Landscape and climate search conditions
In the basis of landscape zoning of territories according to the conditions of conducting prospecting works, a set of characteristics characterizing the features of the geographical landscape is adopted. The main landscape complexes are relief, soil-vegetation layer, cover of loose sediments, weathering crusts, bedrock, soil-ground and surface waters. All the components of the landscape are closely interrelated and depend on the geological structure, neotectonics and the climate of the area.
In order to judge the difficulty in prospecting for the territories to be evaluated in the practice of prospecting, the concepts of critical powers of loose sediments and representative horizons of prospecting are used.
The critical thickness of loose sediments is the maximum their thickness, at which the aureoles of scattering of elements emerging on the day surface are clearly identified by modern search methods. If the thickness of the sediments is higher than the critical one, during search operations it is necessary to go deeper into the loose cover to a representative horizon of prospecting. Critical powers of most long-range friable deposits do not exceed the first fractions of a meter, in autochthonous deposits they reach several meters, and sometimes tens of meters.
A horizon of stable and maximum area development of secondary aureoles, most closely located to the surface of the day, is called a representative horizon.
Principles of landscape zoning
A complex of features characterizing the features of the geographical landscape is taken as the basis for landscape zoning of territories according to the conditions of geological exploration. The main components (components) of the landscape are: relief, soil-vegetation layer, cover of loose sediments, weathering crusts, outcrops of bedrock, soil-ground and surface waters. All these components are closely interrelated and depend mainly on the geological structure, manifestations of neotectonics and climatic features of the area.
The essence of the regionalization of the territory by landscape conditions is to identify the connections and dependencies between the individual components of the landscape. Understanding these relationships makes it possible to really assess the conditions for the formation and likely manifestation of uranium and rare metal mineralization features in a specific landscape and geographic situation.
The smallest area within which extremely homogeneous parts of the landscape are combined is the elementary landscape . According to B.B. Polynov , this is a certain element of the relief, composed of one rock, one type of loose sediments, within which a soil-vegetation cover of a certain type is developed. Taking into account the most important geomorphological features and location relative to the groundwater level, four dominant types of elementary landscapes are distinguished: the watershed (eluvial), slope (trans-luvial), the foot of the slopes (superaqual) and the local water bodies (aqual).
Elementary landscapes of watersheds are confined to elevated parts of the relief, cover watershed plateaus and flat upper slopes. In the terminology of B.B. They are autonomous, as they are covered with loose eluvial and eluvial-deluvial deposits formed due to the destruction of local (autochthonous) underlying bedrock. In the watershed landscapes unshifted residual (or almost unshifted secondary) halos of the dispersion of rare, radioactive metals and their satellites are formed.
Elementary landscapes of slopes are located in their middle parts, covered with loose deposits of the deluvial type. Like the two following landscapes, they are subordinate, since the composition of loose sediments and diffusion haloes in them depends on the composition of the bedrock within the autonomous elementary landscape. For landscapes of slopes, mixed residual and superimposed halos or fluxes of scattering of uranium, rare metals and their satellites are characterized to varying degrees.
Elementary landscapes of the slopes of the slopes are located in their lower, designed parts, in local relief depressions or within the floodplain terraces of river valleys. They are characterized by a shallow groundwater table and increased thicknesses of deluvial (less often colluvial, proluvial or alluvial) loose sediments. Under favorable conditions within these landscapes, the displaced residual halos may persist, and due to the increased concentrations of uranium and some of its satellites, secondary accumulations in the form of superimposed salt halos are often formed in groundwater.
To elementary landscapes of local reservoirs include areas of marshes, river beds, ponds and lakes ponds in which water and salt halos (streams) of uranium and some of its satellites develop.
The natural aggregate of elementary landscapes forms a geochemical landscape . According to A.I. Perelman , the geochemical landscape is a paragenetic association of conjugate elementary landscapes, interconnected by the water migration of elements. For example, the mountain-taiga geochemical landscape can consist of the following elementary landscapes: the upper (watershed) part of the slope, the middle part of the slope with the spruce taiga, the lower part of the slope with the marshy taiga and the forest swampy lake. The more energetic the biogesochemical cycle of atoms in the landscape takes place, the stronger the connection between the various elementary landscapes. The most perfect geochemical connection between elementary landscapes is manifested in hot tropical regions, and the least perfect in conditions of deserts and polar regions.
The concept geochemical landscape meets the requirements of zoning of territories to assess their uranium content, since geochemical methods are leading in the search for uranium deposits. However, for estimates of ore content of territories not only for uranium but also for rare metals, a broader notion of a geographic landscape is preferred, which takes into account the influence of the processes of both chemical and physical weathering. In the conditions of imperfect geochemical connections between elementary landscapes, the processes of physical weathering and denudation, as well as the associated mechanical halos and scattering fluxes of rare and radioactive metals, are particularly pronounced.Elementary landscapes and their aggregates (geochemical landscapes) are manifested in various bioclimatic environments, which largely determines the types of soil and vegetation cover, hydrographic network, and groundwater and surface water regimes. The more humid and warmer the climate, the more living matter (bios) is formed, the processes of its decomposition and migration of many chemical elements are more intensive. It is practically the most important to distinguish two types of bioclimatic regions, arid and humid , which create fundamentally different conditions for near-surface migration of chemical elements.
Arid regions are characterized by a dry climate with a clear predominance of evaporation over the amount of precipitation. For arid regions there is typically a lack of forest cover, and often a weak development of grassy vegetation, a non-washing regime, a hydrocarbonate-calcium composition, and a slightly alkaline reaction of soil-groundwater. In such conditions, rapid decomposition and mineralization of organic substances occur, and uranium and many of its satellites have weak chemical mobility, which leads to the formation of open unbiased or weakly displaced radioactive halos.
Humid areas are characterized by a humid climate, as a result of which the amount of precipitation prevails over their evaporation. Humid areas are characterized by the development of rich forest, shrubby and grassy vegetation, the accumulation of a large amount of organic matter in relief depressions, the washing regime and the acid reaction of nocturnal-іruntovyh waters. Unlike arid regions, geochemical processes in many humid regions are limited not by moisture deficit, but by heat deficit.
In tropical and subtropical humid regions with a hot climate, the washing regime of water leads to the formation of strong weathering agents of lateritic type and to the almost complete leaching of uranium and its satellites from loose sediments and near-surface areas of bedrock. In moderately warm humid regions, the high migration capacity of uranium is also maintained, which leads to the formation of halos of greater length and far removed from the indigenous uranium ore concentrations. In the cold humid regions, the processes of physical disintegration and frost weathering of rocks dominate, and the chemical migration of uranium and its satellite elements is weak.
In arid areas, there are desert, semi-desert and steppe landscapes.
Humid areas with hot and humid climates include tropical and subtropical landscape areas.
In temperate latitudes, the composition of humid areas includes forest-steppe, forest, mountain-taiga, tundra and polar zones.
A similar vertical landscape-climatic zoning is observed in mountainous areas, where the types and number of vertical belt zones depend on the geographical location of the mountainous region and its absolute marks. The vertical zone of the mountain regions is not completely analogous to the horizontal georaphy zonality. Individual landscape belts may fall out of the general scheme, but at the same time in the mountains there are unique landscapes, for example, landscapes of mountain meadows.
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