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Show Surveying by Air Not As Accurate as Reported Airborne radiation surveying has proved a rapid, cheap, and effec- bve method for uranium explora tion. The technique is relatively simple when applied as a supporting function of a general exploration program and can be managed and financed with a small staff and resonable capital investment. Airborne surveying can also be done on a contract basis and several commercial survey companies ' effer this service. The effective- f Bess of the technique can be meas- re in terms of millions of dol-j tars worth of uranium ore that has been detected from the air smd that has resulted from mine ' production in the last three years. ( Equally valuable has been the ex- tension of mineralized areas and i the information supplied by air- borne work used in guiding ground reconnaissance. , Uranium ore on the ground can i be located from the air by de- . tecting the radiation that is al- 1 ways given off by natural uran- lum ore. This is generally true several qualifications are In order. Sbut Airborne surveying can re-I . suit in the detection and location of outcropping uranium ore only f If the outcrop Is large enough or high enough in grade. The actual ' size and grade that can be de-i tected depends upon the altitude ef the survey, the speed at which , the aircraft flies, and the type of J Instrument utilized. At 100 ft. or less with the proper technique, a survey should be able to detect an outcrop several hundred square feet in area of an average grade of 0.1 percent I! 308. Generally speaking a smaller area can be detected if the grade is higher. At between 200 and 500 ft. a survey should detect all outcrops with an area larger than 1,000 sq. ft. and a grade of around 0.2 or 0.3 percent U308. These are very general estimates and are offered only to give an Idea as to what might be expected. Certain other factors must be considered in the evaluation of the technique. Production of radia-tion is not unique to uranium ore. There Is radiation present at any location on the earth and what to look for is an increase in rate of radiation and not lust the detection of radiation. The indication of natural radiation by an Instrument Is called the background reading and atl indications of additional radiation or "anomalies' are measured In terms of increase over the background reading. There must be enough uranium ire outcropping at the surface to supply enough radiation for a readable increase. With the aircraft flying at some particular altitude there may be small amounts of uranium mineralization outcropping below that cannot be detected. The ore must be exposed at the surface (for all practical purposes) because a foot or so of barren overburden will render undetectable the gamma radiation from the ore beneath it The grade of outcropping ore cannot be determined by an air-! borne survey, although the general extent of a deposit can be determined in special cases where something Is known of the geolog-I leal control and it is possible to 'fly close enough to the outcrop I 120-50 feet). It is necessary to i fly close to any outcrop or above any area because the radiation given off by uranium decreases in intensity as you get farther away from it.. Flying at altitudes above 500 feet, many small areas of mineralization will not be detected even with the best instruments. Outcrops that are delected at or above 500 ft will be difficult to locate on the ground and difficult to partially evaluate by an observer from the air. To be effective, an airborne survey must be planned on th basis of geologic guidance. The probability of success is greatly increased by flying not merely geographical areas but areas selected on geologic favorability. Some examples of effective application would be surveying cf areas that might be extensions of already existing deposits, extension of structures known to b favorable, or extensions of sedimentary horizons know to be favorable. On the Colorado Plateau the nature of terrain and outcrops makes it a very favorable area for the application of low level airborne surveying. |