Вестник МГТУ. 2019, Т. 22, № 1.

Сорохтин Н. О. и др. Первая находка алмаза на полуостровах Средний и Рыбачий. According to the geodynamic analysis and timeline of the crustal formation in the eastern Baltic Shield, the most promising areas for diamond-bearing rocks are intersection points of deep-seated breaks in the lithosphere and defined belts of possible diamond-bearing kimberlitic magmatism (Fig. 1; 3). Thus, Fig. 4 shows the most promising areas for prospecting for diamond-bearing kimberlitic explosion pipes. These areas can be united into the single diamond-bearing Norwegian-Mesensky belt. Fig. 4. Location of the Norwegian-Mesensky diamond-bearing belt within the north-eastern Baltic Shield and northern Russian Platform Рис. 4. Схема расположения Норвежско-Мезенского алмазоносного пояса в пределах северо-восточной части Балтийского щита и севера Русской платформы The Rybachy and Sredny Peninsulas have been prospected for diamonds (Fig. 5). Detailed decoding of large-scale aerial photographs and in situ measuring of fractures in the northern margin of the Sredny Peninsula allowed defining prospective intersection nodes of deep faults. Heavy mineral concentrate has been sampled here and indicated diamonds and associated minerals. The obtained results are provided below. They can indicate either native wash-out origins, or immediate scouring of Paleo-marine terraces that used to be rich in these minerals. Samples have been picked out the middle flow of a creek, upstream a bit from its crossing with the road that goes from the isthmus to the Zemlyanoy Cape of the Sredny Peninsula (Fig. 6). During the sampling, 480 kg of alluvial deposits from fluvial and coastal facies have been processed. After sieving and washing, 1.5 kg of gray sand has been prepared for further analyses. The sand has been processed in the Laboratory for Mineralogy of Geological Institute KSC RAS, as described below. Three samples of -0.75В class with an average weight of ~300 g have been transferred to the laboratory. The samples have been processed for the reduced mineralogical analysis, according to the following technique: 1. VLTK-500 counter balance is used to determine the weights with accuracy of 0.1 g. 2. The material is separated according to its specific weight in bromoform with a specific weight of 2.9 g/cm3. As a result, heavy fraction is produced. 3. The heavy fraction is subject to the magnetic and electromagnetic separation (using the Sochnev magnet). As a result, magnetic, electromagnetic and nonmagnetic fractions have been obtained. All fractions are weighted. 4. All fractions have been studied under the binocular magnifying glass. Minerals have been identified visually, using a microscope in immersion fluids. In some cases, the X-ray and microprobe analysis on Cameca MS-46 have been provided. Pictures of single grains have been taken using the Stemi binocular. The content (%) of zircon, rutile, ilmenite has been calculated regarding the heavy fraction weight. 40