Vol 45 Iss. 2

The distribution of germanium and other impurity elements in brown coals of Mesozoic age was studied (1957-1961) in the deposits confined to depressions of the ancient basement. The coal-bearing strata at these deposits are composed of Continental-type sediments and contain thick deposits of brown coal of complex structure.

Considering the possibility of estimating the scale of expected native mineralization on the basis of calculating the total (integral) metal content in the halo, A. P. Solovovov for ore bodies of linearly elongated shape proposed a formula ...

The Lyubavinskoye gold deposit, located in the upper reaches of the Onon River, has been developed since the end of the last century. V. A. Obruchev, who visited the deposit in 1912, published the first summary work on the geology and minerals of the area, which has not lost its significance to this day. Later, V.M. Sergievsky (1936) and M.I. Tulokhonov (1958) carried out geological survey works in the area. In the summer of 1960 within the limits of the Lyubavinskoye ore field were carried out complex geological-geophysical and geochemical studies by teachers and students of the Leningrad Mining Institute.

The method of accounting for thorium in three gamma ray log interpretations recommended by the existing gamma ray logging manual provides for multiple determinations of thorium in core samples. Samples are analyzed for thorium by gamma ray spectrometry or by chemical and radiochemical methods. The absence in some laboratories of stable scintillation analyzers and in field parties of logging stations that allow reliable separation of uranium and thorium in boreholes forces expensive radiochemical analyses for thorium and radium (due to the need to determine the equilibrium coefficient of uranium and radium).

The main methodological issues in geochemical studies are: the determination of absolute concentrations of individual elements, clarification of their paragenetic associations, as well as patterns of distribution of elements depending on the specific geological setting. In this connection there is a necessity to study the companion elements of any minerals, including uranium. Important methodological moments are: processing of stone material, reliability and sensitivity of the applied complex of analyses, methods of statistical processing of results and ways of the most visual representation of the obtained data. Correctly chosen methods of statistical processing and visualization of the material help to reveal essentially important regularities, which can be hidden or not caught behind the abundance of analytical results.

Determination of the volumetric weight of rocks and ores by gamma ray attenuation in them is performed in situ without disturbing the structure, natural moisture regime, etc. This automatically takes into account macro- and micro-cracking, cavernousness and other features of the structure and texture of rocks and ores. Determination of the volumetric weight of rocks and ores by attenuation of gamma rays has undoubted advantages over other methods: simplicity, high productivity and cost-effectiveness.

One of the pressing problems of geochemistry is the study of the forms of finding and patterns of distribution of elements in rocks and minerals. Of great interest is the importance and technical possibilities of determining small concentrations of radioactive elements. In recent years, a number of works have been published, mainly devoted to the distribution of radioactive elements in rocks mainly of granitoid composition. Considerably less attention has been paid to metamorphic rocks.

Testing of uranium ores in natural occurrence (boreholes and mine workings) is performed by gamma radiation. It is based on the proportional relationship between the intensity of radiation and the amount of radioactive elements in the ore. The coefficient of proportionality in this case is usually called the conversion coefficient. Since 93-98% of gamma-radiation of equilibrium uranium ore is caused by gamma-radiation of Ra226 and its decay products, the conversion factor is, in fact, the specific (per unit of content) intensity of the equilibrium spectrum of Ra226 registered by the detector at uniform distribution of gamma-emitters in an infinite medium (case of gamma logging) or in a half-space (case of gamma-testing in mine workings).

The formation of secondary eluvial-deluvial scattering halos at lead and molybdenum deposits was usually considered as a process of mechanical dispersion of weathering products of ore bodies and host rocks. As the study of the mineral composition of loose eluvial-deluvial deposits of some deposits of the Eastern Transbaikalia has shown, the formation of secondary scattering halos appears to be more complex.

As it is known, almost all gamma-radiation of equilibrium uranium series is accounted for by the radium part: short-lived radon decay products Ra (B + C). For the MS-type counters the gamma-radiation of the uranium part of the series is only 5.1%, and Ra (B + C) -94.9% of the total intensity. Removal of radon from the rock as a result of emanation leads to a corresponding decrease in the content of its decay products in the rock and, consequently, to a decrease in the intensity of gamma-radiation. The emanation factor of ores in the crushed state reaches several tens of percent. Although the emanation factor in natural conditions is usually lower, this fact requires mandatory study. The emanation correction α' must be taken into account in the interpretation of gamma-ray measurements.

In the metallogeny of magmatic rocks of the Khapcheranginsky ore district some researchers assign the leading role to granite porphyries and granodiorite porphyries, felsites and quartz porphyries of the Verkhneononskaya group of small intrusions, granite porphyries of the Khapcheranginsky stock and granodiorites of the Khamaro-Tyrinsky intrusive massif.

In the search for gold deposits since time immemorial successfully used schlich survey, based on the study of mechanical halos and scattering fluxes of nugget gold. The use of geochemical methods based on the direct indication of finely dispersed gold in samples of small weight has become possible only in recent years due to the introduction into practice of the adsorption-spectral method of analyzing lithochemical samples, proposed by N. I. Safronov. However, this method, which achieves a sensitivity of 1-3·10^(-6) %, involves complex preliminary chemical treatment of samples. Even more complicated is the chemical preparation of samples for analysis in the assay-spectral method (sensitivity 10^(-8) %). The chemical preparation of samples is somewhat simpler in the electrochemical-spectral method, which has approximately the same sensitivity as the adsorption-spectral.

The present article presents data on the content of uranium, thorium, potassium in the geological formations of southwestern Priargunya and attempts to classify rocks according to their radioactive properties (based on the results of 670 luminescent, 290 radiochemical, 160 chemical analyses performed in the laboratories of VSEGEI and other organizations, and many thousands of field gamma measurements). The relative error in determining the content of radioactive elements by repeated analyses does not exceed 25%.

Rocks, minerals, and ores are often analyzed by the spectral line attenuation step technique. The advantages of this method over other accelerated spectral analysis techniques are the simultaneous determination of many elements, speed and ease of grade estimation over a large range of detectable concentrations. This makes the method promising for geochemical studies over large areas, prospecting and other geological tasks. In this connection, the reproducibility and accuracy of the method were characterized and its capabilities were evaluated. It was shown that the spectrogram allows to take into account the composition of the sample and determine the content of impurities directly from the calibration graph (not in intervals). On the example of a series of determinations of various elements it is established that the average error with respect to chemical analysis is ±25%.

Identification of regional geochemical regularities by the character of chemical elements distribution in sedimentary rock strata can be achieved by accelerated methods of spectral analysis. However, this requires sufficient accuracy in determining the content of chemical elements in rocks and preservation of the main advantages of spectral analysis: speed, high sensitivity and simplicity. Based on the consideration of the peculiarities of rock samples and simple methods of analysis, it is advisable to use the method of line appearance in combination with a three-stage attenuator (for individual elements) and the method of step attenuation of lines by three orders of magnitude according to M. M. Clair. The M. M. Clair method, unlike other accelerated methods of analysis, simultaneously determines many elements on a single spectrum, in addition, the estimation of content is simple in a large range of determined concentrations. This makes the method promising for mass analysis of rock samples in regional studies.

In the far north in the conditions of moraine deposits, plant litter serves as a source material for samples in biochemical surveys in connection with the search for copper-nickel and polymetallic ores. After sampling on a certain network (depending on the survey scale), the litter is dried, ash-dried and its ash (usually by volume) is submitted for spectral analysis. Based on the results of analysis, graphs of copper, nickel and other elements content or maps of isoconcentrations are constructed. According to such a scheme is currently carried out biochemical survey by production organizations.

At lithochemical searches of deposits of fluorspar by secondary halos of fluorine scattering it is important to solve the question about optimum depth of lithochemical sampling and character of the material taken in the sample from eluvial-deluvial deposits. Analysis of the results of production work shows that errors in the methodology of lithochemical sampling and processing of lithochemical samples often lead to unfortunate blunders and reduce the efficiency of prospecting.