Whole-rock chemistry of the Gameleira I uranium deposit,Lagoa Real,Brazil

The Lagoa Real uranium (U) province, referred to as Lagoa Real, is located in the state of Bahia, north-eastern Brazil. Lagoa Real has ∼112,000 metric tonnes and average grade of 2700 ppm of U₃O₈, being one of the largest U deposits in the world and the largest in Brazil. Despite its economic and strategic importance, there are gaps in the geological knowledge of the Lagoa Real U deposits. One of them is the lack of extensive whole-rock chemical data sets. Here, we present whole-rock chemical analyses for major and trace elements, including the rare-earth elements (REE), from barren country rocks to uraniferous ore shoot, systematically sampled from an exploratory drill hole. The chemical data indicate that albitite rocks, with and without uraniferous mineralisation, cannot result from sodic syenitic magmatism, as proposed by recent studies. Petrographical and geochemical evidence supports the previously suggested concept that the Lagoa Real albitite rocks resulted from sodic metasomatism of the granitic country rock, known as the São Timóteo granite. Their ore-mineral assemblages and geochemical characteristics are similar to albitite-hosted U deposits worldwide.     

砂岩碎屑组份变化对库车坳陷和南天山盆山演化的指示

为研究库车坳陷中-新生代物源变化与南天山构造演化的关系,对该坳陷中-新生界砂岩进行了系统取样,应用Dickinson砂岩分析方法详细研究了其沉积背景和物源变化。库车坳陷中-新生代沉积物源始终为再造山旋回带,自老到新砂岩中不稳定岩屑组份的含量有规律地变化:从三叠系到侏罗系,岩屑组份中沉积岩岩屑含量最高;白垩系中变质岩岩屑增多;新生界特别是新近系,碳酸盐岩岩屑所占的比例很大。岩屑组份的这种变化反映了天山地区隆升和剥蚀的一个历史过程。随着山脉隆升幅度和剥蚀强度的加大,古生界变质岩和碳酸盐岩逐步接受剥蚀,并在白垩纪以后成为盆地沉积物的主要物源。根据风化指数半定量计算的结果,结合前人古气候的研究成果,早-中三叠世该区沉积物风化程度低,推测此时地形高差较大;在晚三叠世至晚侏罗世该区风化程度较高,地形起伏较低;白垩纪是一个转折期,沉积物风化程度由强转变为弱,地形高差在该期也有所增大;古近纪延续了这种趋势。新近纪以后地形高差显著加大,沉积物风化程度明显降低,说明此时南天山的隆升速率和库车坳陷的沉积速率都很快,源区与沉积区的距离很近。     

Formation and stability of mixed Mg/Ca/phytate species in synthetic seawater media: Consequences on ligand speciation

The results of a potentiometric investigation (by ISE-H⁺, glass electrode) on the speciation of phytate ion (Phy¹²⁻) in an ionic medium simulating the major components (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO₄²⁻) of natural seawater, at different salinities and t = 25 °C, are reported. The work was particularly aimed at determining the possible formation of mixed Ca²⁺–Mg²⁺–phytate ion pairs, and to establish how including the formation of these mixed species would affect the speciation modeling in seawater media. After testing various speciation models, that considering the formation of the MgCaH₃Phy⁵⁻, MgCaH₄Phy⁴⁻, Mg₂CaH₃Phy³⁻ and Mg₂CaH₄Phy²⁻ species was accepted, and corresponding stability constants were determined at two salinities (S = 5, 10). A discussion is reported both on the choice of the experimental conditions and on the possibility to extend these results to those typical of real seawater. A detailed procedure is also described to demonstrate that the stability of these species is higher than that statistically predicted. As reported in literature, a parameter, namely log X, has been determined in order to quantify this extra stability for the formation of each mixed species at various salinities. For example, at S = 10, log X₁₁₃ = 2.67 and log X₁₁₄ = 1.37 for MgCaH₃Phy⁵⁻ and MgCaH₄Phy⁴⁻ (statistical value is log X_stat = 0.60), and log X₂₁₃ = 6.11 and log X₂₁₄ = 2.15 for Mg₂CaH₃Phy³⁻ and Mg₂CaH₄Phy²⁻ (log X_stat = 1.43), respectively. Results obtained also showed that the formation of these species may occur even in conditions of low salinity (i.e. low concentration of alkaline earth cations) and low pH (i.e., more protonated ligand).     

Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K_i^equ), total ligands concentration (L_iT) and association/dissociation rate constants (k_i¹,k_i^- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K₁^equ: 11.2–13.0, log K₂^equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k₁¹:6.1–20 × 10³ (M s)^− 1, k₂¹: 1.3–6.3 × 10³ (M s)^− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM_C, i.e. 1 mg_CL^− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).     

珠江口及附近海域夏季氮的化学形式分布研究

根据1998年夏季对珠江河口及附近海域的水质调查，研究了氮的各种化学形式的空间分布特征、相关系数和环境条件的影响。结果表明：珠江河口中，无机氮含量很高，占总氮的85％；而硝酸氮占无机氮的95％，NO2^--N和NH4^ -N含量很低。在外海，则以有机氮为主，占总氮的80％。NH4^ -N和NO2^--N在伶仃洋河口中部出现最大值，在外海的值最小；其它形式的氮从伶仃洋内河口到外海，其浓度都逐渐降低。NO3^--N是各种形式氮中的主要因素，它与各形式氮之间具有良好的相关性；NH4^ -N和NO2^--N与其它形式氮之间的相关性都很差，而其余各种形式氮之间都有较好的相关性。涨潮时不利于污染物的扩散；与小潮相比，大潮时伶仃洋河口中部表层氮的浓度偏高。     

自然金的化学分离方法

作者用物理方法和化学方法相结合分离了九个矿区的自然金,效果良好,其纯度一般达99％以上。X光、化学分析和物性测试表明,化学处理对自然金的物性、化学成分和结构无明显影响。文中分别对几种矿物组合的化学分离方法作了具体介绍。     

砂岩风化晕厚度在广东晚更新世测年中的应用

广东地区河流阶地和冲积扇沉积物中砂岩砾石风化晕随时间增厚。风化晕生长速度呈指数衰减,并拟合于下列公式:T 1485D4.13这里T=时间,以年表示,D=沉积物表部约50块砾石风化晕厚度的加权平均值,以毫米表示。利用风化晕厚度确定出广东地区河流第一和第二级阶地分别为1000—13300年和8600—26500年,肇庆盆地北部山前地带第Ⅰ和第Ⅱ级冲积扇分别为51500年和24400年。同时,在构造地貌变形分析的基础上,估算出本区三条主要北东向断裂带在晚更新世—中全新世的垂直断层作用速度为0.6—1.6毫米/年,中全新世甚或晚更新世晚期以来的活动速度极小     

河北东坪金矿区水泉沟岩体的地球化学特征

水泉沟岩体主要由二长岩构成。主要矿物是碱性长石和斜长石,它们的含量高达80%以上。石英不多见,暗色矿物含量少。副矿物主要是磁铁矿、石榴石、榍石和锆石。交代结构发育,蚀变现象普遍。主要化学组分和微量元素含量及δ¹⁸O值变化范围大。该二长岩体是由老片麻岩经热液碱交代作用而成。     

Tafoni on coastal slopes,South Devon,U.K.

Cavernous weathering (tafoni development) occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level. The freshly weathered surfaces of the cavern interiors are irregular in morphology, discordant to major rock structure, formed by substantially weakened rock and associated with granular weathering debris. The weathering debris contains soluble elements in proportions similar to those present in seawater, and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0·1–0·2 m is indicated by the presence of chlorine. Scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries. The mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog.