[en] The Ilimaussaq intrusion may be characterized as a geochemically abnormal region, since its rocks are strongly enriched in a number of rare elements, including elements which accompany uranium in deposits in other parts of the world. Examples are the rare earth metals, Nb, Ta, Be, Li, and metals as Cu, Pb, Zn, Mo and Sn. It was proposed to develop and test a model for the supergene distribution of uranium and accompanying elements around a known uranium deposit associated with an alkaline intrusion. The most promising results are those obtained by the PCA technique. For a more preliminary study of a region fjord and river sediments might be the sampling target. These sediments were found to be mixtures in which the proportion of material from the Ilimaussaq U-deposit could be evaluated by the PCA technique involving a distance function related to the loadings in the first principal dimen- sion of the elements characterizing the Ilimaussaq Intrusion. One of the major features of the material sampled in this study is the general high degree of preservation in the sub-arctic environment of the primary igneous mineralogy in the sediments, and in other areas, the structure of data should be investigated in order to test them in this respect. One obvious way is X-ray diffraction analysis. It was indicated that uranium is selectively absorbed on the organic material in lakes and is able to reflect the concentration of U in the lake waters, informing the ultimate potential of the drainage areas in question. It is however yet to be established whether the correlation of uranium and the organic material of the lake sediments actually reflects the long term U concentrations of the lake water. The use of the cluster analysis and discriminant analysis techniques proved to be of lesser value in this project. (author)

[en] Two types of mineral occurrences near the town of Narssaq in South Greenland are recorded to be worth mining in the near future: the uranium occurrences at Kvanefjeld in the northern part of the Ilimaussaq intrusion and the zirconium occurrences in the southern part on the south coast of the Kangerdluarssuk fjord. Consideration of the environment plays a large part in discussions regarding the exploitation of these minerals. A report is given of the geochemical, ecological environmental investigations carried out at Narssaq since 1974. (BP)

[en] The U-Th-REE deposit located at the Kvanefjeld plateau in the north-west corner of the Ilimaussaq alkaline complex, South Greenland, consists of lujavrites which are melanocratic agpaitic nepheline syenites. The fine-grained lujavrites of the Kvanefjeld plateau can be divided into a northern and a southern part with an intermediate zone between them. The northern part is situated along the north contact of the Ilimaussaq complex and continues east of the Kvanefjeld plateau as a lujavrite belt along the contact. This part has relatively 'low' contents of U, Th, and REE, and hyperagpaitic mineralogy is restricted to its highest-lying parts. The fine-grained lujavrites of the intermediate and southern part of the Kvanefjeld plateau occur between and below huge masses of country rocks which we show are practically in situ remnants of the roof of the lujavrite magma chamber. These lujavrites have high contents of U, Th, and REE, and hyperagpaitic varieties with naujakasite, steenstrupine and villiaumite are widespread. We present a model for the formation of the fine-grained lujavrites of the Kvanefjeld plateau. In this model, an off-shoot from the large lujavrite magma body in the central part of the complex intruded into a fracture zone along the north contact of the Ilimaussaq complex and was forcefully emplaced from north-west to south-east. The intruding lujavrite magma was bounded to the west, north, and at its roof by strong volcanic country rocks, and to the south by the weaker, earlier rocks of the complex. The magma stored in the fracture crystallized, squeezing volatile and residual ele-ments upwards. A subsequent violent explosion opened up fractures in the weaker southern rocks, and the residual volatile-enriched magma was squeezed into fractures in augite syenite, naujaite, and also in the overlying volcanic roof rocks. The removal of the volatile-rich lujavrite magma in the upper part of the fracture-bounded magma chamber made room for the rise of volatile-poor magma from the lower part of the magma chamber, and these lujavrites crystallized to form the northern continuous lujavrite belt. Transfer and accumulation of volatile and residual elements in a lujavrite magma crystallizing below an impervious cover played a key role in the formation of the Kvanefjeld U-Th-REE deposit, as it also did in the crystallization of the lujavrite magma body in the central part of the Ilimaussaq complex. (Author)

[en] This study is part of a more detailed investigation of the stability and the natural decomposition process of steenstrupine, initiated to help delineate the conditions during the later stages of solidification of the Ilimaussaq rocks. Interest in steenstrupine also arises from the potential importance regarding Kvanefjeld as a uranium ore reserve, steenstrupine being the most important uranium-bearing mineral in the Kvanefjeld area. Major emphasis has been placed on the decomposition of steenstrupine in Na²CO³ solution in the 200 deg to 600 deg C range at pressures up to 1000 bars. (author)

[en] A Th- and U-enriched granite has been found within a sequence of high-grade metamorphic gneisses and migmatites in the Flekkefjord area bordering the S Rogaland anorthosite province in SW Norway, where the country rocks and the other intrusions all have very low contents of these elements. The major-element distribution within the Homme granite suggests a certain magmatic differentiation, although a K- and Si-rich zone in connection with the discordant northern contact is supposed to be due to assimilation of felsic country rocks. This model was tested by studying the radioelements which exhibit the lowest values exactly in the northern K- and Si-rich zone, thus supporting the model of assimilation, while the alkali enrichment in the southermost part is connected with high contents of radioelements, thus suggesting a rest magmatic stage. (Auth.)

[en] A great variety of investigations have been made on the distribution of Th and U in the Ilimaussaq alkaline, South Greenland. The major emphasis has been placed on economic assessment of the Kvanefjeld uranium deposit but attention has also been given to the Th and U contents of rocks and minerals outside the deposit. In the present study, we present Th and U values largely obtained by laboratory gamma-ray spectrometric (GRS) analysis of a large collection of representative samples taken from all rock types of the intrusion. The results are discussed in relation to current knowledge and ideas on the petrologic evolution of the Ilimaussaq intrusion. The behaviour of Th and U in igneous systems is moderately well known. During closed-system fractional crystallization, Th and U are generally excluded from the cumulus phases and attain higher levels in successive residual magmas. In most cumulate sequences, they are held in the trapped liquid (mesostasis). In both magmas and cumulates, the Th/U ratio remains virtually unchanged from the ratio of the parent magma. Only a few examples are known where significant amounts of Th-, U-rich cumulus phases (e.g. perovskite, eudialyte) crystallise and disturb the Th/U ratio. At many loctions, fractional crystallization occurred under open-system conditions and Th and U were redistributed by mobile fluids. These are frequently concentrated in roof zones or added to the surrounding country rocks. Elsewhere, post-magmatic Th-U metasomatism may be so intense that few of the primary, magmatic features are preserved. Previous invetigators of Th and U at Ilimaussaq have found evidence for closed- and open-system conditions at different stages of the evolution, and also for post-magmatic metasomatism. (author)

No abstract available

[en] Experience with the use of γ-spectrometry for field determination of thorium, uranium, and potassium has shown that sampling of geologic formations by direct γ-spectrometric analysis of rock outcrops and beach sand deposits is more efficient than collecting material for later radioelement analysis in the laboratory. A portable γ-spectrometer is quick to use and provides a direct means of selecting optimum sample patterns and a single field determination of the natural radioelements by γ-spectrometry is representative of a rock mass of as much as several tens of kilograms. The problem of determining the coefficient matrix which characterizes the γ-spectrometer conversion equations is considered. An accurate evaluation of this matrix is more difficult than in γ-spectrometric analysis of small samples in the laboratory. However, a field γ spectrometer is readily calibrated with Th-U-K standards, which are only a few meters in diameter, provided that the directly measured calibration constants are corrected for the finite dimensions of the standards. If the chemical composition of the geologic formations to be sampled by field γ-spectrometry is very different from the chemical composition of the standards, another set of correction factors must be applied to the calibration constants. To allow for corrections like these, a computer model was developed whose first part permits an accurate calculation of the spectral composition of the γ flux near the surface of large, but finite, as well as semi-infinite, source media. The second part of the model is used for a simplified calculation of the pulse-height distribution produced by the γ flux at the output of a crystal photomultiplier assembly. Therefore, besides giving a practical solution to the calibration problem in field γ-spectrometric rock analysis, a method for the prediction of detailed scintillation spectra from various geologic formations is also presented. (U.S.)

[en] The project described in this report is a contribution to a large project on the beneficiation of the Kvanefjeld uranium deposit in the Ilimaussaq intrusion in South Greenland. The main object of our project has been to undertake laboratory experiments on steenstrupine in order to define the optimum extraction conditions. A pressurized carbonate leaching method was introduced. The Risoe experiments are carried out on bulk samples of the ore while we decided to study the minerals, first of all steenstrupine, and carbonate solutions as leaching media. Our experiments demonstrated that the leaching conditions arrived at by the Risoe group give the highest recovery and thus may be termed the optimum conditions using sodium carbonate leaching methods. Studies of the solid products left after the leaching experiments by means of the electron microprobe show that the grains of steenstrupine remain and that the leaching of uranium proceeds from the margins of the grains and towards their interior. We decided also to study the effect of applying ammonium sulphate solutions. These gave significantly higher recoveries. We consider the results of the experiments using ammonium sulphate solutions as an essential new information on the extractability of the Kvanefjeld ore and as a main result of our study. It is demonstrated that in the 13 types of rocks examined, including lujavrites, 25-75 % of the thorium and 2-58 % of the uranium contained in the rocks can be leached out and are thus not firmly bound in the minerals. (author)

[en] The development of a relatively rapid neutron activation technique, involving fast-transfer of samples from the reactor followed by Cerenkov counting, has allowed us to extend analytical coverage of Li and F in the Ilimaussaq lujavrites and their minerals. On geological grounds the lujavrites have been regarded as crystallising from the final agpaitic magmas at Ilimaussaq. In agreement with this, contents of Li and F - which are normally maximal in residual magmas - have been shown to attain their highest levels within the lujavrites. However, these studies failed to agree on the absolute contents of Li in the lujavrites. For aegirine lujavrite and arfvedsonite lujavrite, Gerasimovsky reported averages of 155 and 791 ppm, respectively, whereas Ferguson found only 90 and 266 ppm. Hamilton only reported 80 ppm Li in a single sample of arfeedsonite lujavrite. More recent mapping within the intrusion has revealed further divisions within the lujavrite sequence. These subdivisions provide an increased geological control for the interpretation of Li and F data. Samples of the various lujavrite varieties were taken from the drill cores obtaned in 1958, 1962 and 1969. (author)