In the structure of Russia's resource base, alluvial deposits account for 18% of reserves and 10% of probable resources. Alluvial placers are the most common type found in nature and the most important source of alluvial gold mining. Based on numerical modeling and on field studies of alluvial placers in Kamchatka, Altai, and the Baikal region, scientists from the NSU (DGG) and the A. A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS (TIPGG) that electrical tomography can be used as the main method of prospecting and exploration of placers.
Vladimir Olenchenko, Candidate of Geological and Mineralogical Sciences, researcher at TIPGG, Associate Professor NSU DGG, talked about the study,
In river sediments, gold lies among boulders and pebbles. This is the facies of reaches and rifts. Electrical tomography makes it possible to map these gold-bearing deposits, as well as to identify 芦pockets禄, local depressions on the surface of bedrocks. These usually contain the maximum metal content. In addition, the method allows you to identify the sources of placer gold content in bedrock, that is, the zones of gold mineralization from which the placer was formed.
Electrical tomography is a modern technology for electrical sounding of rocks. It has been actively developing in Russia over the past 10 years. It is used to solve a wide range of geological problems from prospecting for ore deposits to archaeological research. Unlike vertical electrical sounding (VES), electrical tomography makes it possible to obtain geophysical information at a qualitatively new level. This information is not in the form of apparent resistivity curves and isom sections, but in the form of two-dimensional and three-dimensional geo-electrical models of the medium.
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Today, there are only a few publications with the results of studies using electrical tomography to study alluvial deposits that can be attributed to experimental work. NSU scientists managed to combine the data of electrical tomography with geological sections along pits and ditches, as well as with the results of sampling collected over several field seasons.
Olenchenko added,
Based on the data obtained, we were able to establish that the geological interpretation criteria for identifying the channel facies of alluvium are local anomalies of elevated and high resistivity from 500 Om鈭檓 to several thousand Om鈭檓. In the plan, they are ribbon-like anomalies that mark paleochannels that are revealed as a result of areal surroundings in river valleys. We also found that the electrical resistivity of alluvial deposits in modern channel placers is significantly higher than the resistivity of the channel facies in valley and terrace placers. This makes it possible to distinguish these types of placers in geoelectric sections.
In the near future, this method will be widely used in alluvial gold prospecting and subsoil users will be able to save on drilling and pitting.
