New data on mineralogy and metallogeny of scarns in the Pitkyaranta ore region

A wide application of modern precision research techniques to the studies of Pitkyaranta ores allowed us to find increased contents of indium (to 0.33%), silver (447 g/t), gold (0.2–0.4 g/t), and palladium (0.2 g/t). A series of rare minerals previously not found here was also discovered. Among ore minerals, these are roquesite, zavartskite, electrum, stutzite, altaite, bismite, glaucodot, cervelleite, hedleyite, pavonite, cannonite, plantnerite, lindkvistite, ashoverite, etc. The discovery of roquesite and electrum is the most important in terms of metallogeny. Roquesite (indium sulfide) is found in Karelia for the first time. The highest indium contents in direct correlation to those of zinc are characteristic for polymetallic ores of the Pitkyaranta ore fields with sphalerite as the concentrating mineral (to 0.5% of In). The predicted zinc resources are evaluated to ∼2.5 million t for the Pitkyaranta group of ore deposits, and to 400 000 t for the Hopunvaara region. Respectively, the resources of indium amount to ∼2400 t (total) and 600 t for the Hopunvaara region.     

Fluorite as an Sm–Nd geochronometer of hydrothermal processes: Dating of mineralization hosted in the Strel’tsovka uranium ore field,eastern Baikal region

The possibility of using hydrothermal fluorite as an Sm–Nd geochronometer is based on the results of an REE pattern study of this mineral (Chernyshev et al., 1986). As a result of REE fractionation, in many cases, the Sm/Nd ratio achieves a multifold increase compared with its level in terrestrial rocks, and the radiogenic shift of the ¹⁴³Nd/¹⁴⁴Nd isotope ratio reaches 10–20 ε_Nd units over a short time interval (as soon as tens of Ma). This is a necessary prerequisite for Sm–Nd isochron dating of fluorite. Zonal polychrome fluorite from a vein referred to the final stage of large-scale uranium mineralization at the Sterl’tsovka deposit in the ore field of the same name located in the eastern Transbaikal region has been dated using the ¹⁴³Nd/¹⁴⁴Nd method. To optimize isochron construction, local probes with high and contrasting Sm/Nd ratios have been sampled from the polished surfaces of two samples, taking into account the REE pattern of zonal fluorite. Sm–Nd isochron dating has been carried out separately for each sample. The ¹⁴⁷Sm/¹⁴⁴Nd и ¹⁴³Nd/¹⁴⁴Nd ratios vary within the intervals 0.5359–2.037 and 0.512799–0.514105, respectively. Two isochrons, each based on six fluorite probes, have been obtained with the following parameters, which coincide within 2σ uncertainty limits: (1) t = 134.8 ± 1.3 Ma, (¹⁴³Nd/¹⁴⁴Nd)₀ = 0.512310 ± 13, MWSD = 0.43 and (2) t = 135.8 ± 1.6 Ma, (¹⁴³Nd/¹⁴⁴Nd)₀ = 0.512318 ± 10, MWSD = 1.5. The mean age of fluorite based on two isochron datings is 135.3 ± 1 Ma. Comparison of this value with the most precise dating of pitchblende related to the ore stage in the Strel’tsovka ore field (135.5 ± 1 Ma) shows that four mineralization stages, distinguished by geological and mineralogical data, that were completed with the formation of polychrome fluorite veins 135.3 ± 1 Ma ago, represent a single and indivisible hydrothermal process whose duration does not exceed 1 Ma.     

Accuracy of tretyakov precipitation gauge: Result of wmo intercomparison

The Tretyakov non-recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period. The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge-measured precipitation data over large regions of the former USSR and central Europe.     

<Superscript>238</Superscript>U and <Superscript>235</Superscript>U isotope fractionation upon oxidation of uranium-bearing rocks by fracture waters

The variations in ²³⁸U/²³⁵U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC–ICP–MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope ²³⁸U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of ²³⁸U and ²³⁵U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO₃ solution [12].     

Interaction between surface gravitational waves and local rise of sea-bed in the uniform ocean

Diffraction of a plane progressive wave on a localized rise of arbitrary height of the sea-bed is studied within the framework of general linear theory of eddy-free waves. The solution is selected using finite-difference method. It is shown that the wave velocity field over the bank displays a character of localized disturbances attenuating as distance. Increase in depth intensifies centres of disturbances over the mountain peak. Vertical velocity amplitude in the area of the sea-bed rise may be an order of magnitude larger compared to its background value.UDK 551.466.8     

A role of aerosol particles in atmospheric ice nucleation

Considered is the process of ice nucleation in the atmosphere as a result of heterogeneous condensation of water vapor in surface inhomogeneities of aerosol particles and of subsequent heterogeneous crystallization of supercooled water accumulation. It is revealed that the size, structure, and composition of aerosol particles determine the thermal regime of crystallization.     

Effect of pH and organic ligands on the kinetics of smectite dissolution at 25 °C

Forward dissolution rates of Na-Montmorillonite (Wyoming) SWy-2 smectite (Ca_0.06Na_0.56)[Al_3.08Fe(III)_0.38Mg_0.54] [Si_7.93 Al_0.07]O₂₀(OH)₄ were measured at 25 °C in a mixed-flow reactor equipped with interior dialysis compartment (6-8 kDa membrane) as a function of pH (1-12), dissolved carbonate (0.5-10 mM), phosphate (10⁻⁵ to 0.03 M), and nine organic ligands (acetate, oxalate, citrate, EDTA, alginate, glucuronic acid, 3,4-dihydroxybenzoic acid, gluconate, and glucosamine) in the concentration range from 10⁻⁵ to 0.03 M. In organic-free solutions, the Si-based rates decrease with increasing pH at 1 ? pH ? 8 with a slope close to −0.2. At 9 ? pH ? 12, the Si-based rates increase with a slope of ∼0.3. In contrast, non-stoichiometric Mg release weakly depends on pH at 1 ? pH ? 12 and decreases with increasing pH. The empirical expression describing Si-release rates [R, mol/cm²/s] obtained in the present study at 25 °C, I = 0.01 M is given by

     

Paleoproterozoic gold-bearing copper deposits and occurrences of the Karelian Craton

Doklady Earth Sciences -     

Adaptive Methods of the Flybys Constructing in the Jovian System with the Orbiter Insertion Around the Galilean Moon

Solar System Research - We consider space expeditions with a long-term spacecraft stay near the studied celestial body (artificial satellites of small bodies of the Solar System), or expeditions...