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Principles of Modern Uranium Exploration by John W

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Principles of Modern Uranium Exploration by John W 235 236 URANIUM - FUEL OF THE FUTURE 238 The Athens Symposium followed the recommendations of a panel meeting in April 1970 on uranium exploration geology. It was attended by 220 participants representing 40 countries and two international organizations; 43 papers were presented. SUPPLY CHALLENGE An overview of the supply challenge of uranium was given by Mr. Robert D. Nininger, of the USAEC, who acted as chairman of the Symposium. He outlined the major topics and problems to be discussed during the conference, with the aim of meeting this challenge: "Uranium deposits in sandstone and quartz pebble conglomerates presently represent the preponderance of uranium resources. Yet there is a question whether geologic limitations on the occurence of such deposits may preclude their discovery in numbers sufficient to meet the eventual resource needs. New types of deposits, low in grade but larger in size, representing the equivalent of the porphyry copper deposits, may supply the bulk of future resource additions. Further investigation is needed on the characteristics of such deposits and the means of their identification. Similarly, additional investigation is needed to determine whether limits on the more conventional deposits do, in fact, exist, and, if not, what advanced approaches to rapid identification of additional such deposits may be employed." "The world probably cannot rely on the very low-grade deposits such as most uraniferous black shales for both and environmental economic reasons. There is probably a minimum grade between 100 and 500 parts per million below which uranium deposits cannot be effectively exploited for nuclear power." Mr. Nininger noted that the Symposium marked the end of the initial period of expanding activity in the field of uranium raw materials, and a much-needed beginning of fuller international co-operation and exchange of information in the critical area of uranium geology and exploration. Principles of Modern Uranium Exploration by John W. King, an IAEA Expert on Nuclear Raw Materials Prospecting, formerly in Mexico, and now Project Manager in Turkey. Exloration for uranium has grown in a quarter of a century from an activity conducted in wartime secrecy in a half dozen countries, to one pursued as openly as industrial competition permits in some 50 countries. Reserves of more than 2 000 tons are known in each of 16 countries who have combined current production capability in excess of 30 000 tons annually. This reserve and production capability must be augmented soon by increased exploration worldwide to meet the demand for nuclear energy that is expected late in this century. 21 235 236 URANIUM - FUEL OF THE FUTURE 238 Uranium reserves are approximately equally divided among those in Precambrian quartz pebble conglomerates, those in younger sandstone hosts, and those in vein-type deposits. EXPLORATION STRATEGY The search for uranium in this variety of deposits is no longer dominated by the lone prospector with a hand-carried Geiger counter. Uranium is sought nowadays largely by team effort of professional geologists with ever more sophisticated geophysical equipment and geochemical technology to support them. Similarly, yesterday's pick and shovel mining operation has grown to where the smallest uranium mines today utilize mechanical equipment, ventilation systems, and even accounting procedures that were used only in larger mines a quarter eentury ago. Indeed, the mines of tomorrow must be capable of moderately large sustained production to be economically competitive. Detailed cost studies indicate that a target of about 2 000 tons of uranium in ore grading at least one kilogram per ton, discovered within a radius of about 100 kilometers, would be a minimum economic objective for any uranium project that would need to sustain a treatment plant. Those studies indicate that uranium milling facilities with capacity of less than about 250 tons of ore per day are neither efficient nor economic. At a more favourable operating level of 350 tons of ore per day, a plant could treat approximately 125 000 tons of ore grading one kilogram per ton to produce some 120 tons of yellow cake annually, which would deplete the 2 000 tons minimum reserve in a reasonable 16-year amortization period. A larger or richer deposit might be found but the economic decision would be made in the range described. Uranium exploration technology is not unique but it is notable for the heavy emphasis on the radiometry of a number of isotopes and on the differential solubility of uranium in the oxidized and in the reduced state. The tactics of exploration for deposits in the sedimentary terrain are very different from those applied to vein-type deposits. Exploration for vein-type deposits is a direct search, oriented toward the identification of a radiometric anomaly and the determination of its persistence in depth and laterally. The anomaly in the sedimentary terrain may not be the surface expression of a related ore deposit but may serve best as an indicator of favourable ground in which to drill. An area may be reconnoitered by widely spaced drilling followed by more detailed exploration in the more favourable parts; drilling patterns may be developed statistically at either stage. OCCURENCE OF URANIUM How does uranium ore occur in nature and where do we look for it? Uranium is an essential element in more than 100 minerals but nowadays uraninite and coffinite preponderate in mill feed everywhere. Uraninite is the oxide; coffinite is the silicate of quadravalent uranium that contains a variable amount of hydroxyl in substitution for silica. These minerals have been concentrated to form economic ore deposits in conglomerate beds, probably as ancient placers; in sandstones from moving ground waters; in veins and at intrusive contacts; and in a variety of other environments. 22 !I235 J236 URANIUM - FUEL OF THE FUTURE "238 The poor geographic distribution, that is, the localized concentration of uranium ores is worth noting. The conglomerate ores occur in an area of less than 200 square miles in Canada and in a single structural basin in South Africa. The sandstone ores are similarly concentrated. More than 90 per cent of the U.S. reserves, which is equal to two thirds of the world's sandstone reserves, are found at Grants, New Mexico and in Central Wyoming. Half of the ores in "veins and other deposits" are found in South West Africa, France, and Australia. The example of the minimum economic ore deposit might be continued to consider its fuel value and cost. At a (rounded) requirement factor of four tons of U3O8 per 1 000 MW(e), the 2000 tons would fuel a 500 MW(e) plant for its 30-year life. In the United States, for example, 2000 tons of yellow cake could be found and produced under favourable circumstances at an average cost of around $20 to $30 million, but those costs are relatively low because the mines and mills are several times larger than the minima considered here. Today's cost of 200 tons of yellow cake in the world market would be about $25 million or more. The cost differential between buying yellow cake and producing it depends largely upon successful exploration and efficient exploitation. If a minimum uranium district is defined as a center of uranium mineralization with 2000 tons or more of U3O8, then only about 40 such localities can be counted in the countries listed by the NEA/IAEA Working Party on Uranium Reserves1. It is interesting to note that those districts, and a few others, represent the successful outcome from among hundreds of projects where exploitable quantities of uranium were not found, and from among many thousands of examinations that were not sufficiently favourable to justify recommendations for physical exploration. Only one in several thousand prospects that are examined, and a very low percentage of the physical exploration projects, will ever develop into exploitable ore deposits. In other words, most exploration fails! Reference 1. Uranium Resources, Production and Demand, published by OECD, Paris; ISBN 92-64-11121-2. "In the Field"- in the Himalayan Foothills by Paul Fent, recently returned from Pakistan Accidentally, somebody had failed to switch off the Geiger counter; accidentally, somebody glanced at it. That is how Pakistani geologists returning from a routine survey along a mountain track discovered "radioactive anomalies" — that was all that could be said at the time - in the foothills of the Suleiman Range which belongs to the western part of the Himalayan arc. The presence of uranium was soon established. 23.
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