Material Composition of the Mesozoic Alkaline Rocks of the Yukhta Massif (Southern Yakutia, Central-Aldan Ore Region)

The paper considers the petrographic composition of the Mesozoic alkaline igneous rocks of the Yukhta massif. It is part of the Central Aldan ore region and is spatially located in the central part of the Nymnyr block. The massif is a large multiphase structure, of the most productive stage of the territory’s development – the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy shield. Determination of the qualitative quantitative-mineralogical characteristics of the 2 and 3 phases of intrusion (emplacement) most promising for gold-radioactive mineralization with the help of crystal-optical methods was the main goal of this work. As a result of petrographic studies of Mesozoic alkaline igneous rocks, it is defined that, the Yukhta massif is a multiphase magmatic structure, with decrease of the content of dark-colored minerals in rocks from the early to later phases of intrusion. In general, the rocks of the massif bear significant traces of secondary changes, which are related to the gradual formation of the massif. According to the features of the composition of the massif rocks, it was found that the latter could be formed from residual differentiates during the fractional crystallization of rock-forming minerals with the involvement of plagioclases. The Yukhta massif is associated with the large Samolazovskoye gold deposit, which formation is related to an intense contact-metasomatic impact on carbonate rocks. Hydrothermal-metasomatic transformations of the latter are the products of multi-stage silica-alkaline metasomatosis associated with the second and especially with the third phases of the massif intrusion, and with further weathering processes, involving karst formation, disintegration of gold-ore metasomatites and the formation of a thick oxidation zone. From whence it is concluded that uranium being a chemically active element does not accumulate in a hypergenic form within the Yukhta massif. Where the weathering crust is intensively developed, a gold-ore type of mineralization is observed. On the other hand, the rocks of the massif itself, in particular syenites of the 2 and 3 phases of intrusion, may be promising for the uranium-thorium-rare earth (U-Tn-REE) type of mineralization. In general, these studies in this direction will provide insight into a number of issues related to the study of the evolution and metallogeny of the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy Shield

Types of Tellurium Mineralization of Gold Deposits of the Aldan Shield (Southern Yakutia, Russia)

The published and original data on the tellurium mineralization of gold ore deposits of the Aldan Shield are systematized and generalized. The gold content is related to hydrothermal-metasomatic processes caused by Mesozoic igneous activity of the region. The formation of tellurides occurred at the very late stages of the generation of gold mineralization of all existing types of metasomatic formations. 29 tellurium minerals, including 16 tellurides, 5 sulfotellurides and 8 tellurates have been identified. Tellurium minerals of two systems predominate: Au-Bi-Te and Au-Ag-Te. Gold is not only in an invisible state in sulfides and in the form of native gold of different fineness, but also is part of a variety of compounds: montbrayite, calaverite, sylvanite, krennerite and petzite. In the gold deposits of the Aldan Shield, three mineral types are distinguished: Au-Ag-Te, Au-Bi-Te, and also a mixed one, which combines the mineralization of both systems. The decrease in the fineness of native gold is consistent with the sequence and temperatures of the formation of Te minerals and associated mineral paragenesis from the epithermal–mesothermal Au-Bi-Te to epithermal Au-Ag-Te. The conducted studies allowed us to determine a wide variety of mineral species and significantly expand the area of distribution of Au-Te mineralization that indicates its large-scale regional occurrence in the Aldan Shield.

Settlement dynamics and development of transport communications in Southern Yakutia in late the XX – early XXI centuries

This article examines the settlement dynamics in relation to the development of transport communications using the statistical, comparative geographical, and cartographic methods. A brief characteristics is given to the system of displacement of population of Southern Yakutia in the late XX – early XXI centuries. The analysis employs the materials of the population censuses of 1959, 1970, 1979, 1989, 2002, and 2010, which allows compiling the population maps that reveal the peculiarities of settlement network, their population density and structure. Spatial representation of the data is presented on the example of population displacement maps and development of transport communications in Southern Yakutia as of 1959 and 2010. Comparative analysis maps of different periods demonstrates a three-fold decrease in the number of settlements in Southern Yakutia during the intercensal period (1959–2010) due to liquidation of unpromising villages and change of nomadic lifestyle of the indigenous population to sedentary life in larger rural settlements during the period of Soviet administrative reforms of the late XX century. The emergence of new transport communications is associated with active industrial development of Southern Yakutia; however the territories were affected unevenly. It is established that spatial peculiarities of population displacement in Southern Yakutia in the late XX – early XXI centuries have remained, although the settlement areas of the indigenous small-numbered peoples of the North- the Evenks – have decreased. The study of transport communications on the maps of different periods revealed the dynamics of their development in different historical periods, determining the historical roads, abandoned transport routes, emergence of new types and categories of communication lines, including the network of technological roads of industrial companies used for infrastructure maintenance.

Migration of 238U and 226Ra Radionuclides in Technogenic Permafrost Taiga Landscapes of Southern Yakutia, Russia

This article describes the features and migration patterns of natural long-lived heavy radionuclides 238U and 226Ra in the major components of the environment including rocks, river waters, soils, and vegetation of permafrost taiga landscapes of Southern Yakutia, which helped us to understand the scale and levels of their radioactive contamination. Different methods have been used in this study to determine the content of 238U and 226Ra in various samples, including gamma-ray spectrometry, X-ray spectroscopy, laser excited luminescence, and emanation method. It was determined that the main source of radioactive pollution of soil and vegetation cover, as well as surface waters in these technogenic landscapes, are the dumps of radioactive rock that were formed here as the result of geological exploration carried out in this area during the last third of the 20th century. The rocks studied were initially characterized by a coarse, mainly stony gravelly composition and contrasting radiation parameters, where the gamma radiation exposure rate varied between 1.71 and 16.7 µSv/h, and the contents of 238U and 226Ra were within the range 126–1620 mg/kg and 428–5508 × 10−7 mg/kg, respectively, and the 226Ra: 238U ratio was 1.0. This ratio shifted later on from the equilibrium state towards the excess of either 238U or 226Ra, due to the processes of air, water, and biogenic migration. Two types of 238U and 226Ra radionuclides migration were observed in studied soils, namely aerotechnogenic and hydrotechnogenic, each of which results in a different intraprofile radionuclide distribution and different levels of radioactive contamination. In this study, we also identified plants capable of selective accumulation of certain radionuclides, including Siberian mountain ash (Sorbus sibiricus), which selectively absorbs 226Ra, and terrestrial green and aquatic mosses, which accumulate significant amounts of 238U.

The Yamalakh Horst (Southern Yakutia): features of geology, geomorphology and history

The paper presents geological and geomorphological details for the Yamalakh horst (Central Aldan region, Yakutia), which hosts the Chompolo field of barren lamprophyre in its southern part and a gold deposit in the north. The rocks resulted from Mesozoic alkaline magmatism in the Aldan shield. The horst origin relates to large-scale alkaline intrusions in post-Early Jurassic time.

Radiation-ecological evaluation of rock dumps in the south zone of the Elkon uranium mine region (the Southern Yakutia)

This study aims at investigating the allocation conditions of rock dumps in the South zone located in the Elkon uranium mine region (the Southern Yakutia), and also at determining their radiation parameters as sources of technogenic contamination of the soil-vegetation cover and surface waters, and assessing the danger of these dumps for people. In this study, the generally accepted geographical methods were used, including comparative geographical and geochemical methods, as well as a combination of various radiometric research methods. The radiation parameters of the rock dumps of the South zone of the Elkon uranium mine region, the content and distribution of uranium, radium and radon in surface waters, as well as 238U content in technogenic soils at different distances from radioactive contamination sources were studied. It was found that the most active dumps, in terms of their radiation parameters, are located close to the radioactive ores, with the EDR of 1600-2150 R/h, effective specific activity - 20441-23640 Bq/kg, and uranium content of 1637-1888 mg/kg. The ranking of the studied dumps according to the degree of radiation hazard showed that 12 out of 31 dumps (39%) belong to the safe category, 6 (19%) belong to the category of potentially dangerous, and 5 and 8 (16% and 26%) were classified as dangerous and very dangerous respectively. In the conditions of the mountainous terrain, cold and humid climate of the studied area, these rock dumps, which are unevenly spread in mountain and taiga landscapes over the area of about 500 km2, are the main source of radioactive contamination of soil and vegetation cover and surface waters. The maximum contents of uranium, radium and radon in the studied surface waters were 18010-7 g/L, 4.710-12 g/L and 256.8 Bq/L respectively, which are 100, 8 and 198 times higher than their background concentrations in waters of natural landscapes. In the studied technogenic zones, a direct relationship was registered between the pollution intensity in surface water and that in the drained alluvial soils formed in the floodplains of these watercourses.