The Morphology of the Buried Valley in the Lena Gold-Bearing Area and Related Features of Alluvial Placers

In this article were summarized data of exploration work conducted in the valleys of the Lena gold-bearing area, starting from the early stages of exploration (1910–1920s) and ending with the 1990s, including large-scale production plans. the drainage system of the area inherits the faults that were formed in the late jurassic – early cretaceous. buried valleys inherit their position during several erosion cycles: in the same reaches the position and width of valleys of different ages remains approximately the same, but in the bottoms of valleys of different ages large transformations are observed. in the formation of the morphology of the buried valley of the Lena gold-bearing area, the leading role belongs to river channel processes. Stable position of the river valleys determines the inherited position of the placers, as a rule, they are located within the contours of the modern valleys or their bottoms, or are slightly shifted to terrace staircases. Inherited are also morphodynamic types of channels, however, in cases of displacement of the valleys to areas with different lithological and tectonic conditions, morphological structure of valleys and alluvial deposits also change. This leads to formation of beads-like widening of the valleys and steps in their longitudinal profiles. Specific examples of such changes are illustrated from the large valleys of the rivers vacha and bodaybo. Three types of buried erosional terraces were considered that alternate along the length of valleys and determine specific position of the placers. a significant influence of the major tributaries to the structure of placers was found that is expressed in the presence of a transverse to the axis of the valley of the gold-bearing layers and sudden changes of elevation values of their beds. the established regularities are relevant to other mining areas and may have great practical importance in prospecting and exploration of mineral deposits.

buried valley, lithological and tectonic conditions, morphodynamic type of river channel, placers, evolution of paleochannels

1. Bilibin Yu.A. Osnovy geologii rossypei (Fundamentals of placer geology). M.: AN SSSR (Publ.), 1956. 463 p.

2. Shilo N.A. Uchenie o rossypyakh (Teaching on placers deposits). M.: Academy of Mining Sciences (Publ.), 2000. 630 p.

3. Gol’dfarb Yu.I. Dinamika formirovaniya, klassifikatsiya i vozrast allyuvial’nykh rossypei zolota Severo-Vostoka Azii (Dynamics of formation, classification and age of alluvial gold placers of NorthEast Asia): PhD thesis. Magadan: SVKNII DVO RAN (Publ.), 2009. 49 p.

4. Postolenko G.A. stanovlenie sovremennykh dolin i ego znachenie dlya geologii rossypei (significance of modern river valleys formation for placer geology). Geomorfologiya (geomorphology ras). 2013. No. 3. P. 11–23. (in Russ.)

5. Postolenko G.A. Vnutridolinnye perestroiki kak faktor formirovaniya rechnykh dolin v chetvertichnoe vremya (Intra-valley rearrangements as a factor of river valley formation in the Quaternary). Novye i traditsionnye idei v geomorfologii. The 5 th Shchukin conference. Faculty of geography MSU. M.: MSU (Publ.), 2005. P. 152–156. (in Russ.)

6. Voskresenskij S.S. Geomorfologiya rossypei (Geomorphology of placers). M.: MSU (Publ.), 1985. 205 p.

7. Kazakevich Yu.P. Usloviya obrazovaniya i sokhraneniya slozhnykh pogrebennykh rossypei zolota (The conditions of formation and preservation of complex buried gold placers). M.: Nedra (Publ.), 1972. 215 p.

8. Sinyugina E.A. O nekotorykh tipakh allyuvial’nykh otlozhenii i zolotonosnykh plastov Lenskogo raiona (bassein reki Bodaibo) (Certain types of alluvial deposits and gold-bearing layers in the Lena river region (Bodaibo river basin). Tr. TsNIGRI. 1961. Vol. 38. P. 86–106. (in Russ.).

9. Patyk-Kara N.G. and Postolenko G.A. Dolinnaya sistema Kolymy, istoriya i faktory ee stanovleniya (Kolyma valley system, its history and formation factors). Geomorfologiya (Geomorphology RAS). 2003. No. 3. P. 62–75. (in Russ.)

10. Osadchii S.S. Usloviya rossypeobrazovaniya v Vostochnom Sayane (Conditions of Placer Formation in the Eastern Sayan). Novosibirsk: Nauka. Sib. Otd. (Publ.), 1984. 71 p.

11. Kazakevich Yu.P. and Reverdato M.V. Lenskii zolotonosnyi raion (The Lena gold-bearing region). Tr. TsNIGRI. 1972. Vol. 88. 149 p. (in Russ.)