On the dynamics of the rhythmic crystallization of magmatic bodies during the directional solidification of cotectic melts

A problem on the directional crystallization of melt was solved taking into account heat and mass exchange between the two-phase zone and the cooling volume of a magmatic body. Conditions were determined for the development of rhythmic crystallization by the example of the solidification of the pseudobinary Di-An system.     

Orthorhombic lazurite from the Tultui deposit in the Baikal region

A lazurite sample taken from the Tultui deposits in the Baikal region has been studied using petrographic examination, X-ray diffraction, and local X-ray spectroscopy (electron microprobe). It is established that the line of the basic cell in the X-ray diffraction pattern of the orthorhombic lazurite is widened, so the unit-cell parameters should be recalculated from the interlayer distances of the superstructural reflections. The chemical compositions and unit-cell parameters of the lazurites from the Baikal region and the Pamirs are different. Two schemes of the chemical substitutions of atoms in the mineral are assumed: (1) the hauyne cluster [Na₃CaSO₄]³⁺ is replaced with a sodalite cluster [Na₄Cl]³⁺, and (2) two hauyne clusters 2[Na₃CaSO₄]³⁺ are substituted by nosean clusters [Na₄SO₄]⁺ and [Na₄H₂O]⁴⁺ with retention of the total charge. The increase in the Na and Cl contents in the orthorhombic lazurite is accompanied by a decrease in the unit-cell dimensions. Orthorhombic lazurites from the southern Baikal region and the southwestern Pamirs were formed in apocarbonate (apocalciphyre) metasomatic rocks at a lower temperature than pyroxene, afghanite, and cubic lazurite.     

Modeling the dynamics of sublimation of fractured rocks in the lithospheric mantle wedge beneath volcanoes of the Avacha group (Kamchatka)

A quantitative analysis of sublimation of intensely fractured rocks in the mantle wedge was performed using a model of planar fracture channel. The use of dimensionless variables allowed us to analyze the influence of the Nusselt and Sherwood criteria on temperature and variation of the rates of dissolution of minerals and films on fracture walls and estimate both linear and mass sublimation rates. The results of this study predict relatively high rates of major element dissolution and remobilization by flows of magmatic and metamorphic gases over wide temperature range. Physical modeling of this process using natural mantle rock samples confirms the plausibility of the proposed model at least for the case of metamorphic-driven remobilization of elements from gas-liquid inclusions in metasomatized ultramafic rocks. This model provides a satisfactory explanation for the observed local heterophase alterations within ultramafic rocks that have experienced multistage deformation beneath volcanoes of the Kamchatka volcanic front.     

Noble metals in ash-cinder wastes of the Far East thermal power plants

The distribution and speciation of gold and platinum in ash-cinder wastes of the thermal power plants of Khabarovsk krai and Primorye are considered in terms of the research methods and the results obtained. The Au and PGE contents attain 2 g/t and higher, being 0.8–1.5 g/t on average. The ash of brown coal from the Pavlovka, Khurmuli, and some other fields is characterized by elevated PGE contents. The causes of discrepancies in the analytical determination of noble metals in coaly and carbonaceous rocks are considered. Accumulation of noble metals in coal is caused largely by their sorption on carbonaceous matter. The content of noble metals in ash-cinder wastes depends on their grade in the burnt coal. The latter, in turn, depends on the metallogenic characteristics of the coalfield. Gold and platinum are of economic importance, and a special technology for their recovery should to be worked out.     

Phase state of the carbonaceous matter in the metalliferous shales of the Russian Far East

Carbonaceous matter (CM) in shales of some deposits and occurrences of the Russian Far East has been studied by scanning and transmission electron microscopy, Raman spectroscopy, and X-ray phase and differential thermal analyses. It was shown that the carbonaceous matter in the high-temperature shales (amphibolite facies) of the Soyuznoe deposit is represented by holocrystalline graphite, while the low-temperature (greenschist facies) shales of the Sutyr and Kimkan sequences contain mainly nanocrystalline graphite. It was substantiated for natural objects that platinum is assimilated by graphite at high temperatures. This should be taken into account in planning the prospecting works, as well as in developing a technique for enrichment of carbonaceous ore, because high-temperature carbonaceous shales with holocrystalline graphite are promising for Pt, unlike their low-temperature analogues with nanocrystalline graphite.     

Some features of sea ice formation in Antarctic coastal waters

Considered are the peculiarities of fast ice formation in the Antarctic coastal waters. It is noted that the fine-crystalline ice with the chaotic orientation of crystals is mainly developed in the surface layers of the ice cover as well as the ice formed due to the infiltration of the sea water and its subsequent freezing in the lower layers of the snow cover. It is demonstrated that under the conditions of coastal Antarctic, the lamination of the structure during the period of ice cover formation and its subsequent development is the result of heavy precipitation in the form of snow and the formation of the large amount of snow sludge and crystals of intrawater ice (frazil ice) on the open water. The main distinctive feature of the Antarctic sea ice is its seasonal stratification with the formation of the surface layer of recrystallized ice and underlying destructive layers including the water interlayer in the ice column. The provision of the safety of overice movement of machinery requires the development of methods of continuous remote control of the snow-ice stratum of the fast ice.     

Possibility of geodynamic monitoring by radon emanations

The crack opening displacement in the ground floor beam of a skeleton-type building on piles and lateral earth pressure between the piles were measured for a long time. In parallel we measured radon and thoron volumetric activity in the soil air samples in the building basement and in the box containing soil fragment. Two time intervals, when the crack opening expanded rapidly due to uneven subsidence of supporting columns, were established. Volumetric activity of radon entering from the soil basement and parent matter fragment was anomalous. Tidal, cyclonic, or technogenic deformations could be the cause of observed phenomena. According to the time series analysis, variability in atmospheric parameters such as pressure, temperature, and air humidity made geodynamic monitoring by radon emanations hard. Influence of described factors on measured parameters is still a matter of debate.     

A mathematical model for 2D heat transfer dynamics in fluid systems with localized sink of magmatic fluid into local fractured zones above the top of crystallizing intrusions

A model describing two-dimensional (2D) dynamics of heat transfer in the fluid systems with a localized sink of a magmatic fluid into local fractured zones above the roof of crystallizing crustal intrusions is suggested. Numerical modeling of the migration of the phase boundaries in 2D intrusive chambers under retrograde boiling of magma with relatively high initial water content in the melt shows that, depending on the character of heat dissipation from a magmatic fluid into the host rock, two types of fluid magmatic systems can arise. (1) At high heat losses, the zoning of fluidogenic ore formation is determined by the changes in temperature of the rocks within the contact aureole of the intrusive bodies. These temperature variations are controlled by the migration of the phase boundaries in the cooling melt towards the center of the magmatic bodies from their contacts. (2) In the case of a localized sink of the magmatic fluid in different parts of the top of the intrusive chambers, a specific characteristic scenario of cooling of the magmatic bodies is probably implemented. In 2D systems with a heat transfer coefficient ?? _k < 5 × 10⁴ W/m² K, an area with quasi-stationary phase boundaries develops close to the region of fluid drainage through the fractured zone in the intrusion. Therefore, as the phase boundaries contract to the sink zone of a fluid, specific thermal tubes arise, whose characteristics depend on the width of the fluid-conductive zone and the heat losses into the side rocks. (3) The time required for the intrusion to solidify varies depending on the particular position of the fluid conductor above the top of the magmatic body.     

A mathematical model for 2D heat transfer dynamics in fluid systems with localized sink of magmatic fluid into local fractured zones above the top of crystallizing intrusions

A model describing two-dimensional (2D) dynamics of heat transfer in the fluid systems with a localized sink of a magmatic fluid into local fractured zones above the roof of crystallizing crustal intrusions is suggested. Numerical modeling of the migration of the phase boundaries in 2D intrusive chambers under retrograde boiling of magma with relatively high initial water content in the melt shows that, depending on the character of heat dissipation from a magmatic fluid into the host rock, two types of fluid magmatic systems can arise. (1) At high heat losses, the zoning of fluidogenic ore formation is determined by the changes in temperature of the rocks within the contact aureole of the intrusive bodies. These temperature variations are controlled by the migration of the phase boundaries in the cooling melt towards the center of the magmatic bodies from their contacts. (2) In the case of a localized sink of the magmatic fluid in different parts of the top of the intrusive chambers, a specific characteristic scenario of cooling of the magmatic bodies is probably implemented. In 2D systems with a heat transfer coefficient α _k < 5 × 10⁴ W/m² K, an area with quasi-stationary phase boundaries develops close to the region of fluid drainage through the fractured zone in the intrusion. Therefore, as the phase boundaries contract to the sink zone of a fluid, specific thermal tubes arise, whose characteristics depend on the width of the fluid-conductive zone and the heat losses into the side rocks. (3) The time required for the intrusion to solidify varies depending on the particular position of the fluid conductor above the top of the magmatic body.