Geochemical Studies of Sodium Enriched Metavolcanite Series in the Area of Longbohe Copper Deposit,Yunnan Province,SW China：Nd,Sr and Pb Isotopic Characteristics and Chronology

The chronological data obtained by a variety of dating methods have confirmed that the sodium enriched metavolcanite series in the area of the Longbohe copper deposit at Jinping, Yunnan Province, was formed during the Proterozoic (its Pb−Pb isochron age=1595±75 Ma), corresponding to the Dahongshan Group sodium enriched metavolcanites. The Sm−Nd isochron age of 1336±46Ma should represent the time at which this series of volcanic rocks experienced spilitization in response to sodium metasomatism, equivalent to the time of sedimentation of the Ailaoshan Group and Yashan Group rocks. The Rb−Sr ages of the volcanic rocks and the Pb−Pb ages of copper ores have recorded the events of strong dynamic metamorphism and of strong reworking-metallogenesis of copper during the Jinningian period. Similarities in forming age, rock assemblage and isotopic characteristics between the sodium enriched metavolcanite series and the Dahongshan Group sodium enriched metavolcanite series have provided new clues to the exploration of the Dahongshan-type copper deposits in this area. Granted jointly by the National Natural Science Foundation of China (Nos. 49702022, 40073001) and the State 973 Program (No. G1999043215).     

Anhydrite-bearing rocks from the Rožná district (Moldanubian zone,Czech Republic): high-grade metamorphosed exhalites?

Several types of anhydrite-bearing rocks have been found in the amphibolite-facies metamorphosed rocks at the north-eastern margin of the Moldanubian Zone. Anhydrite either forms monomineralic bands up to 40 cm thick, or occurs in the form of disseminated grains in surrounding calc-silicate gneiss together with feldspar, scapolite, amphibole, pyroxene, epidote and pyrite. The isotopic composition of sulphur ('³⁴S=30.6 to 32.3‰) and strontium (⁸⁷Sr/⁸⁶Sr=0.70797 to 0.70781) in anhydrite may indicate a marine source of sulphate. The isotopic ratio of strontium is in the same range as that of metamorphosed strata-bound barite-sulphide ores, which have been previously described in the same area. The '³⁴S values of coexisting pyrite range from 21.4 to 22.5‰, the (³⁴S_{anhydrite-pyrite} corresponding to the metamorphic temperature of 600 to 660 °C. In contrast to many submarine-exhalative deposits, the oxygen isotopic compositions of anhydrite ('¹⁸O=9.3 to 10.2‰) are lighter than that of barite ('¹⁸O=10.4 to 13.8‰). This indicates that the both minerals are not in isotopic equilibrium. Therefore, it is probable that anhydrite and barite from the Ro—ná district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks. The '¹³C values in calcite ('¹³C=-17.2 to -18.7‰) from anhydrite-bearing rock are lower than those in distant marbles. As graphite is absent in anhydrite- and calcite-bearing rocks, impoverishment in the ¹³C isotope cannot be attributed to the graphite-carbonate isotopic exchange during metamorphism. It is proposed that low '¹³C values in carbonates are caused by pre-metamorphic oxidation of organic matter in course of hydrothermal processes. Anhydrite and anhydrite-bearing calc-silicate gneiss from the north-eastern part of the Moldanubian Zone are interpreted to be the high-grade metamorphosed analogue of anhydrite-rich exhalites commonly found in submarine-exhalative hydrothermal deposits.     

Occurrence of naphthalenesulfonates and their condensates with formaldehyde in a landfill leachate and their transport behavior in groundwater of the Upper Rhine Valley, Germany

. Naphthalenesulfonates and their condensation products with formaldehyde are manufactured in the chemical industry for broad application as tanning agents, dispersing agents, and as superplasticizers for concrete. With the disposal of waste they have found their way into the aquatic environment. Five monomeric naphthalenesulfonates and a group of dimeric sulfonated naphthalene-formaldehyde condensates (SNFC) were identified in the leachate and in groundwater observation wells downstream in the plume of the Karlsruhe-West landfill, situated in the Upper Rhine Valley in southwest Germany. For the main monomer of technical SNFC products, 2-naphthalenesulfonate (2-NS), the concentration in the leachate was 170 µg l^–1, which decreased to 9.5 µg l^–1 at a distance of about 300 m from the boundary of the landfill. In the Merdingen tracer test field, the transport of these compounds was studied under more controlled conditions in two tracer experiments with (1) two model compounds, and (2) a technical SNFC product and uranine as a reference tracer. In these experiments, the monomeric naphthalenesulfonates and the SNFC with n=2 behave as conservative tracers. Thus, the findings of the landfill study were supported by these results. Higher molecular SNFC were strongly retarded, which is attributed to adsorption to soil particles. The results of the second tracer experiment suggest a degradation of 2-NS and 2,6-naphthalenedisulfonate (2,6-NDS) after adaptation of the microorganisms in the groundwater aquifer as a consequence of the first tracer experiment.     

Landslide risk assessment and management: an overview

Landslides can result in enormous casualties and huge economic losses in mountainous regions. In order to mitigate landslide hazard effectively, new methodologies are required to develop a better understanding of landslide hazard and to make rational decisions on the allocation of funds for management of landslide risk. Recent advances in risk analysis and risk assessment are beginning to provide systematic and rigorous processes to enhance slope management. In recent years, risk analysis and assessment has become an important tool in addressing uncertainty inherent in landslide hazards.This article reviews recent advances in landslide risk assessment and management, and discusses the applicability of a variety of approaches to assessing landslide risk. Firstly, a framework for landslide risk assessment and management by which landslide risk can be reduced is proposed. This is followed by a critical review of the current state of research on assessing the probability of landsliding, runout behavior, and vulnerability. Effective management strategies for reducing economic and social losses due to landslides are described. Problems in landslide risk assessment and management are also examined.     

3D characterization of coarse aggregates

A new and accurate characterization method for dimensions, shape and roughness of aggregate particles has been developed. The method is based on the 3D-laser scanning technique and evaluation of coarse-grain aggregate-particle images. Parameters are obtained with either analytical Fourier analysis or geometrical analysis. The results from the two methods are compared with each other as well as with manual measurements. Although the Fourier-based analysis gives about 10% smaller size values, the comparison of the results shows, in general, a good agreement between the different techniques. This new method for analysis of coarse-grain aggregates gives reliable results for both the shape and topographical parameters of particles.     

Morphologic and spectral investigation of exceptionally well-preserved bacterial biofilms from the Oligocene Enspel formation, Germany

The fossilised soft tissues of a tadpole and an associated coprolitic structure from the organic-rich volcanoclastic lacustrine Upper Oligocene Enspel sediments (Germany) were investigated using high-resolution imaging techniques and nondestructive in situ surface analysis. Total organic carbon analysis of the coprolite and the sediment revealed values of 28.9 and 8.9% respectively. The soft tissues from the tadpole and the coprolite were found to be composed of 0.5 to 1 μm-sized spheres and rod shapes. These features are interpreted as the fossil remains of bacterial biofilms consisting probably of heterotrophic bacteria and fossilised extracellular polymeric substances. They became fossilised while in the process of degrading the organic matter of the organism and the coprolite. Comparison with a modern marine biofilm revealed morphologic details identical to those observed in the fossil bacterial biofilms. Although the fossil biofilms on both macrofossils exhibited identical microtextures, their mode of preservation was inhomogeneous and varied between calcium phosphate and an as yet unidentified mineral phase consisting mainly of Si, Ca, Ti, P, and S, but also showing the presence of Mg, Al, and Fe. The coprolite consists purely of fossilised bacterial cells in a densely packed arrangement and associated fossilised extracellular polymeric substances.In addition to preliminary imaging and energy-dispersive X-ray analysis, both the fossil biofilms and the sediment were investigated by nondestructive in situ analysis using time of flight-secondary ion mass spectroscopy (ToF-SIMS). The mass spectra obtained on the coprolite in mass-resolved chemical mapping mode allowed the tentative identification of a number of organic secondary ion species. Some spectra appear to indicate the presence of bacterial hopanoids, but further work using standard techniques such as gas chromatography mass spectroscopy is needed to conclusively verify the presence of these substances. Nevertheless, ToF-SIMS chemical maps were successfully correlated with electron microscopy images, allowing the correlation of molecular spectra, the spatial distribution of individual organic species, and specific morphologic features to demonstrate the potential of this approach in the analysis of microfossils.     

δC of low-molecular-weight organic acids generated by the hydrous pyrolysis of oil-prone source rocks

Low-molecular-weight (LMW) aqueous organic acids were generated from six oil-prone source rocks under hydrous-pyrolysis conditions. Differences in total organic carbon-normalized acid generation are a function of the initial thermal maturity of the source rock and the oxygen content of the kerogen (OI). Carbon-isotope analyses were used to identify potential generation mechanisms and other chemical reactions that might influence the occurrence of LMW organic acids. The generated LMW acids display increasing ¹³C content as a function of decreasing molecular weight and increasing thermal maturity. The magnitudes of observed isotope fractionations are source-rock dependent. These data are consistent with δ¹³C values of organic acids presented in a field study of the San Joaquin Basin and likely reflect the contributions from alkyl-carbons and carboxyl-carbons with distinct δ¹³C values. The data do not support any particular organic acid generation mechanism. The isotopic trends observed as a function of molecular weight, thermal maturity, and rock type are not supported by either generation mechanisms or destructive decarboxylation. It is therefore proposed that organic acids experience isotopic fractionation during generation consistent with a primary kinetic isotope effect and subsequently undergo an exchange reaction between the carboxyl carbon and dissolved inorganic carbon that significantly influences the carbon isotope composition observed for the entire molecule. Although generation and decarboxylation may influence the δ¹³C values of organic acids, in the hydrous pyrolysis system described, the nondestructive, pH-dependent exchange of carboxyl carbon with inorganic carbon appears to be the most important reaction mechanism controlling the δ¹³C values of the organic acids.     

Stirring geochemistry in mantle convection models with stiff plates and slabs

Numerical models of mantle convection are presented that readily yield midocean ridge basalt (MORB) and oceanic island basalt (OIB) ages equaling or exceeding the apparent ∼1.8-Ga lead isotopic ages of trace-element heterogeneities in the mantle. These models feature high-viscosity surface plates and subducting lithosphere, and higher viscosities in the lower mantle. The formation and subduction of oceanic crust are simulated by means of tracers that represent a basaltic component. The models are run at the full mantle Rayleigh number and take account of faster mantle overturning and deeper melting in the past. More than 97% of the mantle is processed in these models. Including the expected excess density of former oceanic crust readily accounts for the depletion of MORB source relative to OIB sources. A novel finding is of gravitational settling of dense tracers within the low-viscosity upper mantle, as well as at the base of the mantle. The models suggest as well that the seismological observation of a change in tomographic character in the deep mantle might be explained without the need to postulate a separate layer in the deep mantle. These results expand the range of models with the potential to reconcile geochemical and geophysical observations of the mantle.