Home – Home – Jornals – Russian Geology and Geophysics 2006 number 7

Late Permian PGE-Cu-Ni-bearing lherzolite-gabbronorite-dolerite and dolerite-kongadiabase-granophyre intrusions of the Song Hien rift structure in northeastern Vietnam (Cao Bang complex) were formed synchronously with the Emeishan traps of the Yangtze Platform. Massifs of this complex are made up of rocks of two series: lherzolite-picrite-picrodolerite-melanogabbro and kongadiabase-dolerite-gabbronorite. The first, essentially ultramafic, series is dominated by plagioperidotites and picritoids composed of labradorite-bytownite (An_66-70), chrysolite (f _Ol = 16-18%), magnesium diopside-augite (f _MP = 18-20%), and low-alumina bronzite (f _RP = 20-22%). They are associated with Pd-dominated PGE-Cu-Ni mineralization. In the sulfide phase of picrite from the endocontact zone of the Suoi Cun massif the contents of noble metals are as follows: 7.67 ppm Pt, 18.58 ppm Pd, 26.55 ppm Au, and 32.44 ppm Ag. Model calculations show that this massif was produced by the single intrusion of a high-Al picrobasalt magma crystallized at 1260-1090

Study was given to a fragment of the phase diagram of the system Fe-FeS-NiS-Ni at 900

The Aldan Shield (Aldan-Stanovoy area) is an ancient lithospheric plate, which repeatedly interacted with surrounding mobile areas throughout the Phanerozoic. This interaction resulted in numerous igneous-rock and ore associations in the Mesozoic, which form several ore-magmatic clusters and districts. The largest and most commercially important of them is the Central Aldan ore district, which is considered a regional ore-magmatic system (ROMS) within the Aldan Shield, a specific ore-magmatic province. The Aldan complex is a polychronous and polyfacies association composed of diverse igneous, metasomatic, and ore products, which form local ore-magmatic systems (LOMS).
The geologic structure and lithology of the Central Aldan ROMS are typical of a within-plate activity setting. The diversity of igneous rocks in Central Aldan is due to its median localization in the laterally zonal area of Mesozoic magmatism, between alkali-earth rocks in the east and south and peralkaline rocks in the west of the shield. Therefore, this region bears almost all igneous rock varieties of different formations typical of the Aldan province.
There are a number of gold deposits and ore occurrences of different association types within the Aldan Shield. Of practical significance are deposits of four commercial types (El'kon, Ryabinovy, Lebediny, and Kuranakh), the major ones being localized in the Central Aldan ore district. Gold deposits of Central Aldan differ in their localization in the Earth's crust section. The post-ore block movements of different amplitudes determined the occurrence of these deposits on the modern Earth's surface or near it. The deposits have both common and different structural and compositional features, which permit them to be referred to different ore associations of a single paragenetic series. The difference in the mineralogy and geochemistry of gold orebodies might be due to different depths of their formation.

The scheme of regionalization of the northern Siberian craton has principally been amended. It is proven that the succession of structural elements distinguished in the north is the same as in the south: oceanic block, pericratonic trough, and belt of intracratonic basins. Each of these structures can be, in turn, divided into several structure-facies zones. As in the south, three main stages of development have been established in the Neoproterozoic of the above structural elements, which correspond to the Mayanian, Baikalian, and Vendian.
The most considerable modifications are made in dating of the earlier established stratigraphic divisions. It is proven that the Debengda and Lower Yusmastakh Formations of the northern Siberian Platform correspond to the Kerpylian. The carbonate marker characterized by fossils of the Lakhanda Horizon plays an extremely important role in all structural elements of the northern Siberian craton. It comprises the Upper Yusmastakh, Khaipakh, Neleger, Sietachan, and somewhat more complicated Udzha Formations of the belt of intracratonic depressions; Chernaya Rechka and coeval Medvezh'ya Formations of the pericratonic trough, as well as the Kolosov and Kan'yon Formations of Taimyr. These modifications were promoted by a revision of biostratigraphy of many taxa of stromatolites and microfossils in the adjacent regions of Siberia. The microphytoliths of the Kalanchevo Complex cannot be used to determine the Baikalian and Vendian ages for the Medvezh'ya and Kolosov Formations. Thus, it was proven that the Baikalian is completely missing from northern Siberia. We argue that this is not due to the pre-Vendian erosion. Most likely, sedimentation was interrupted throughout the area by pre-Baikalian tectonic events.
The age of the oceanic volcanosedimentary and volcanogenic deposits in the Chukchi-Borzov and Zhdanov structure-facies zones is essentially refined. It is proven that they correspond to the Mayanian alone. An argument is that the wide fields made up of the island-arc volcanogenic complexes of this age are cut by narrow tabular bodies of ophiolites related to the pre-Baikalian rifting. As a result, we have corroborated the conclusion by V.E. Khain that there are two main borders of the Taimyr evolution: Grenvillian (1100 Ma) and Early Baikalian (850 Ma). We have shown that two principal events characterize the northern platform in the Neoproterozoic: formation of the supercontinent Rodinia in the Mayanian and the beginning of its breakup in the Baikalian. In the Vendian, after a large gap the superimposed troughs initiated as early as the Baikalian continued to develop.

Detailed study was given to the hydrogeology of the coal methane-promising Erunakovo region. We have established that all aquifers there are mutually related and form a single aquifer complex consisting of a series of microbeds of different water transmissivities and permeabilities. Two zones have been recognized in the Erunakovo region - of intense and slow water exchange (fresh- and brackish-water, respectively). Fresh waters with mineralization of up to 1 g/l and pH = 7-8 occur at depths down to ~300 m or, seldom, 500 m. Brackish waters have mineralization of 1-13 g/l and pH reaching 10.1. The higher mineralization is due to the higher contents of HCO₃^- and Na and, sometimes, SO₄², produced through sulfide oxidation, and Cl^-, concentrated as a result of evaporation. In the study region, CO₂ is not of mantle genesis but is the product of coal metamorphism.

We develop the electric-hydrodynamic theory of oil-water layered systems and reveal factors that allow control over the stability of these systems. Anisotropy of dielectric susceptibility, conductivity, and periodic current in a distributed system causes parametric resonance and makes the system prone to destruction.

We estimated the instrumental error introduced by logging tools into the measured plane and axisymmetrical electric fields. The problem can be solved either through investigation of analytical solutions or using integral equations. The difference between the true and the measured fields increases with frequency of electromagnetic waves and tool thickness and conductivity. The difference is lower in the case when the axisymmetrical electric field is measured by a closed loop than in the case of logging with a straight tool for the plane field. The greater the radius of the closed loop for the axisymmetrical field logging, the larger instrumental errors, the frequency being the same.

There are some reasons to publish my comments. First, the paper in question [1] is devoted to the region whose study has been my concern for a long time and, naturally, I paid attention to the manuscript as soon as it was received by Editorial Board of the journal. Second, the abstract declares important issues, which either are missing from the text body or are discussed with many errors, thus misleading the reader. Third, it is necessary to clear up what