Redox problems in the “metallogenic specialization” of magmatic rocks and the genesis of hydrothermal ore mineralization

Considering the history and current state of the problem of the so-called metallogenic specialization of magmatic rocks, the paper places emphasis onto various aspects of the genesis of ore mineralization depending on the redox state of magmas (as a logical continuation of S. Ishihara’s works), fluids, and host rocks. These problems were inadequately poorly explored and discussed by researchers dealing with ore deposits. Various possible variants of ore-forming redox processes for different types of mineral deposits, with ore mineralization affiliated to granites (Ta, Sn, W, Mo, and Be) and mafic magmas (Au, Ag, U, Cu, Zn, Pb, As, Sb, and Hg) and, accordingly, to crustal and mantle origin, are discussed. On the basis of analyzed geological data, including those published over the past three decades, it is shown that the redox state of ore-producing magmas commonly significantly impacted not only the ore potential of magmatic complexes but also the genetic type of the ore mineralization. The redox state of the fluids predetermined the transport and precipitation speciation of metals. Influence mechanisms of hydrocarbons from sedimentary country rocks and gaseous products of their pyrolysis on ore deposition of various metals are considered. Understanding these mechanisms can be helpful for predicting the possible precipitation sites of ore mineralization of noble, radioactive, and chalcophile metals.     

On the energy spectrum of galactic primary cosmic rays: Results from the transport equation

The spectrum of galactic primary cosmic rays at relativistic monenta is calculated. The primaries are assumed to be accelerated continuously from the thermal galactic background medium by first- and second-order Fermi acceleration. We show that the observed spectrum is readily obtained from the transport equation conventionally invoked to discuss propagation and loss of cosmic rays in our Galaxy from a distribution of sources. We have previously (Lerche and Schlickeiser, 1985) shown that the observed secondary to primary ratio is satisfactorily explained by a similar use of the transport equation, allowing for secondary production from the primaries. Accordingly, when the results of this paper are added to those concerning the secondary/primary ratio behaviour, it would seem that continuous Fermi acceleration accounts, in a quantitative fashion, for the spectral behaviours observed at Earth.     

Mass motions in a heated flare filament

Energy transport in a hot flare plasma is examined with particular reference to the influence of fluid motion. On the basis of dimensional considerations the dynamical timescale of the flare plasma is shown to be comparable to the timescale for energy loss by conduction and radiation. It is argued that mass motion is likely to have a profound influence on the evolution of the flare.The detailed response of a flare filament to a localized injection of energy is then analyzed. Radiative, conductive and all dynamical terms are included in the energy equation. Apart from greatly enhancing the rate of propagation of the thermal disturbance through space, mass motion is found to be significant in transferring energy through the moving fluid.Finally the predicted thermal structure is discussed and it is concluded that the presence of mass motions in the flare may be inferred from the form of the soft X-ray differential emission measure.     

New insights into geochemical behaviour in ancient marine carbonates (Upper Jurassic Ammonitico Rosso): Novel proxies for interpreting sea‐level dynamics and palaeoceanography

Elemental concentrations in Phanerozoic sea water are known to fluctuate both in time and space. With regard to carbonates precipitated from marine fluids, elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non‐equilibrium as well as post‐depositional alteration processes. To assess the potential of carbonate elemental chemostratigraphy, seven Upper Jurassic sections were investigated along a proximal to distal transect across the south‐east Iberian palaeomargin. The aim was to explore stratigraphic and spatial variations in calcium, strontium, magnesium, iron and manganese elemental abundances. The epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint. In contrast, the epioceanic geochemical record agrees with reconstructed open marine sea water values, reflecting a moderate degree of syn‐depositional to early marine pore water diagenesis. Establishing a fair degree of preservation of matrix micrite, a thorough statistical approach was applied and elemental associations tested for their environmental significance. Principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium, iron and strontium abundances. Processes related to early diagenetic nodulation in Ammonitico Rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice. The clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the Late Jurassic. The investigation of potential time‐fluctuation of geochemical patterns was approached through variogram computation. The observed temporal behaviour is most likely to be forced by relative sea‐level dynamics, reflecting Late Jurassic palaeoceanographic conditions and potential planetary interactions. The data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors.     

Hydrogeophysical investigation and estimation of groundwater potentials of the Lower Palaeozoic to Precambrian crystalline basement rocks in Keffi area, north-central Nigeria, using resistivity methods

The use of resistivity sounding and two-dimensional (2-D) resistivity imaging was investigated with the aim of delineating and estimating the groundwater potential in Keffi area. Rock types identified are mainly gneisses and granites. Twenty-five resistivity soundings employing the Schlumberger electrode array were conducted across the area. Resistivity sounding data obtained were interpreted using partial curve matching approach and 1-D inversion algorithm, RESIST version 1.0. The 2-D resistivity imaging was also carried out along two traverses using dipole–dipole array, and the data obtained were subjected to finite element method modeling using DIPRO inversion algorithm to produce a two-dimensional subsurface geological model. Interpretation of results showed three to four geoelectrical layers. Layer thickness values were generally less than 2 m for collapsed zone, and ranged from 5 to 30 m for weathered bedrock (saprolite). Two major aquifer units, namely weathered bedrock (saprolite) aquifer and fractured bedrock (saprock) aquifer, have been delineated with the latter usually occurring beneath the former in most areas. Aquifer potentials in the area were estimated using simple schemes that involved the use of three geoelectrical parameters, namely: depth to fresh bedrock, weathered bedrock (saprolite) resistivity and fractured bedrock (saprock) resistivity. The assessment delineated the area into prospective high, medium and low groundwater potential zones.     

The partitioning of Zr and Nb between diopside and melts in the system diopside-albite-anorthite

The crystal liquid partitioning of Zr and Nb has been measured experimentally between diopsidic clinopyroxene and melts in the system Di-Ab-An. Nb was found to be excluded from diopside (D(Nb) is always less than 0.02). D(Zr) is quite variable, ranging from 0.05 to 0.45. D(Zr) is positively correlated with the Al content of both the melt and the pyroxene and is negatively correlated with temperature. Both D(Zr) and D(Nb) were found to be independent of oxygen fugacity. This implies that neither Zr or Nb suffer valence changes over a range of oxygen fugacities spanning both lunar and terrestrial conditions.     

Organochlorine compounds in bottom sediments of a delta Branch of the Northern Dvina

Organochlorine compounds in bottom sediments of a delta branch of the Northern Dvina have been studied. Data on the concentration and distribution of organically bound chlorine are given. The specific features of the formation of the levels and profiles of chlorinated phenolic compounds in bottom sediments under the effect of specific primary and secondary sources in the territory of Arkhangelsk Industrial Center are demonstrated.     

Preliminary Results from the Magnetic Field Measurements Using MAGDAS at Ilorin, Nigeria

MAGDAS, the Magnetic Data Acquisition System, was successfully installed at the University of Ilorin, Nigeria—an equatorial station—in August 2006. MAGDAS is an important component of the International Heliophysical Year, IHY. We examined the preliminary results obtained from the analysis of the geomagnetic data obtained from the MAGDAS measurement. Diurnal variations of the solar quiet daily variation in the three geomagnetic elements, H, D, Z were studied. The obtained signatures of the magnetic field variations were discussed in the context of the literature. The day-to-day variability of the horizontal and vertical intensities as well as the declination of the geomagnetic field were examined. The study justified the need for a partner magnetic field observatory along same meridian as Ilorin, north or south of it, to facilitate synthesis of the equatorial electrojet effect.