Mikroskopische und mikroanalytische Untersuchungen an metallischen Kügelchen aus Tiefseesedimenten des Zentralen Pazifik

Metallic spherules from Central Pacific Ocean sediments (“Valdivia” expedition VA 05-1, 1973) were studied by means of the ore microscope and by electron microprobe. The data suggest that most of the spherules are of meteoritic origin, i.e. ablation drops from meteorites as suggested in former studies on spherules from marine environment by Schmidt and Keil (1966), Finkelmann (1970, 1972) and others. The metallic spherules contain up to about 60% Ni, 37% Fe and 3% Co. Unusually high contents of Cr (up to 12%) were noted in some spherules.     

Geochemistry and mineralogy of laterites in the Sula Mountains greenstone belt, Lake Sonfon gold district, Sierra Leone

Geochemical and mineralogical investigations have been carried out on laterite profiles developed in the Lake Sonfon Au district of northern Sierra Leone. The area is underlain by Archean metavolcanics and constitutes part of the Sula Mountains greenstone belt, which is mineralized in Au. Extensive lateritization has affected the rocks of this region, resulting in a profile which from bottom to top consists typically of a decomposed bedrock zone, a pisolitic laterite layer and a duricrust layer. Both the pisolitic and duricrust layers of the laterite are sometimes punctuated by lenses of ironstones containing high amounts of Cu, Zn, Ni, Co and Ce. Gold occurs as small grains within the heavy mineral fraction recovered from the decomposed rock zones and pisolitic layers of the profiles and also in gravels of streams draining the area. The mineralogy of the duricrust and pisolitic layers is dominated by goethite, gibbsite and quartz, with minor amounts (<5% by volume) of ilmenite, magnetite, haematite, rutile and kaolinite. The kaolinite content increases towards the decomposed rock zone, where talc, vermiculite and other layer lattice silicates become abundant. The heavy-mineral fraction of stream sediments is composed essentially of ilmenite, magnetite, haematite, and traces of rutile, zircon, tourmaline and Au. The Au grains are often characterized by a 10–200-μm-wide rim having a much lower content of Ag (0.3 wt.% or lower) than the grain interior (about 5 wt.% on average). Dissolution effects are also observed on the grain surfaces. It is considered that Au derived from the amphibolite parent rock is dissolved, transported, and redeposited during laterization.The duricrust cover of the laterite profiles is characterized by high contents of Fe₂O₃ (ca. 60 wt.%) and Al₂O₃ (ca. 32wt.%) and low content of SiO₂ (ca. 9 wt.%). In comparison, the pisolitic layer is higher in SiO₂ (ca. 18 wt.%) as well as a slightly higher in Al₂O₃ (ca. 34 wt.%). Lateritic weathering has resulted in the removal of CaO, Na₂O, MgO and SiO₂, with relative enrichment of Fe₂O₃ and Al₂O₃. The geochemical distribution of the trace elements in the laterite profiles can be related to the occurrence of the auriferous mineralization. The significance of these observations is discussed in relation to the origin of the lateritic Au and the role of the associated trace elements as indicators of the mineralization.     

Volume relaxation of compacted SiO2 glass: a model for the conservation of natural diaplectic glasses

Relaxation experiments on vitreous SiO₂, densified at 900°C, 20 kbar to a permanent density of 2.36 g cm^?3 yield an activation energy of69 ± 5kcal mol^?1 in the temperature range 700–800°C. The data can be used to estimate minimum cooling rates, maximum depositional temperatures or maximum thicknesses of shock-metamorphosed rocks containing diaplectic glasses, if relaxation of a glass densified under dynamic conditions is assumed to be similar to that of statically densified glass.     

Development and changes in the Eastern Province of Saudi Arabia

Due to a particularly favourable geologic and tectonic setting in the Eastern Province, Saudi Arabia has the world largest oil reserves and is the third largest oil-producing nation in the world. Based on oil and gas revenues, the Kingdom experienced an overwhelming development during the last few decades, changing a desert country into a modern industrialized nation. Main characteristics of spatial changes are based on processes of urbanization and industrialization, on agricultural reclamations and infra-structural developments. Since the natural environment of deserts and semi-deserts in the Eastern Province is determined by an extremely sensitive equilibrium, environmental impacts, shortages in water resources, as well as limited human resources are causing basic problems, which will influence future developments.     

Refractory- and metallurgical-type chromite ores,Zambales ophiolite,Luzon, Philippines

The Zambales ophiolite is the major source of chromite ore in the Philippines. The chromitites are concordant cumulates and are associated with distinct chromitite-bearing sequences within the mantle peridotites. Refractory and metallurgical chromite deposits are spatially separated and related to different lithologic associations, which crystallized from different parental magmas. — Refractory chromite ores (30–44 wt% Cr₂O₃; 20–30 wt% Al₂O₃) are linked with the peridotite-troctolite-olivine gabbro lineage. Two main types were found: (1) Al-rich refractory ores associated with harzburgites and feldspathic periodotites and (2) more Cr-rich varieties associated with lherzolites. — Metallurgical chromite ores (45–53 wt% Cr₂O₃; 12–18 wt% Al₂O₃) are linked with the peridotite-pyroxenite-norite lineage. Two main types were also found: (1) Cr-rich metallurgical ores associated with orthopyroxenites and (2) more Al-rich varieties related to clinopyroxenites. — The chemical composition of chromite within the deposits varies depending on the chromite/silicate ratios of the ore types and grades continuously into accessory chrome spinels in the wall-rock peridotites. — The geochemistry of accessory chrome spinels in various peridotites and mafic cumulates depends on the mineralogical composition and the stratigraphic position of their host rocks.New address: BEB Erdgas und Erdöl GmbH, Riethorst 12, D-3000 Hannover 51The terms chrome-spinels and chromite are used as follows: 1. Chrome-spinel is only used for those occuring as accessory minerals in various ultramafic and mafic rocks (= accessory chrome-spinels). Their chemical composition has been determined only by microprobe analysis. — 2. Chromite is used for ore and ore deposits (=chromitites); the chemical composition has been determined by wet chemistry (AAS) or by microprobe analysis     

Transmission electron microscopic study of antiphase domains in CaAl2Ge2O8-Feldspar

Transmission electron microscopic study of synthetic CaAl₂Ge₂O₈-feldspar revealed two types of antiphase domains: type “b”-antiphase domains with the displacement vector 1/2 [110] and type “c”-antiphase domains with the displacement vector 1/2 [111]. The “b”-domains were on the order of 0.1 μm in size, while the “c”-domains displayed wall to wall distances mostly between 0.1 and 1 μm. The formation of the two types of antiphase domains is due to reductions in translational symmetry associated with the phase transitions \(C\bar 1 \to I\bar 1 \to P\bar 1\) . The antiphase domain textures of CaAl₂Ge₂O₈-feldspar are very similar to the textures found in natural and synthetic anorthite, CaAl₂Si₂O₈.     

Bestimmung der Phytoplanktonvolumina — Methodik und Ergebnisse am Beispiel Niederrhein

For data treatment of phytoplankton countings in the Lower Rhine the specific biovolume was calculated. The used computer-aided method is described, and the correlation between phytoplankton biomass, cell number and chlorophyll a is presented.     

Zwei neue Harpacticoidenformen aus dem Grundwasser

Ohne Zusammenfassung     

Die Westwärts-Intensivierung des Polarfront-Jetstream in den Winkel zwischen Polarfront und Tropopause an der Ostseite eines polaren Kälteausbruchs,eine Erweiterung des klassischen Grenzflächenproblems von Margules

Zusammenfassung Es wird eine auf rein dynamischen Grundlagen beruhende Erklärung für die starke Westwärts-Intensivierung des Polar-front-Jetstream in den Winkel zwischen der geneigten Polarfrontfläche und der gegengeneigten Tropopause an der Ostflanke eines polaren Kälteausbruches gegeben.Eine gewisse Ähnlichkeit des Atmosphärenaufbaues mit dem Aufbau des Ozeans im Stromstrich des Golfstromes führt dazu, die Trägheitsgrenzschichten-Theorie vonJ. Charney [1] auf ein solches atmosphärisches System anzuwenden. Ein dreigeschichtetes Atmosphärenmodell wird entwickelt, und für dieses werden Bewegungsgleichungen abgeleitet, die es erlauben, das Problem entsprechend dem LösungsgangCharneys zu behandeln.Der Vergleich mit den aus den Beobachtungen abgeleiteten Neigungen der Polarfront und der Tropopause und der beobachteten Westwärts-Intensivierung des Stromes fällt sehr befriedigend aus. Diese Theorie erfaßt selbstverständlich nur die rein dynamische Seite der Erscheinung und berücksichtigt den sicher wichtigen Beitrag der thermodynamischen Prozesse durch die Verwendung des rohen Modells nur näherungsweise.

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Summary Based on purely dynamical reasoning an explanation for the strong westward-intensification of the polarfront jetstream into the angle between the inclined polarfront surface and the opposite inclined tropopause on the eastern side of an outbreak of cold polar air is presented.Certain similarity of the structure of the atmosphere with that of the ocean in the main core of the gulf stream has guided me to apply the inertial boundary layer theory ofJ. Charney [1] to such an atmospheric system. A three-layered model of the atmosphere has been developed and corresponding equations of motion were derived, which allow to handle the problem according to the solution ofCharney.The comparison with the slopes of polarfront and tropopause according to the observations and with the observed westward intensification of the flow is rather satisfactory. However, we must understand that this theory only considers the dynamical side of the phenomenon and does only approximately account for the important contribution of thermodynamic processes by the use of the rather simple model.

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Résumé L'auteur tente d'expliquer du point de vue purement dynamique l'intensification vers l'Ouest du jet situé dans l'angle compris entre le front polaire et la tropopause d'inclinaison contraire, sur le flanc oriental d'un afflux d'air polaire.Une certaine analogie entre la structure de l'atmosphère et celle de l'océan à l'endroit du Gulf-stream incite à appliquer au cas évoqué ici la théorie de la couche limite d'inertie deJ. Charney [1]. On imagine un type d'atmosphère à trois couches pour lequel on établit les équations du mouvement permettant de traiter le problème en cause à l'aide du procédé deJ. Charney.Les observations concernant l'inclinaison du front polaire et de la tropopause ainsi que celles de l'intensification du jet vers l'Ouest confirment la théorie de façon très satisfaisante. Cette dernière, purement dynamique, ne tient compte que d'une manière approchée des processus thermodynamiques sans doute importants.

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