Problems of Siderite Formation and Iron Ore Epochs: Communication 1. Types of Siderite-Bearing Iron Ore Deposits

It is shown that siderite is unstable during sedimentation, diagenesis, and metamorphism of sedimentary and volcanosedimentary rocks. Regularities in the distribution of siderite in Precambrian jaspilites (iron formations), metasomatic ores of the Bakal type, continental–marine coaliferous formations, and oolitic iron ores are discussed. The genesis of the Precambrian iron formations and Riphean–Lower Paleozoic elisional–hydrothermal deposits is considered. The genetic relation of nodular siderites from coaliferous formations and oolitic iron ores with lowmoor coal-forming peat deposits is noted.     

Search for differences in the velocities and directions of the kiloparsec-scale jets of quasars with and without X-ray emission

The X-ray emission of the kiloparsec-scale jets of core-dominant quasars is usually interpreted as inverse Compton scattering on the cosmic microwave background (CMB) emission (Sample I). By analogy with the situation on parsec scales, ultrarelativistic motion along a jet oriented at a small angle to the line of sight is usually invoked to explain the X-ray emission while also satisfying the condition of equipartition between the energies associated with the relativistic particles and the magnetic field on kiloparsec scales. This leads to an increase in the energy flux of the CMB radiation in the rest frame of the kiloparsec-scale jets. Consequently, the intensity of the CMB radiation is enhanced to the level required for detectable X-ray emission. This suggests that kiloparsec jets of quasars with similar extents and radio flux densities that are not detected in the X-ray (Sample II) could have subrelativistic speeds and larger angles to the line of sight, due to deceleration and bending of the jet between parsec and kiloparsec scales. This suggests the possible presence of differences in the distributions of the difference between the position angle for the parsec-scale and kiloparsec-scale jets for these two groups of quasars; this is not confirmed by a statistical analysis of the data for Samples I and II. It is deduced that most of the sources considered exhibit bending of their jets by less than about 1.5 times the angle of the parsec-scale jet to the line of sight. This suggests that the X-ray emission is generated by other mechanisms that there is no equipartition.     

Authigenic zeolites in the sedimentary mantle of the world ocean

The paper deals with results of general and systematic analysis of data from deep-sea drilling (360 stations) and a personal study carried out by the authors on the distribution and facies location of authigenic zeolites in the sedimentary mantle of the World Ocean.The scheme of zeolite distribution, compiled for the Holocene—Pleistocene, Miocene, Eocene and Cretaceous periods confirmed the previously established global stratification of zeolites. It showed that the main mass of phillipsite was formed during the Pleistocene—Holocene, while clinoptilolite was a predominant mineral in Eocene and Cretaceous rocks. Both zeolites were wide-spread in the Oligocene and Miocene. Facies location and paragenesis of associated minerals as well as the original material of their formation are different for phillipsite and clinoptilolite.The most probable reasons for vertical stratification of oceanic zeolites of global significance are changes of the character of volcanism in time and general evolution of sedimentation in the World Ocean.     

Problems of Siderite Formation and Iron Ore Epochs: Communication 2. General Issues of the Precambrian and Phanerozoic Ore Accumulation

It is shown that peat bogs, which accumulate coal- and siderite-bearing sediments, serve as a generator of ferruginous solutions with the significant part of Fe migrating from them in the form of metalloorganic compounds. The stability of organic Fe-bearing complexes provides favorable conditions for the late diagenetic–catagenetic siderite formation in adjacent sea basins. It has been established that the formation of Phanerozoic coals, oil shales, and black shales was nearly coeval with the formation of goethite–chlorite–siderite ores. The paper discusses the influence of volcanic activity on the formation of Precambrian–Phanerozoic iron ore deposits and emphasizes the significance of siderite formation in the general evolution of the sedimentary iron ore formation.     

Inverse Compton Scattering of Radiation from a Central Source as a Possible Mechanism for the Formation of X-Ray Radiation from Kiloparsec Jets of Core-Dominated Quasars

Astronomy Reports - For the interpretation of X-ray radiation from kiloparsec jets of quasars, the inverse Compton scattering of the cosmic microwave background has been widely used for almost 20...     

Periods of the Long-Term Variability of the Blazar 0716+714 and Their Inter-Correlations in a Helical Jet Model

Various quasi-periods for the long-term variability of the radio emission, optical emission, and structural position angle of the inner part of the parsec-scale jet in the blazar 0716+714 have been detected. The relationships between these quasi-periods are interpreted assuming that the variability arises due to helical structure of the jet, which is preserved from regions near the jet base to at least 1milliarcsecond from the core observed in radio interferometric observations. The radiating jet components should display radial motions with Lorentz factors of≈3, and decelerate with distance from the jet base. The best agreement with the data is given in the case of non-radial motions of these components with a constant physical speed. It is also shown that the helical shape of the jet strongly influences correlations both between fluxes observed in different spectral ranges and between the flux and position angle of the inner part of the parsec-scale jet.     

Siderite formation and evolution of sedimentary iron ore deposition in the Earth’s history

The role of siderite in Phanerozoic and Precambrian iron formations is discussed. Various types of iron formations are characterized, and their place in the evolution of sedimentary iron ore deposition is outlined. In Precambrian iron ore deposition, siderite is a primary mineral, whereas in Phanerozoic iron formations it becomes a secondary mineral and is commonly related to diagenetic and catagenetic processes.     

Problems of Iron and Phosphorus Geochemistry in the Precambrian

The localization of economic sedimentary iron ore and phosphorite resources is discussed in comparative aspects. It is shown that the major economic resources of iron ore are hosted in Precambrian rocks, whereas the phosphorites are related to Upper Phanerozoic. High-temperature hydrothermal solutions served as an important source of iron for jaspilite ores. The low P₂O₅content therein indicates that the phosphorus deposition was only weakly related to the hydrothermal activity. Thus, the hydrothermal origin of phosphorite is denied from the geochemical standpoint.     

Evidence of submarine hydrothermal discharge to the northwest of Guadeloupe Island (Lesser Antilles island arc)

During the Soviet-French survey carried out on board of the R.V. Akademik N. Strakhov, between Guadeloupe and Montserrat island in the central Lesser Antilles, evidence of submarine hydrothermal activity was discovered on the southeastern tip of the Shoe-Rock escarpment. The latter is part of a large, 130 km long, transverse structure, the Montserrat-Marie Galante fault, which crosses the Guadeloupe archipelago. Another locus of activity, probably of subdued importance nowadays, is represented by the d'Entrecasteaux dome, a small faulted seamount, located about 25 km to the SW of the former area.The evidence for hydrothermal activity is: (a) a wide range of values of conductive heat flow (q=6–11 mW/m²) and regular vertical variation at some sites with extreme values located close to the two above-mentioned features (average regional value, q = 105 mW/m², s.d. = 32); (b) occurrence of secondary mineralizations (todorokite, nontronite, etc.) replacing locally the primary matrix of basal upper Pliocene deposits; (c) geochemical anomalies in seawater near the sea bottom, showing enrichment in mantle-derived ³He (δ³He up to 10.2%), correlated with a sharp Zn anomaly (content up to 523 ppb).Further investigations along the submerged segments of the Montserrat-Marie Galante fault should probably lead to other discoveries of hydrothermal venting and/or mineralizations.     

Geometrical and Kinematic Parameters of the Jet of the Blazar S5 0716+71 in a Helical-Jet Model

Periodic variations of the position angle of the inner jet of the blazar S5 0716+71 suggest a helical structure for the jet. The geometrical parameters of a model helical jet are determined. It is shown that, when the trajectories of the jet components are non-ballistic, the angle between their velocity vectors and the line of sight lies in a broader interval than is the case for ballistic motions of the components, in agreement with available estimates. The contradictory results for the apparent speeds of components in the inner and outer jet at epochs 2004 and 2008–2010 can be explained in such a model. The ratio of the apparent speeds in the inner and outer jet are used to derive a lower limit for the physical speed of the components (β > 0.999) and to determine the pitch angle of the helical jet (p = 5.5°). The derived parameters can give rise to the conditions required to observe high speeds (right to 37c) for individual jet components.