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We report the method of azimuthal QVO (QVOA) analysis (seismic quality factor Q versus offset and azimuth) of P -wave attenuation variations as a function of wave-propagation direction in an azimuthally anisotropic (HTI) medium, which is an effective model of vertically fractured rocks. The method is intended to determine crack orientation in fractured reservoirs. The derived approximation of attenuation as a function of the wave-normal direction appears to have the same structure as Rüger's approximation for the PP reflection coefficient widely applied in the azimuthal AVO (AVOA) analysis. We introduced two new parameters: QVO gradient, an azimuth-dependent seismic attribute, and the QVO intercept corresponding to attenuation in the isotropy plane. The use of the QVO gradient, suggested by analogy with the AVO gradient, approaches the new QVOA method to the known AVOA analysis. The QVO gradient is maximum when the source-receiver line is directed along the symmetry axis (or normal to crack planes) and minimum when the two are orthogonal. The relative difference in P -wave attenuation in crack-parallel and crack-normal directions was found out to depend on crack parameters and on V_S/V_P ratio in the background rock, the impact of V_S/V_P being greater than that of the crack density and aspect ratios of cracks and their filling. Azimuthal variations of the QVO gradient can be used to determine crack orientation, and the maximum QVO gradient divided by the intercept provides estimates of V_S/V_P ratio.

Systematic monitoring of the geomagnetic field at secular variation and repeat stations was stopped 15 years ago in expectation of satellite measurements. Comparison of secular geomagnetic variations estimated directly from annual observatory data and those inferred from changes of IGRF-modeled components measured at observatories shows that much of information is lost because satellite measurements cannot provide the appropriate monitoring of space and time secular variations and regional observatory networks are scarce in many regions of the world, especially in Siberia. Therefore, systematic monitoring of the geomagnetic field by the system of observatories and secular variation stations should be resumed.

The paper presents a new method of focusing electrical logging (FL) which implies a nontraditional layout of transmitter and receiver electrodes. This configuration provides compensation of the background signal from formation and highlights anomaly signals. We suggest a 1D numerical model to process the synthetic differential signal from a FL ring loop and analyze apparent resistivity curves obtained from a 1D two-layer

Stress dependence of seismic velocities and attenuation has been studied using the available reported data and original laboratory experiments on quartz single crystals and sandstone samples. The experiments show velocity decrease and attenuation increase with stress in quartz crystals.P and S velocities in sandstone decrease also with changing pore pressure at invariable hydrostatic pressure. The velocity and attenuation functions show open hysteresis loops in a full loading-unloading cycle.

The Sukhoi Log gold deposit is centrally located in the Lena goldfield region, approximately 850 km NE from the city of Irkutsk, and is hosted in Upper Proterozoic marine sandstone, carbonaceous slate and phyllite, metamorphosed to low greenschist facies in an outlying part of the major Akitkan Foldbelt. The disseminated pyritic tabular orebody has no outcrop, is defined solely by assay grades and is located in the axial zone of a large, near-isoclinal, reclining anticline. Highest ore grades occur in pyritic black shale beds, especially where they cross the axial zone and include two elongate higher grade (4-9 ppm gold) cylindrical zones, termed ore pillars, along the gently plunging anticlinal crest. The anticline is exposed E-W over a length of 3 km and plunges at approximately 10

Gold-mercury deposits in Central Asia form a heterogeneous group of gold orebodies spatially and genetically related to different types of endogenous mineralization (ore deposit complexes). Four types of gold-mercury mineralization have been recognized: Au-As-Hg, Au-Sb-Hg, Au-Te-Hg, and Au-Cu-Hg. They are the products of different ore-magmatic systems, formed at their subsurface levels. The classification of these gold-mercury deposits is based on the specific mineral and geochemical compositions of their ores, including the content of Hg in native gold, relationship with different complexes of accessory endogenous mineralization, and physicochemical conditions of their formation.

The problem of the dimensions and boundaries of porphyry Cu-Mo ore association is discussed in terms of the genesis and occurrence of ore-forming porphyry magmatism, geochemistry and zoning of mineralization, and geologic and physicochemical conditions of ore-metasomatic processes. With regard to the common Cu-Mo composition of deposits (though essentially copper and essentially molybdenum deposits were also considered) and their intimate relationship with granitoid porphyry intrusions (of both deep-level basaltoid and shallow-depth genesis in a relatively open environment), all porphyry Cu-Mo deposits can be united into a single porphyry Cu-Mo association, which is subdivided into porphyry Cu, porphyry Mo-Cu, porphyry Cu-Mo, and porphyry Mo types. Defining the boundaries of ore association requires analysis of all products of a porphyry Cu-Mo ore-magmatic system with regard to the common zoning of produced mineralization: Fe-Mo (Cu)-Cu (Mo)-Cu (Au)-Fe (Au)-Pb, Zn-Au (Ag).

Based on results of studying the geochemistry and gold distribution of groundwaters in the Egor'evskoe gold-bearing area, a mechanism of gold mobilization, migration, and accumulation in mountain-forest landscape is proposed. Gold mass transfer is part of an ore-generating process running in a water-rock system. Hydrogenic concentration of gold in placers is equally determined by physicochemical processes of secondary mineral formation and hydrodynamic conditions. The amounts of accumulated gold depend on the gold-producing capacity and volume of waters involved in the mineral formation and on the duration of this process.

New geochemical data are reported for 63 samples of heterochronous Cenozoic basalts taken from separate areas of Mongolia. The rock compositions are strongly heterogeneous indicating lateral and temporary variability of the mantle magma sources. The Taryat-Chulutuin and Dariganga basalts were derived from the most enriched sources. The Early Cenozoic basaltoids of southern Mongolia were formed from melts compositionally close to a depleted mantle. In general, on different geochemical diagrams the compositions of the Mongolian basalts lie within the fields located among the sources of the DM, MORB, EM, PM, HIMU, REC, and OIB types. According to the melt mixture model, the average basaltic magma of Mongolia was generated from a mixture composed of 90% DM melt and 10% enriched magma. Some geochemical parameters (Sm/Nd, La/Yb, etc.) suggest that the mixed melts could have been supplied from different mantle sources. The melting depth corresponds to the region of existence of garnet-spinel lherzolite. Our geochemical data together with the earlier obtained ratios ³He/⁴He evidence the presence of a mantle plume whose composition is close to sources of alkaline magma of oceanic islands.

Offset wavefield continuation (DMO procedure) precedes migration or AVO analysis and simplifies the processing by reducing common-offset seismic gathers to zero offset. Then, the DMO algorithm itself should be quite elegant. Frequency-domain solutions can employ FFT but the available spectral algorithms fail to resolve the true geometry of reflections even in the high-frequency limit. We suggest to solve the DMO equation using the WKB method. The new algorithm includes several transformations of variables applied to reduce Fomel's partial differential equation to an equation resolvable by the classical WKB method. The WKB-based solution was tested in several numerical experiments and showed to resolve the geometry of plane and curved shallow dipping reflectors to a sufficient accuracy.