Determination of Platinum-Group Elements and Gold in Geological Matrices by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) after Separation with Selenium and Tellurium Carriers

The present study describes a method for the extraction of Pt, Pd, Rh, Ru, Ir and Au from various geological materials after fusion with sodium peroxide in zirconium crucibles involving samples that vary in mass from 1 g to more than 20 g. Precipitation is brought about by reduction of the platinum-group elements (PGEs) with Sn²⁺, using selenium and tellurium as carriers in the presence of a catalyst (KI). The extraction yields obtained by this method are between 95 and 100% for PGEs. Gold is less well extracted (around 80%). Detection of the noble metals in the extraction residues is carried out by using ICP-MS. The results obtained by this technique are reported for five CCRMP certified reference materials and are close to their certified values. The elements were also determined in a natural glass sample melted during a meteoritic impact and contaminated by PGEs at ultra-trace concentrations.     

Numerical modelling of landscape evolution on geological time-scales: a parameter analysis and comparison with the south-eastern highlands of Australia

Surface-process models (SPMs) have the potential to become an important tool in predicting sediment flux to basins, but currently suffer from a lack of quantitative understanding of their controlling parameters, as well as difficulties in identifying landscape properties that can be used to test model predictions. We attempt to constrain the parameter values that enter a SPM by comparing predictions of landscape form (as expressed by hypsometric and fractal measures) and process rates obtained for different parameter sets with observations from the south-eastern Australian highlands, a rifted margin mountain belt that has remained tectonically stable during Cenozoic times. We map the hypsometry and fractal characteristics of south-eastern Australia and find that the roughness amplitude (G) correlates well with local relief, whereas the hypsometric integral (H ) correlates slightly better with elevation than with relief. The fractal dimension (D) does not correlate with any other morphometric measure and varies randomly throughout the region. Variograms generally show three kinds of scaling behaviour of topography with increasing wavelength, with topography only being truly self-affine at wavelengths between ～1 and 10 km. From a review of the available data on long-term denudation rates in south-eastern Australia, we infer that these have been 1–10 m Myr^?1, and average escarpment retreat rates 0.2–1.0 km Myr^?1, throughout the Cenozoic. Model predictions, using a SPM that includes hillslope diffusion and long-range fluvial transport, suggest that landscape form evolves with time; after an initial phase where D, G and relief increase, all morphometric measures decrease with increasing denudation. The behaviour of GandH in the models is qualitatively compatible with the observations; D, however, varies predictably in the models, in contrast with its random behaviour in the real world. The observed present-day morphology of SE Australia does not impose quantitative constraints on parameter values. The fractal analyses do impose general conditions of relative parameter values that have to be met in order to create ‘realistic’ topographies. They also suggest that there is no theoretical basis for including hillslope diffusion in SPMs with a spatial resolution coarser than 1 km. A comparison of the observed denudation and retreat rates with model predictions places order-of-magnitude constraints on parameter values. Thus, data pertaining to landscape evolution are much more valuable than static present-day topography data for calibrating SPMs.     

Fourier transform infrared studies of the reaction of Cl atoms with PAN,PPN, CH3OOH,HCOOH, CH3COCH3 and CH3COC2H5 at 295±2 K

The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with peroxyacetylnitrate (PAN), peroxypropionylnitrate (PPN), methylhydroperoxide, formic acid, acetone and butanone. Decay rates of these organic species were measured relative to one or more of the following reference compounds; ethene, ethane, chloroethane, chloromethane, and methane. Using rate constants of 9.29×10^–11, 5.7×10^–11, 8.04×10^–12, 4.9×10^–13, and 1.0×10^–13 cm³ molecule^–1 sec^–1 for the reaction of Cl atoms with ethene, ethane, chloroethane, chloromethane, and methane respectively, the following rate constants were derived, in units of cm³ molecule^–1 s^–1: PAN, <7×10^–15; PPN, (1.14±0.12)×10^–12; HCOOH, (2.00±0.25)×10^–13; CH₃OOH, (5.70±0.23)×10^–11; CH₃COCH₃, (2.37±0.12)×10^–12; and CH₃COC₂H₅, (4.13±0.57)×10^–11. Quoted errors represent 2 and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295±2 K and 700 torr total pressure of nitrogen or synthetic air. The results are discussed with respect to the previous literature data and to the modelling of nonmethane hydrocarbon oxidation in the atmosphere.In recent discussions with Dr. R. A. Cox of Harwell Laboratory, UKAEA, we learnt of a preliminary value for the rate constant of the reaction of Cl with acetone of (2.5±1.0)×10^–12 cm³ molecule^–1 sec^–1 measured by R. A. Cox, M. E. Jenkin, and G. D. Hayman using molecular modulation techniques. This value is in good agreement with our results.     

Expériences sur la précipitation directe de l'apatite dans l'eau de mer: Implication dans la genèse des phosphorites

The direct precipitation of apatite in seawater is inhibited by Mg ions. The action of various factors on this precipitation is studied: addition of Ca, addition of F, reduction of pH and simultaneous effect of reduction of pH and addition either of F or of Ca. It is established that the reduction of the pH of seawater to 7 allows the precipitation of the apatite with a Ca/Mg ratio in the water of 1.2. The favourable environment for the settlement of natural apatite must then be either neutral or acid. This result is corroborated by the re-study of Gulbrandsen's equation. Such an acid environment with a high phosphorus content may be the result of oxidation of large quantities of organic matter due to previous intense biological activity. The acidity is probably brought about by bubbling of CO₂.     

Sweeping through a second order resonance

The adiabatic invariant theory and its extension to the case of separatrix crossing have been instrumental in setting up simple models describing the effects of the passage through a first order resonance forced by small non conservative forces. These models have been helpful in understanding the processes of capture into resonance and of formation of gaps at resonances. Second order resonances (3/1 or 5/3 ...) have not been so thoroughly investigated and present some special features. We shall show how to disencumber first the problem from its secular term and how to modelize the mixed resonance term involving the sum of the resonant angles. A modelization of the two single satellite resonant terms has already been proposed by Lemaître and Borderies and Goldreich. We shall then assemble those three simple models to show the effect of a passage through the resonance under the assumption that the natural precession rates are large enough for the three individual resonances to be sufficiently separated.     

缓变型地球化学灾害:特征、模型和应用

“缓变型地球化学灾害”是通过长期积累而存在于土壤或沉积物中的包括重金属和有机污染物在内的环境污染物,因环境物理化学条件（例如温度、pH值、湿度、有机质含量等）的改变减小了环境容量,某种或某些形态的污染物大量地被重新活化和突然释放出来并造成严重生态和环境损害的灾害现象。这种灾害具有明显的特征,其定量数学模型可较完整地概括出环境系统从“干净”到“污染”再到“灾害”的整个过程,可以用于灾害的风险概率评估、预测、灾害爆发轨迹等方面的研究,为土壤污染防治和灾害预警提供了定量研究工具和可供实际采用的基本手段,对当前国土资源调查中的“生态环境地球化学评价”具有重要的借鉴意义。     

Constraints on the ore fluids in the Sando Alcalde AuAg epithermal deposit,southwestern Peru: fluid inclusions and stable isotope data

The Sando Alcalde ore deposit (southwestern Peru) has been studied in order to characterize the physicochemical parameters of the ore fluids and to determine the fluid process (mixing or boiling) which involves the precious metal mineralization. Mineralogy, ${\delta }^{18}{\mathrm{O}}_{\mathrm{quartz}}$ isotopic values and fluid inclusion data give arguments in favour of a boiling phenomenon. This conclusion corroborates fluid inclusion studies previously performed in this area on the low-sulphidation epithermal deposits of Arcata, Orcopampa and Apacheta, where boiling has been described as the main factor for ore deposition. To cite this article: A.-S. André-Mayer et al., C. R. Geoscience 337 (2005).     

Real-Time Tsunami Forecasting: Challenges and Solutions

A new method for real-time tsunami forecasting will provide NOAAs Tsunami Warning Centers with forecast guidance tools during an actual tsunami event. PMEL has developed the methodology of combining real-time data from tsunameters with numerical model estimates to provide site- and event-specific forecasts for tsunamis in real time. An overview of the technique and testing of this methodology is presented.     

Monitoring chemical contamination levels in the Mediterranean based on the use of mussel caging

Within the framework of the biointegrator network (RINBIO), 92 man-made cages containing mussels (Mytilus galloprovincialis), distributed over 1800 km of the French Mediterranean coast, made it possible to assess chemical contamination by heavy metals (Cd, Hg, Zn, Pb, Cu, Ni, Cr, As) and organic compounds (DDT, PCBs, HAP). The caging technique was adopted to compensate for the scarcity of natural shellfish stocks in the Mediterranean and to enable comparison of the sites regardless of their physicochemical and trophic characteristics. Models linking a biometric parameter (the condition index) to pollutant levels make it possible to adjust raw data on contamination for a reference individual, by making a clear distinction between physiological factors (growth) and environmental ones. The results demonstrate significant levels of pollutants in sites heretofore unsampled; the pollution occurs at limited areas, and the sources have been identified. Moreover, average contamination levels are comparable to those measured in wild species and in other areas. Overall, the research demonstrates the reliability of this methodological approach for monitoring marine pollution, especially in the Mediterranean.