Впервые исследованы бугры пучения в долине р. Сенца на Окинском плоскогорье Восточного Саяна. Охарактеризованы состав и текстуры вмещающих отложений и температурный режим сезонноталого слоя, морфология и структура одного из крупных бугров, химический состав льда, слагающего его ядро. Для режимных температурных наблюдений на одном из крупных бугров пучения в долине р. Сенцы пробуре-на скважина глубиной 4,8 м. Установлено, что с поверхности бугор пучения сложен переслаивающимися льдистыми суглинками и линзами чистого льда. Криотекстуры грунта слоистые, косослоистые, тонкошли-ровые, крупносетчатые, базальные. Химический состав расплавов линз подземного льда HCO 3 и SO 4 -HCO 3 Ca с минерализацией 6,5-153 мг/дм 3 . В вертикальном изотопном профиле вариации стабильных изотопов водорода и кислорода составляют: δD -157,9… -142,7 ‰, δ 18 О -20,27… -18,61 ‰, а d exc изменяется от 11,78 до 2,58 ‰. Мерзлота в долине р. Сенца представлена льдистыми озерно-аллювиальными отложениями. Тем-пература пород в активном слое на глубине 4,4 м понижается до -1,6 °С. В ходе промерзания отложений происходило формирование бугров пучения. Сформулирован вывод о том, что изученный бугор пучения сформировался в результате как сегрегационного, так и инъекционного льдообразования в рыхлых озерно-аллювиальных отложениях. Research has been conducted on the permafrost in the Sentsa River valley for the fi rst time. The features of the permafrost that have been investigated are cryogenic structure of unconsolidated deposits and active layer temperature, the morphology and structure of large frost mound and the chemical composition of the core ice. On one of the large frost mound in the Sentsa River valley the borehole was drilled to a depth of 4,8 m for the regime geothermal observations. From the surface the frost mound consists of interlayering silts, ice-rich clayey silts and pure ice lenses, cryostructures are layered, cross-laminated, lenticular, reticulate and basal. The chemical composition of ground ice is HCO 3 and SO 4 -HCO 3 Ca with salinity of 6,5-153 mg/L. The vertical isotope variations are from -157,9 to -142,7 ‰ δD, from -20,27 to -18,61 ‰ δ 18 О, and 11,78 to 2,58 ‰ d exc . The permafrost in the Sentsa River Valley is presented by ice-rich lacustrine-alluvial deposits. The active layer temperature decreases to -1,6 °C at a depth of 4,4 m. Frost mounds were formed during sediments freezing. It has a cryogenic formation probably mixed segregation-injection genesis.
The study was focused on groundwaters sampled from boreholes drilled to deep horizons of the Udachnaya kimberlite pipe and the host sedimentary strata. Brines in the rocks significantly complicate underground mining. Analysis of the hydrogeological setting is required to ensure safety during mining to the design levels. The features of chemical composition and the geochemical evolution of brines in the crust can be clarified in a more detail on the basis of new reliable data on strong chloride saline solutions that formed in complex geological and tectonic conditions. Kimberlite and water samples were taken from the ore bodies and host sedimentary strata at the depth of 680–980 m. Conventional methods of quantitative and instrumental analysis were applied to study the chemical composition of brines. Mineral composition of kimberlite was determined by powder diffractography and X-ray fluorescence methods. Geological, structural and tectonophysical methods were used to reveal and describe the tectonic structure of the kimberlite pipe area. Groundwaters with salinity of 280–406 g/L are strong and very strong calcium chloride brines. The chlorine-bromine ratio has a small range of 48–57; the sodium-chlorine ratio varies from 0.11 to 0.18. According to their geochemical features, the studied groundwaters are metamorphosed brines that have analogues across the Siberian platform. Physical and chemical processes were simulated to investigate the degrees of saturation of strong brines relative to the minerals of water-bearing rocks. The simulation results show that the brines in the Western ore body of the Udachnaya pipe are strongly undersaturated in the deep horizons in comparison to carbonate, sulfate and chloride minerals. This suggests possible dilution of brines during their geochemical evolution. A detailed study of the tectonic structure identified structural elements that control the distribution and migration of groundwaters in the rocks. In the mining sites, brines occur mainly in the fault zones, fault junctions and intersections with the contacts of kimberlite bodies. Integration of hydrogeological and geostructural data can provide a basis for prediction and assessment of the sites with increased water inflow in the deep horizons involved in mining.
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