Research On Mechanism And Application Of Geogas Measurement In Concealed Uranium Deposit Prospecting

With the development of China's nuclear energy and national defense nuclear resources strategy,uranium ore prospecting direction has gradually shifted to deeply concealed uranium exploration.Nowadays,there is an increasingly prominent contradiction between the sharp increase of uranium resource demand and the limited extremely uranium exploration depth.The geogas measurement method has excellent prospecting ability for deeply concealed uranium deposits due to its deep penetration characteristics.The promotion of geogas measurement method can help to improve the exploration depth of most of the current uranium deposits in China,especially the typical hydrothermal uranium deposits in South China,from hundreds of meters to deeper depth.In order to do simulation studies of migrating behavior of uranium element in geological media,the coupled physics numerical analysis and experimental observations on the fluid flow characteristics and the dispersion mechanism of uranium elements with fluid in porous blanket medium were completed,and the behavior of element as well as uranium-containing particles migrating with geogas or groundwater in blanket was analyzed and summarized.Horizontal uranium migration model,vertical column uranium migration models and cubic uranium migration model,with automatically controllable model system parameters,were designed and developed.Before that,the structure of experimental models was optimized.The results of research show that uranium micro-particles can migrate with gas-phase fluid in porous geomaterial,and the migration behavior is not determined by specific gas composition.Rapid convection is not the necessary driving force for migration of uranium particles in pores,but the migration is affected by the variety and porosity of medium.For instance,shale medium has a strong retention and adsorption effect on uranium-containing particles,but it is not enough to suppress the strong penetrability of uranium particles in the earth-bearing gas;and the larger porosity medium means more migration of uranium-containing particles under the same conditions.Uranium ions mainly migrate with the groundwater in aquiferous blanket other than uranium-containing particles in anhydrous pores.Compared with geogas,the groundwater in blanket has a stronger carrying capacity for uranium in pores.Transversely convective groundwater and fracture zones in blanket can largely offset the surficial position of abnormal information caused by concealed uranium deposits.On the time scale,transversely convective groundwater could greatly slow the forming of observable abnormal information on the ground;inversely,fracture zones and fissures cause directed and faster migrating of uranium element to accelerate the forming of observable abnormal information on the ground.In field exploration operation,the self-developed constant-flow geogas-collectors were used for extracting geogas actively.Element contents of geogas samples collected were assayed by ICP-MS.A comprehensivly radioactive exploration method combined application of geogas measurement,ground gamma spectroscopy measurement,Po-210 activity measurement and soil thermoluminescence measurement is proposed through the experimental study of known profiles in Julong An area.With the data processing methods such as principal component analysis and coefficient of variation,the abnormal information caused by deeply concealed uranium mine could be effectively extracted to explore uranium deposits buried in shallow and deep layers of blankets.According to results of prospecting with comprehensively radioactive exploration methods for typically hydrothermal uranium deposits deeply concealed in Xiangshan area,there are two uranium ore prediction target areas with preferably deep ore-forming conditions,respectively near Xingshuxia and Shangjialing;and two prediction targets with preferably ore-forming conditions in less deep blankets,including northeast part of Lejia and middle part between Yanwo and Xiangshi.Obvious intermediate-high abnormal values of comprehensive radioactivity occur in these predicted target areas,which matches basically with the characteristics of structural faults controlling uranium ores.The aforesaid interpretation results are in good agreement with other geochemical exploration results in project group.Through massive researches of model experiment,simulated calculation and application in field,the formation of geogas elements anomalies aboveground from deeply concealed uranium deposits was understood further to provide important means of studying migrating behavior of uranium element in geogas.At the same time,application of geogas measuring in uranium exploration was promoted to provide technical support for prospecting deeply concealed uranium deposits.