Application Study Of Deep-penetrating Geochemical Exploration For Concealed Sandstone-type Uranium Deposit

In-situ recoverable concealed sandstone-type uranium deposits are generally buried in the oxidation-reduction zone of the inclined sandstone layers at a depth of greater than 100 m.The thick overburden above the ore bodies and weak surface mineralization information make traditional geochemical exploration methods incapable to effectively delineate favorable areas for uranium mineralization in sedimentary basins.In order to identify and trace the geochemical anomalous sources from the deposits in covered areas,the mobile forms of uranium,polonium-210(210Po)and instantaneous radon concentration in surface soil were measured in different-grade ore-bearing borehole and non-mineralization borehole areas of Hadatu sandstone-type uranium deposit in the Erlian Basin.Furthermore,systematical luminescence intensity analyses have also been carried out on mineral particles from both Quaternary sediments and drillcores,which buried at a certain depth above the concealed sandstone-type uranium deposits,for the first timeResults of surface geochemical anomaly analysis showed that the soil instantaneous radon concentration is strongly positively correlated with the borehole grade.However,the contents of mobile forms of uranium and 210Pu in fine-grained soil have no obvious correlation with the borehole grade.There is no significant difference between the ore-bearing borehole area and non-mineralization borehole area.Luminescence intensity analyses yielded much older optically stimulated luminescence(OSL)ages for quartz minerals in late Quaternary sediments than their true depositional ages.At the same sampling depth,the quartz OSL appearance age is directly proportional to the grade of the borehole;And at the same borehole,the quartz OSL appearance age is positively correlated with the sampling depth.At the same time,the increase rate of the appearance age and the decay rate of the radioactive system from deep anomalies were calculated as 0.063 ka/cm and 0.19 Gy/cm,respectively,based on the OSL appearance ages and equivalent dose of Quaternary sediments.In contrast,the feldspar infrared stimulated luminescence signals of drillcore samples show no co-variations with deposits grade and sampling depth,indicating that the luminescence signals of the feldspar have reached saturation.The mineral OSL age/signal characteristics from certain buried sediments show that the quartz OSL age anomalies of late Quaternary sediments can indicate concealed sandstone-type uranium deposits beneath.Given the oversaturated OSL signals on minerals from drillcores,they have no potential to unravel concealed sandstone-type uranium deposits.In addition,the surface geochemical anomalies were examined by using the mineral OSL age/signal characteristics of the sediments.The results showed that the mineral OSL age anomalies of the Quaternary sediments buried at a certain depth above the concealed sandstone-type uranium deposits could effectively identify the surface ore-induced anomalies.By the test of mineral OSL age in the Quaternary sediments with a certain depth,it is shown that the instantaneous radon concentration anomaly is an ore-induced anomaly caused by concealed sandstone type uranium deposits,while the content anomalies of mobile forms of uranium and 210Po in the fine-grained soil are uncertain.This is the first reliable test of surface geochemical anomalies in concealed sandstone-type uranium deposits in covered areas.