铀有机地球化学研究进展

与铀矿有密切关系的有机质主要是腐殖酸（HAs)、富里酸（FAs)、微生物及细菌。腐殖酸与铀酰存在着强烈的吸附、络合及还原作用关系。微生物和细菌在铀矿形成过程中也起到一定的作用。在研究手段上包括试验、计算、热解分析、X－线分析、裂变径迹分析、电子探针、红外光谱、紫外光谱、荧光光谱、顺磁共振、色谱质谱联用等方法。     

Interactions of uranium with bacteria and kaolinite clay

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10^− 6 M- and 4 × 10^− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH₃COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10^− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH₃COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.     

湖南前震旦系铀矿化成因探讨

湖南前震旦系冷家溪群和板溪群是一套浅变质沉积岩,主要由各种板岩、变质砂岩、凝灰质板岩组成,夹有基性、中-酸性火山熔岩、火山碎屑岩及碳酸盐岩。现已落实铀矿床3个、矿(化)点14个。铀成矿年龄为85—50Ma,最晚者16Ma。稳定同位素研究结果表明,前震旦系铀矿化属岩浆岩源及沉积(变质)岩源中-新生代大气降水热液成因;铀矿化受断裂构造控制;凝灰质板岩、砂质板岩及角岩等是矿化有利的围岩。     

Geochemical assessment of an analogue site for an engineered landform at Ranger Uranium Mine, Northern Territory, Australia

 An essential element in identifying sites as analogues for the long-term development of soils and vegetation on engineered landforms of the rehabilitated Ranger Uranium Mine, Northern Territory, Australia, is the need to match rocks. Comparison of the geochemistry of rocks from the waste rock dump of Ranger Uranium Mine and the potential analogue site of Tin Camp Creek area, Western Arnhem Land, indicates that there are several sites along Tin Camp Creek that may be used as analogue sites. Detailed comparisons between the Ranger and Tin Camp Creek lithologies have been undertaken using a variety of techniques, including cluster analysis. It is demonstrated that at least 70% of the rocks being mined at Ranger have analogues in the Tin Camp Creek area. Received: 2 October 1996 · Accepted: 4 November 1997     

Geology of the Ranger Uranium Mine, Northern Territory, Australia: structural constraints on the timing of uranium emplacement

The geology of the No 1 and 3 pits at the Ranger Mine in the Pine Creek Inlier (PCI) of Australia is dominated by Palaeoproterozoic volcanic, carbonate and sedimentary sequences that unconformably overlie Archaean granitic gneiss of the Nanambu Complex (2470±50 Ma). These sequences are folded, faulted and sheared, and crosscut by east-trending granite (sensu stricto) dykes and pegmatite veins, and gently dipping N–NE trending mafic dykes of the Oenpelli Dolerite (1690 Ma). Regional metamorphism is to greenschist facies and contact metamorphism is to hornblende-hornfels facies.The rocks of the Ranger Mine have been subjected to at least two phases of ductile–brittle deformation (D2–D3) and one phase of brittle deformation (D4). These events were preceded by regional diastathermal or extension-related metamorphism (D1) and the development of an ubiquitous bedding-parallel cleavage (S1).D2 resulted in the development of NNE–NNW trending mesoscopic folds (F2) and a network of thrusts and dextral reverse shears. The modelled palaeo-stress directions for the emplacement of pegmatite veins suggests that they formed early in D2. D3 resulted in the development of WNW–NW trending mesoscopic folds (F3), a weakly defined axial planar cleavage (S3) and sinistral reactivation of D2 shears. D2–D3 are correlated with deformation during the Maud Creek Event of the Top End Orogeny (1870–1780 Ma), while the emplacement of granite dykes and pegmatite veins is correlated with emplacement of regional granites at 1870–1860 Ma.D4 is associated with brittle deformation and resulted in the development of normal faults and fault breccias during a period of east–west extension. This event is correlated with regional east–west extension during deposition of Palaeo- to Mesoproterozoic platform sequences.The sequence of tectonic events established in this study indicates that uranium-bearing ore shoots in the Ranger No 1 and 3 pits formed during extension in D4, and after emplacement of the Oenpelli Dolerite at 1690 Ma. However, the currently accepted 1737±20 U–Pb Ma age places the mineralising event at time of regional post-orogenic erosion, after the Top End Orogeny and before emplacement of the Oenpelli Dolerite and extension in D4. The U–Pb age is not consistent with Sm–Nd ages for primary uranium mineralisation at Nabarlek and Jabiluka at 1650 Ma [Econ. Geol. 84 (1989) 64] and does not concur with currently accepted regional tectonic data of Johnston [Johnston, J.D., 1984. Structural evolution of the Pine Creek Inlier and mineralisation therein, Northern Territory, Australia. Unpublished PhD Thesis, Monash University, Australia], Needham et al. [Precambrian Res. 40/41 (1988) 543] and others. Consequently, the absolute age of uranium mineralisation at the Ranger Mine is open.     

Arsenic fixation on iron-hydroxide-rich and plant litter-containing sediments in natural environments

Iron-hydroxide-rich and plant litter-containing sediments from natural sites contaminated with uranium mine tailing leachates were examined for their ability to adsorb arsenic. The samples with high contents of iron hydroxides (Fe_total concentration, >300 g kg⁻¹) exhibited remarkable fixation of arsenic (up to 40 g As kg⁻¹). This value corresponded approximately to the supersaturation point for natural iron hydroxides under the present conditions, and it was significantly lower than the value found for synthetic iron hydroxides. There was a strong correlation (R=0.8999) between the concentration of iron and that of arsenic at low arsenic contents, indicating adsorption on strong binding sites. Although all the samples had noticeable contents of organic carbon (plant litter), calcium, and manganese, no obvious effect of these elements on arsenic fixation could be detected. The amount of iron hydroxides was found the only fixation-controlling parameter immediately below a leaching water source.     

加拿大萨斯喀彻温(Saskatchewan)省北部铀成矿作用的主要特点与启示

本文扼要介绍了加拿大萨斯喀彻温省北部比弗洛支地区脉型 (veintype)和阿萨巴斯卡盆地中与不整合面有关的 (Unconformity associated)铀资源概况 ;比较系统地阐述了两类铀矿化成矿作用的共同特征 ,指出控矿的核心因素是热点活动与构造作用的叠加。这从本质上与我国华南铀矿富集区的控矿因素是相似的。因此 ,通过两个铀矿富集区的对比 ,认识铀成矿作用的本质 ,拓宽找矿思路 ,对于探索寻找新成矿区和新类型铀矿具有一定的启发意义。     

Uranium and Thorium Isotope Distribution in an Offshore Bottom Sediment Core of the Selenga Delta, Lake Baikal, Siberia

Distribution of uranium and thorium isotopes in a short sediment core obtained offshore of the Selenga Delta in Lake Baikal, Siberia, was investigated to establish their sedimentary behaviors and to look for a linkage to paleoenvironmental changes. The sediments were composed of dominantly fine detrital materials (70–85%) and a relatively high sedimentation rate (ca. 0.03 cm y⁻¹). The depth profile of ²³⁸U content in bulk sediment samples showed a large variation of 70–123 Bq kg⁻¹, while ²³²Th profile showed a relatively narrow range from 36 to 56 Bq kg⁻¹. The observed ²³⁴U/²³⁸U activity ratios revealed a marked disequilibrium ranging from 1.53 to 1.84 with a mean value of 1.71 ± 0.07, demonstrating the presence of 50–80% authigenic ²³⁸U in the bulk sediments. The distribution of this authigenic ²³⁸U did not display any clear correlation with variations in sediment composition (organic, carbonate, Bio-SiO₂ and mineral contents) including grain size median. The profile of terrigenous ²³⁸U showed a relatively similar pattern to that of ²³²Th. Results of sequential leaching indicate that ²³⁸U in Fe–Mn oxyhydroxides fractions were responsible for the distribution of authigenic ²³⁸U rather than in Bio-SiO₂ fraction. The distribution of authigenic ²³⁸U in the bottom sediments may be explained by the fluctuation of U adsorption capacity on particles including organic matter and Fe–Mn oxyhydroxides before they entered the lake. This study highlights the potential use of authigenic and terrigenous U (Th) signatures in sediments to trace the behavior of U (Th) and to reconstruct environmental (e.g., hydrological) changes in the lake catchment area.     

汞在460、534地区的分布特征及其找铀矿的意义

本文在介绍一种新的土壤汞量测量找矿方法的同时,着重用大量的实测数据阐明汞在460铀矿床上的分布特征。汞在该矿床上部“黑矿”中的平均含量高达11430ppb,最高达193800ppb,而一般岩石中的汞含量只有数十至数百个ppb。通过对铀矿石及其主岩中的汞的热释谱分析,发现释汞主峰温度在350℃以上的中温、高温相态汞与铀矿化关系密切。铀矿床上部土壤汞晕规模大(550×350m~2),平均含量可达563ppb,最高达6080ppb,平均衬度16,最高达174。汞含量随着采样深度的加深而升高。在矿床外围测出了相似的汞晕,并进行了成矿预测。上述成果已用于生产。     

纳米比亚欢乐谷地区构造演化对铀成矿的制约

欢乐谷地区由新元古代泥砂质岩层夹铁镁质岩层组成。受达马拉期陆块碰撞事件的影响,发生区域中深地壳层次的强烈韧性变形。后碰撞期,在地壳增厚背景下,发生大规模伸展减薄和花岗岩浆作用,形成多种浅色花岗岩体即白岗岩。产铀白岗岩主要为D型及E型白岗岩,为S型壳源花岗岩。欢乐谷地区经历了四期五个阶段的构造演化,分别是:前达马拉期构造变形、达马拉碰撞造山期韧性变形(早阶段的挤压逆冲、晚阶段的走滑剪切韧性变形)、后达马拉期脆性变形和新生代整体抬升引起的脆性变形。广泛发育的白岗岩属于同构造期岩体。通过对变质岩和白岗岩的节理测量统计,基本确定了研究区的碰撞后区域应力场。最优势的主压应力方向介于N26°~35°方位间,其次为介于N110°~129°方位间和N345°~360°方位间的主压应力。目前保留在各类岩石中的密集节理构造,是碰撞造山后构造折返或岩浆上涌到达上地壳层次后才发生的,与铀矿富集关系密切。本研究初步探讨了达马拉期构造作用、韧性剪切、后期脆性断裂(基性岩墙侵位通道)与铀成矿作用的成因联系和制约作用。