Simultaneous radio and optical observations of the mid-latitude atmospheric response to a major geomagnetic storm of 6–8 April 2000

Basic properties of the mid-latitude traveling ionospheric disturbances (TIDs) during the maximum phase of a major magnetic storm of 6–8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics (51.9°N,103.0°E), and MORTI located at the observatory of the Institute of Ionosphere (43.2°N, 77.0°E). Observations of the O (557.7 and 630.0 nm) emissions originating from atmospheric layers centered at altitudes of 90 and 250 km were carried out at Irkutsk and of the O₂(b¹∑_g⁺−X³∑_g⁻) (0-1) emission originating from an atmospheric layer centered at altitude of 94 km was carried out at Almaty. Our radio and optical measurement network observed a storm-induced solitary large-scale wave with duration of 1 h and a wave front width of no less than 5000 km, while it traveled equatorward with a velocity of 200 m/s from 62°N to 38°N geographic latitude. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being different for different altitudes. A comparison of the auroral oval parameters with dynamic spectra of TEC variations and optical 630 nm emissions in the frequency range 0.4–4 mHz (250–2500 s periods) showed that as the auroral oval expands into mid-latitudes, also does the region with a developed medium-sale and small-scale TEC structure.     

Occurrence Forms of Carbon,Sulfur, and Noble Metals in Deposits of the Black-Shale Formation by the Example of the Degdekan Gold-Ore Deposit (Northeastern Russia)

Pyrite crystals and ore-bearing shales of the Degdekan deposit were studied by means of XPS, SEM–EDX, EPMA, and AAS. Five peaks of carbon organic forms were identified, conforming to polymer compounds containing either double bonds of carbon or alkyne groups and compounds containing C–OH and C=O bonds, as well as, probably, small amounts of S-containing compounds and those with functional groups of carboxylic acids. Sulfate prevails over sulfite in pyrites; among the surface sulfide forms, disulfide prevails over monosulfide; the presence of polysulfide is registered. The occurrence of various chemical forms of sulfur on the surface might provide for concentrating of microelements including the noble metals (NMs) in their surface-bound forms. The regular behavior of NMs (Au, Pt, Pd, and Ru) depending on the grain sizes (specific surfaces) of pyrite crystals along with the narrow range of the ratios of structural and surface components of the concentrations of different NMs points to NM coprecipitation with pyrite during the same productive stage. No capture of NM-containing carbonaceous phases took place, which should violate the regularity of Au distribution in pyrites of the Sukhoi Log deposit.     

Surface typochemistry of hydrothermal pyrite: Electron spectroscopic and scanning probe microscopic data. II. Natural pyrite

Pyrite crystals from gold deposits of various genetic types (mesothermal and epithermal) were examined by techniques of x-ray photoelectron and Auger electron microscopy and by scanning probe microscopy. The results confirm a conclusion made in earlier hydrothermal experiments that nonautonomous phases (NP) of variable composition occur on the surface of pyrite crystals. These phases are localized within a layer of submicrometer (nanometer) thickness (up to ～0.5 μm) within which the typochemistry of pyrite surface is pronounced. The development of sulfate on the surface of pyrite crystals from epithermal Au-Ag deposits is a typochemical feature of the origin of their ore mineralization at low temperatures and shallow depths. Supergene conditions are characterized by the presence of an oxi-hydroxide or oxide film of FeIII, which morphologically differs from the layer of a pyrite-like NP. The composition and properties of the NPs are different for pyrite from mesothermal and epithermal deposits: they are close to those of a pyrrhotite-like NP discovered on synthetic hydrothermal pyrite and contain an additional sulfite anion for pyrite from the former type of deposits and are close to sulfide-disulfide ensembles with trivalent Fe for pyrite from the latter type of deposits. Trace elements, including precious metals, can be accommodated in such a phase via the stabilization of clusters with Fe³⁺ and SO ₄ ^2? in its structure. The instability of the crystallization process in epithermal environments may bring about the development of double-level nanostructure because of the structural transformation of vicinal surfaces into a set of ordered domains and the synthesis of nonautonomous “precursor” phases. Such systems can be stabilized via the excess dissolution of admixtures or the transition of the surface layer into another phase state.     

Exploration of magnetic anomalies of the Baikal rift zone

The paper presents the results of an experimental study of natural magnetic field anomalies in the Baikal rift zone.     

Trace elements as indicators of the physicochemical conditions of mineral formation in hydrothermal sulfide systems

The three-mode distribution of trace-element (TE) concentrations is observed in accordance with three main forms of TE occurrence in mineral: structural, surficial, and phase (native TE phases). Minerals of hydrothermally synthesized pyrite–pyrrhotite–magnetite–greenockite assemblage in the presence of Au and Mn are studied. Discrimination of modes is made, using the method of statistical sample of analytical data for single crystals (SSADSC), which is based on the postulate that individual crystals can contain predominantly one of possible forms. This is supported by study of Cd modes of occurrence by element thermorelease atomic-absorption spectrometry. X-ray photoelectron spectroscopy and atomic-force microscopy were used to examine the surficial TE forms. It has been confirmed that the dependence of the TE content on the crystal size in the sample is mainly due to surficial nonautonomous phases absorbing TEs. The effect of correspondence of chemical-component forms on the surfaces of coexisting minerals is also corroborated. This phenomenon is not related to the mutual contamination of phases but is due to the induction of the corresponding states of chemical forms in coexisting nonautonomous phases. It is possible to obtain true coefficients of interface distribution, characterizing structural TE impurities. These coefficients differ strongly from apparent distribution coefficients calculated from the bulk contents of impurities, except for Mn in pyrrhotite and magnetite, where its structural mode is predominant. The results obtained show that TEs can be used as quantitative geochemical indicators, which help to obtain correct information about the parameters of mineral formation and TE contents in the fluid phase.     

Dualistic distribution coefficients of trace elements in the system mineral–hydrothermal solution. III. precious metals (Au and Pd) in magnetite and manganmagnetite

Distribution coefficients D of Au and Pd between magnetite (manganmagnetite) and ammonium chloride hydrothermal solution and the structural D^str and surface-related D^sur terms of these coefficients were determined at 450 and 500°С and a pressure of 1 kbar using internal sampling techniques. Quantitative data on the speciation of precious metals are obtained using the technique of statistical selections of analytical data on single crystals SSADSC and compared with LA-ICP-MS data. Both Pd and Au are elements compatible with magnetite and its manganoan variety: D^str is ≈3 for Pd and ≈1 for Au, although Au seems to weakly enrich fluid at 500°C: D^str ≈ 0.5–0.8. The trends of postmagmatic Pd and Au fractionation can thus strongly depend on the presence of spinel-group minerals, first of all, magnetite and its solid solutions. The dualistic nature of the distribution coefficients provides sound grounds to believe that both elements are highly compatible, with regard not only for the structural but also for the surface-related modes of their occurrence (D^sur ≈ 17 and ≈50–70 for Au and Pd, respectively). The maximum concentrations of structural modes of the elements are 5.3 ppm for Au and 5.1 ppm for Pd and were found in the solid solution whose jacobsite mole fractions were 0.82 and 0.49, respectively. The principal distribution patterns of the elements in crystals are confirmed by LA-ICP-MS data. Data on this system testify that the distribution coefficients of minor and trace elements are geochemically dualistic because of the abnormal absorption properties of nanometer-sized nonautonomous phases on the surface of ore minerals, and this dualism plays an important geochemical role.