Vol 56 Iss. 2

Head of the Department of Geochemical and Radioactive Exploration Methods, Professor, Doctor of Geological and Mineralogical Sciences Nikolai Konstantinovich Morozenko was a communist, a major scientist, one of the best experts in the geology of rock crystal deposits and natural riches of Central Asia, Pamir and Altai.

Geochemistry, as a science that studies the chemistry of the Earth in its historical development, originated at the end of the XIX century and finally formed as an independent branch at the beginning of the next century, mainly due to the works of our compatriots - V. I. Vernadsky and A. E. Fersman, as well as W. M. Goldschmidt, F. W. Clarke and X. С. Washington. The further development of geochemistry is due to the studies of A. P. Vinogradov, A. A. Saukov, V. V. Shcherbina, and others. Practical use of the general provisions formulated in the works of the founders of this science, also began in our country in the years of the first Five-Year Plan.

According to the law of universal dispersion of chemical elements (Clark-Vernadsky law) in each drop or dust particle of matter on our planet can be found all the elements of the Mendeleev table. Their quantitative ratio in different shells of the globe and more local geological objects is determined by the nature of each element - its individual geochemical features. The closeness of geochemical (chemical and physical) properties is due to the similar behavior of elements in geological processes and joint accumulation in certain geological formations or shells of the globe. The latter circumstance makes it possible to subdivide chemical elements into a number of categories according to geochemical features and, first of all, according to their relative abundance in various geological objects or shells of the globe.

As a rule, works considering the geochemical specialization of rocks concern intrusive formations and mainly granitoids, since they dominate the lithosphere and are naturally the most thoroughly and comprehensively studied. It seems interesting to analyze the geochemical specialization of the main effusives (basalts) of some areas of the Pacific ore belt, mainly from the point of view of its relation to the tin content of the region.

In connection with the search for blind ore bodies and the evaluation of mineralization at depth, the study of vertical and horizontal zonation has recently received increasing attention. In this regard, the area of the central part of the Miao-Chan Ridge belongs to the region of Mesocenozoic folding and is composed of terrigenous formations of Jurassic age and Cretaceous effusives. Sand-shale strata of the Middle and Upper Jurassic are crushed into northeastern strike-slip folds and unconformably overlain by Cretaceous effusives of acidic and medium composition. The Cretaceous sediments are also folded into gentle folds. Discordant small intrusions of Upper Cretaceous age are widely developed in the area, more often with a characteristic hybrid composition - gabbro, gabbro-monzonites, diorites, diorite-porphyrites. Magmatic activity in the area ended with the introduction of a series of dykes of lamprophyre composition.

According to the nature of changes in the relations of productivity of the main ore elements of sulfide-cassiterite deposits of the Miao-Chan Ridge from the center to the upper edge of ore bodies and the degree of remoteness of these bodies from small hybrid intrusions, with which tin mineralization is closely associated, it is possible to estimate the cut-off levels of ore bodies.

The liquation type of magmatic deposits proper includes commercial accumulations of disseminated sulfide copper-nickel ores, which occur in rocks of basic-ultrabasic composition (norites, gabbro-norites, olivine diabases, pyroxenites, peridotites). According to modern ideas, the formation of liquation-type deposits occurs by separation of magma into immiscible liquids - silicate and sulfide even before the onset of crystallization. The isolated sulfide secretions merge into droplets and under the influence of high specific gravity sink to the bottom parts of intrusions, where they form accumulations. Deposits of liquation disseminated ores are syngenetic with the host rocks. Consequently, the primary halos of these deposits are also syngenetic. The degree of study of the conditions of formation of deposits of this genetic type is clearly insufficient, so the following ideas about the occurrence of halos of syngenetic disseminated ores and the interpretation of these halos can be satisfactory only insofar as they correspond to the accepted liquation-magmatic hypothesis of formation of the ores themselves.

The significance of climatic factors in geochemical processes occurring in the near-surface layer, in the oxidation zones of ore deposits, as well as their significance in the formation of peculiarities of the chemical composition of waters, was considered usually for large regions. Thus, A.P. Solovov revealed the conditions of formation of secondary dispersion halos characteristic of arid and humid regions. He cited Central Kazakhstan and the Far East as examples. Eastern Transbaikalia is allocated to a single region, intermediate in climatic characteristic.

In prospecting lithochemical survey on residual eluvio-deluvial scattering halos, samples are taken, as a rule, from a depth of 15-20 cm, immediately below the vegetation layer. At the same time, it is known that metal concentration in the halo decreases with increasing thickness of deluvium. Obviously, when the thickness of the deluvium is significant, the metal concentration in the subsurface layer may become below the sensitivity limit for the determination of this element. With very sensitive methods of sample analysis, the depth of the lithochemical survey will be limited by the accuracy of the analysis and the irregularity of the useful metal content in the bedrock containing the ore body. On this basis, in lithochemical survey it is necessary to have at least a rough idea of the depth of the method - the limiting thickness of eluvium-deluvium, at which in the subsurface layer metal concentrations will still be sufficient for reliable detection of the halo.

The North of Siberia is characterized by gentle sloping relief, subarctic climate, and the development of a thick layer of permafrost. Permafrost- taiga soils are formed here throughout the whole territory. The article considers their main types developed on the eluvio-deluvium of pre-Quaternary rocks and the regularities of metal distribution in soil profiles of the area of the eastern slope of the Anabar anteclise.

The search for sulfide copper-nickel ores on the Kola Peninsula and Karelia in the areas of continuous overlapping of bedrock by moraine sediments is very difficult. Geophysical methods, widely used in these conditions for prospecting purposes, often do not give an unambiguous answer about the causal relationship of the induced anomalies. The methodology of lithochemical survey developed by the Leningrad Mining Institute in relation to these conditions can provide significant assistance in improving the efficiency of prospecting. It is currently being implemented in a number of geophysical parties of the Kola District Geological Exploration Department and the Western Geophysical Trust in order to sort out geophysical anomalies. Application of lithochemical survey in one of such parties in 1966 in combination with geophysical methods led to the discovery of mineralization at a depth.

The studied areas of mountainous taiga terrain are developed mainly by eruptive rocks of granitoid series. All sites are located in a typically humid zone. The valleys of rivers and springs are forested, often swamped, channel sediments contain abundance of organic matter in the form of fallen leaves, needles, etc. The relief is medium-sized, but rather strongly indented. Exposedness is poor, eluvial-deluvial deposits of medium clastic character with a small (up to 20 cm) soil layer. The thickness of loose formations usually does not exceed 2-3 m. Flat tops are often swamped.

The formation of voids in rocks during the development of karst is usually explained by the dissolving action of water and mechanical destruction of rocks with the removal of particles by groundwater. The study of deep karst at the Leningrad oil shale deposit shows that the formation of voids in carbonate rocks can also go at metasomatic processes - as a result of secondary dolomitization of limestone.

Influence of sample bulk composition on the accuracy of semi-quantitative spectral analysis. The precision of the analysis is the sum of all random confounders; the correctness of the analysis is the systematic error. The effect of sample bulk composition on systematic error, i.e., correctness of analysis, is well known. The effect of sample bulk composition on the accuracy of spectral analysis, however, depends on the methodology, spectral setup, and other factors specific to a particular laboratory.

In addition to fluorite, apatite, phosphorite, fluorine is most often associated with tin ore deposits. According to I.G. Magakyan, tin-bearing hydrothermal solutions carry tin in the form of SnF₄, and increased fluorine content in the rock and the presence of fluorine-bearing minerals are a search sign. According to the study of tin deposits in the Far East, tin is transported by hydrothermal solutions in the form of Na₂[Sn(OH,F)₆] compounds. These tin deposits are characterized by the presence of fluorite and increased fluorine content in chlorite and sericite. This was the prerequisite for studying the possibility of using fluorine as one of the indicators in hydrochemical searches for tin ore deposits. Most researchers studied fluorine content in water mainly from the position of biological impact of water on humans (dental caries, dental fluorosis). They noted fluoride deficiency in landscapes with humid climates and relative excess in dry, climates and in areas of modern and ancient volcanism.

Gamma-spectrometry is increasingly used in the sampling of uranium-thorium ores. It is based on measurements of pulse count rate in the optimal for uranium and thorium areas of the gamma-radiation spectrum. One of the main conditions ensuring high accuracy of sampling is the correct choice of gamma-spectrometer energy windows. This question arises most acutely at creation of spectrometric equipment with small size of scintillators in connection with low speed of counting of pulses in narrow energy windows, recommended usually in the literature.

As it is known, a significant part of the error of uranium and thorium content determination by gamma-spectral method is a statistical error. Unfavorable conditions of measurement are formed first of all for scintillators of small size. So, to provide with NaJ(Tl) crystals, 18x30 mm, the error of U and Th determination not more than 10% in ores with the content of these elements 0,03%, the measurement exposure should be about 10 min. If, however, when calculating the content of U and Th from gamma-spectral data to use not the count rate of pulses, and the area of gamma-spectral logging diagrams recorded by the recorder or built on the results of point measurements in the optimal energy intervals of the gamma-spectrum, the error in determining the area of the curve is relatively small even with a small exposure measurement of the count rate of pulses.

The calculation of the concentration of emanation in a mine workings traversed in radioactive rocks is of interest for mining and radiometric applications. Let, for example, there are two environments - an active space A and a cylindrical mine workings B of diameter 2a . Space A is characterized by the apparent diffusion coefficient D₁ and porosity coefficient η₁, space B by the apparent diffusion coefficient D and porosity coefficient η.

The X-ray radiometric method is realized in a line-of-sight geometry, when the detector is oriented so that it “sees” a part of the surface of the investigated medium irradiated by the source. In this geometry the detector registers mainly single scattered gamma-quanta and X-ray fluorescence of the element to be determined. A secondary role is played by multiple scattering, the influence of which is significantly reduced by collimation of primary and secondary radiation. When using soft gamma radiation sources (energy e=70-80 kev), measurements can be made in a wide solid angle. In ordinary cases, the spectra of secondary radiation have a general character.

When sampling ores by selective γ-γ-method the source of significant interferences are variable diameter and cavernosity of boreholes, irregularities of the sampled surface of walls in mine workings and variable density of rocks and ores. Inversion probes are proposed to eliminate these interferences. Theoretical and methodological issues related to the development and use of complex inversion probes of the selective u-method have not been addressed to date. The proposed paper represents a first step in this direction.

When studying the material composition and physical properties of ores (density, moisture) by nuclear geophysics methods, in most cases the result of physical field measurement depends on several parameters of the medium. Usually the problem is reduced to a one-parameter problem by selecting the appropriate conditions and observation technique. The possibilities of nuclear geophysics are significantly extended if the study of rocks and ores is considered as a multi-parameter problem, solving it by several conjugate measurements. There is, for example, simultaneous determination of ore density and content of heavy elements in them by two measurements of the u-field of Co-60 and Cs-137 sources under wide beam conditions; simultaneous determination of rock density and clay crust thickness by two measurements of scattered u-radiation with two different probe lengths. Similarly, the problem of sampling two-component mercury ores by integrated measurements of the y-field and thermal neutron field was solved. It is possible to formulate a number of three-parameter, four-parameter and similar problems, the solution of which is of great practical importance. An example of a three-parameter problem is the determination of the effective atomic number of the ore, its density and simultaneous consideration of the influence of the borehole diameter.

In order to exclude the influence of borehole diameter on the results of density γ-γ logging, special clamping 2π-probes are used. In small diameter wells (36—50 mm) it is difficult to use clamping probes. Symmetrical 4π-probes are widely used for such boreholes. However, the presence of an intermediate zone (air, water, drilling mud) between the probe and the borehole walls leads to a significant dependence of the 4π-probe readings on the borehole diameter. When the borehole diameter is constant, this dependence can be taken into account when benchmarking the probes. Violation of the identical conditions of reference and measurement when the borehole diameter is changed leads to differences between the measured R_ism and true R_ism values of density.

Estimating the strength properties of a rock mass by radiating the physical and mechanical properties of rock samples is inefficient due to the influence of scale factor. Both geologic and mining engineering features of the deposits influence rock stability. It is necessary to study rock properties directly in the massif. In this respect, the U-method of measuring the density of rocks in natural occurrence has great possibilities, since the density of rocks in the massif is either functionally or correlatively related to other physical and mechanical properties of rocks.