[en] The Madadzang uranium occurrence is situated about 250km SSW of N'djamena and at only 5km from the Cameroon border. Tectonically the occurrence is located close to the eastern arm of the Benue Trough and it lies within a well-defined intrusion of alkaline granite. Two uranium occurrences at a distance of 7km from each other have been recognized but only the southern one, Madadzang, has been investigated so far. The uranium mineralization consists of autunite at surface, and uraninite, Y-rich-coffinite and kasolite at depth. Some sulphides are present. Thorium is very low in all mineral phases but yttrium is unusually high. Two inclined reconnaissance drill holes have intersected 20 and 29m of mineralization, assaying more than 700ppm U, the maximum value being 0.95% U over 1.3m. The Madadzang prospect consists of an essentially subvertical uranium mineralization of primary uraninite and uranium silicates, probably of hydrothermal origin, in a homogeneous but fractured alkaline intrusion. The mineralization is occasionally expressed in highly mineralized veinlets probably structurally controlled. A possible metallogenic relationship between the mineralization and the Benue aulacogene is suggested. Both the vertical and the lateral extension of the mineralization are still untested. (author)

[en] Madagascar is well endowed with radioactive raw materials. Some of these occurrences have been partially exploited, yielding substantial amounts of uranium and thorium. Uranium mineralizations are present in a number of different geological environments both igneous and sedimentary. Viable deposits of uranothorianite have been proved and partially worked in the south of the island near Fort Dauphin. The deposits consist of numerous lenses of uranothorianite in pyroxenite occurring over an area of 80x30 km. The age of the uranothorianite is 485 m.y. Pegmatites, occasionally uraniferous, are widespread throughout the crystalline basement of the island but they seem to offer only a mediocre economic potential. Their age can be correlated with the last Pan-African orogeny. Interesting uranium occurrences are known in the sedimentary platform covers of Madagascar: carnotite in Karroo sandstones at Folakara and uranocircite (barium autunite) in Plio-Pleistocene lacustrine sediments near Antsirabe. Thorium is present in economic quantities on the southeast coast of the island where it forms beach placers of monazite. These deposits have been intermittently exploited in the past. Other radioactive mineralizations include occurrences of bastnaesite or pyrochlore in tectonically controlled perialkaline intrusions of post-Jurassic age. The geological setting of all these occurrences seems to indicate a considerable potential for radioactive raw materials in a variety of environments, most of them comparable, in age and minerogenetic processes, with other occurrences or deposits throughout the world and particularly in Gondwana. (author)

[en] The advantages to the developing countries of exploiting their uranium deposits in the next two decades to aid their own economic growth are considered. It is pointed out that in spite of the little known geology of these countries less sophisticated surveying methods have turned up large uranium deposits even in developed countries. Carborne surveys with simple crystal-detectors coupled to scintillators can be effective. Intelligent exploration in developing countries can be cheap due to low labour costs and less stringent environmental restraints and the uranium found could be sold to developed countries for their nuclear power programme. (U.K.)

[en] All recent uranium exploration activities in the wet tropical Andean regions of Ecuador and Colombia are reviewed. During the last few years, both countries have been the object of intense exploratory efforts, and a number of significant uranium occurrences have been discovered. The exploration methods used have been LANDSAT imagery interpretation, photogeology, airborne spectrometry, ground radiometry, emanometry, strategic and tactical geochemistry, detailed geological mapping, trenching and drilling. The applicability of these techniques and their relative cost/effectiveness are examined. Case studies are discussed, typical of the wet tropical environment of Central Colombia, where two especially promising uranium occurrences (the Berlin and Zapatoca prospects) have been discovered and intensively explored. The exploration lessons learned in the humid rugged environments of the Northern Andes is thought to be broadly applicable, not only to South and Central America, but also to several Southern Asian regions where wet tropical conditions, coupled with alpine orogenies, create a very similar environment. (author)

[en] In 1978 the government of Paraguay embarked on a programme covering the whole national territory to assess the potential of its radioactive raw materials. This programme was carried out, with some assistance from the International Atomic Energy Agency (IAEA), for a period of six months. Given the vastness of the country and the limited means available, precise metallogenetic targets were selected as a guide for the search. A severely cost-controlled approach was chosen on the assumption that in geologically poorly explored countries even a limited exploration expenditure can still be very effective in selecting attractive targets for follow-up work. Maximum emphasis was put on the practical training of national personnel, particularly on exploration strategies and management. Satellite imagery, photo interpretation, airborne and car-borne reconnaissance, field and laboratory geochemistry and, above all, direct field investigation were the techniques used. Three metallogenetic themes were selected as having good exploration potential: (1) uraniferous calcrete; and uranium in (2) continental sandstones, or in (3) orthomagmatic differentiations. Significant areas of interest and one significant occurrence were pinpointed during this first six months regional exploration phase. (author)

[en] The main Colombian geostructural units are discussed in relation to their uranium possibilities. The characteristics of the more representative models of Colombian uranium occurrences are described and the possibility that some of them could be developed into workable uranium deposits is studied. Where possible, genetic interpretations are provided or suggested for some uranium occurrences. (author)

[en] During the last eight years at least six carbonatites or clusters of carbonatites have been discovered in the western parts of the South American cratons. In contrast to the carbonatites of the eastern part of the South American shields, which have been well studied and placed in a tectonic context together with the West African carbonatite provinces, those of the western part of the South American cratons have received litte attention. This paper is a compilation of published and original data on these occurrences, their geology, geochemistry, structural setting and radioactive mineral potential. An exploration strategy is devised based on experiences in this rainforest-clad area and the peculiar genetic aspect of carbonatites. Some details of a possibly new uranium mineral encountered in Cerro Cora carbonatite are given. (author)