我国某地沥青铀矿中U^235相对富集的初步研究

The discovery of the gamma spectrum abnomal is reported for the uranium ore sample No. 15, In comparison with a parallel investigation on a reference natural uranium saraple the relative abundance of U^235 is obtained and the U^233 content of sample No. 15 turns out to be 5 percent higher than that of the reference natural sample, Discussion is given to the mechanism by which U^235 is enriched in the ore.     

Determining depleted uranium （DU） contamination in soils and salt marsh sediments in the vicinity of DU munitions testing sites in SW Scotland and NW England, UK

In its natural state uranium has three isotopes; ^238U （99.27 atom % abundance）, ^235U （0.72%） and ^234U （0.0055%）, with the ^235U ： ^238U activity ratio having a constant value of 0.045 and the ^234U：^238U activity ratio commonly ranging 0.8-1.2 for soils and sediments （e.g. Fisenne 1996）. Uranium enrichment, the process by which the fissile isotope ^235U is concentrated for the production of nuclear fuel, generates a waste product that is depleted in both ^235U and ^234U. Depleted uranium （DU） therefore has a distinct isotopic signature that can be used to monitor contamination arising from the use of munitions containing it （i.e., DU weapons and armour）. The UK Ministry of Defense has tested such munitions at coastal locations in SW Scotland and NW England, resulting in possible contamination of the surrounding terrestrial and marine environments. We examined the U isotope distribution in surface soil （top 10 cm） and salt marsh sediment samples from these locations using alpha spectrometry to determine the extent of any DU contamination from the munitions testing programme. Despite 〉30 t of DU shells having been fired into the sea in this region there was no evidence of deviation from the natural ^234U ： ^238U activity ratio range in salt marsh samples. The ^235U ： ^238U activity ratio could not be used to assess these salt marsh samples because ^235U activities were at the limit of detection for alpha spectrometry.     

Associations and mobility of uranium in soils near a depleted uranium （DU） weapons testing site, SW Scotland

Natural uranium has three isotopes, ^238U, ^235U and ^234U, with natural abundances of 99.27 atom %, 0.72% and 0.0055%, respectively. Only ^235U is fissile and the production of nuclear fuel and nuclear weapons involves enrichment of uranium in ^235U. This process also results in separation of ^234U from ^238U, leaving depleted uranium （DU）, with typical ^234U/^238U and ^235U/^238U activity ratios of about 0.19 and 0.013, respectively, as a waste product. The high density, high melting and boiling points and chemical stability of uranium and the availability of DU in relatively pure form mean that DU has many uses, including armour-piercing munitions. Such munitions have been developed in the UK since the 1960s and testing has been carried out by the Ministry of Defence （MoD） at firing ranges such as Dundrennan, SW Scotland and Eskmeals, NW England. The firing of DU munitions can result in the dispersion of DU and its combustion products （oxides） as aerosols or as larger fragments, with the potential for human exposure either directly at the site of detonation or via post-depositional migration in the environment. The aim of this work was to investigate the potential environmental mobility of DU by characterizing the associations of U in soil porewaters with increasing distance from a firing site. To this end, several soil cores located down-wind of the firing site at Dundrennan, near Kirkcudbright, SW Scotland, were collected in May 2006. These were sectioned on-site into 1- or 2-cm depth intervals and porewaters were isolated by centfifugation （10 minutes; 8873 g） on return to the laboratory. Following filtration through 0.2-micron cellulose nitrate filters, the porewaters were analyzed by ICP-QMS （U concentration） and ICP-OES （Fe, Al, Ca, Mg, Mn concentrations）. Sub-samples were also subjected to centrifugal ultrafiltration （100, 30, and 3 kD） and to gel electrophoretic fractionation （agarose; 0.045 M Tris-borate; 20 mA, 30 minutes）. Results showed that U was present at up to 4 μg/L in the soil porewater and that the associations of U varied with sample location and soil depth.     

Distribution of uranium and thorium in Irtysh River and the upriver wastewater from a rare metal mine impact on it

Uranium and Th are important radioactive elements. Most studies were focused on their environmental impact from uranium deposits and mining sites. But other sorts of mines such as rare metals mines are associated highly with uranium and thorium, too. In China, the Irtysh River is the only river that runs into the Arctic Ocean. The famous Koktokay rare metal pegmatite deposit is located in the headwater region of this river and has been exploited for several decades. The waste ore piled along the riverside as long as several kilometers. The wastewater flom the concentrating plant is discharged into the river directly. In addition, uranium and thorium can be leached from the waste ore into the river in the weathering process. So it is necessary to study the uranium and thorium distribution in the branch and trunk streams of the Irtysh River and the wastewater from the mining site impact on it. In this study, the contents of uranium and thorium in water samples from the Irtysh River and rare metal mine wastewater have been detected directly with ICP-MS. Uranium and thorium distribution and geochemical behaviors in the Irtysh River basin have been studied. The environmental uranium and thorium pollution status in the Irtysh River and wastewater from a rare metal mine impact on it have also been evaluated. The study shows that uranium and thorium contents in wastewater from a rare metal mine are as high as 78.311 μg/L and 0.627 μg/L, respectively, so we should also pay attention to the radioactive pollution from the rare metal mine. The average contents of U and Th in the branch streams of the Irtysh River are 0.572 μg/L and 0.015 μg/L, respectively. At the mean time, in the trunk of the Irtysh River, average thorium content is 0.019 μg/L while U is up to 2.234 μg/L, much higher than the average content （0.0309 μg/L） of the world rivers. From upstream to downstream in the trunk of the Irtysh River, thorium content declines gradually due to dilution by other branches and deposition itself.     

A Novel Approach in Hydrogeochemical Exploration for Uranium Mineralization: an Example from West Central Sinai, Egypt

Groundwater in contact with ore deposits may acquire a chemical composition that could be used as a guide for exploration. Eight well-water samples are collected from a known uranium-mineralized area near Abu Zenima, west central Sinai to examine the applicability of using the hydrogeochemical technique in the search for uranium mineralization in similar arid areas. The analytical chemical data of the ground water is compared with ground radiometric measurements. The obtained results indicate that groundwater affected by uranium mineralization has a specific relativity of major anions expressed essentially as SO4>Cl>HCO3 and to a lesser extent as Cl>SO4>HCO3, associated as a rule with low magnesium content. This association constitutes a signature of uranium mineralization on the composition of groundwater in west central Sinai and could be used as an important exploration guide in the search for uranium deposits in similar areas. Anomalies in Ni, Fe, Zn and Cr and other pathfinder elements in groundwater can furnish geochemical guides to uranium ores. The immobile trace element anomalies, including Zn, Ni and Fe are strongly distributed near the orebody; whereas the relatively mobile trace elements, including Co, U, V and Cr, constitute the dispersion haloes away from the orebody. A new hydrogeochemical discrimination diagram is constructed to be used as a quick and cost effective exploration tool in the search for uranium occurrences in environmentally similar arid areas. Based on the obtained results, a new site for uranium occurrence, west of W. Baba, is delineated and recommended for future detailed geological and geochemical surveying.     

α谱法测定低微量铀、钍含量的研究

Alpha-spectrometric technique is described as an independent method of determining micro-content of U^233 and Th^233. This method is based on the comparison of U^234 and Th^233 alpha spectral activity in geological samples with U^232 and Th^233 spectral activity contributed by the spike of known concentration. The experiment procedure consists in dissolving fine powdered sample with acid and adding a given amount of U^232-Th^223 spike. The uranium and thorium are then separated by ion exchange. After purification each fraction is mounted on a separate stainless steel disk for measurement by alpha spectrometer which consist essentially of a surface barrier deterctor and a low noise amplification system connected to a multichannel analyser. After correcting for background, tail and other factors, the desired U^232 and Th^232 concentrations can be calculated. The data obtained by the alpha-spectrometric method using U^232-Th^223 spike are compared with colorimetric determination. Excellent agreement is obtained between the two sets of results. The coefficient of correlation is about 0.98 for U^234 and 0.97 for Th^232. The accuracy of uranium and thorium analyses by this method depends primarily upon the counting statistics of U^233, U^232, Th^233 and Th^223 and, to a lesser extent, upon the calibration of U^233-Th^238 spike. Errors of uranium and thorium concentration by this method are generally 2 to 5 per cent.     

华南某花岗岩型铀矿床成矿机理的铀铅同位素体系研究

The uranium deposit studied in this paper occurs in a Precambrian (Xuefengian)granite batholith. The emplacement age of the granite is 760 m.y. The average content of uranium in the granite is 7 ppm, but the yield of leachsd U is higher With an average of about 33.8%. The granitic rocks, contain; Some uraninite. Uranium mineralization mainly takes the form of siliceous veins With an age of 47 m.y. K-feldspar. present in the granite and pyrite associated with pitchblende were massspectrometrically analyzed for Pb isotopic compositious, characterized by anomalous lead. A reasonably linear array can be seen on the ^207Pb/^206Pb--^205Pb/^204Pb plot, implying a genetic connection between the rock and the ore, and a derivation of rock-forming materials from. a uranium-rich source. According to the continuous-growth model for anomalous lead, evolution, two isochrons give the. ages-of about 764 m.y. and 708 m.y.for ore-forming materials, close to the emplacement age of .the granite batholith. This indicates that the ore-forming materials came from the granite batholith. Eight granite samples collected from the mining .area were analyzed, but no uranium-lead ages could be worked out because of the pregressive destruction of the closed U-Pb isotopic system since granite emplacement, which resulted in the loss of uranium(78%). It can be imagined that in the period of continental weathering the surface water would infiltrate downwards, leaching out large amounts of uranium from the granitic rocks to form infiltration solution. The solution was heated at great depth and then found its way upwards, on which it dissolved constantly U from the rocks to form the uranium deposit.     

Mineralogy,M-type tetrad effect and radioactivity of altered granites at the G. Abu Garadi shear zone,central Eastern Desert,Egypt

The G. Abu Garadi area is covered mainly by metasediments, alkali feldspar granites and stream sediments. The alkali feldspar granite is traversed by a major strike-slip fault trending in an N-S direction as well as two subordinate sets of faults trending NW to WNW for the first one and NE for the second one. These faults represent the shear zones affected by magmatic (syngenetic) as well as hydrothermal (epigenetic) activities causing alteration of the granitic rocks. The most common alteration features are albitization, greisenization and koalinitization. The mass balance calculations of the studied altered samples show enrichments in Zr, Y, Ni, U, Th and Ga and depletions in Zn, Sr, Nb, Ba, Pb, Cu and V. Only the greisenized samples exhibit a significant enrichment in Nb, ∑REE budget and pronounced lanthanide tetrad effect (M-type), especially TE1,4, while weakly expressed tetrad effects are for the other albitized and koalinitized samples. Mineralogically, the common accessory minerals in the altered samples include samarskite-(Y), betafite, uranothorite, zircon, fluorite and cassiterite. The greisenized granites contain high eU and eTh than the other altered types, where they are characterized by an assemblage of the radioactive minerals; samarskite-(Y), betafite, uranothorite in addition to zircon. The inter-element relationships between U and Th and also their ratios illustrate that the radioelement distribution in these granites is mainly governed by magmatic processes, in addition to post-magmatic ones. The distribution of chemical elements and the fractionation of some isovalents within the shear zone are largely controlled by the newly formed mineral phases. With respect to uranium mobilization, uranium migrated from the host alkali feldspar granites of G. Abu Garadi, while the shear zones acted as traps for the migrated uranium. Moreover, U migrated in the shear zone during greisenization and albitization, and migrated out during koalinitization.     

试论地下热水的铀成矿作用

The studies uranium deposit occurs in a geothermally abnormal area. It has the following four features: 1. Uranium mineralization is observed in a certain temperature zone. 2. The uranium deposit occurs in an area characterized by relatively low but highly varying radioactivity in a regionally high radioactive field. 3. Uranium closely coexists with cubic pyrite of hot water origin. 4. Pitchblende is characteristic of hot water origin. This paper focuses on the relationship between ground hot waters and uranium mineralization. Uranium in the deposit is considered to have come from the host rocks, The possible explanation of the formation of this uranium deposit is that uranium was first leached out of the host rocks by ground hot waters and then transported to where uranium enrichment and deposition were favoured, forming uranium deposit under certain conditions. Based on this explanation, this uranium deposit is believed to be the product of hot water activity in the regionally geothermal abnormal zone.     

Development of highly sensitive analytical methods for radionuclides in marine environmental studies

The determination of natural and artificial radionuclides, such as Th, U and Pu isotopes, in the marine environmental studies is important and has been an active research field in the environmental analytical geochemistry. For example, uranium isotope ratios give information regarding the source of the uranium in the environment, and are important for studying its biogeochemical behavior, while thorium isotope （^230Th） and Pu isotopes are good tracers for particle scavenging process study in the ocean. Due to the extremely low concentrations of these radionuclides in the marine environment, the accurate analysis of these radionuclides is still a challenging task. In this presentation, we will present the recent development of highly sensitive analytical methods for ^230Th, ^234U, ^235U, ^238U, ^239Pu and ^240Pu and their isotope ratios （^234U/^238U, ^235U/^238U, ^240Pu/^239Pu） in radionuclides in marine environmental samples, such as seawater, sediments, settling particles, using quadrupole and sector field ICP-MS. Applications of the radionuclide analysis in the marine environmental studies, such as the radioactivity environmental monitoring,     

Early Mineralization Age of the Hengjian Uranium Deposit: Constraints from Zircon SIMS U-Pb Dating

正Objective The Hengjian uranium deposit is a typical hydrothermal deposit in the Xiangshan uranium ore field.The uranium mineralization ages of the Xiangshan deposits are poorly constrained,and only a few mineralization ages using the pitchblende U-Pb method have been published.These ages are commonly discordant and dispersed for abundant inclusions and an open U-Pb system.Zircon grains after strong hydrothermal alteration are usually characterized by high common Pb contents,and their U-Pb isochron ages recorded the hydrothermal alteration event without interference of common Pb components.The Hengjian gray/grayish-green granite porphyry experienced strong     

On the Genesis of Uranium Deposit 720 with Special Reference to the Double Solution—Mixing Model

Presented in this paper is an approach to the analysis of “series-stage“division.The processes of hydrothermal evolution involved in ore deposition,the factors affecting the enrichment of uranium and the source of ore forming elements in uranium deposit 720 are also discussed .In addition,the ore-forming tem-perature and pressure as well as the pH,Eh and chemical composition of ore-forming medium are studied with reference to the fluid inclusion data available.A double solution-mixing model has been proposed to explain the genesis of the uranium deposit studied.     

铀-铅同位素谱系研究及其在铀矿地质中的应用

The main purpose of this paper is to present a fundamental concept of U-Pb isotopic spectrum-system and to apply this idea to the interpretation of the mechanism of uranium ore formation. It is evident from a number of examples of uranium deposits that the uranium deposits formed in various processes are characterized by different types of U-Pb isotopic spectrum-system.     

The Equilibrium Coefficient Kp and Petroleum Exploration:Design of the New Generation of Petroleum Exploration Instrument

The main reason why the application of nuclear technology in petroleum exploration has not yet been accepted by most exploration workers is that they are not clear about the homologous distribution features of oil and gas fields and radioactive radiation. The authors hold that the disequilibrium of uranium, radium and radon as a natural radioactive series is the basic feature in the use of this technology in petroleum exploration. The invention Gamma-ray Spectral Measurement of the Equilibium Coefficient Kp and Its Embodiment of the senior author now can readily solve that problem and replace the impedient measure of normalization of uranium and potassium to thorium that had to be proposed before. Application of this impedient measure has some limitations. In areas where the surface is covered by beach or river sands, thorium minerals such as monazite may be concentrated by placering. This could result in local thorium highs that would yield local uranium and potassium lows after normalization to thoriu     

U—Series Dating of Fossil Bones：Results from Chinese Sites and Discussions on Its Reliability

Calculations,according to some open-system models,point out that while a statistically significant discrepancy between the results of two U-series methods,^230Th/^234U and ^227Th/^220Th(or ^231Pa/^235U),attests a relatively recent and important uranium migration,concordant dates cannot guarantee closes-system behavior of sample.The results of 20 fossil bones from 10 Chinese sites,19 of which are determined by two U-series methods,are given,Judging from independent age controls,8 out of the 11 concordant age sets are unacceptable,The results in this paper suggest that uranium may cycle into or out of fossil bones,such geochemical events may take place at any time and no known preserving condition may securely protect them from being affected.So for the sitew we have studied,the U-series dating of fossil bones is of limited reliability.     

New Evidence for Genesis of the Zoige Carbonate-Siliceous-Pelitic Rock Type Uranium Deposit in Southern Qinling: Discovery and Significance of the 64 Ma Intrusions

The carbonaceous-siliceous-argillitic rock type uranium deposit in the Zoige area is located in the northeastern margin of the Tibetan Plateau, and has gained much attention of many geologists and ore deposit experts due to its scale, high grade and abundant associated ores. Because of the insufficient reliable dating of intrusive rocks, the relationship between mineralization and the magmatic activities is still unknown. In order to study this key scientific issue and the ore-forming processes of the Zoige uranium ore field, the LA-ICP-MS zircon U-Pb dating of magmatic rocks was obtained:64.08±0.59 Ma for the granite-prophyry and ~200 Ma for the dolerite. U-Pb dating results of uraninite from the Zoige uranium ore field are mainly concentrated on ~90 Ma and ~60 Ma. According to LA-ICP-MS U-Pb zircon dating, the ages for the dolerite, porphyry granite and granodiorite are 200 Ma, 64.08 Ma approximately and 226.5-200.88 Ma, respectively. This indicates that the mineralization has close relationship with activities of the intermediate-acidic magma. The ages of the granite porphyry are consistent with those uraninite U-Pb dating results achieved by previous studies, which reflects the magmatic and ore-forming event during the later Yanshanian. Based on the data from previous researches, the ore bodies in the Zoige uranium ore field can be divided into two categories:the single uranium type and the uranium with polymetal mineralization type. The former formed at late Cretaceous(about 90 Ma), while the latter, closely related to the granite porphyry, formed at early Paleogene(about 60 Ma). And apart from ore forming elemental uranium, the latter is often associated with polymetallic elements, such as molybdenum, nickel, zinc, etc.     

Characteristics of Uranium Mineralization in Red Clastic Formations in the Southwestern Margin of the Ordos Basin

In the southwestern margin of the Ordos Basin, uranium mineralization is primarily hosted by predominantly oxidative red clastic formations in the Lower Cretaceous. The main target layers for uranium exploration are the Madongshan and Liwaxia formations of the Liupanshan Group, followed by the Jingchuan Formation of the Zhidan Group. The host rocks (medium-fine feldspar quartz sandstone), which are bleached to a light grayish white color, contain a minor organic matter component and pyrite. Uranium mineralization changes from surficial infiltration or phreatic oxidation in the upper part to interlayer oxidation in the lower part. Uranium ore bodies are mostly lenticular or tabular in shape, locally shaped like crescent rolls. Individual ore bodies are typically small and shallow. Uranium predominantly manifests as pitchblende and coffinite. Coffinite is usually short and columnar or granular in habit, whereas pitchblende occurs as an irregular colloidal covering on the surface or in fissures of ferric oxide, silicate, clay or carbonate. Secondary uranium minerals are torbernite, uranophane, and uranopilite. Minerals associated with uranium are mainly pyrite, chalcopyrite and, to a minor extent, arsenopyrite and fluorite. The associated elements are Mo, V, Se, Co, Ni, and Mn, the host sandstone being high in Cu and Ba. Overall, the red clastic formations in the southwestern margin of the Ordos Basin are characterized by ‘five multiples but one low’ which means multiple target layers, multiple stages of mineralization, multiple ore body shapes, multiple kinds of uranium minerals, multiple associated elements, but low organic matter. This implies an overall complex uranium metallogenic environment and mineralization process. It is recommended that future uranium exploration should take into consideration regional metallogenic conditions and mineralization features, with target layers in the wide-smooth synclinal slope being focused on. Most uranium deposits are small to medium in size, and the main type of uranium mineralization can vary by target layer.     

湿热水解法测定岩矿中的氯

In this paper, a procedure of pyrohydrolysis-spectrophotometric determination has been estahlished for chlorine in ores and rocks.The catalyst selection and its required quantity,the time and temperature of sample decomposition and the influence of interferring elements and others are also discussed in detail. Because samples are usually fused with alkali, higher blank is an insurmountable problem. However, with our procedure, the above-mentloned drawback can be effectively overcome, and the determination of trace chlorine either in large or in minor quantities of samples also is rather ideal. The determined results indicate that the relative standard deviation in the former is 8.7%, and 4.5% in the latter case. This procedure is simple, rapid and well reproduceable. The detection limit of the method is 10ppm. The results obtained by our procedure are in good agreement with the proposed values from two reference samples in China (DZ∑-1 and DZ∑-2) and one international geochemical reference sample (RGM-1). This method has been proved to be reliable.     

Determination of total selenium in geological samples by HG-AFS after concentration with thiol cotton fiber

Standard reference material and different geological samples were dissolved by system A （the mixture of nitric and perchloric acids） and system B （mixture of nitric, perchloric and hydrofluoric acids）, and total Se in all samples was measured by hydride-generation atomic fluorescence spectrometry （HG-AFS） after concentration with thiol cotton fiber （TCF）. The analytical results obtained by the two digestion method are in good agreement （within the limit of errors） for most of the samples, particularly for those having recommended values. The Se concentrations determined by the two methods are of no difference, and the correlation coefficient is 0.9986; the relative standard deviation （RSD） for the determination of 0.04 μg/g Se is 10.2%. The recovery rates of systems A and B by the standard-addition method were 96%-106% and 99%-104%, respectively.     

Factors Controlling Low Uranium and Thorium Concentrations in the ?ay?rhan Bituminous Shales (?BS) in the Beypazar? (Ankara) Area, Turkey

In this study uranium and thorium contents and depositional characteristics of ay rhan bituminous shales（ BS）, west of Ankara（central Anatolia）, are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The H rka formation which hosts bituminous shale deposits is a volcanosedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of BS（1.83/2.62 ppm） are much lower than averages of UC, NASK and PAAS（uranium： 2.70/2.66/3.10 ppm; thorium： 8.50/12.30/14.60 ppm）. Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of BS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites（e.g. gneiss, schist） which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals（e.g. autunite, torbernite） which occur in granite, gneiss and schist. BS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma-Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements.