Normative quartz as an indicator of the mass transfer intensity during the postmagmatic alteration of the Botuobinskaya pipe kimberlites (Yakutia)

The intensity of postmagmatic processes in the Botuobinskaya pipe kimberlites was estimated from the calculated content of normative secondary quartz (Q). Several simple algorithms are proposed to calculate the Q content from chemical analyses of kimberlites. Ten groups of altered kimberlites have been recognized from the Q contents. The contents of MgO, some trace elements, and LREE in the groups, the contents of Cr and Ca of crimson garnets, the diamond contents of kimberlites, and the average weight of diamonds decrease as the Q content increases. It is shown that the negative SiO₂–MgO correlation is the most effective indicator of the postmagmatic alteration of kimberlites. As the degree of their secondary alteration increases, the kimberlites transform into an assemblage of quartz and clay minerals enriched in some trace elements and almost completely lacking REE and diamonds.     

Structural and Morphological Features of the Participation of Microorganisms in the Formation of Nb–REE–Rich Ores of the Tomtor Field (Russia)

Doklady Earth Sciences - Data indicating the important role of microorganisms in the redistribution of REEs in the weathering crust and the decisive role in the concentration of REEs during the...     

Multigroup radiative transfer in supernova shock breakout models

The physical peculiarities of supernova shock breakout are discussed. A number of models for various types of supernovae have been constructed based on multigroup radiative transfer by taking these peculiarities into account. The results of numerical simulations and the influence of the effects of photon scattering by electrons and the thermalization depth on them are considered. It is shown under which conditions the appearance of hard X-ray emission is possible at shock breakout. It is pointed out what refinements are necessary in the computational algorithms for radiative transfer and hydrodynamics.     

Gold-Bearing Placer Assemblages in the East of the Siberian Platform: Origin and Prospects

Geology of Ore Deposits - For the first time, based on a study of the typomorphic features of placer gold and its distribution patterns, the predicted gold potential of the east of the Siberian...     

Distribution of REE,Y, Sc,and Th in the unique complex rare-metal ores of the Tomtor deposit

The REE (Ln), Y, Sc, and Th distribution in the unique complex rare-metal ores of the Tomtor deposit is considered. Significant variability of these components and REE composition is revealed. Ore blocks with elevated Y and HREE contents are identified among prevailing LREE-enriched ores. It is established that the REE variations in the ores are correlated with evolution of REE carriers during epigenetic transformations of the carbonatite weathering products, in particular, with a replacement of Ce-bearing minerals (monazite and florencite) by Y-bearing mineral, xenotime. It is found that LREE and HREE exhibit different behavior during formation of the Tomtor ores, which is expressed in the inert behavior and residual accumulation of Ce-group REE at essential introduction of Y, HREE, Sc, and Th during epigenetic transformation of weathering products of carbonatites, which represent one of the main factors of the formation of the unique rare-metal ores of the Tomtor deposit.     

Ultrapotassic Rock from the Tomtor Complex of Ultrabasic Alkaline Rocks and Carbonatites (Arctic Siberia)

Doklady Earth Sciences - Among the rich REE–Nb ores of the upper ore horizon of the Tomtor deposit, under the Jurassic deposits (borehole 324, interval 47–62 m), ultrapotassiс...     

Petrogeochemical characteristics of the kimberlites from the Middle Markha region with application to the problem of the geochemical heterogeneity of kimberlites

A comparative geochemical investigation of kimberlites from the Middle Markha region and traditional diamond-bearing areas of Yakutia supported the division of kimberlites into two geochemical types. One of them includes kimberlites from the traditional diamond-bearing areas of Yakutia, and the other is represented by the kimberlites of the Middle Markha region and the rocks of the Zolotitsa field and V. Grib pipe of the Arkhangelsk province. The obtained representative parameters of the two kimberlite types indicate a sharp geochemical contrast between them, and the individual features of correlation relationships between the elements in the rocks of the two types suggest that these differences are related to fundamental genetic factors, which concern primarily the group of highly charged incompatible trace and radioactive elements. The presence of geochemically contrasting rocks within a rather uniform petrochemical association and the geochemically specialized occurrences of kimberlites and related rocks are consequences of repeated metasomatic transformations of mantle rocks under the influence of deep-derived fluids or volatiles released during the recycling of subneous source and subsequent derivation of geochemically specialized types of deep magmas showing signatures of individual mantle sources.     

Spectra and light curves of GRB afterglows

We performed accurate numerical calculations of angle-, time-, and frequency-dependent radiative transfer for the relativistic motion of matter in gamma-ray burst (GRB) models. Our technique for solving the transfer equation, which is based on the method of characteristics, can be applied to the motion of matter with a Lorentz factor up to 1000. The effect of synchrotron self-absorption is taken into account. We computed the spectra and light curves from electrons with a power-law energy distribution in an expanding relativistic shock and compare them with available analytic estimates. The behavior of the optical afterglows from GRB 990510 and GRB 000301c is discussed qualitatively.     

Behavior of major and rare-earth elements during the postmagmatic alteration of kimberlites

During serpentinization and subsequent alteration in the absence of brucite, kimberlites accumulate uncompensated silica. Its amount can be calculated from the average compositions of the rock-forming minerals (olivine, calcite, phlogopite) and the chemical compositions of the rocks. The contents of rock-forming oxides and REE were determined in 12 kimberlite pipes of the Yakutian kimberlite province, in 413 samples from secondary-alteration zones and of unaltered kimberlites. Columns of successive kimberlite alterations were constructed for each pipe on the basis of secondary-quartz data; here, the behavior of rock-forming oxides and REE was assessed. All the studied rocks had experienced different degrees of postmagmatic hydrothermal metasomatism at different depths in all the pipes. The changes were reflected in the supply/loss of rock-forming oxides and REE. The supply of REE during the hydrothermal metasomatism enriched the kimberlites with TiO₂, P₂O₅, and CaO. During the removal of REE, most of the rock-forming oxides were partially lost. The maximum REE supply was 67% in the Udachnaya-Vostochnaya pipe and 59% in the Nyurbinskaya pipe as compared with the unaltered kimberlites. The maximum REE loss was 87% in the Aikhal pipe and 81% in the Internatsional’naya pipe as compared with the unaltered kimberlites. The initial REE contents of the postmagmatically altered kimberlites changed considerably in all the studied cases. This conclusion was drawn owing to the use of normative-quartz content as a criterion for secondary alteration.