Home – Home – Jornals – Russian Geology and Geophysics 2007 number 8

The structure and petrologic composition of new gold-ore provinces in southeastern East Sayan (Tissa-Sarkhoi cluster) are considered. Several morphogenetic types of gold mineralization have been established: quartz veins with beresitization zones, veinlet-disseminated ores in granitoids, and listwaenitization and sulfidation zones in effusions of the Sarkhoi Group and intrusive rocks of the Late Riphean Khorin-Gol complex. According to geochronological dates and some mineralogical and geochemical features, the gold mineralization is close in age to these Precambrian island-arc complexes. Parageneses of two stages of ore formation have been recognized: early high-temperature (250-460

Contents of Pt and Pd were determined in weakly mineralized rocks, ores, and flotation concentrates of the Aksug porphyry Cu-Mo deposit, northeastern Tuva. In all studied samples they are above the detection limits: Pt = 17-96 ppb and Pd = 9-924 ppb. These elements are unevenly distributed throughout the rocks and ores, with Pd/Pt varying from 0.5 to 37. Study of Pd-rich ores (up to 924 ppb, Pd/Pt = 37) on a JEOL JSM 5600 scanning electron microscope revealed finest (2-5 μm) merenskyite inclusions (25.20% Pd, 1.21% Pt, 72.31% Te) in chalcopyrite. The calculated crystallochemical formula of merenskyite from ores of the Aksug deposit is (Pd_0.862 Pt_0.023 Cu_0.026 Fe_0.025)Te_2.064. The merenskyite is associated with electrum (79.92% Au, 18.96% Ag), monazite, cobaltite, tennantite, and Sr-containing barite (4.6-18.0% Sr). Palladium mineralization occurs in massive chalcopyrite veinlets in zones of intensely propylitized rocks. The Devonian Aksug ore-bearing porphyry complex developed in the field of Early-Middle Cambrian intrusions of gabbro-diorite-plagiogranites associated with basalt-andesite effusions of island-arc complex. This might have led to high PGE contents in the Aksug rocks. The deposit formation proceeded with the participation of ore-bearing Cl-enriched fluids favoring the concentration and transport of PGE in porphyry copper systems.

The subject of study was the chemical composition of common fresh-water springs precipitating travertines in tectonically passive regions of the Kolyvan'-Tomsk folded area and northwestern Salair. Attention was paid to the specific character of manifestation, mineralogy, and petrography of the produced travertines. Results of the study of isotopic composition of carbon in hydrocarbonate ion of waters and carbonate travertines are reported. It is shown that the genetic type of CO₂ accompanying the formation of travertines is biogenic. Study of the equilibrium of the underground waters with aluminosilicate and carbonate minerals has shown that the travertines are the product of evolution of an equilibrium-nonequilibrium water-rock system. New mechanisms of travertine formation from cool fresh waters are proposed.

In dividing supracrustal strata, formation and horizon have been and are basic stratigraphic units. Stratigraphic boundaries of a formation, a natural geologic body, are drawn mostly on the basis of its composition. Paleontological remains constrain the formation in time and spatially locate it in the Earth's crust. Boundaries between formations can be of three types: strictly stratigraphic, parastratigraphic, and allostratographic. The stratigraphic interval can range from a fraction of a horizon or chronozone to several stages. At the boundary between two systems the adjacent parts of the formation can relate to both systems. The main stratigraphic characteristics for recognizing horizons are paleontologic (biostratigraphic) features, revealed by zonal, paleoecosystemic (ecostratigraphic), bioeventual, and other methods to make a basis for their immanent signature. Horizon can be characterized by boundaries of only two types: strictly stratigraphic and allostratigraphic. The stratigraphic interval of a horizon can vary from a single chronozone to a stage. Boundaries of neighboring horizons at the contact between two stages or systems should coincide with the latter. The stratigraphic units of the International Stratigraphic Chart, in contrary to formation and horizon, are characterized by borders of only one type - strictly stratigraphic.

Fossil seed assemblages of Paleogene and Neogene strata in northeastern Asia are reviewed based on data of Novosibirsk paleocarpologists and literature data. The composition and age of flora are refined, and recommendations on improving stratigraphic charts of deposits in northeastern Russia are given.

We obtained a macroseismic equation with a convergent solution at a hypocentral distance D ~ 0 (independent of magnitude) for relative shaking intensity. The logarithmic distance dependence of intensity turned out to be piecewise linear no matter whether it is expressed in relative units of intensity degree or in logarithmic ground motion velocity. The macroseismic intensity shows high correlation with motion velocity. Another result is the magnitude dependence of dominant periods of ground motion velocity for large earthquakes.

An analytical solution of Maxwell's equations for layered anisotropic media is presented in a form which allows estimating the sought parameters by layer stripping without round-off accumulation. The solution in each layer is reduced to the standard procedures of solving a fourth-order algebraic equation, multiplication, addition, and inversion of second-order non-singular matrices. The algorithm has no limitations on layer thickness and is applicable to both very thick and very thin layers. The new numerical code is straightforward and can be easily parallelized.