A. V. Ignat’ev

The Oxygen Isotopic Composition as an Indicator of the Genesis of "Basaltic" Corundum

This paper reports an oxygen isotopic study of corundums and associated minerals from the Yogo lamprophyres (Montana, US), plagioclase-corundum inclusions in alkali basalt (Tunkin depression, Russia), and from modern alluvium of Podgelbanochnyi alkaline basaltic volcano (Primorye, Russia). It is shown that all sapphires genetically related to mafic magmatic rocks have a similar oxygen isotopic composition (the variations of δ18O are within 2.5‰) with most values plotting between +4.5 and +7.0‰ SMOW. The oxygen isotopic ratios in the associated minerals (olivines, pyroxenes, mica, and others) and host rocks are plotted in the same interval. This indicates that the sapphire crystallized during evolution of the parental mafic magma. However, there are xenogenic corundums, which were only transported by basaltic magma to the Earth’s surface. They have a sharply distinct oxygen isotopic composition, which suggests their disequilibrium with the host lavas, and, correspondingly, a different genetic nature.

Anomalous Light Oxygen Isotope Composition in Minerals of Corundum-Bearing Rocks in Northern Karelia

The oxygen isotope composition of genetically related minerals is known to form a compact common field of values, the area of which depends only on variations in physicochemical parameters of the mineralforming medium. After a mineral has formed, the oxygen isotope composition does not change only if the mineral has not been transformed completely as a result of melting, chemical replacement, or other such reactions changing the primary structure. Therefore, the oxygen isotope composition has long served as an indicator of specific conditions for the formation both of minerals and rocks in general. We have studied samples of corundum-bearing garnet‐amphibole‐phlogopite plagiogneiss of the Proterozoic age from the Chupa Sequence of the Belomorian Complex of the Khitostrov deposit (Fig. 1).

Geochemistry of stable oxygen and hydrogen isotopes in minerals and corundum-bearing rocks in northern Karelia as an indicator of their unusual genesis

The paper presents newly obtained data on the oxygen and hydrogen isotopic composition of minerals in corundum occurrences and their host rocks in northern Karelia. Minerals in the Khitoostrov and Varaka corundum-bearing zones have extremely low δ18O (lower than −26‰) and δ D (lower than −215‰), which suggest that the mineral-forming process involved glacial waters and that the minerals preserve the isotopic ratios of their protolith. Aluminous corundum plagioclasites were produced by high-pressure Svecofennian (1.9-1.8 Ga) metamorphism of Paleoproterozoic rocks that had been metasomatized with the involvement of meteoric waters during the Guronian glaciation epoch.

Ag-Sb Mineralization of the Yana-Kolyma Belt, Northeast Russia

The mineral assemblages of the Ag-Sb deposits from the Yana-Kolyma Foldbelt were studied. The compositions of ore minerals, the isotopic compositions of sulfur in ore minerals, and the carbon and oxygen in carbonates are given. Arsenopyrite of the deposits is significantly enriched in Sb (1–16 wt %), which is related to the primary enrichment of the ore-hosting sequences in Sb and the ore formation at shallow depths. Based on the fluid inclusions study, the deposits were formed at T = 329–149°C and P = 0.30–1.04 kb from low-salinity chloride-sulfate-bicarbonate solutions enriched in Sb and Ag. The sequence of precipitation of Ag-Sb minerals was mainly controlled by the Sb concentration and the sulfur fugacity and potential in the fluid.

New data on stable isotopes in minerals from corundum-bearing formations of Northern Karelia (Russia)

Corundum occurrences in Northern Karelia at a small number of minerals are characterized by a wide diversity of textural and structural peculiarities. Varia� tions of quantitative relationships, abundance of gen� erations of mineral phases (garnet, amphibole, and plagioclase), and the presence of early corroded min� eral relics in late newly formed assemblages are con� trolled by the zoned structure of the bodies and evolu� tion of parageneses formed in a wide range of temper� atures and pressures [6]. This paper contains the

A Method for Determining Argon Isotopes in a Continuous Helium Flow for K/Ar Geochronology

A new method for the measurement of the argon isotope composition in a continuous helium flow using isotope mass spectrometers is described for potassium-argon geochronology. Argon was extracted from the samples in a chamber with a multiple-sample holder by successively heating the samples with a continuous infrared laser. Argon extracted in the chamber was preconcentrated in a capillary, separated on a chromatographic capillary column in a helium flow, and then injected into the ion source of a mass spectrometer through an open splitter. Measurements of the 36Ar, 38Ar, and 40Ar isotopes were carried out on isotope mass spectrometers in a dynamic mode using a triple-collector ion detector and three electrometric amplifiers. Preliminary experiments on the developed device for measuring argon isotopes in a continuous helium flow have shown that the proposed method can be used for the determination of radiogenic argon in an amount of n × 10−12 g with the accuracy satisfying the solution of many geochronological problems. In sensitivity and reproducibility, the proposed method is highly competitive to the isotope dilution method for measuring argon and simpler than the conventional methods for measuring radiogenic argon.

Production of Manganese Alloys from Rich High-Basicity Ore

Most manganese ores exported by world producers are characterized by low basicity (<0.5) and may accordingly be used in single-stage smelting of ferrosilicomanganese by the slag method. We know that many deposits have large reserves of highly basic manganese ore [1, 2]. The chemical composition of such ore is outlined in Table 1. The ore basicity is in the range 0.76‐2.93, which is 1.5‐6.0 times the permissible level for ferrosilicomanganese production by the slag method. Only high-carbon ferromanganese may be produced from such ore. The smelting of carbon ferromanganese by the flux method on the basis of low-basicity (acidic) ore has been adequately covered in the literature and introduced in practice [3‐5].

First Diamonds from Placers in Primorie

The paper reports the results obtained by the detailed studying of carbonado (the first find in a gold placer in Primorie) and a collection of diamonds that was confiscated in 1937 from a poaching small digger and was kept safe at the Nezametnyi mine (near the village of Vostretsovo), which had developed this placer deposit. In the concentrate from the placer, carbonado is associated with green corundum, various ilmenite, zircon titanian amphiboles and pyroxenes, rutile, anatase, and fragments of subvolcanic biotite picrites. All of these minerals, native aluminum, and tin occur as inclusions in the diamonds. The carbonado from Primorie was determined to be practically identical to this mineral from Brazil, has a porous structure, is characterized by orange luminescence, contains inclusions of Y, Ce, La, Ba, and Sr phosphates, and has an isotopically light composition of its carbon (13C from −25 to −32‰). Pores of the carbonado aggregates contain clusters of diamond crystals. The collection of diamonds from an unknown source included six gem-quality transparent crystals, one rounded ballas, two cuboctahedral crystals (one of greenish and the other of silver-gray color, both with outer coats), and one black carbonado grain. The data obtained on the mineralogy of the diamonds have demonstrated that they are completely identical to this mineral from kimberlites and lamproites but bear traces of intense dissolution, fragmentation, multiple recrystallization, and graphitization at defects, which are the most widespread in the ballas. One of the crystals was determined to contain inclusions: aggregates of potassic omphacite (0.50 wt % K2O) and corundum. Ilmenite (containing up to 8 wt % MgO), titanaugite, kaersutite (4 wt % TiO2, 0.8 wt % K2O), and churchite (aqueous phosphate) were obtained from the core of the ballas. The titanaugite, kaersutite, and ilmenite were proven to be compositionally analogous to these minerals from picrites occurring near the placer. The carbon isotopic composition δ13C of the cores of the single diamond crystals varies from −6 to −11‰. The margins of the grains were proved to be enriched in the light carbon isotope (δ13C from −19 to −21‰). The gem-quality transparent diamond crystals are characterized by blue luminescence, and the color of luminescence in the carbonado varies from orange red in the bulk of the aggregate to yellowish green in its core. The aforementioned transformations of diamonds were likely caused by their transportation in pipes of micaceous picrites of the Jurassic meymechite complex. The carbonado are thought to correspond to the final stage of the metastable recrystallization (in pores, within the temperature range of the rutile-anatase transition) of the original isotopically heavy diamonds under the effect of various oxidizers (H2O, CO2, F, and others) and in the presence of catalytically acting REE, Ti, and P. The primary diamond source (kimberlite or lamproite) can be older and more distant from the study area. The complete geological analogy between the study area in Primorie, Kalimantan Island in Indonesia, and West Australia (where no sources of the placers are known) led us to consider the territory of Primorie as promising for exploration for diamondiferous placers.

The TESIS Solar imaging spectroscopy experiment on board the CORONAS-Photon satellite

The CORONAS-Photon spacecraft was successfully launched in January 2009. Its scientific payload included the TESIS complex of telescopes and spectrometers, designed to obtain high spectral, temporal and spatial resolution solar corona images in soft X-ray to far UV spectral range.

Stable Carbon Isotope Ratio in Xylotrophic Fungi and Their Substrates

Data on the ratio of stable carbon isotopes in xylotrophic fungi and their xylic substrates are presented for the first time. It is shown that coniferous substrates are more enriched in the heavy carbon isotope, compared to deciduous substrates. In both cases, however, their carbon isotope composition is characterized by low variability and does not correlate with the species or physiological type of decomposer fungus but shows a statistically significant correlation with the degree of wood mineralization. The ratio of stable carbon isotopes in the fungi depends on that in their substrates but is shifted in favor of the heavier isotope. This trophic shift lacks species specificity, is equally manifested in decomposers of deciduous and coniferous substrates, remains unchanged along the latitudinal climatic gradient, and is positively correlated with the carbon isotope composition of substrates, in the absence of correlation with the degree of their mineralization.