma surveys with operated aircraft systems use scintillation detectors with a volume of tens or hundreds of litres. In this paper, we present the comparison result of radiometric and spectrometric surveys with small volume detectors made at different altitudes and ground surveys. We prove that with properly designed and applied ultralight UAS for aerial gamma spectrometry it is possible to obtain high-quality and informative data.

A Fast Method for Modelling A Gamma-Ray Field over Inhomogeneous Ground Sources

Designing airborne gamma-ray surveys for geological purposes, mineral prospecting, environmental applications or radioactive contamination mapping requires the optimal choice of survey parameters such as the survey altitude, line spacing and survey speed with respect to the sensitivity of the instruments employed and the presumed size and intensity of the detected anomalies. The gamma-ray field attenuates significantly with the distance from the source; being able to model gamma-ray field intensity in various detector positions can be very useful. In recent years, the use of mini-airborne UAV radiometric measurement has developed rapidly. On the one hand, the low payload capacity of UAV results in low sensitivity of the employed detectors; the possibility of increasing gamma-ray signals from low altitude surveys and low speeds on the other hand raises the demand for simulating the gamma-ray field of local inhomogeneous radiometric anomalies. The gamma-ray field modelling method introduced in this paper is based on the monoenergetic approach and discretization of geological radioactive sources utilizing a three-dimensional net of point sources. The optimal density of point sources depends on the detection altitude and the degree of inhomogeneity of the radioactive source. The designed modelling method was verified by comparing the model data with experimental data from three localities where uranium anomalies occur. The degree of conformity of the model and experimental data is acceptable and confirms the applicability of the modelling method. The paper describes a relatively fast and simple gamma-ray field modelling method that is appropriate for ground planar radioactive anomalies. The method is useful for designing survey parameters and for interpretation of detected airborne gamma-ray anomalies.

Modeling Aerial Gamma-Ray Backgrounds Using Non-negative Matrix Factorization

Airborne gamma-ray surveys are useful for many applications, ranging from geology and mining to public health and nuclear security. In all these contexts, the ability to decompose a measured spectrum into a linear combination of background source terms can provide useful insights into the data and lead to improvements over techniques that use spectral energy windows. Multiple methods for the linear decomposition of spectra exist but are subject to various drawbacks, such as allowing negative photon fluxes or requiring detailed Monte Carlo modeling. We propose using Non-negative Matrix Factorization (NMF) as a data-driven approach to spectral decomposition. Using aerial surveys that include flights over water, we demonstrate that the mathematical approach of NMF finds physically relevant structure in aerial gamma-ray background, namely that measured spectra can be expressed as the sum of nearby terrestrial emission, distant terrestrial emission, and radon and cosmic emission. These NMF background components are compared to the background components obtained using Noise-Adjusted Singular Value Decomposition (NASVD), which contain negative photon fluxes and thus do not represent emission spectra in as straightforward a way. Finally, we comment on potential areas of research that are enabled by NMF decompositions, such as new approaches to spectral anomaly detection and data fusion.

Background correction method for improving the automated detection of radioisotopes from airborne gamma-ray surveys

An altitude-based background correction strategy was developed for use in the application of pattern recognition methods to the classification of gamma-ray spectra collected during airborne surveys. Application of this methodology helped to suppress the background spectral variation that serves to obscure the photopeaks associated with low levels of gamma-ray emission. The correction method was implemented by optimizing a database of background gamma-ray spectra collected at various locations and altitudes. Given this background database, a field-collected spectrum was corrected by performing linear regression onto a background spectrum from the database at a matching altitude. The residuals about the regression fit were then digitally filtered and submitted to nonparametric linear discriminant analysis for the purpose of computing classification models for targeted radioisotopes. The resulting classifiers were applied to predict the presence or absence of specific radioisotope signatures in data acquired during airborne surveys. Employing data provided by the U.S Environmental Protection Agency Airborne Spectral Photometric Environmental Collection Technology (ASPECT) program, classification models were computed to detect the presence of cesium-137 (137Cs) and cobalt-60 (60Co). The optimized classifiers were tested over 12 diverse locations, with nine of these data sets containing the target radioisotopes. Correct classification percentages of 99.4% and 99.8% were obtained for the 137Cs and 60Co classifiers, respectively, on the basis of comparisons to visual inspections of the corresponding spectra.

Highly varying radiogenic heat production in Finland, Fennoscandian Shield

Radiogenic heat production in Finland has been previously studied using airborne gamma-ray surveys and glacial till measurements alike. For the first time, this paper presents a detailed survey on the spatial variation in radiogenic heat production determined using outcrop samples obtained from all important lithologies of the country. The dataset of 6465 samples represents mostly Mesoarchean (about 2.7 Ga), Paleoproterozoic (ca. 2.2–1.8 Ga) and Mesoproterozoic (ca. 1.6–1.3 Ga) rocks. Nearly all data are from Precambrian Fennoscandian Shield area, but heat production appears to be highly variable, and above global Archean and Proterozoic averages. Spot readings show an arithmetic average of 1.34 ± 1.19 μWm−3, and a range from 0.02 to 19.4 μWm−3. The interpolated areal average of the whole area is 1.42 ± 1.41 μWm−3. The high standard deviation of data is related to the geochemical characteristics of uranium (U), thorium (Th) and potassium (K) resulting in a skewed distribution of heat production. Mesoproterozoic anorogenic rapakivi granites, and late Paleoproterozoic Svecofennian granitoids show the highest heat production values in the range of 3–5 μWm−3. The results show no distinct dependencies of heat production with geological age, metamorphic grade nor seismic P-wave velocity, but an increasing trend of heat production with SiO2 content and decreasing trends of heat production with Fe2O3 content and with rock density are evident. Surface heat flow (44 borehole data values) correlates weakly with heat production (r = 0.35). The general heterogeneity of heat production calls for supporting information from other geophysical methods for better understanding of the thermal state of the lithosphere in Finland and beyond.

Radiometric survey in geological mapping of basement complex area of parts of Southwestern Nigeria

Radiometric methods were used to investigate the radioactive properties of rocks in parts of southwestern Nigeria with a view to interpreting the geological structure and abundance of natural radioactive elements in the main type rocks. The airborne radiometric dataset of Ikole Sheet and ground radiometric data recorded from eight traverses in Akoko axis of the study area were processed. Results presented as maps and profiles displayed variations of high and low radioactive concentrations across the area. These maps showed moderate to very high concentrations and very low to low concentrations of the radioelements; uranium (4.5-13.0 ppm); (LLD-low limit of detection -3.0 ppm), Th (25.0-70.0 ppm); (8.5-16.0 ppm) and K (2.0-4.0 %); but the most often observed values are in the range 2.5-7.0 ppm, 22.0-30.0 ppm and 3.0-4.0% for U, Th, and K respectively. High concentrations imply that the rocks are crystalline, undeformed and are rich in feldspar and U-Th bearing minerals. While low radioactivity is attributed to varying geologic framework compositions; weathered materials or fluids formed as a result of intense metamorphism. The radiometric datasets proved valuable in delineating different rock types and serve as a complementary tool in identifying geochemical zoning of rocks in the area.ReferencesAjibade A.C. and Fitches W.R., 1988. The Nigerian Precambrian and the Pan-African Orogeny, Precambrian Geology of Nigeria, 45-53.Ajibade A.C., Woakes M. and Rahaman M.A., 1987.Proterozoic crustal development in Pan-African regime of Nigeria: In A. Croner (ed.) Proterozoic Lithospheric Evolution Geodynamics, 17, 259-231.Appleton J.D., Miles J.C.H., Green B.M.R, Larmour R., 2008. Pilot study of the application of Tellus airborne radiometric and soil geochemical data for radon mapping. Journal of Environmental Radioactivity, 99, 1687-1697.Arisekola T.M. and Ajenipa R.A., 2013. Geophysical data results preliminary application to uranium and thorium exploration. IAEA-CYTED-UNECE Workshop on UNFC-2009 at Santiago, Chile 9-12, July, 12.Bayowa O.G., Olorunfemi O.M., Akinluyi O.F. and Ademilua O.L., 2014.A Preliminary Approach to Groundwater Potential Appraisal of Ekiti State, Southwestern Nigeria. International Journal of Science and Technology (IJST), 4(3), 48-58.Bierwirth P.N., 1997. The use of airborne gamma-emission data for detecting soil properties.Proceedings of the Third International Airborne Remote Sensing Conference and Exhibition.Copenhagen, Denmark.Grasty R.L. and Multala J., 1991. A correlation technique for separating natural and man-made airborne gamma-ray spectra. In: Current Research, Part D, Geological Survey of Canada, 111-116.Grasty R.L., Minty B.R.S., 1995a. A guide to the technical specifications for airborne gamma ray surveys. Australian Geological Survey Organization, Record.Grasty R.L., Minty B.R.S., 1995b. The standardization of airborne gamma-ray surveys in Australia. Exploration Geophysics, 26, 276-283.IAEA, 1991. Airborne gamma ray spectrometer surveying, International Atomic Energy Agency, Technical Report Series, 323.IAEA, 2007.International Atomic Energy Agency. Safety Glossary, Terminology used in Nuclear Safety and Radiation Protection-2007 Edition.Jones H.A. and Hockey, 1964.The Geology of part of’ Southwestern Nigeria.Geological Survey, Nigeria bulletin, 31.Kearey P., Brooks M. and Hill I., 2002. An Introduction to Geophysical Exploration.3rd ed. Oxford: Blackwell Science, 262.Milsom J., 2003. Field Geophysics: The geological field guide series, John Milsom University College, London. Published by John Wiley and Sons Ltd. Third edition, 51-70.MontajTM Tutorial, 2004. Two - Dimensional frequency domain processing of potential field data.Nigeria Geological Survey Agency (NGSA), 2009. Geological map of Nigeria prepared by Nigeria Geological Survey Agency, 31, ShetimaMangono Crescent Utako District, Garki, Abuja, Nigeria.Omosanya K.O., Ariyo S.O., Kaigama U., Mosuro G.O., and Laniyan T.A., 2015. An outcrop evidence for polycyclic orogenies in the basement complex of Southwestern Nigeria. Journal of Geography and Geology, 7(3), 24-34.Oyawoye, M.O., 1972. The Basement Complex of Nigeria.In African Geology. T.F.J. Dessauvagie and A.J. Whiteman (Eds) Ibadan University Press, 67-99.Oyinloye A.O., 2011. Geology and Geotectonic Setting of the Basement Complex Rocks in Southwestern Nigeria: Implications on Provenance and Evolution. Earth and Environmental Sciences, 98-117. ISBN: 978-953-307-468-9.Rahaman M.A., 1981. Recent Advances in the Study of the Basement Complex of Nigeria.First Symposium on the Precambrian Geology of Nigeria, Summary.Rahaman M.A., Emofureta W.O. and Vachette M., 1983. The potassic-grades of the Igbeti area: Further evaluation of the polycyclic evolution of the Pan-African Belt in South-western Nigeria. Precambrian Resources, 22, 75-92.Woakes M., Rahaman M.A., Ajibade A.C., 1987. Some Metallogenetic Features of the Nigerian Basement. Journal of African Earth Sciences, 6(5), 655-664.

Airborne Gamma-Ray Spectroscopy for Modeling Cosmic Radiation and Effective Dose in the Lower Atmosphere

In this paper we present the results of a $\sim$5 hour airborne gamma-ray survey carried out over the Tyrrhenian sea in which the height range (77-3066) m has been investigated. Gamma-ray spectroscopy measurements have been performed by using the AGRS_16L detector, a module of four 4L NaI(Tl) crystals. The experimental setup was mounted on the Radgyro, a prototype aircraft designed for multisensorial acquisitions in the field of proximal remote sensing. By acquiring high-statistics spectra over the sea (i.e. in the absence of signals having geological origin) and by spanning a wide spectrum of altitudes it has been possible to split the measured count rate into a constant aircraft component and a cosmic component exponentially increasing with increasing height. The monitoring of the count rate having pure cosmic origin in the >3 MeV energy region allowed to infer the background count rates in the $^{40}$K, $^{214}$Bi and $^{208}$Tl photopeaks, which need to be subtracted in processing airborne gamma-ray data in order to estimate the potassium, uranium and thorium abundances in the ground. Moreover, a calibration procedure has been carried out by implementing the CARI-6P and EXPACS dosimetry tools, according to which the annual cosmic effective dose to human population has been linearly related to the measured cosmic count rates.

The predictive power of airborne gamma ray survey data on the locations of domestic radon hazards in Norway: A strong case for utilizing airborne data in large-scale radon potential mapping

It is estimated that exposure to radon in Norwegian dwellings is responsible for as many as 300 deaths a year due to lung cancer. To address this, the authorities in Norway have developed a national action plan that has the aim of reducing exposure to radon in Norway (Norwegian Ministries, 2010). The plan includes further investigation of the relationship between radon hazard and geological conditions, and development of map-based tools for assessing the large spatial variation in radon hazard levels across Norway. The main focus of the present contribution is to describe how we generate map predictions of radon potential (RP), a measure of radon hazard, from available airborne gamma ray spectrometry (AGRS) surveys in Norway, and what impact these map predictions can be expected to have on radon protection work including land-use planning and targeted surveying.We have compiled 11 contiguous AGRS surveys centred on the most populated part of Norway around Oslo to produce an equivalent uranium map measuring 180 km × 102 km that represents the relative concentrations of radon in the near surface of the ground with a spatial resolution in the 100 s of metres. We find that this map of radon in the ground offers a far more detailed and reliable picture of the distribution of radon in the sub-surface than can be deduced from the available digital geology maps.We tested the performances of digital geology and AGRS data as predictors of RP. We find that digital geology explains approximately 40% of the observed variance in ln RP nationally, while the AGRS data in the Oslo area split into 14 bands explains approximately 70% of the variance in the same parameter. We also notice that there are too few indoor data to characterise all geological settings in Norway which leaves areas in the geology-based RP map in the Oslo area, and elsewhere, unclassified. The AGRS RP map is derived from fewer classes, all characterised by more than 30 indoor measurements, and the corresponding RP map of the Oslo area has no unclassified parts. We used statistics of proportions to add 95% confidence limits to estimates of RP on our predictive maps, offering public health strategists an objective measure of uncertainty in the model. The geological and AGRS RP maps were further compared in terms of their performances in correctly classifying local areas known to be radon affected and less affected. Both maps were accurate in their predictions; however the AGRS map out-performed the geology map in its ability to offer confident predictions of RP for all of the local areas tested.We compared the AGRS RP map with the 2015 distribution of population in the Oslo area to determine the likely impact of radon contamination on the population. 11.4% of the population currently reside in the area classified as radon affected. 34% of ground floor living spaces in this affected area are expected to exceed the maximum limit of 200 Bq/m3, while 8.4% of similar spaces outside the affected area exceed this same limit, indicating that the map is very efficient at separating areas with quite different radon contamination profiles.The usefulness of the AGRS RP map in guiding new indoor radon surveys in the Oslo area was also examined. It is shown that indoor measuring programmes targeted on elevated RP areas could be as much as 6 times more efficient at identifying ground floor living spaces above the radon action level compared with surveys based on a random sampling strategy. Also, targeted measuring using the AGRS RP map as a guide makes it practical to search for the worst affected homes in the Oslo area: 10% of the incidences of very high radon contamination in ground floor living spaces (≥800 Bq/m3) are concentrated in just 1.2% of the populated part of the area.

Monitoring airborne gamma ray spectrometer sensitivities using the natural background

In many airborne gamma-ray surveys, uranium and thorium sources are required to verify that the airborne system maintains the same sensitivity for each survey flight. Recently, due to radioactive material regulations, it has become increasingly difficult to transport these radioactive sources around the world. Measurements of the natural radioactivity of the ground, recorded as part of source tests carried out in Tanzania were analysed. These data involved three different aircraft at two bases of operation. The results have shown that in all cases the potassium and thorium background measurements were more consistent than the measurements from the uranium and thorium sources. In addition, the variations in the potassium and thorium measurements could be reduced even further by removing the effect of airborne radon daughter fluctuations using stripping ratios derived from measurements on concrete calibration pads.

NATURAL RADIOACTIVITY AT AN URANIFEROUS SITE

The aim of this study is to evaluate the soil composition, the radioactive isotopes concentration and the outdoor air Kerma in the region of the Uraniferous Province of Lagoa Real, Bahia State, located at northeast of Brazil. It has used data from an airborne gamma-ray survey previously carried out in the region, namely Projeto Sao Timoteo and computer simulations of the soil and radiation transport by the Monte Carlo method. The simulation, considering environmental characteristics, mainly soil chemical composition and density, provide means to evaluate the air Kerma rate due to radionuclides present in the different types of soils. The evaluation was carried out considering the main contributors to the terrestrial natural radioactivity: 40K and the isotopes of the radioactive series of 238U and 232Th. In radiometric studies used to quantify exposure to natural radioactivity, a normal trend showed that regions with high values of the surface distribution of radionuclides had the highest values of air Kerma. The highest value was found for soil type LVe1 (146.40 nGy.h-1 average, ranging from 23.97 nGy.h-1 to 450.62 nGy.h-1), this type of soil and most of the anomalies located in this region, being rich in silica minerals, is of granitic rocks type.

Envionmental applications of airborne radiometric surveys

Airborne gamma-ray measurements, primarily developed for uranium exploration (e.g. Bristow 1983), have many applications in environmental monitoring and geological mapping (e.g. IAEA 1991; Jaques et al.1997; Wilford et al. 1997). For example, they have been used to map radioactive fallout from nuclear accidents (e.g. Mellander 1989) and contaminant plumes from power plants (e.g. Rangelov et al. 1993) as well as monitoring the impact of uranium mining. Airborne measurements can be used for quick and effective mapping of large areas. Although the gamma-ray measurements record variations in the radioactivity of a relatively shallow surface layer (c. 0.3 m), the results are useful for both regional and targeted surveys. The results are normally presented as total gamma activity and as equivalent ground concentrations of uranium, thorium, potassium and other radionuclides (e.g. 137Cs) or as ratios (including ternary K, U, Th plots). Methods have been developed to separate natural and man-made radioactivity. This paper presents some examples of environmental applications of airborne gamma-ray surveys from Germany and the UK. In both cases, the results of multisensor (radiometric, electromagnetic and magnetic) airborne surveys are validated by ground measurements and sampling. The AERA project (Assessment of environmental risks by airborne geophysical techniques validated by geophysical field measurements) was an EC-funded project in south-east Germany, coordinated by the Geological Survey of Finland (GTK) (Gaál et al. 2001). A 1100 km2 site in the Zwickau area of Saxony was selected because of its extensive mining and industrial activities over several centuries. Uranium, black coal and nickel mining and smelting, military activities, modern heavy industry, and industrial and domestic waste have caused considerable environmental impacts. The HiRES-1 survey of central Britain was carried out to assess a range of environmental and resource applications of airborne survey data. The 14000 km2 area surveyed encompasses a wide range of rock and soil types. The area includes many urban centres and has a long history of extractive and manufacturing industry. There are regions with relatively high indoor radon levels and areas contaminated by fallout from nuclear weapons testing, the Chernobyl accident and discharges from the Sellafield nuclear fuel reprocessing plant. Small targets within the HiRES-1 area were flown as part of a collaborative GTK-BGS (British Geological Survey) project to investigate specific sites in more detail. These included landfills, colliery spoil heaps and gravel workings used for power station fly ash disposal. Although a multisensor approach was adopted for these projects, this paper concentrates on the environmental applications of airborne gamma-ray data.

An airborne gamma-ray spectrometry survey of nuclear sites in Belgium

As part of a wider study to define the existing background levels in Belgium an airborne gamma-ray survey was conducted in two areas associated with nuclear sites. In the Mol area, the survey zone included areas surrounding the SCK-CEN nuclear research centre, and its associated neighbourhood which includes radioactive waste stores, fuel manufacture and fabrication facilities and an international accelerator laboratory. In the vicinity of Fleurus, the survey included the IRE complex with radiochemical laboratories, irradiation facilities and stores, and isotope production accelerators. The survey was conducted using a twin engined helicopter equipped with a combined scintillation and semiconductor spectrometer. The system was installed and tested in the UK, and then transferred to Belgium for operations. The complete survey was conducted successfully within 1 week. The results provide a comprehensive record of the radiation environment of the nuclear sites at time of survey, and show a range of signals associated with the types of activity present in each area. They confirm that radiation fields are largely confined to the operational sites, and provide a traceable record against which future changes could be assessed. The demonstration of efficient deployment between two European countries, coupled with rapid mapping of many different radiometric signals around these sites confirms the utility of the airborne gamma spectrometry approach for accurate definition of enhanced radiation fields. This has important implications for emergency response.

Relationships Between Soil Properties and High-Resolution Radiometrics, Central Eastern Wheatbelt, Western Australia

A quantitative investigation was undertaken to ascertain the relationships between radiometrics and surface soil properties within a 77 km2 survey area, on the Elashgin Creek catchment, Wyalkatchem, Western Australia. A high-resolution airborne gamma-ray survey, with a measurement ‘footprint’ width of approximately 40 m and length of 80 m, provided measurements of radionuclide distributions across the study area. Ground-based gamma-spectrometry measurements, with a much smaller ‘footprint’ of one metre diameter, were also made at the majority of sampling sites. Field texture and gravel content from 132 sampling sites were recorded, with particle-size and mineralogical analysis conducted on a selection of sites. Mineralogical analysis provided an understanding of the sources of radionuclides. Using discriminant function analysis (DFA), areas of shallow soil over rock and rock outcrop were successfully discriminated using airborne radiometric and DEM data. The presence or absence of gravel grades was also successfully discriminated with radiometric data using DFA. In addition, a statistically significant correlation was identified between airborne thorium/potassium ratio and ironstone gravel content in the top 0 to 10 cm of soil (r2 = 0.56, P-value < 0.001). Stronger linear relationships were identified between airborne data and surface texture (e.g., 0–10 cm % clay and total count, r2 = 0.71, P-value < 0.001). Signal attenuation prevented the accurate determination of deeper subsurface soil texture (e.g., 20–30 cm % clay and total count, r2 = 0.24, P-value < 0.05). Of the airborne radiometric data, total count exhibited the strongest correlation to soil texture and potassium the least. It is concluded that high-resolution radiometric data can aid the mapping of important soil properties such as shallow granitic bedrock, presence or absence of gravel and the percentage clay in the top 0–10 cm of soil.

Regional‐scale sedimentation process models from airborne gamma ray remote sensing and digital elevation data

Airborne gamma ray survey data were used to provide information on potassium, thorium and uranium concentrations in surface soil and rock in arid central Australia. Spatial patterns in these radioelements allow tracing of paths of sediment at catchment scale. Survey elevation data are combined with contour data to produce digital elevation models for terrain analysis, tracing of sediment flow paths and modelling of extreme floods. Gamma ray data show consistent variation with slope, a limited range of drainage areas, and erosion/deposition models derived from the conservation of mass equation. Supply-limited sediment transport models give a reasonable reproduction of observed radioelement distribution but some elements of the distribution pattern reflect the area inundated by 500–1000 year floods rather than the effects of simple downslope movement. Partial area sediment supply models are derived by downstream accumulation of erosion and deposition rates calculated using the conservation of mass equation with transport laws based on slope alone and stream power. Comparison with observed radioelement patterns suggests that both transport laws apply in different parts of the landscape. Regional-scale sediment transport models will require a range of models depending on location in the landscape and event frequency. This approach may allow estimation of sediment delivery ratios. Copyright © 2001 John Wiley & Sons, Ltd.

Chernobyl-derived radiocesium in heather honey and its dependence on deposition patterns.

Gamma-ray spectra were measured from Scottish heather honey samples gathered from hive locations with associated airborne gamma-ray survey data. The honeys all contained radiocesium, with activity concentrations ranging from 43-680 Bq kg(-1) 137Cs, and 134Cs/137Cs ratios consistent with Chernobyl deposition. Activity concentrations in honey were highly correlated with ground deposition within 2.5 km of the hive location over two successive years. Both isotope ratios and the quantitative relationships between environmental and food levels suggest that weapons testing fallout is significantly less available than recent deposition. The implications for design of future monitoring programs and radiological consequences are discussed. The whole-body retention of 137Cs in honey ingested by a volunteer was consistent with the ICRP's metabolic model for cesium.

Correcting aerial gamma-ray survey data for aircraft altitude

In their ascent to the aircraft detector system, the gamma-rays recorded in airborne radiometric surveys are attenuated, first by the surface materials wherein they originate, then by the intervening atmosphere. Increased ground-clearance thus entails reduced count-rates. It also implies diminished spatial resolution, because the same cone of incident radiation derives from progressively larger ‘footprints’ that, for a given sampling rate, increasingly overlap. But suitable post-processing of the gridded, twodimensional imagery can be used to correct these types of height-dependent degradation and hence produce sharper, quantitatively useful maps of radioactive isotope distribution. An essential prerequisite for such inverse filtering is noise-suppression, achieved here through maximum-noise-fraction (MNF) transformation of multi-channel data. High-frequency noise amplified by the deconvolution step is brought under control by a variant of Wiener filtering. The combined de-noising and deconvolution process is illustrated by application to an airborne gamma-ray survey from the Marble Bar area, Western Australia.

Airborne gamma-ray spectrometry in uranium exploration

Abstract Uranium exploration is of paramount importance to India to maximize the indigeneous resources to meet the ever increasing demand for energy. Comprehensive regional and local zones of uranium mineralization are needed to be resolved. Such data comprise information on radioactivity in various energy ranges and on lithological knowledge. Airborne gamma-ray spectrometric techniques are particularly suited to provide spatial information. This review briefly discusses the conventional data presentation, statistically significant maps and the schemes suitable for classification of mineralized zones. A brief introduction is provided to airborne gamma-ray data, their acquisition, analysis, processing and interpretation to bring out their role in designing suitable models of uranium resources. State-of-the-art in uranium exploration covers radiometric mapping through airborne gamma-ray surveys. Through the examples of the Indian work done during this decade, the state-of-the-art and its usefulness in the country has been illustrated. It is concluded that the high sensitivity airborne gamma-ray spectrometric surveys coupled with modern methods of data analysis can further narrow down the targets.

Tin exploration at Mount Isa — A case history

Abstract Minor tin, tungsten, tantalum and beryllium mineralization occurs near Mount Isa in pegmatites along the eastern rim of the Queen Elizabeth pluton, a multi-phase pluton in the Proterozoic Sybella Granite batholith of northwest Queensland. The Queen Elizabeth pluton and adjacent metamorphic rocks were explored by Mount Isa Mines Limited during 1980–1983 to assess the tin potential of the area. An orientation study was carried out over an existing tin deposit, using stream-sediment, soil and rock-chip sampling, magnetometer and scintillometer surveys and percussion drilling. This defined the geophysical and geochemical features of the deposit, and indicated that monazite and cassiterite had related distributions and could be used as heavy-mineral tracers. Broader exploration used stream-sediment and rock-chip sampling, and airborne magnetic and gamma-ray spectrometry surveys. The eastern rim of the Queen Elizabeth pluton was found to be enriched in thorium and tin, and an area of approximately 2000 × 400 m with anomalously high tin values in bedrock was delineated in a part of the pluton not previously known to be mineralized. An economic assessment led to relinquishment of the area at that stage. Although no new areas of economic mineralization were found, the study indicated that in this region the thorium gamma-ray response can be used in regional airborne surveys to define areas of prime interest for tin exploration, and that monazite in stream sediments can be used as a heavy-mineral tracer for pegmatitic tin mineralization.

Uranium Mineralization in Hopi Buttes, Arizona: ABSTRACT

The Hopi Buttes dominate the landscape north of Holbrook, Arizona, rising to heights of ~1,000 ft (305 m) above the surrounding countryside. The buttes, erosional remnants of lava-filled diatremes and associated sediment-filled diatremes, are approximately 5 m.y. in age. The volcanic rocks of the diatremes are limburgite and monchiquite, which are distinguished from normal alkalic basalts of the Colorado Plateau in their extreme silica unsaturation, high water, TiO2, and P2O5. Many trace elements are also unusually abundant, most notably Zr, Ba, Nb, Ce, and U (average value of about 4 ppm U compared to an average of 1 ppm for continental basalts). Many of the diatremes are filled with local maar lake sediments believed to have been deposit d in part by rising thermal solutions. Limestone lake beds locally resemble travertine deposits and contain high concentrations of phosphate, sulfate, Ba, Sr, and As, as well as U and Se. Areas of high Se content are recognizable in the Hopi Buttes by the abundance of Astragalus patersoni (loco weed). Approximately 300 diatremes occur in the Hopi Buttes area. Of 79 studied during the past year, 35 contain lake-bed deposits with radioactivity exceeding background levels. Scintillometer traverses have shown 20 of these diatremes to have radioactivity exceeding 5 times background. An airborne gamma-ray survey shows sharp-peaked anomalies over all 20 of these diatremes. Hydrogeochemical sampling in the area also revealed anomalous concentrations of uranium in spring and well waters from the Hopi Buttes area. Uranium ore was mined during the 1950s from the Morale claim. Production records show the average grade for 186 tons of ore was 0.15% U3O8. Extensive drilling in this diatreme in October 1979 revealed intervals within limestone and siltstone maar lake sediment up to 20 ft (6 m) thick and 500 × 300 ft (152 × 91 m) in area containing an average of 0.015% U3O8. The potential for uranium in the Hopi Buttes is for low grade deposits within 50 ft (15 m) of the surface, some of which may contain on the order of 100 tens of U3O8 per diatreme. End_of_Article - Last_Page 802------------