The lower carboniferous black shale formation,a possible source for noble and base metal deposits in the NE Rhenish Massif,Federal Republic of Germany

Summary In the northeastern Rhenish Massif the Lower Carboniferous black shale formation, comprising black shales, black lydites, siliceous limestones and clayshales, host low concentrations of stratabound sulfides, which are interpreted as sedimentary-exhalative depositions. Intraformational mobilizations and migrations of metals and their reprecipitation in physico-chemical traps led locally to minable ores. Further metal concentration has been caused by supergene processes.

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Die unterkarbonische Schwarzschieferserie: potentielle Muttergesteine für Edel- und Buntmetall-Vorkommen im nordöstlichen Rheinischen Schiefergebirge, Bundesrepublik Deutschland

Zusammenfassung Im nordöstlichen Rheinischen Schiefergebirge treten in der unterkarbonischen Schwarzschieferserie, die sich aus Schwarzschiefern, schwarzen Lyditen, Kieselkalken und Tonschiefern zusammensetzt, geringe Konzentrationen an schichtgebundenen Sulfiden auf. Die schichtgebundenen Sulfide werden als sedimentär-exhalative Bildungen gedeutet. Intraformationale Mobilisationen und Migrationen von primär in Sulfiden fixierten Metallen sowie deren Wiederabsetzung in physikalisch-chemischen Fallen führten lokal zur Bildung von bauwürdigen Erzen. Weitere Anreicherungen erfolgten teilweise durch supergene Prozesse.

     

In-situ fluid-pressure measurements for earthquake prediction: An example from a deep well at Hi Vista,California

Short-term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes. Instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur, and it is now recognized that even to have the possibility of a reliable earthquake-prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals. We are conducting experiments to determine the maximum signal-to-noise improvement that can be obtained in drill holes. In a 592 m well in the Mojave Desert near Hi Vista, California, we measured water-level changes with amplitudes greater than 10 cm, induced by earth tides. By removing the effects of barometric pressure and the stress related to earth tides, we have achieved a sensitivity to volumetric strain rates of 10^–9 to 10^–10 per day. Further improvement may be possible, and it appears that a successful earthquake-prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km, assuming that the premonitory strain signals are, in fact, present.     

Sampling the Chemistry of Shallow Aquifer Systems — A Case Study

Pumped waters from 14 Pennsylvania wells, located in shallow sandstone, siltstone and shale aquifers, were continuously monitored for dissolved oxygen (D. O.), nitrate (NO₃), pH, electrical conductivity (EC) and water temperature in a discharge manifold at the well head. The amount of pumping or purging required to stabilize these parameter readings varied by well site and parameter being analyzed. However, the purging required was generally greatest for D. O. and least for water temperature where: D. O. < NO₃ pH < EC < water temperature. Wells located near the siltstone-shale interface generally required far more purging than did wells located elsewhere. Although parameter stability was often achieved within purging one bore volume, the complexity, diversity, and variability in the data and these well-ground water systems, suggest that no single purging rule is appropriate. Instead, the extent of purging required before sampling these shallow aquifers should be determined by incorporating on-site monitoring of target or related parameters into the purging process.
From a sampling perspective, the relationship between NO₃ and D. O. concentrations during purging were analyzed relative to aquifer type. For most wells located in sandstone or siltstone, NO₃ concentrations remained relatively constant during purging irrespective of changes in D. O. For most wells located in shale, these two were positively and similarly correlated, suggesting that a general relationship exists.     

Zur Kenntnis der präkambrischen,schichtgebundenen Molybdänitvorkommen in Südnorwegen

The southern Norwegian molybdenum deposits have hitherto been looked upon as typical examples of deposits of pneumatolytic — catathermal origin formed by emanations from intrusive granites. It is now demonstrated that all these deposits are to be found stratabound in a series of grey gneisses. They are accompanied by varying amounts of graphite and apatite of biogenetic origin and all of them show the same sulphide and oxide ore mineral paragenesis. It is concluded that the concentration and precipitation of metals took place in marine environments. Both the ores and their host rocks later underwent the same highmetamorphic processes.     

Zur Kenntnis der schichtgebundenen Wolfram-Molybdän-Vererzung im Örsdalen (Rogaland), Norwegen

Zusammenfassung Die Vererzung im Örsdalen (Rogaland), Norwegen tritt innerhalb einer migmatitischen Gneis-Serie auf, welche durch zahlreiche graphitführende Amphibolit-Horizonte gekennzeichnet ist. Die Erze liegen schichtgebunden in einem der graphitführenden Amphibolite. Die Zufuhr der metallhaltigen Lösungen erfolgte in der gleichen Periode, in der auch das Ausgangsmaterial der heute in engster Verknüpfung mit dem Erzbestand auftretenden Amphibolite als vulkano-sedimentäres Material zugeführt worden ist. Intensive orogenetische Prozesse führten zu einer isochemischen Umwandlung des Erzbestandes. Die Annahme einer Beteiligung von metasomatisch-hydrothermalen Metallzufuhren aus unbekannten Tiefen erübrigt sich.

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The ores in Örsdalen (Rogaland), Norway, occur in a migmatitic folded gneiss series, which in the inner part of the Schåningsmulde is characterized by numerous amphibolitic bands. The ores are found stratiform in only one of the graphite-bearing amphibolites. The metal-bearing solutions belong to the effusive activity which gave rise to the volcanic rocks interbedded in the geosynclinal series. Isochemical alterations of rock and ore minerals were produced during intensive orogenic processes. It is not necessary to assume that metasomatic-hydrothermal solutions have brought the metal content from unknown depths.

     

Simulating Oxygen Intrusion into Highly Heterogeneous Fractured Media Using High Performance Computing

Fractured crystalline rocks are under consideration by several countries as host formations for high-level nuclear waste repositories. The redox evolution in these host rock formations is an important issue for the stability and safety of these disposal sites. If, for example, during a glaciation/deglaciation event, oxygen-rich glacial meltwater penetrates to the depth of the planned repository, some of the engineered barriers would be adversely affected. Moreover, oxidizing conditions would increase the solubility and mobility of many radionuclides. Reactive transport simulations, which are typically used to assess the redox buffering capacity of these host rock formations, are computationally demanding, and thus, calculations for the evaluation of oxygen penetration are usually carried out over simplified geometries and the heterogeneity of the site, both physical (e.g., variability in the groundwater flow field and the kinematic porosity) and mineralogical (e.g., variability in the abundance of Fe(II)-bearing minerals), is usually represented in a simplified fashion. Here, it is shown how a recently developed numerical framework, combined with high performance computing technologies, allows the full geometrical, physical and mineralogical complexity of the site under study to be efficiently included in these types of reactive transport calculations. A synthetically generated realistic three-dimensional fractured medium is used to assess oxygen penetration patterns and their dependence on both the hydrogeological conditions and the availability of Fe(II)-bearing minerals. The results of the calculations point out the significant influence of both physical and mineralogical heterogeneity on the oxygen penetration patterns, thus highlighting the importance of a model parameterisation consistent with the site complexity.     

Fine structure of optical aurora

This is a review paper on the fine structure of optical aurora. Spatial scales smaller than about 1 km and temporal scales shorter than about 1 s are considered. Fine structure is present in most types of aurora, but earlier much of it has not been possible to study properly due to instrument limitations. Recent advancements in optical instrumentation have provided considerable improvements of temporal and spatial resolution. Optical measurements are able to give higher resolution than any other types of ground-based instruments used in auroral studies. To interpret the information, both more advanced modelling and analysis methods are being developed. This gives access to new knowledge on the physical processes responsible for particle acceleration, precipitation, atmospheric ion chemistry, and auroral light production.     

Projected temperature changes indicate significant increase in interannual variability of U.S. maize yields

Climate change has the potential to be a source of increased variability if crops are more frequently exposed to damaging weather conditions. Yield variability could respond to a shift in the frequency of extreme events to which crops are susceptible, or if weather becomes more variable. Here we focus on the United States, which produces about 40% of the world’s maize, much of it in areas that are expected to see increased interannual variability in temperature. We combine a statistical crop model based on historical climate and yield data for 1950–2005 with temperature and precipitation projections from 15 different global circulation models. Holding current growing area constant, aggregate yields are projected to decrease by an average of 18% by 2030–2050 relative to 1980–2000 while the coefficient of variation of yield increases by an average of 47%. Projections from 13 out of 15 climate models result in an aggregate increase in national yield coefficient of variation, indicating that maize yields are likely to become more volatile in this key growing region without effective adaptation responses. Rising CO₂ could partially dampen this increase in variability through improved water use efficiency in dry years, but we expect any interactions between CO₂ and temperature or precipitation to have little effect on mean yield changes.