水－岩反应的铀系不平衡判别

天然体系中水－岩反应的铀系不平衡判别,是基于水－岩反应使岩石中天然铀衰变系子体核素＾２３４Ｕ,＾２２６Ｒｂ和六价铀的选择性溶失,造成原始放射性平衡遭到不同程度破坏,因而可利用现今测得的岩石中３组核素放射性活度比值Ａ（＾２３４Ｕ）／Ａ（＾２３８Ｕ）,Ａ（＾２３０Ｔｈ）／Ａ（＾２３４Ｕ）和Ａ（＾２２６Ｒａ）／Ａ（＾２３０Ｔｈ）反演判别该岩石曾经历了近代水－岩反应的大致强度和出现,持续时间,这是近十余年     

不采用同位素示踪剂测定地质样品中^234U,^238U,^230Th和^232Th比活…

本提出了不采用同位素示踪剂测定铀，钍同位素比活度的方法。用标准方法准确的测定地质样品中的铀，钍含量及＾２３４Ｕ／＾２３８Ｕ，＾２３０Ｔｈ／＾２３２Ｔｈ的活度比值，再应用铀，钍系的衰变特性，推导出计算样品中＾２３４Ｕ，＾２３８Ｕ，＾２３０Ｔｈ和＾２３２Ｔｈ经活度的方法，本方法计算所得之结果与＾２３２Ｕ示踪法对比。均在１σ范围内，符合很好。     

不采用同位素示踪剂测定地质样品中~（234）U，~（238）U，~（230）Th和~（232）Th比活度的方法研究

本文提出了不采用同位素示踪剂测定铀、钍同位素比活度的方法。用标准方法准确的测定地质样品中的铀、钍含量~［１］及~（２３４）Ｕ／~（２３８）Ｕ，~（２３０）Ｔｈ／~（２３２）Ｔｈ的活度比值~［２］，再应用铀、钍系的衰变特性，推导出计算样品中~（２３４）Ｕ，~（２３８）Ｕ，~（２３０）Ｔｈ和~（２３２）Ｔｈ比活度的方法。本方法计算所得之结果与~（２３２）Ｕ示踪法对比，均在１σ范围内，符合很好。     

应用中子活化分析技术测定铀和钍放射性同位素的α能谱内标法

开发了一种用＾２３８Ｕ和＾２３２Ｔｈ作为内标的α能谱测定铀和钍放射性同位新方法。应用中子活化分析技术精确地测定样品中的＾２３８Ｕ和２３２Ｔｈ。将其他部分样品全部溶解,采用阴离子交换法分离铀和钍,制备为α能谱测定的电镀薄（低强度）源。人已知的＾２３８Ｕ和＾２３２Ｔｈ质量浓度,求得它们的活度浓度,之后据α能谱,从Ｕ（＾２３Ｕ、＾２３５Ｕ、＾２３８Ｕ）和Ｔｈ（＾２２８Ｔｈ、＾２３０Ｔｈ、２３２Ｔｈ）放射     

花岗岩—伟晶岩接触带元素地球化学迁移：高放废物地质处置库安全评价…

我国苏州花岗岩－伟晶岩接触带岩石中，与高放废物内某些长寿命超铀锕系元素和裂变产物化学性质相似的微量元素，同位素迁移行为天然类比研究表明，伟晶岩脉中的、Ｌｉ，Ｓｒ，Ｂｅ，Ｍｏ，Ｎｂ，Ｅｒ，Ｙ和＆２３４Ｕ，＾２３８Ｕ在该岩脉形成后约１３０Ｍａ期间，在水－岩反应作用下，仅向花岗岩中迁移１０－３０ｃｍ，而Ｔｈ，Ｐｂ，＾２０６Ｐｂ，＾２０８Ｐｂ，＾８７Ｒｂ，＾８７Ｓｒ，＾８７６Ｓｒ则未发生明显迁移。这一研究     

激光探针等离子体质谱法（LAM—ICPMS）用于年龄锆石U—Pb定年

利用激光探针等离子体普（ＬＡＭ－ＩＣＰＭＳ）技术对中生代锆石进行了详细的２０６Ｐｂ／＾２３８定年研究。采用线扫描（Ｌｉｎｅ ｓｃａｎ）进样法减小了传统的剥深（Ｄｅｐｔｈ ｐｒｏｆｉｌｅ）进样法所引起的激光熔蚀分异效应;优化仪器参数可三ＩＣＰ－ＭＳ对Ｐｂ和Ｕ的质量歧视效应。测得了精确的＾２０６Ｐｂ／＾２３８Ｕ比值及年龄。研究结果表明,均匀颗粒锆石的＾２０６Ｐｂ／＾２３８Ｕ比值测量精度为２％～１０％,     

234Th/238U不平衡法在真光层颗粒动力学研究中的应用

真光层是海洋浮游生物活动最为活跃的区域,其间发生的颗粒动力学过程及其机制对于海洋碳的生物地球化学循环有着重要影响,利用放射性核素示踪海洋真光层颗粒动力学过程成为近年来海洋科学的前沿课题。介绍了该领域＾２３４Ｔｈ－＾２３８Ｕ不平衡法的原理、发展历程及其在ＰＯＣ输出通量的估算、沉积物捕集器捕集效率的校正、真光层层化结构的揭示、颗粒活性元素固／液界面分配机制的研究、海洋胶体性质的研究及近岸海域悬浮颗粒活     

洋中脊：石榴石信息的提取

讨论了洋中脊Ｔｈ、Ｕ和Ｓｍ、Ｙｂ及Ｎｂ、Ｈｆ等同位素的示踪,浅水洋和深水洋的洋中脊有着不同的同位素特征,反映了没的石榴石信息。现在对此还不能作出完美的解释,但（＾２３０Ｔｈ）／（＾２８８Ｕ）和水深呈负相关的关系为洋壳产生过程的模型提供了一个重要的约束条件。     

花岗岩－伟晶岩接触带元素地球化学迁移──高放废物地质处置库安全评价的天然类比研究

我国苏州花岗岩－伟晶岩接触带岩石中，与高放废物内某些长寿命超铀铜系元素和裂变产物化学性质相似的微量元素、同位素迁移行为天然类比研究表明，伟晶岩脉中的Ｕ、Ｌｉ、Ｓｒ、Ｂｅ、Ｍｏ、Ｎｂ、Ｅｒ、Ｙ和２３４Ｕ、２３８Ｕ在该岩脉形成后约１３０Ｍａ期间，在水－岩反应作用下，仅向花岗岩中迁移１０－３０ｃｍ，而Ｔｈ、Ｐｂ、２０６Ｐｂ、２０７Ｐｂ、２０８Ｐｂ、８７Ｒｂ、８７Ｓｒ、８６Ｓｒ则未发生明显迁移。这一研究结果为我国拟在花岗岩中处置高放废物提供了长期安全评价的依据。     

长α粒子中止距离对（U—Th）／He年龄的影响

现已开发了一个定量评估α粒子中止距离对（Ｕ－Ｔｈ）／Ｈｅ年龄影响的数学模型。在＾２３８Ｕ、＾２３５Ｕ和２３２Ｔｈ链中,α粒子中止距离在约１０￣３０μｍ之间变化,它取决于衰变能和中止介质的密度与组成。在富Ｕ和Ｔｈ的副矿物情况中（例如磷灰石、锆石、金红石）,长中止距离的主要影响是α粒子发射到邻近矿物。对小于几百微米的颗粒,发射效应将造成测定的Ｈｅ年龄大大低于起真实年龄。如何,１００μｍ半径的球体仅保留     

砂岩铀矿成矿过程与氧化还原分带: 铀系不平衡证据

铀系不平衡技术被用来研究新疆伊犁盆地库捷尔太砂岩型铀矿床的氧化还原分带和成矿过程.取自该矿床的26个样品的铀、钍含量以及234 U/ 238U, 230 Th/ 234 U和230 Th/ 238U活度比值分别用ICP -MS和α能谱仪进行了测量.不同氧化还原带岩石的铀、钍含量和钍/铀比明显不同: 强氧化带岩石的U、Th含量和Th/U比分别为12.4 μg/g, 4.5 μg/g和0.48; 弱氧化带分别为20.4 μg/g, 5.0 μg/g和0.38; 过渡带(矿化带)分别为169.7μg/g, 4.7μg/g和0.07; 还原带(未蚀变带)分别为6.8μg/g, 3.7μg/g和0.87.其同位素特征亦有明显差异: 氧化带岩石234 U/ 238U大多大于1, 过渡带(矿化带)岩石部分大于或等于1, 部分小于1, 还原带(未蚀变带)岩石大多大于1; 氧化带岩石230 Th/ 234 U和230 Th/ 238U大多大于1, 过渡带(矿化带)岩石大多小于或等于1, 还原带(未蚀变带)岩石大多大于1.这可作为砂岩型铀矿床矿体定位的指示剂.铀系不平衡特征还示踪了该矿床的成矿作用过程.      

Uranium series disequilibria in the sedimentary uranium deposit at Yeelirrie,Western Australia

The weighted mean values of the ²³⁴U/²³⁸U and the ²³⁰Th/²³⁴U ratios in ore samples collected above the modern water table of the Yeelirrie uranium deposit in Western Australia are 1.38 ± 0.10 and 0.83 ± 0.28, respectively. The relatively larger variability in the latter ratio is evidence for the translocation of uranium subsequent to deposition. Daughter product separation is due to differences in the mobilities of the thorium and uranium species. Factors involved in interpreting the observed ratios, in terms of the dynamics of the accumulation of the deposit, are assessed in terms of an open system model. The observed disequilibria provide a quantitative basis for the evaluation of hypotheses developed from geological and other considerations.     

松辽盆地钱家店铀矿床层间氧化带结构定量表征及制约因素

层间氧化带精细结构的量化表征对揭示砂岩型铀成矿规律至关重要.利用系列沉积学和地球化学编图对松辽盆地钱家店铀矿床层间氧化带结构进行了量化表征,发现该矿床层间氧化带主要由红色砂岩、浅黄色砂岩、灰白色砂岩、灰色含矿砂岩和原生灰色砂岩构成,分别对应于强氧化亚带、弱氧化亚带、微弱氧化亚带、过渡带和还原带.铀矿化与层间氧化带内部结构关系密切:工业铀矿体主要发育在过渡带,微弱氧化亚带矿体连续性相对较差,弱氧化亚带发育零星铀矿化,还原带靠近过渡带一侧发育低品位的零星铀矿化.铀储层内部结构和沉积相对层间氧化带发育具有重要制约作用:辫状河砂体及辫状分流河道砂体是氧化带发育区域;辫状分流河道边部及分流间湾中决口扇砂体是过渡带发育区域.      

新疆伊犁盆地砂岩型铀矿床层间氧化带中粘土矿物特征及与铀矿化关系研究

新疆伊犁盆地砂岩型铀矿床,由于规模大、成矿环境和成矿条件好,在同类型矿床中具有良好的代表性,研究矿床的成矿作用对今后找矿勘查以及开采具有重要理论意义。本文在区域赋铀层位沉积环境研究基础上,以赋矿围岩为研究主体,对伊犁盆地典型铀矿床沉积序列和矿床的控矿层位开展研究,通过对赋矿沉积层位中粘土质对铀矿成矿的控制作用及与铀矿的空间联系和成因分析,开展系统的铀矿床学、能谱测试、显微结构、扫描电镜、地球化学、氢氧同位素等研究,特别是开展了富矿砂体中粘土矿物的种类、成分、结构、同位素、成因等的研究,对粘土质矿物对铀矿成矿的控制作用进行了系统研究。通过研究粘土矿物在伊犁盆地蒙其古尔砂岩型铀矿床成矿过程中的作用及与铀矿的空间联系和成因分析表明:粘土矿物在层间氧化带中分布较为广泛,在主要矿体的氧化还原过渡带中,尤其是部分具有强烈粘土蚀变的砂岩层中铀含量较其他层位要高,反映出粘土矿物与铀成矿是有成因关联的。通过系统的扫描电镜、能谱测试研究,从微观证明粘土矿物与铀成矿有相关关系;粘土矿物的存在导致在近地表含氧含铀水在经过砂岩孔隙时被具有较强吸附能力和巨大表面自由能的粘土矿物所吸附,形成了铀含量较高的片状,团块状的粘土矿物,其在铀成矿作用中起到了吸附和界面的作用,有利于赋矿空间的形成及定位。结合沉积作用、构造活动和后期流体成矿作用等因素,分析了成矿机制和成矿作用,赋矿层位中的粘土矿物、其它成矿条件如岩性(赋矿层和矿源层)、构造(对铀矿化的动力和对地下水径流及铀矿体)等共同控制了铀成矿作用。     

Uranium isotopic evidence for the origin of the Bahariya iron deposits, Egypt

The economic iron ore deposits of Egypt are located at Bahariya Oasis in the Lower Middle Eocene limestone. The main iron minerals are goethite, hematite, siderite, pyrite, and jarosite. Manganese minerals are pyrolusite and manganite. Gangue minerals are barite, glauconite, gibbsite, alunite, quartz, halite, kaolinite, illite, smectite, palygorskite, and halloysite. Geochemical comparison between the ore and the Nubia sandstone showed that the ore is depleted in the residual elements (Al, Ti, V, and Ni) and enriched in the mobile elements (Fe, Mn, Zn, Ba, and U) which indicates that the Bahariya iron ore is not a lateritic deposit despite the deep weathering in this area. On the other hand, the Nubia sandstone showed depletion in the mobile elements, which demonstrates the leaching process in the Nubia Aquifer. The presence of such indicator minerals as jarosite, alunite, glauconite, gibbsite, palygorskite, and halloysite indicate that the ore was deposited under strong acidic conditions in fresh water.Isotopic analyses of the uranium in the amorphous and crystalline phases of the ore, in the country rocks, and dissolved in the Nubia Aquifer water, all support the conclusion that U and Fe were precipitated together from warm ascending groundwater. U and Fe display strong co-variation in the ore, and the ²³⁴U/²³⁸U activity ratio of the newly precipitated U in the country rock and the leached component of U in the groundwater are identical. There is only slightly more uranium in the amorphous phase than in the crystalline and only a slightly lower ²³⁴U/²³⁸U activity ratio, suggesting that the iron in the two phases have a similar origin. Comparison of the excess ²³⁴U in the water and in the total ore leads to the conclusion that the precipitation of the U, and by inference the iron, occurred within the last million years. However, that both precipitation and leaching of U have occurred over the last 300,000 years is evidenced by the extreme ²³⁰Th/²³⁴U disequilibria observed in some of the samples. Some of the amorphous depositional events have been very recent, perhaps within the last 10,000 years.     

氧化还原障在热液铀矿成矿中的作用

铀是变价元素,氧化还原条件控制铀的迁移和沉淀。铀在氧化环境中呈U~(6+)形式存在,在还原条件下则以U~(4+)形式存在。氧化态六价铀主要以可溶的碳酸铀酰/氟化铀酰络合物形式在水溶液中迁移,还原态四价铀主要以沥青铀矿和铀石等形式富集沉淀成矿。热液铀矿的形成需要一对空间上密切共生的氧化障/氧化剂和还原障/还原剂,二者缺一不可。首先,氧化障中氧化剂将富铀岩石中的铀大量氧化形成U~(6+),溶解进入水溶液迁移;第二,高氧化性富铀溶液遇到还原障,U~(6+)还原成U~(4+)沉淀下来,富集形成铀矿。前人虽然对铀的地球化学性质及氧化还原反应在铀成矿中作用已比较了解,但如何在实际铀矿成矿系统中准确识别氧化还原障,有效利用氧化还原障的控矿机理指导找矿,还存在一些模糊认识,制约了铀成矿理论的发展和找矿方法的提升。本文以我国最重要的砂岩型铀矿、火山岩型铀矿、花岗岩型铀矿和变质型铀矿为例,总结了与铀矿化有关的氧化还原障的主要类型,探讨了红层等蒸发盐地层(氧化障),有机质、煌斑岩等中基性岩脉(还原障)与铀矿之间的关系及控矿机制,揭示了成矿盆地中铀-煤、铀-气(油)共生的机制,阐明了翁泉沟硼、铁、铀矿共生原因,建立了不同类型铀矿成矿模型。     

U-Pb systems and U isotopic composition of the sandstone-hosted paleovalley Dybryn uranium deposit, Vitim uranium district, Russia

The isotopic (U-Pb, ²³⁸U-²³⁵U, ²³⁴U-²³⁸U) and chemical study of whole-rock samples and finegrained fractions of rocks in a vertical section of the terrigenous sequence at the Dybryn uranium deposit in the Khiagda ore field shows that a wide U-Pb isotopic age range (26.9-6.5 Ma) is caused by oxidation and disturbance of the U-Pb isotopic system in combination with protracted uranium ore deposition. The oxidation of rocks resulted in the loss of uranium relative to lead and eventually to an overestimated ²⁰⁶Pb/²³⁸U age at sites with a low U content. The ²³⁸U/²³⁵U ratios in the studied samples are within the range of 137.74–137.88. Samples with a high uranium content are characterized by a decreasing ²³⁸U/²³⁵U ratio with a decrease in ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ages. A nonequilibrium ²³⁴U/²³⁸U ratio in most studied samples furnishes evidence for young (<1.5 Ma) transformation of the Miocene uranium ore, which is responsible for uranium migration and its redeposition.     

诸广山中段“三九”地区铀矿放射性同位素特征及找矿潜力

“三九”地区位于诸广山复式岩体中段,隶属华南花岗岩型铀矿富集区。放射性同位素及其比值是反映铀成矿信息的重要参数,可直接反映浅部到深部的铀、镭富集的地球化学特征及其迁移规律。本文重点探讨“三九”地区不同地段、不同含量、不同埋深和不同矿体部位的²³⁸U、²³⁴U、²²⁶Ra、²³⁰Th和²³¹Pa同位素特征及其比值,分析铀、镭迁移富集规律。结果表明：“三九”地区铀矿体由近地表至深部铀镭平衡系数具有高-低-高变化特征;U元素的相对富集、Th元素相对减低及其U/Th比值的急剧升高等特征,与U、Th丰度区间具有明显分带特征关系密切;当地表有矿化或异常显示且浅、深部有工业矿时,其同位素组成具有铀、镭同时迁出,且铀大量迁出特征;当地表无异常显示时,其同位素组成具有铀大量迁出、镭明显迁入特征。大于1的²³⁴U/²³⁸U比值可有效指示找铀矿化。综上,利用放射性同位素及其比值法在“三九”地区预测深部铀成矿有利地段,取得较好应用效果,其中九龙江、石壁窝和木...     

Uranium geochemistry and dating of Pacific island apatite

Uranium-series disequilibrium dating of island phosphate deposits is evaluated in terms of known associated coral ages, uranium geochemistry, and stratigraphic sequences as well as the concordance between the geochronometers ²³⁴U/²³⁸U, ²³⁰Th/²³⁴U and ²²⁶Ra/²³⁸U. U(VI) is the predominant oxidation state of uranium in island phosphorites and by analogy to the youngest surficial deposits, most of the uranium initially bound is in the form of U(VI) sorbed by surfaces from seawater. Insular deposits contain more organic matter than even very young ocean floor samples and this leads to a greater probability of reduction of available recoil uranium than occurs in marine deposits. As a consequence, R(VI) ? R(T) ? R(VI), where R represents the ²³⁴U/²³⁸U activity ratio. This situation is completely opposite from that observed for marine-origin phosphorites. We determined that a fraction of U(VI) in ancient insular phosphorites is very labile and lost to alkaline carbonate solutions with a uranium activity ratio even more depleted in ²³⁴U than the bulk R(VI).Most younger samples appear to have no more discordance between ²³⁴U/²³⁸U, ²³⁰Th/²³⁴U and ²²⁶Ra/²³⁸U than marine phosphorites of similar apparent age. Young, surficial atoll-rim apatite cements and unconsolidated phosphorites date in the range of 1500–8000 years B.P., consistent with the concept of partial submergence of low-lying coral islands prior to 2000 years B.P. Sub-surficial samples in the same environment date older at about 20,000 years B.P. Violation of the closed system assumption occurs in at least 6 out of 13 ancient (> 800,000 year) samples. Uranium-series disequilibrium dating of insular apatite shows some promise as a recorder of climatic/sea level events, but the assumptions necessary for valid ages must be carefully evaluated for each occurrence.