铀矿的找矿知识(一)

自然界没有純鈾,它总是与其它物質化合成矿物。现在已知的含铀矿物有100种以上;其中含铀量高的比較少只有少数几种,含铀量較高,铀在其中成为矿物的主要成分。由于铀矿物常常彼此共生,因此发现某一种,常常就可以找到其它各种,所以无論是有工業价值,或是沒有工業价值的常见铀矿物,对铀矿找寻者来說,最好都要了解。     

我国发现的一种新铀矿物——湘江铀矿

湘江铀矿产于湖南某地二迭系岩层中一铀矿床的氧化带中。对该铀矿床的成因目前有两种看法,一种认为是沉积变质型;另一种认为是沉积迭加热液型。湘江铀矿呈浅黄色的粉末状微晶集合体产于硅质岩的裂隙内或风化孔洞中。与铝铀云母,黄铁矿,石英,磷铝石等矿物共生。根据产地命名为湘江铀矿。     

测定碱性长石有序度的红外光谱法、X光衍射法和光学方法的对比

五十年代以来,红外光谱技术开始应用于研究长石的成份、结构状态及其细微结构,随着研究工作的深入,应用红外吸收光谱测量碱性长石的Al/Si有序度日趋广泛,并有发展成为一种测量体系的趋势。 本文介绍了用X-光衍射法、红外光谱法和光学方法测量碱性长石的有序度。     

铀矿床定年研究进展评述

往往由于铀矿物(沥青铀矿)颗粒细小、易蚀变成铀的次生矿物及多期铀矿化作用相互叠加等在组成和结构上的固有特点,通常难以用挑选铀矿物(沥青铀矿)样品溶样的传统定年方法精确确定其形成年龄。随着分析技术的不断更新和发展,对铀矿床成矿年代学的研究也不断深入。但受铀矿床中铀矿物U-Pb定年方法本身的制约,以及以往对铀矿物U-Pb定年体系中铀矿物样品要求认识的不足,常常导致获得的年龄无实际地质意义或无法获得理想的等时线年龄。本文针对铀矿化定年方法的发展历程进行了系统梳理和分析,评述了铀矿物定年的五种主要方法:(1)铀矿物U-Th-totalPb化学年龄;(2)铀矿物模式年龄;(3)铀矿物传统等时线年龄;(4)铀矿物矿伴生矿物年龄;(5)原位微区铀矿物U-Pb年龄。在此基础上,深入探讨了铀矿化作用定年研究中存在的问题和对应方案,期望促进未来铀矿床成矿年代学的发展。     

热红外遥感技术在铀矿勘查中的应用潜力探讨

随着新型热红外传感器的相继问世及热辐射相关理论的不断发展,热红外遥感在资源勘查尤其是铀矿勘查领域呈现出了巨大的应用潜力。从地表温度、热惯量和热红外光谱3个方面对热红外遥感在资源勘查应用中的理论依据、研究现状进行了阐述,对其在铀矿勘查应用中的研究目标、研究内容进行了详细论述,并以ASTER热红外波段为数据源在华南某花岗岩铀矿区进行了实例应用,取得了良好的效果。实践表明,热红外遥感技术在铀矿勘查领域具有良好的应用前景和独特的应用价值,必将在铀矿找矿工作中发挥重要的指导作用。     

高岭石-多水高岭石演化系列的红外吸收光谱研究

本文用红外吸收光谱对我国所产高岭石-多水高岭石演化系列的四种不同类型的矿物及其热处理产物进行了初步研究,分析了各类矿物的吸收特征,探讨了它们之间的变化关系和脱水过程在红外光谱上的反映。 实验使用KBr压片法制备样品,在Perkin-Elmer 577型红外分光光度计记录红外光谱图。文中所用样品有江苏苏州与河北宣化的结晶完好的高岭石,广东清远清草岭与湖南谭家山的耐火粘土石,福建德化与湖南四青水库的多水高岭石以及四川叙永大树区与山西阳泉的水合多水高岭石。     

不同形态的次生铀矿物主折射率的快速测定

致细次生铀矿物主折射率的测定,是鉴定次生铀矿物的重要手段。作者在原有方法的基础上,通过实验,提出了两种较准确而迅速的综合方法:一特是中间值换油的中心明暗比较法,此种方法适用于细针状、细棒状次生铀矿物。另一种为焦点屏蔽法与中心明暗法交替使用的方法,它适合于土状,细鳞片状,短柱状次生铀矿物。     

东北辽河盆地混合层粘土矿物及其与沉积环境的关系

混合层粘土矿物是由两种或两种以上不同类型的粘土矿物晶层按不同比例、沿(001)基面平行地、相互重迭地组成规则或不规则结构的一种过渡型矿物。它是从一种粘土矿物向另一种粘土矿物转变的中间产物。自格鲁那(J.W.Gruner)于1934年在研究蛭石的过程中首次发现混合层矿物以来,相继有许多学者陆续报道了混合层矿物。经大量研究证明,混合层矿物分布极为广泛。     

华南混合岩中的铀矿化

以浸染扶晶质铀矿形式产于混合岩中的铀矿化是华南一种新的铀矿化类型。根据晶质铀矿在矿体中的存在形式,可划分为原生型和改造型。原生型矿床中主要铀矿物是晶质铀矿,改造型矿床中的主要铀矿物是沥青铀矿和残余的晶质铀矿。此类型矿床是富铀地层选择性熔融,并在此过程中导致铀的活化、转移和局部富集的结果。     

铀矿物热荧光现象的研究

利用铀矿物的荧光性质鉴定铀矿物是一种有效的方法。这是指常温下的荧光性质。前人曾对某些铀矿物的荧光性质进行过升温过程的研究,但对降温过程的荧光性质未作研究。最近我们对一些铀矿物在加热和降温过程中的荧光性质进行了研究。除不同的铀矿物其荧光消失温度不同外,荧光强度,荧光颜色等也随温度的变化而变化,更有意义的是当降温时,有     

Geochemical behaviour of LREE,Y and Zr in uranium mineralized and non-mineralized granite from Darshanapur area,in the Gogi-Kurlagere fault zone,Bhima basin,Yadgiri district,Karnataka

Granite core samples (n=14) from the Gogi-Kurlagere fault zone in the central part of the Bhima basin were studied in terms of LREE, Y and Zr mobility during uranium mineralization. LREE, Zr and Y along with LILE (Ba, Rb) and P show behavioral differences in the mineralised and the non-mineralised samples. Average ΣLREE in mineralised granite (240 ppm) is higher than in non-mineralised samples (157 ppm). The average Zr and Y in the mineralised granite are 193 ppm and 17 ppm, while the corresponding abundances of these elements in non-mineralised portion are 148 ppm and 11 ppm respectively. Besides enrichment of U, Th, Ba, Pb and Rb and depletion of Sr are observed in mineralized granite in comparison to non-mineralized granite. Hydrothermal alteration has led to the mobility of these elements, which again dependent on the overall geochemical behavior of the migrating fluid. REE and Y in association with uranyl [(UO₂)²⁺] ion were transported as carbonate complexes like [UO₂(CO₃)₃]^4- and [REE (CO₃)₃]^3- and were later incorporated into favourable structural loci by precipitating minerals like pitchblende and coffinite.     

显生宙全球海水化学成分演化及其对蒸发岩沉积的约束

通过搜集显生宙以来不同地质时期内海相碳酸盐岩鲕粒及胶结物矿物成分、钾盐矿床矿物种类及组合特征、蒸发岩盆地中石盐流体包裹体成分,并利用这些资料与人工海水模拟实验得到的石盐中Br分配特征的对比,得出海水成分在5.5亿年以来的显生宙期间,经历了五个阶段:其中晚元古代至寒武纪早期、二叠纪早期至中生代早期、新生代早期至现今,这些时期的原始海水组成特征系数m(SO_4~(2-))+m(HCO_3~-)/2m(Ca~(2+)),为Na-Mg-K-SO_4-Cl型海水,此期间沉积的钾盐矿床的钾镁盐矿物主要为钾盐镁矾、无水钾镁矾、杂卤石、硫酸镁石等含MgSO_4矿物,海相鲕粒和碳酸盐胶结物矿物成分为文石;而寒武纪早期至石炭纪、中生代早期至新生代早期,原始海水组成特征系数m(Ca~(2+))m(SO_4~(2-))+m(HCO_3~-)/2,为Na-Mg-KCa-Cl型海水,此期间沉积的钾镁盐矿物主要为光卤石和钾石盐,甚至含有溢晶石,海相鲕粒和碳酸盐胶结物矿物成分为方解石。根据石盐流体包裹体成分计算得出:显生宙期间,海水K+含量大部分时间变化幅度较小,为9.3～11.5mmol/kg H_2O(除了石炭纪和晚元古代),平均为10.55mmol/kg H_2O。Mg~(2+)含量在早寒武世≥67mmol/kg H_2O、晚志留世至中泥盆世31～41mmol/kg H_2O、晚古生代≥48mmol/kg H22O、晚白垩世34mmol/kg H_2O和现代55.1mmol/kg H_2O。Ca~+含量在晚元古代至古生代早期≤11mmol/kg H_2O、古生代早期至石炭纪22～35mmol/kg H_2O、石炭纪至中生代早期≤17mmol/kg H_2O、中生代早期至新生代早期19～39mmol/kg H_2O及新生代早期至今7～21mmol/kg H_2O。SO_4~(2-)含量在晚元古代至古生代早期≥23mmol/kg H_2O、古生代早期至石炭纪5～17mmol/kg H_2O、石炭纪至中生代早期13～22mmol/kg H_2O、中生代早期至新生代早期5～19mmol/kg H_2O及新生代早期至今12～29.2mmol/kg H_2O。海水Ca~(2+)与SO_4~(2-)含量的相对变化是控制海相钾盐矿床钾镁盐矿物类型的基本因素。同时,利用以上数据计算得到的显生宙各时期海水[m(Mg~(2+))+m(SO_4~(2-))]/[m(K~+)+m(Ca~(2+))]的变化与各时期海相蒸发岩系石盐层底部的Br含量变化具有同步性,进一步验证了显生宙期间海水成分是不断变化的,是约束海相蒸发岩钾盐矿物类型的主要因素。海水成分变化的控制因素为洋中脊热液和陆地水,其中洋中脊热液起主要作用,而控制这些因素变化的根本原因为板块构造运动。     

Boron speciation in aqueous fluids at 22 to 600°C and 0.1 MPa to 2 GPa

The speciation of boron in H₂O+H₃BO₃±NaCl and H₂O+Na₂B₄O₇ fluids was studied in situ at temperatures between 22 and 600°C and pressures from 0.1 MPa to ∼2 GPa using Raman spectroscopy and a hydrothermal diamond anvil cell. Additionally, we determined the frequency shifts of the 877 cm⁻¹ Raman line of [B(OH)₃]⁰ in aqueous fluids with temperature (∂ν₈₇₇/∂T)_{p = 0.1 MPa} = −0.02532 cm⁻¹K⁻¹ and pressure (∂ν₈₇₇/∂P)_{T = 22°C} = 4.06 cm⁻¹GPa⁻¹. The observed species in acidic fluids were [B(OH)₃]⁰ and smaller amounts of a four-coordinated boron species which may be attributed to dissolved metaboric acid HBO₂(aq). The ratio of this B^[4]-O species to [B(OH)₃]⁰ increases with temperature and decreases slightly with addition of NaCl. In alkaline solutions, polyboric ions depolymerize rapidly with temperature. Thus, [B(OH)₃]⁰ and [B(OH)₄]⁻ were the only remaining detectable species at 500 and 600°C. The Raman spectra showed an increase of [B(OH)₃]⁰ relative to [B(OH)₄]⁻ with temperature and an increase of [B(OH)₄]⁻ relative to [B(OH)₃]⁰ with pressure.The general trend in the boron speciation is a higher stability of simpler complexes with temperature. The experimental observations strongly indicate that planar three-coordinated [B(OH)₃]⁰ is the predominant boron species in the aqueous phase over a wide range of P-T-pH conditions. This supports the validity of previous assumptions on boron coordination in crustal and mantle wedge fluids.     

Experimental studies of equilibrium iron isotope fractionation in ferric aquo-chloro complexes

Here we compare new experimental studies with theoretical predictions of equilibrium iron isotopic fractionation among aqueous ferric chloride complexes (Fe(H₂O)₆³⁺, FeCl(H₂O)₅²⁺, FeCl₂(H₂O)₄⁺, FeCl₃ (H₂O)₃, and FeCl₄^-), using the Fe-Cl-H₂O system as a simple, easily-modeled example of the larger variety of iron-ligand compounds, such as chlorides, sulfides, simple organic acids, and siderophores. Isotopic fractionation (⁵⁶Fe/⁵⁴Fe) among naturally occuring iron-bearing species at Earth surface temperatures (up to ∼3‰) is usually attributed to redox effects in the environment. However, theoretical modeling of reduced isotopic partition functions among iron-bearing species in solution also predicts fractionations of similar magnitude due to non-redox changes in speciation (i.e., ligand bond strength and coordination number). In the present study, fractionations are measured in a series of low pH ([H⁺] = 5 M) solutions of ferric chloride (total Fe = 0.0749 mol/L) at chlorinities ranging from 0.5 to 5.0 mol/L. Advantage is taken of the unique solubility of FeCl₄^- in immiscible diethyl ether to create a separate spectator phase, used to monitor changing fractionation in the aqueous solution. Δ⁵⁶Fe_aq-eth = δ⁵⁶Fe (total Fe remaining in aqueous phase)−δ⁵⁶Fe (FeCl₄^- in ether phase) is determined for each solution via MC-ICPMS analysis.Both experiments and theoretical calculations of Δ⁵⁶Fe_aq-eth show a downward trend with increasing chlorinity: Δ⁵⁶Fe_aq-eth is greatest at low chlorinity, where FeCl₂(H₂O)₄⁺ is the dominant species, and smallest at high chlorinity where FeCl₃(H₂O)₃ is dominant. The experimental Δ⁵⁶Fe_aq-eth ranges from 0.8‰ at [Cl^-] = 0.5 M to 0.0‰ at [Cl^-] = 5.0 M, a decrease in aqueous-ether fractionation of 0.8‰. This is very close to the theoretically predicted decreases in Δ⁵⁶Fe_aq-eth, which range from 1.0 to 0.7‰, depending on the ab initio model.The rate of isotopic exchange and attainment of equilibrium are shown using spiked reversal experiments in conjunction with the two-phase aqueous-ether system. Equilibrium under the experimental conditions is established within 30 min.The general agreement between theoretical predictions and experimental results points to substantial equilibrium isotopic fractionation among aqueous ferric chloride complexes and a decrease in ⁵⁶Fe/⁵⁴Fe as the Cl^-/Fe³⁺ ion ratio increases. The effects on isotopic fractionation shown by the modeling of this simple iron-ligand system imply that ligands present in an aqueous environment are potentially important drivers of fractionation, are indicative of possible fractionation effects due to other speciation effects (such as iron-sulfide systems or iron bonding with organic ligands), and must be considered when interpreting iron isotope fractionation in the geological record.     

57Fe-Mössbauer spectroscopy on natural eosphorite-childrenite-ernstite samples

Samples of the eosphorite-childrenite [(Mn²⁺, Fe²⁺)AlPO₄(OH)₂H₂O] series from Divino das Laranjeiras and Araçuaí (Minas Gerais State) and Parelhas (Rio Grande do Norte State) pegmatites have been investigated by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy at 295 and 77 K. The Mössbauer spectra of ernstite [(Mn²⁺, Fe³⁺)AlPO₄(OH)_2-xO_x] showed the existence of ferric ions in both A and B sites, whereas ferrous ions seem to be located exclusively in the A site. Nonoxidised samples show ferrous ions located in both sites, and no Fe³⁺ could be detected. The interpretation of the Mössbauer spectra of both, oxidised and nonoxidised samples, is difficult because the hyperfine parameters of these minerals are rather similar, rendering it difficult to make proper site assignments.     

G2 theory calculations on [H3SiO4]−, [H4]SiO4], [H3AlO4]2−, [H4AlO4]− and [H5AlO4]: Basis set and electron correlation effects on molecular structures,atomic charges,infrared spectra,and potential energies

G2 theory calculations were performed on [H₃SiO₄]^?, H₄SiO₄, [H₃AlO₄]^2?, [H₄AlO₄]^?, and [H₅AlO₄]. Molecular structures, atomic charges, and infrared spectra at the HF/6-31G^* and MP2/6-31G^* levels are compared. The influence of polarization and diffuse functions on the structure of [H₃SiO₄]^? is also examined. Basis set and electron correlation effects on potential energies are assessed by comparing various levels of theory. Proton affinities of these gas-phase molecules and related mineral surface species are predicted based on corrections for cluster-size effects.     

Application of hydrogeochemistry to uranium exploration in the pine creek geosyncline, northern territory, Australia

In the Pine Creek Geosyncline, fast moving, annually recharged, low-salinity ground waters dissolve uranium- and magnesium-enriched gangue minerals from mineralized aquifer rocks. The level of dissolved uranium depends on prevailing pH, Eh, salinity and degree of adsorption, which limits its effectiveness as an exploration indicator. Near each known deposit, leaching of magnesium-enriched gangue minerals produces ground waters with very similar major-element concentration plots, the shape of which constitutes a mineralized aquifer “signature”. Gangue minerals also supply high levels of Mg²⁺ (expressed as NMg = [Mg²⁺]/[Ca²⁺ + Mg²⁺ + Na⁺ + K⁺] in milliequivalents per litre) to contained ground waters, NMg > 0.8 being common in ground waters from mineralized aquifers at each Pine Creek Geosyncline deposit. Data from Ranger One No. 3 ore body illustrates how progressive mixing of waters from mineralized and unmineralized aquifers causes graded reductions in NMg, which, when plotted onto a ground plan, delineate a hydrogeochemical aureole.High NMg (> 0.8) coincides with high uranium concentration (> 20 μg/l of U) in ground waters near Nabarlek and Ranger. Because pH-Eh conditions in aquifers at Jabiluka depress uranium solution, < 10 μg/l of U is present, although NMg values are generally > 0.8. To date NMg has always been < 0.8 in nonmineralized aquifer waters, whereas uranium may be > 50 μg/l in ground waters from felsic igneous aquifers, which can be identified as uneconomic by low (< 0.4) NMg, and by a fixed relationship between uranium and co-leached species such as F^- and soluble salts.Measurements of pH, Eh, salinity, Fe(II), Ca, Mg, Na, K, Cl, SO₄, total carbonate, phosphate, F^-, Cu, Pb, Zn and U in waters from 48 percussion holes in and near the Koongarra ore bodies have been related to mineralogy recorded in drill logs. The composition of waters from 20 holes near and along strike from known mineralization, fitted the mineralized aquifer “signature”, had NMg > 0.8 and uranium up to 4100 μ/l. These data confirm the use in this region of NMg as a hydrogeochemical indicator of uranium mineralization; they also indicate additional zones of possible mineralization.     

Uranium co-precipitation with iron oxide minerals

In oxidizing environments, the toxic and radioactive element uranium (U) is most soluble and mobile in the hexavalent oxidation state. Sorption of U(VI) on Fe-oxides minerals (such as hematite [α-Fe₂O₃] and goethite [α-FeOOH]) and occlusion of U(VI) by Fe-oxide coatings are processes that can retard U transport in environments. In aged U-contaminated geologic materials, the transport and the biological availability of U toward reduction may be limited by coprecipitation with Fe-oxide minerals. These processes also affect the biological availability of U(VI) species toward reduction and precipitation as the less soluble U(IV) species by metal-reducing bacteria.To examine the dynamics of interactions between U(VI) and Fe oxides during crystallization, Fe-oxide phases (containing 0.5 to 5.4 mol% U/(U + Fe)) were synthesized by means of solutions of U(VI) and Fe(III). Wet chemical (digestions and chemical extractions) and spectroscopic techniques were used to characterize the synthesized Fe oxide coprecipitates after rinsing in deionized water. Leaching the high mol% U solids with concentrated carbonate solution (for sorbed and solid-phase U(VI) species) typically removed most of the U, leaving, on average, about 0.6 mol% U. Oxalate leaching of solids with low mol% U contents (about 1 mol% U or less) indicated that almost all of the Fe in these solids was crystalline and that most of the U was associated with these crystalline Fe oxides. X-ray diffraction and Fourier-transform infrared (FT-IR) spectroscopic studies indicate that hematite formation is preferred over that of goethite when the amount of U in the Fe-oxides exceeds 1 mol% U (∼4 wt% U). FT-IR and room temperature continuous wave luminescence spectroscopic studies with unleached U/Fe solids indicate a relationship between the mol% U in the Fe oxide and the intensity or existence of the spectra features that can be assigned to UO₂²⁺ species (such as the IR asymmetric υ₃ stretch for O = U = O for uranyl). These spectral features were undetectable in carbonate- or oxalate-leached solids, suggesting solid phase and sorbed U(VI)O₂²⁺ species are extracted by the leach solutions. Uranium L₃-edge x-ray absorption spectroscopic (XAFS) analyses of the unleached U-Fe oxide solids with less than 1 mol% U reveal that U(VI) exists with four O atoms at radial distances of 2.19 and 2.36 Å and second shell Fe at a radial distance at 3.19 Å.Because of the large ionic radius of UO₂²⁺ (∼1.8 Å) relative to that of Fe³⁺ (0.65 Å), the UO₂²⁺ ion is unlikely to be incorporated in the place of Fe in Fe(III)-oxide structures. Solid-phase U(VI) can exist as the uranyl [U(VI)O₂²⁺] species with two axial U-O double bonds and four or more equatorial U-O bonds or as the uranate species (such as γ-UO₃) without axial U-O bonds. Our findings indicate U⁶⁺ (with ionic radii of 0.72 to 0.8 Å, depending on the coordination environment) is incorporated in the Fe oxides as uranate (without axial O atoms) until a point of saturation is reached. Beyond this excess in U concentration, precipitating U(VI) forms discrete crystalline uranyl phases that resemble the uranyl oxide hydrate schoepite [UO₂(OH)₂·2H₂O]. Molecular modeling studies reveal that U⁶⁺ species could bond with O atoms from distorted Fe octahedra in the hematite structure with an environment that is consistent with the results of the XAFS. The results provide compelling evidence of U incorporation within the hematite structure.     

平衡热液体系中硫同位素演化的几个图解

根据含硫矿物的同位素组成推断热液矿床成因是很有意义的。 1968年首先由H.Sakai指出热液的温度和pH值可以影响硫化物的同位素组成。接着,1972年H.Ohmoto以及1979年他和R.O.Rye系统讨论了平衡条件下热液的物理化学条件对硫同位素分馏的影响,建立了高温热液系统和低温热液系统的热液流体以及含硫矿物与热液成分和物理化学条件(温度、压力、氧逸度和酸碱度等)之间的数学表达式。     

Molecular orbital calculations of vibrations in three-membered aluminosilicate rings

Ab initio, molecular orbital calculations at the 3–21G^* level were carried out on H₆Si₃O₉, [H₆Si₂AlO₂]^1?, [H₆SiAl₂O₉]^2?, and [H₆A1₃O₉]^3? cyclic molecules in order to determine their structures and vibrational frequencies. These three-membered rings were found to have minima in their potential energy surfaces indicating stability of the species. The H₆Si₃O₉ ring was found to be slightly non-planar, but the [H₆SiAl₂O₉]^2? and [H₆Al₃3O₉]^3? configurations are more planar. Vibrational frequencies of the Raman-active, bridging oxygen “breathing” modes increase with Si⁴⁺ content. Galeener's (1982a, b) assignment of the D₂ peak (606 cm^?1) in the Raman spectrum of vitreous silica to an oxygen breathing mode in rings of three SiO₄ tetrahedra is reconfirmed. Correlation of the ring breathing mode frequencies as a function of (AI/AI + Si) with Raman peaks in the SiO₂-NaAlSiO₄ system is high. Three-membered aluminosilicate rings are likely to exist and give rise to Raman peaks between 540 and 600 cm_?1 in fully-polymerized aluminosilicate glasses.