Die nordschwedischen Eisenerze und verwandte Lagerstätten als Beispiele eruptiver Spaltungsprozesse

Zusammenfassung Seit einem früheren Stadium der geologischen Erforschung der nordschwedischen Eisenerzlagerstätten vom Typus Kiruna — meistens apatitreiche Magnetiterze — war es den damit beschäftigten Forschern klar, daß die Substanz der Erze im magmatischen Stadium von dem Magma der begleitenden Porphyrgesteine abgespaltet wurde. Die Natur und die Ursachen dieses Abspaltens müssen nach dem geologischen Befund beurteilt werden, denn es handelt sich um spätmagmatische Ereignisse in einem experimentell noch nicht erforschbaren Gebiet. Mineralparagenese, Struktur, Kontaktverhältnisse usw. deuten auf Kristallisation aus einem an leichtflüchtigen Gemengteilen reichen Magma (pneumotektische Gebilde). Der spätmagmatische oder restmagmatische Charakter der Erzbildung wird auch durch Übergänge nach Erztypen, die bei niedrigeren Temperaturen gebildet sind, klargelegt. Die Trennung zwischen Erz und Gestein erscheint ebenso scharf wie in den Fällen, in denen erzbildende Lösungen gasförmig abgeschieden worden sind. Die Abscheidung muß auch bei den hier behandelten spätmagmatischen Erzen auf die Wirkung der leichtflüchtigen Gemengteile (Magmagase) zurückgeführt werden. Genetisch verwandt sind sulfidische Erze, deren Anknüpfung an den Kirunatypus aus ihrem Apatit- und Magnetitgehalt hervorgeht, und die sich entweder aus pneumotektischen Magmen oder aus gasförmigen Lösungen kristallisierten. Mehr entfernt von der magmatischen Kristallisation folgen gewisse metasomatische Erze ähnlicher Zusammensetzung. Eigentümlicherweise zeigen aber die kontaktmetasomatischen Eisenerze in Kalkstein eine wesentlich andere Zusammensetzung der aus dem Magma stammenden Gemengteile, obgleich auch ihr Material aus dem Magma in Gasform entwich. Besonders auffallend ist der hohe Kieselsäuregehalt und die Seltenheit des Apatits. Diese Eigenschaften findet man auch in den Lagerstätten von diesem Typus, die in demselben Gebiet wie die Kiruna-Erze auftreten, und die mit den dortigen Tiefengesteinen verbunden sind.     

Probable causes for cyanobacterial expansion in the Baltic Sea: Role of anoxia and phosphorus retention

This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,500¹⁴C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to 7,100¹⁴C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen. This is also verified by a contemporaneous drop in the δ¹⁵N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around 3 μmol g⁻¹ at the freshwater-brackish water transition. All P pools except the CaCO₃ fraction showed a distinct increase around 9,300¹⁴C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source of the sediment. Slightly after 4,000¹⁴C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased from around 75 to 25–30 μmol g⁻¹. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of 3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent anoxic conditions.     

Distribution surfaces in solvent extraction systems

In the solvent extraction of metals, the distribution of the metal is usually dependent on the concentrations of several different species in the two phases. Despite this fact, distribution isotherms are usually presented as plots of C_o as a function of C_aq and these are used for a McCabe-Thiele type evaluation of a number of stages and flow rates, etc., each individual isotherm being valid only for one set of initial conditions; this treatment limits the possibilities of optimizing the system. In the present paper an extension of three-dimensional plots is suggested with special reference to the Cu/LIX64N extraction system. The distribution surface is defined and the general properties of the plots are outlined.A procedure is outlined whereby the surface can be represented on a two dimensional plot and a theoretical model for the surface can be superimposed.The paper also shows how distribution ratios (D values) are related to the surface.     

Filamentary structures in planetary nebulae

We have studied small-scale, filamentary features in 14 planetary nebulae and found that some structures are recurrent and shaped like the letters V and Y, with the apex or stem pointing toward the central parts of the nebula. Two such filaments containing dust, one in NGC 3132 and one in NGC 7293, were investigated in more detail. The mass and density of the filaments were obtained from extinction measurements, and their physical properties were derived. We propose that the structures are confined by magnetic fields, and derive magnetic field strengths of about 10⁻⁸ T, in line with earlier estimates. We also estimate the magnitude of the electric currents that we expect are generated in these dynamic systems. We propose a theory where the magnetic fields control the sculpting and evolution of small-scale filaments. This theory demonstrates how the substructures may form magnetized flux ropes that are twisted around each other, in the shape of double helices. Similar structures, and with similar origin, are found in many other astrophysical environments.     

EPR investigation of NO2 and CO2 − and other radicals in beryl

A number of different impurities are located in the open channels of natural beryl crystals. The rare Maxixe beryl contains an unusual amount of NO₂. The isoelectronic CO₂ ⁻ radical is found in the irradiated Maxixe-type beryl. The NO₂ radicals are distributed in the Be–Al plane of the crystal, with the nitrogen atom close to the oxygens of the beryl cavity wall. These oxygens repel the negative CO₂ ⁻ radical, which is located at the center of the beryl cavity and rotates around its O–O axis, which is parallel to the crystal c-axis. When there is a nearby alkali ion at the center of the beryl channel, it reorients the CO₂ ⁻ radical so that its bisector is parallel to the c-axis and points toward the positive ion. Different signals are analyzed for Li⁺, Na⁺, and another counter-ion, which probably is Cs⁺. The related NO₃ and CO₃ ⁻ radicals are the color centers in the investigated deep blue beryls. The slow decay of the color, which makes these beryls useless as gem stones, is related to the decay of the hydrogen atoms which are present in these crystals. Evidence is given that NO₃ is created in Maxixe beryl by a natural process, while CO₃ ⁻ in Maxixe-type beryl has been created by irradiation. The temperature dependence of the EPR signals of these two radicals was investigated, but a definitive proof that they rotate at the center of the beryl cavity could not be given. EPR signals from some other radicals in beryl have been observed and described.