稳定同位素和放射性同位素方法在铀矿水化找矿中的应用

在水文地球化学找矿研究中,采用稳定同位素和放射性同泣素方法判别放射性水异常及其成圈是一个重要的课题。在宝昌盆地采用氢氧同位素及氚的研究确定了3种类型的地下水异常。它们是:(1)局部淋滤富集和蒸发浓缩作用形成;(2)铀矿化引起的异常水;(3)深部与浅部水的混合作用形成。异常水的补给高程估计为1796m。异常地下水中~(234)U的过剩显示了矿化存在的可能性。同位素水文学的研究为水文地球化学找铀提出了一个新的方向。     

Radon-rich waters in Russia

In radon mineral curative waters, according to Russian mineral water classification, the radon concentration should be greater than 185 Bq/l. There are about 30 mineral waters with high levels of radon in Russia. Radon-rich waters have high therapeutic effects. It is proven that natural background radiation stimulates the human immune system. Radon is a natural radioactive gas that has no taste, smell or color. Radon-222 is one of the heaviest elements in the zero groups of inert gases. It is a gaseous radioactive element. All radon isotopes are -emitters while the transformation of its decay products is accompanied by the emitting of -or -particles. The main products of radon decay are short-lived isotopes Po, Pb, Bi, and TL. Belonging to the uranium and thorium decay chain, radon isotopes form directly during the decay of radium isotopes. Therefore the radon concentration depends upon the concentration of its parent's isotope in water and rocks washed by it as well as upon the amount of radon emanation. Loose rocks or rocks with a great number of cracks are characterized by higher radon concentration (zones of tectonic disturbance, weathering crusts, etc.).Crystalline rocks usually have higher uranium concentrations than the average bedrock. Examples of rock types, which often have enhanced uranium concentration >5% ppm U includes the following: granites, syenites, pegmatite, acid volcanic rocks and acid gneisses. In the earth's crust radon migrates either in a gaseous or dissolved state. It can go to the surface without any chemical reaction. Formation of the radon-rich therapeutics waters of Russia has been analyzed, and most of them are genetically connected to crystalline acid rocks that have exceeded uranium-radium mineralization. The radon content in Russia reaches more than 8,000 Bq/l. Radon-rich waters of this type occur in the Altai, Karelia, St Petersburg and Trans-Baikal regions. Another type is connected to geodynamic activity of regions and secondary radioactivity. A well-known example of radon-rich waters of the second type is Pyatigorsk in the North Caucasus. Mixing confined carbon dioxide-hydrogen sulfide water and unconfined groundwater forms radon waters. The radon concentration is 1,170–2,430 Bq/l. The occurrence of radon-rich water deposits in other regions of Russia is described. Further investigation of the radon content in other geological environments will contribute to the environmental safety as well as to the solution to many genetic, hydrogeochronological, paleoreconstructive and prediction problems in hydrogeology.     

The behaviour of uranium, thorium and tin during leaching from a coarse-grained porphyritic granite in an arid environment

During the routine analysis of chip samples from water boreholes it was noted that the DeBakken granite south of Kenhardt has high uranium and tin contents. Rock samples collected on surface, however, revealed low concentrations of both these elements indicating that they have been leached from the surface samples. The distribution of thorium in the borehole profiles showed that while both tin and uranium have been removed above the water table, other “immobile” elements and thorium remained unaffected.The geological data showed that the leaching took place since the start of the Tertiary. Initially, the movement of uranium was vertical and accumulated in pedogenic calcrete above the granite. This vertical leaching was controlled by fluctuations in the water table and took place from the Pliocene to Pleistocene. Later, in the Holocene, the pedogenic calcrete was removed and deposited as non-pedogenic calcrete along the rivers. These nodular calcrete deposits, which are abundant in Namaqualand, are mineralized only along those rivers which drain the DeBakken granite, indicating that this granite was the source of the uranium.When the water table reached depths of ten metres or more the vertical migration of uranium ceased and horizontal leaching caused by the movement of ground water became active. Where the water table cuts the surface, such as in the pans, uranium deposition due to evaporation of groundwater is still active.Leaching of uranium from this granite, together with the formation of the secondary deposits is mineralogically controlled, and is ascribed to the fact that uranium is not hosted in zircon. Granites such as the DeBakken granite, in which the uranium is hosted in biotite, monazite and apatite, cannot be recognized by surface sampling and hence a lithogeochemical approach, using sub-surface samples has to be adopted. Calculations showed that approximately 1400 tons of uranium metal has been leached from this granite since the start of the Tertiary and that the maximum reserve of the province as a whole is relatively small.The distribution of tin is erratic, and although it has been leached from the surface samples, it has not been transported for any significant distance. Thus the tin distribution in the profiles does not show the same degree of leaching as does uranium. This is ascribed to the fact that samples from a percussion drill would include both the rock fragments from which tin has been leached and the clay-rich alteration products in which it has been trapped. Tin is generally immobile when present as cassiterite, but when enclosed in biotite, and when the groundwater is enriched in chlorine and fluorine, it leaches readily from the biotite.     

重庆歌乐山隧址区地下水同位素组成特征及意义

同位素测试作为一种先进的技术手段在地质科学的各个研究领域得到越来越广泛地应用。运用同位素方法研究流体及矿床成因关系方面取得了较大的进展。目前，环境同位素方法被广泛用于识别地下水系统，研究自然界水循环过程和地下水运动规律。不同成因的地下水具有不同的同位素组成特征，而且氢、氧稳定同位素在低温条件下不与围岩发生同位素交换，放射性同位素变化遵循各自的衰变规律，水中HCO3碳、氧同位素组成与被溶解的碳酸盐岩同位素组成有关。在歌乐山隧道施工涌水对周边地下水系统的影响及环境效应评价过程中，取得许多同位素数据，对该区地下水的同位素特征有了新的认识。文章借助同位素方法探讨了隧址区地下水的补给源、年龄等基本特征。该区地下水主要补给来源为大气降水。碳、氧稳定同位素的研究结果也证实了这一点。对放射性同位素氚研究表明，该区地下水年龄基本都较小，属近期大气降水直接渗入补给。     

The geochemistry of uranium occurrences and speciation in groundwater of Chinnar sub basin,South India

An attempt has been made in Chinnar sub basin of Dharmapuri district, South India to isolate the geochemistry of uranium occurrences in groundwater. The geology of the area is mainly of charnockite and granite gneiss. Groundwater samples were collected for two different seasons post and pre monsoon in two different litho units (granite gneiss and charnockite) and analysed for major, minor and uranium concentrations. Higher uranium (18.45 μg L^?1) has been recorded during pre monsoon season in granite gneiss with increasing pH. The saturation index calculation for the groundwater isolated minerals like uaraninite, coffinite, haiweeite and soddyite to be precipitating and uranium oxides like UO_2.25, UO_2.25beta, UO_2.33beta as oversaturated. The Eh-pH diagram attempted represents solubility of uraninite within the pH range of 6.0 to 8.0. The study isolate uranium in groundwater of the study area is controlled by the presence of (U₄O₉) uranium oxide.     

Uranium geochemistry in groundwater from tertiary sediments

Dissolved U concentrations and activity ratios (ARs) of the U isotopes in the ²³⁸U decay series were measured in ground and surface waters as part of an investigation to delineate the water quality in a proposed uranium mining area of northwest Nebraska. In oxidizing groundwaters from 67 wells completed in the Tertiary sediments, increasing U concentrations in the direction of groundwater flow generally were associated with a maturation of the formation water as evidenced by evolutionary trends in major ion character. The increased U levels probably are associated with leaching as shown by the positive correlation between U concentrations and total dissolved solids (TDS) (r = +0.83). The inverse relationships between TDS and U ARs (r = ?0.73) and U levels and ARs (r = 0.72) indicate that the decay of excess U-234 is related to maturation of the formation water and to sediment leaching along the flowpath. The data are described by a model which incorporates etching, decay and recoil and suggests that aquifer residence time can be estimated from the TDS level.The levels of soluble U in a reducing uraniferous hydrogeologic unit near Crawford, Nebraska are affected by the proximity of the sample collection to ore. In groundwater samples having similar chemistries (Na-SO₄ + Cl type), similar Ehs, and collected from a close-knit pattern, U concentrations ranged from 0.01 to 2,037 μg l^?1 and ARs ranged from 0.75 to 12.6. This high variability in U levels and ARs is indicative of uranium ore in small areal studies where low ARs almost always are associated with high U concentrations.     

某铀钨矿床中钨矿化特征及其成因研究

铀钨矿床是一种新矿床类型。其主要矿物是白钨矿和沥青铀矿，它们既有共生，也有伴生。钨以白钨矿细脉、分散状微粒白钨矿和吸附状等形式产出。钨与铀的成矿过程可划分为六个阶段。矿岩时差较大。钨来源于已固结的花岗石，它是由地下热水或热卤水从已固结的花岗岩中浸取出来的。钨（铀）矿化是在低温条件下，在有利的构造岩性中沉淀富集而成的，不是岩浆热液矿床     

Uranium isotopes (234U/238U) in rivers of the Yukon Basin (Alaska and Canada) as an aid in identifying water sources, with implications for monitoring hydrologic change in arctic regions

The ability to detect hydrologic variation in large arctic river systems is of major importance in understanding and predicting effects of climate change in high-latitude environments. Monitoring uranium isotopes (²³⁴U and ²³⁸U) in river water of the Yukon River Basin of Alaska and northwestern Canada (2001?C2005) has enhanced the ability to identify water sources to rivers, as well as detect flow changes that have occurred over the 5-year study. Uranium isotopic data for the Yukon River and major tributaries (the Porcupine and Tanana rivers) identify several sources that contribute to river flow, including: deep groundwater, seasonally frozen river-valley alluvium groundwater, and high-elevation glacial melt water. The main-stem Yukon River exhibits patterns of uranium isotopic variation at several locations that reflect input from ice melt and shallow groundwater in the spring, as well as a multi-year pattern of increased variability in timing and relative amount of water supplied from higher elevations within the basin. Results of this study demonstrate both the utility of uranium isotopes in revealing sources of water in large river systems and of incorporating uranium isotope analysis in long-term monitoring of arctic river systems that attempt to assess the effects of climate change.     

新疆十红滩层间氧化带型砂岩铀矿同位素地球化学研究

文章在对吐哈盆地十红滩层间氧化带型砂岩铀矿床地下水和粘土矿物的氢、氧同位素，钙质砂岩的碳、氧同位素，黄铁矿和长石的铅、硫同位素组成进行分析测试的基础上，系统总结了矿床的地球化学特征；认为形成层间氧化带和铀矿化的层间水主要来自大气降水，研究区水与有机烃类气体同位素交换、强烈的蒸发作用和水岩反应是控制地下水和矿物中同位素分馏的主要机制，层间氧化带和铀富集成矿是地下水在低温、常压下对围岩长期作用的结果，钙质砂岩的碳和黄铁矿的硫均主要为生物有机成因，盆地深部的煤成油、气也参与了成矿作用。     

Radium isotopic measurements in the search for uranium in palaeodrainage channels

Analyses have been made of many groundwater samples, some of which were collected from the vicinity of uranium deposits and others from unmineralized areas, for dissolved uranium and for the four naturally occurring isotopes of radium: ²²⁶Ra (²³⁸U decay series, y), ²²⁸Ra and ²²⁴Ra (²³²Th decay series, y and 3.8 d) and ²²³Ra (²³⁵U decay series, d). The radium isotopes ²²⁶Ra, ²²⁴Ra and ²²³Ra, are measured by alpha-spectrometry after extraction from a water sample soon after collection and ²²⁸Ra at a later time by determining the amount of ingrown ²¹²Po.     

Determining uraniferous host rocks and minerals as a source of dissolved uranium in granite aquifers near the central Ogcheon metamorphic belt,Korea

Korea has suffered from high U concentrations in some groundwater, especially in Daejeon near the central Ogcheon metamorphic belt. However, clear explanation has not been yet reported for the uranium sources in groundwater. This study is focused on identifying the potential uraniferous host rocks and finding the exact U-minerals serving as uranium sources in groundwater near Daejeon, Korea. For this work, we performed an in situ gamma ray spectrometer survey and a laboratory microscopic study with electron micro-probe analysis. The measurements for radioactive element content did not show any prominent K- and Th-anomaly spots, but they did result in several observations of considerable U-anomalies in pegmatite and hydrothermally altered granite, in which uraninite, coffinite and uranophane were found by electron micro-probe analysis. The occurrences of U-minerals are the first such discovery except in the low-grade U deposits of the Ogcheon metamorphic belt in Korea. All observed U-minerals were intimately associated with hydrothermal alteration. The remarkably low Th/U ratios in the studied uraniferous rocks also suggest that the U enrichment was genetically related to a post-magmatic hydrothermal process. However, many of the uraniferous parts were controlled by a reducing environment and occurred near the border between graphite-rich mica-schist and Jurassic leucocratic granite. The findings on these uraniferous rocks can be used in elucidating the source of highly enriched U groundwater in granite aquifers as well as in understanding the occurrence of igneous U-minerals, which has not been previously reported in Korea.     

Reactive transport modeling of uranium 238 and radium 226 in groundwater of the Königstein uranium mine, Germany

Knowledge of the transport behavior of radionuclides in groundwater is needed for both groundwater protection and remediation of abandoned uranium mines and milling sites. Dispersion, diffusion, mixing, recharge to the aquifer, and chemical interactions, as well as radioactive decay, should be taken into account to obtain reliable predictions on transport of primordial nuclides in groundwater. This paper demonstrates the need for carrying out rehabilitation strategies before closure of the Königstein in-situ leaching uranium mine near Dresden, Germany. Column experiments on drilling cores with uranium-enriched tap water provided data about the exchange behavior of uranium. Uranium breakthrough was observed after more than 20 pore volumes. This strong retardation is due to the exchange of positively charged uranium ions. The code TReAC is a 1-D, 2-D, and 3-D reactive transport code that was modified to take into account the radioactive decay of uranium and the most important daughter nuclides, and to include double-porosity flow. TReAC satisfactorily simulated the breakthrough curves of the column experiments and provided a first approximation of exchange parameters. Groundwater flow in the region of the Königstein mine was simulated using the FLOWPATH code. Reactive transport behavior was simulated with TReAC in one dimension along a 6000-m path line. Results show that uranium migration is relatively slow, but that due to decay of uranium, the concentration of radium along the flow path increases. Results are highly sensitive to the influence of double-porosity flow.     

201富铀矿床氢,氧,碳,硫,铅同位素研究

产于花岗岩中的２０１铀矿床是我国花岗岩型铀矿富矿之一。本文通过氢、氧、碳、硫、铅同位素组成的研究，探讨成矿溶液和成矿物质的来源，推测成矿环境。研究结果表明，该矿床成矿流体是以大气降水为主，主要成矿物质来自前燕山期花岗岩体，可能部分来自下部地壳，成矿作用是在较稳定的物化条件下进行。     

Groundwater flow and radioactivity in Namaqualand, South Africa

The Namaqualand area is located in the Northern Cape Province of South Africa which is characterised by arid climate where groundwater is the only source of water supply for local communities. Extensive groundwater sampling was carried out in the area and the physico-chemical parameters, inorganic constituents, stable isotopes and trace metals were measured. The hydrochemistry of the area indicates dissimilar groundwater composition due to complex geochemical processes where groundwater flow takes place from catchment F30A to the catchment D82B, and the chemistry is controlled primarily by Redox reaction, dissolution and mixing processes. The Br^?/Cl^? ratio revealed that the salinity in the area is derived from seawater mixing, halite dissolution and atmospheric deposition/sea aerosol spray. Under excessive evaporative condition due to climatic aridity, groundwater salinity shows increasing trend. Isotope results show the presence of shallow-weathered zone and deep-fracture controlled circulating groundwater in the crystalline basement aquifer of the area. In comparison to the South African water quality standard, the results obtained for gross alpha activity which could be derived from uranium isotopes show that 41 % of the reported data in the area fall above the drinking water limit.     

Assessment of natural radioactivity in aquifer medium bearing uranium ores in Koprubasi,Turkey

Koprubasi, located within Manisa Province near the Izmir, is the biggest uranium mine where uranium ores originate from Neogene aged altered sandstone and conglomerate layers. The main objective of this study is to determine the radiation hazard associated with radioactivity levels of uranium ores, and the rocks and sediments around Koprubasi. In this regard, measured activity levels of ²²⁶Ra, ²³²Th and ⁴⁰K were compared with world averages. The average activity levels of ²²⁶ Ra, ²³²Th and ⁴⁰K were measured to be 5369.75, 124.78 and 10.0 Bq/kg in uranium ores, 24.32, 52.94 and 623.38 Bq/kg in gneiss, 46.24, 45.13 and 762.26 Bq/kg in sandstone and conglomerate, 73.11, 43.15 and 810.65 Bq/kg in sediments, respectively. All samples have high ²²⁶Ra and ⁴⁰K levels according to world average level. As these sediments are used as construction materials and in agricultural activities within the study area, the radiation hazard are calculated by using dose rate (D), annual effective dose rate (He), radium equivalent activity (Ra_eq) and radiation hazard index (I_yr). All the samples have Ra_eq levels that are lower than the world average limit of 370 Bq/kg. On the other hand, D, He and I_yr values are higher than world average values. These results indicate that the uranium ores in the Koprubasi is the most important contributor to the natural radiation level. The radioactivity levels of sediments and rocks make them unsuitable for use as agricultural soil and as construction materials. Moreover, it is determined that shallow groundwater in sediments and deep groundwater in conglomerate rocks and also surface water sources in the Koprubasi have high ²²⁶Ra content. According to environmental radioactive baseline, some environmental protection study must be taken in Koprubasi uranium site and the environment.     

东胜铀矿砂岩中方解石富集及铀矿成因

东胜铀矿区方解石富集特征、无机碳氧同位素以及邻近气藏包裹体捕获压力、有机碳同位素和~3He/~4He的相关研究表明,东胜铀成矿与深层天然气存在密切关系。方解石的δ~(13)C值-19.6‰~-1.11‰,δ~(18)O值-17.13‰~-9.00‰,δ~(13)C值的变化范围较宽,可能是地表水和深层天然气影响程度不同所致。鄂尔多斯盆地北部气藏储层包裹体捕获压力从深部向浅部和从盆地西南向东北方向逐渐降低的变化趋势表明,天然气为铀的转化提供了充足的还原剂,为大型东胜铀矿形成提供了必要条件。天然气中~3He/~4He比值证明东胜直罗组铀矿砂岩中没有有意义的幔源流体贡献。这些证据表明东胜铀矿砂岩中的方解石是地表水和深部天然气共同作用的结果,这暗示了东胜大型铀矿床是由低温混合成矿作用形成的。     

Uranium isotopes in the Platte River drainage basin of the North American High plains Region

The North and South Platte Rivers contribute sigficant concentrations of dissolved uranium to the Platte River system from the weathering of uraniferous rocks at their headwaters in Colorado and Wyoming. Uranium isotopes measured in three groups of samples collected from the Platte River and its major tributaries exhibted a wide range of concentrations (0.27–31.7 μg/l) and activity ratios (1.03–1.72) reflecting variations in the contributions of different sources under differing flow conditions. Locally elevated uranium concentrations and higher activity ratios were associated with groundwater sources during low flow periods. Uranium concentrations in surface runoff were lower than in baseflow and correlated significantly with dissolved solids. Uranium activity ratios in runoff were closer to equilibrium values than those in baseflow suggesting that dissolved uranium in runoff is less affected by disequilibrium processes. Mixing calculations using uranium concentrations and activity ratios indicate considerable variations in longitudinal and transverse mixing of tributary water with Plate River water, and temporal variations of groundwater contributions (baseflow and irrigation return flow) in the Plate River system.     

Hydrogeochemical and isotopic study of groundwater in the Habor Lake Basin of the Ordos Plateau,NW China

Hydrogeochemistry and isotopes were used to understand the origin and geochemical evolution in the Habor Lake Basin, northwestern China. Groundwater samples were taken, and the isotopic compositions δD, δ¹⁸O and major ions were analyzed. The groundwater can be divided into three types: the Quaternary groundwater, the shallow Cretaceous groundwater and the deep Cretaceous groundwater. The groundwater chemistry is mainly controlled by the feldspar weathering and dolomite weathering, the dissolution of Glauber’s salt, and cation exchange. Chemistry of lake water is mainly controlled by evaporation and precipitation. The stable isotopes of oxygen and hydrogen in groundwater cluster along the local meteoric water line, indicating that groundwater is of meteoric origin. Comparing with shallow groundwater, deep groundwater is depleted in heavy isotopes indicating that deep groundwater was recharged during late Pleistocene and Holocene, during which the climate was more wetter and colder than today.     

铀在北山花岗岩中的吸附迁移影响因素研究

运用水文地球化学模拟软件PHREEQC-Ⅱ,对铀元素进入中国高放废物处置预选场研究区地下水后的状况进行了模拟和预测。模拟得到核素铀进入研究区地下水后的元素浓度分布和迁移情况及外界因素变化引起地下水中铀迁移的行为,同时采用批式法测定不同条件下铀在甘肃北山花岗岩中的分配系数,研究了岩石粒径、溶液初始浓度、水相pH和温度对分配系数的影响,实验结果表明花岗岩对铀的吸附能力较弱,其中溶液初始浓度、粒径、温度影响较小,pH值对岩石的吸附性能有较大影响,在接近中性条件下影响达到最大,这与采用模拟软件模拟结果基本吻合。通过模拟和实验对比,能更好地研究在北山预选区处置条件下地下水-废物-岩石的相互作用过程中核素的迁移行为,从而为处置库系统安全评价提供有关依据。