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In areas of semi-covered and covered terrains with thick overburden of different origin, the routine geochemical prospecting methods, aimed at revelation of open dispersion patterns, are not effective. In such territories, to make prediction of mineral deposits and geochemical exploration more successful, one have to use special methods and technologies, oriented to revelation of superimposed secondary dispersion patterns, with detection of non-mineral mobile or secondary fixed modes of presence of chemical elements in the secondary environment.
A new geochemical method of exploration for mineral deposits covered by thick overburden, called the Method of Analysis of Superfine Fraction (MASF), has been developed at VSEGEI. This method uses extraction and analysis of superfine fraction of soils or stream sediments (<3-10 ?Ým) with sequential specific sample digestion to extract adsorbed and saline (secondary sulphates, carbonates, etc.) forms of elements, and determination of contents of indicator elements using precise analytical techniques (ICP-AES, ICP-MS, etc.) with detection limits less than average content in the Earth's crust. When carrying out MASF geochemical field surveying, it is preferable to position sampling points in places of local geochemical accumulations and geochemical barriers, such as local depressions, seepage zones, bog margins, etc. Samples are usually taken from the B-horizon of soils. In saturated soils of boggy areas, samples are taken from the gley horizon laying under peat. So, usual sampling depth is about 0.3¡V0.6 m, sometimes up to 1.5 m, depending on position of the horizon should be sampled. Typical mass of a taken sample is 200-300 g for clayee or silty soils, and 500-600 g for sandy soils. To extract superfine fraction, the special device and technology have been developed and used in VSEGEI, enabling the high speed of the extraction process. The extracted material is undergone partial dissolution with acids and then analyzed.
As to geological information obtained by MASF, this method corresponds to the world level of other leading-edge methods of exploration geochemistry, such as NAMEG, MOMEO, MMI, etc. However, MASF is more adjusted to typical landscapes of Russia. The application of MASF to exploration leads to high productivity of works and optimal relationship of cost and quality.
Recently, MASF is widely used in different regions of Russia, including Karelia-Kola region, Far East, Siberia and Ural, as a method of geochemical exploration of various scales: from 1:1,000,000 to 1:10,000. Since 2003 MASF exploration has been carrying out just for several years, but first positive results of confirmation of MASF geochemical anomalies by drilling have already been obtained. These positive case histories are those in two prospecting areas in Karelia-Kola region (base and precious metals), in the area of Burakovsky massif in south-east Karelia, in Kingash territory (Sayany), in Kamenskaya area (Taimyr).
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