Vol 39 Iss. 2

Leonid Ya. Nesterov, a talented geophysicist, professor at the Leningrad Mining Institute, head of the Department of Geophysical Methods for Exploration of Ore Deposits, began his teaching and research activities at the Institute in 1930. In those years the methods of electrical exploration of minerals were being born. L.Y. Nesterov began his scientific work by developing them. It resulted in 1931 in practical manuals - “Method of electrical resistances”, “Method of measuring natural electric fields” and in 1932 - “Electrical exploration by direct current” (together with A. A. Petrovsky).

The initial data used in determining the velocity from the hodographs of reflected waves always contain random errors. The influence of these errors can be minimized by using mathematical statistics methods in the processing. In addition, it is possible to evaluate the accuracy of the obtained result.

As is known, when using seismic exploration methods, the problem of elastic wave generation is of paramount importance. However, many issues in this area are still very poorly studied. In particular, there is no information about the dependence of the amplitude of seismic oscillations on the size (weight) of the charge, although this issue is of theoretical and practical importance. This paper presents some information on this dependence, obtained on the basis of special experimental work, supplemented by the results of processing of conventional RWCV and DSS seismograms.

The use of the higher derivatives of the magnetic potential to calculate the depth and other elements of occurrence from complex magnetic anomalies indicating the presence of a number of disconnected bodies with the same magnetization or rocks with changing magnetization provides a number of advantages over the methods of calculations directly from Z or ∆T curves: 1) the possibility of dissecting complex curves depicting the total field of a number of magnetized bodies; 2) a sharp reduction or complete elimination of the dependence of the problem solution on errors in the choice of the normal field; 3) the ability to calculate the total field of a number of magnetized bodies.

As it is known, the field strength ∆Т can be expressed through Za and Ha by the following approximate formula ...

The importance of simultaneous use of magnetic and gravity anomalies in the study of geologic structure is well known. In the study of regional geology is usually used data from aeromagnetic surveys and maps (or curves on the profiles) of ∆Т and ∆g are compared. Comparison of these data is complicated by two circumstances: 1) the shape of the ∆Т curves is strongly influenced by oblique magnetization to such an extent that under known conditions the ∆Т curves are more similar to the second derivatives of the gravitational potential Uxzv. than to Uzz; 2) the analytical expression of ∆Т is a derivative of the gravitational potential one order of magnitude higher than ∆g. The above difficulties can be eliminated. Let us consider the first question.

Recently, short-lever fast-acting gradientometers are beginning to be used in gravity exploration. Observations with the gradientometer are made rather quickly, but the accounting of the influence of the terrain is labor-intensive, time-consuming and often insufficiently accurate. When the relief is developed, errors in determining corrections for its influence have a decisive effect on the total error of anomalous values of gravity gradients.

The method of current registration is based on the study of electrical conductivity of torny rocks with the help of an electrode moving in drilling mud along the borehole axis. It is most widely used to determine the location of ore bodies in geological sections of boreholes and dissection of these sections.

In the first approximation the field of a charged isometric body can be considered as a field of a point source. Strictly speaking, it is true for a body of spherical shape lying in a boundless and homogeneous medium. Simplifying the calculations, it is possible to use the field of a point source to replace the field of a charged sphere and in inhomogeneous medium. Despite this assumption, the general conclusions derived from the present work are also acceptable for isometric bodies under certain conditions.

At present, materials of thermal measurements in wells are widely used to determine the geothermal gradient, temperature of formation water and rocks in their natural conditions of occurrence. However, these materials do not always have proper accuracy. One of the main reasons causing the appearance of errors in determining the temperature of rocks and formation water is the violation of the natural thermal field of the Earth by the borehole, i.e., violation of the stationary thermal regime of the area.

In the east of the Russian Platform the seismic method of reflected waves is the main method of searching for buried oil-bearing structures. Due to the complex seismogeological conditions of this region, the geological efficiency of seismic exploration in search of localized hollow concepts in Carboniferous and Devonian sediments remains low in some areas. There are significant difficulties both in conducting field observations and in geologic interpretation of the obtained materials.

Geological study of closed areas is the main task of exploration geophysics. It can be best solved only by combining different research methods. At the same time, in specific geological conditions requires a careful assessment of the geological and economic efficiency of each of them. Refinement of our ideas about possible structural-geological forms in a given area and improvement of geological interpretation of observed physical fields often lead to the fact that the effectiveness of one or another method with time changes and previously used materials of field surveys again provide the researcher with valuable information.

The method of combined electro-profiling was first proposed in 1937 by A. S. Semenov. Laboratory and field experimental works carried out by him and N. P. Grigorieva showed high efficiency of the method when searching for wellconducting steeply dipping ore bodies occurring in electrically homogeneous medium.

Complex geophysical works were put in one of the regions of Kazakhstan for the purpose of detailed geological mapping. The relief of the territory is a weakly hilly plain with relative elevations not more than a few meters. The thickness of sediment within the mapped area ranged from 0.3 to 1-1.5 meters.

For successful interpretation of the results of any metallometric survey (including those based on scattering streams) it is necessary, in addition to taking into account geological, geomorphological and other conditions, to know the local clarks of the desired elements and their geochemical behavior in a particular natural environment. Without this, it is impossible to correctly select the “normal field”, to assess the prospectivity of anomalous concentrations, to use the paragenetic associations of elements characteristic of the area for prospecting purposes. All these issues are especially acute at the first stages of prospecting: during ground verification of anomalies detected by aerial survey, during the study of little-studied areas, as well as during regional metallogenetic constructions.

One of the most effective methods for ore deposits prospecting is metallometric survey based on the study of secondary scattering halos developed in loose eluvial-deluvial sediments. Metallometric survey is annually used to study significant areas in all ore districts of the country, including Eastern Transbaikalia, where almost all known deposits and ore occurrences are accompanied by secondary scattering halos of various shapes. More often the shape of the halos repeats the outlines of ore bodies, but there are also halos that are strongly elongated down the slope. In this case, the strike of the ore bodies usually does not coincide with the strike of the scattering halos. In some cases, secondary scattering halos are not detected above known, rather rich ore bodies. For example, at one of the tungsten deposits in the Eastern Transbaikalia, rich quartz-wolframite veins confined to the endocontact zone of a small granite massif remained undetected during a detailed metallometric survey. At the same time, much less rich quartz-wolframite veins developed in the exocontact zone of the massif were accompanied by quite clear halos of tungsten scattering. The reasons for this phenomenon were established by analyzing the geomorphological situation of the studied areas of the deposit. It turned out that the nature of secondary scattering halos confined to eluvial-deluvial deposits depends on the conditions of formation of these deposits. The formation of loose eluvial-deluvial deposits is closely related to the process of relief formation of a particular site.

Metallometric survey on the basis of spectral analysis as a prospecting method was applied for the first time in the Union in 1935 at the Khapcher Anninskoye tin deposit. At present metallometry has become the leading prospecting method in a number of areas promising for tin, non-ferrous and rare metals. Nevertheless, its implementation faces difficulties specifically in the search for tin deposits.

Tungsten is one of the elements, in the search for which metallometric survey faces some difficulties. Thus, in the Eastern Transbaikalia on a number of ore occurrences represented by quartz-wolframite veins occurring among granitoids, no clear halos of tungsten dispersion were recorded with the usual survey methodology. Sometimes it is fixed in scattered samples, which does not allow with satisfactory accuracy to set mining excavations for opening of ore bodies. For development of the most rational methodology of selection and processing of metallometric samples it is necessary to know the distribution of the sought elements in loose sediments.

As studies in the South Urals have shown, the determination of nickel, copper and zinc or the last two of these elements is of great importance in the metallometric survey for the search for copper and cobalt ores, spatially gravitating to ultramafic rocks or occurring among metamorphic shales or rocks of the greenstone belt of this province.

In geological practice, simple productive methods of spectral analysis are successfully used for geochemical characterization of various complexes of rocks and ore occurrences when searching for ore deposits. The accuracy of content determination within some intervals (for example, 0.001-0.003; 0.003-0.01; 0.01-0.03%, etc.) when searching for scattering halos of molybdenum, tin, lead, zinc, tungsten and other ore components can be sufficient. But in a number of cases there is a need to apply mass methods of analysis with more accurate determination of the content of the elements under study.