Search

Based on the results of field research, as well as data from stock reports, two types of placer gold were identified within the Vagran placer cluster, which are indicators of primary mineralization. They are used as benchmarks for developing a digital system for predicting parameters and localizing primary sources of placer gold. Formalized typomorphic characteristics of placer gold (size, roundness, fineness, sorting and content of impurity elements), combined in multiplicative indicators, make it possible to forecast the composition and localization of the primary mineralization with greater confidence than ordinary parameters separately. The data required for such an assessment do not require additional field and highly qualified laboratory studies, they are contained in standard reports on the heavy minerals testing, and, in contrast to the characteristics of individual indicator types of placer gold, they give more stable results. The study of the correlation system allowed to identify characteristic indicators for the primary mineralization of gold-sulfide-quartz and hypogenic-hypergenic types, and to give recommendations for conducting prospecting and exploration in order to identify the primary gold content of the cluster. The proposed method of creating forecast estimates allows to computerize the process of determining the prospects for primary mineralization of territories.

Placer deposits are an accumulation of valuable minerals both dense and resistant to weathering processes, formed by gravity separation during sedimentary processes. Placer deposits of the Russian Arctic zone (RAZ) include gold, platinum group minerals (PGM), tin, diamonds, rare metals, zircon-titanium mineral deposits and a specific type of related to placer deposits - fossil ivory. There are an insufficient number of scientific geological articles on placer deposits of RAZ in the English-language literature at present, especially of an overview nature. This review paper attempts to fill the gap and marshal on the regional scale all available data aiming to provide a framework for generating and testing new ideas on the placer deposits of RAZ. The focus is on main factors and conditions of generation of the placer deposits of industrial importance, details of key placer deposits, and perspectives of development of placer mineral resources in the region. Localization and scales of placer deposits are controlled by metallogenic, tectonic, climatic and geomorphological factors which have regional and local characters. The metallogenic factor specifies the primary sources of the placer minerals, especially for proximal (retained and partly transient) placers that have moderate transportation. Tectonics have a dual role: on the regional level it determines rate of the erosion and disintegration of the host rocks due to weathering process; while on the local level, tectonic dislocation forms structural traps of placer deposits. Climatic factor is determinative for the character of supergene processes: warm humid conditions (especially combined with stable tectonics) result in deep chemical weathering and disintegration of the host rocks containing primary mineralization which is favorable for the placer forming process; in frozen (periglacial) climate conditions, mechanical weathering processes are prevalent. Geomorphological factors are closely connected with the dynamic state of the placer forming area, from the source location to the final sedimentary accumulations. Industrial placer deposits are formed when an optimal ratio of the main factors of placer forming processes occurs. A special type of anthropogenic (technogenic) placers are formed as result of human mining activities. It is impossible to distinguish only one or two of the main universal factors which are responsible for the formation of placer deposits, as all types of placers will have one or more of these. However, the formation of placers of economic importance are always the result of an optimal combination of the metallogenic, tectonic, climatic and geomorphological factors, and the absence of even one of these may result in placers of weak or non-economic ore concentrations. As evidenced by the extensive historical mining of placer deposits and the presence of undeveloped inferred placer mineral resources, the Arctic region is a large polymineral and polygenic megaprovince with considerable placer potential.

Geostatistical analysis of the composition of mineral assemblages of Oligocene sediments in the Mansi and Severnaya Sosva areas of the Transural titanium-zirconium placer district was accomplished by the method of the principal components. High significance of the first principal component and its composition revealed by this analysis suggest the existence of an efficient placer-forming process that can produce commercial concentrations of ore minerals. Interpretation of statistical indicators is given. The results confirm the facies zoning of sediments revealed previously in the Oligocene basin. They show that the paleolittoral and shallow-water zones with a moderate hydrodynamic activity in the depositional environment have the highest potential of titanium-zirconium raw material. Analysis of the mineral potential revealed that the Mansi and Severnaya Sosva areas can accommodate a medium-scale placer deposit.

The Vinogradovsky District is located at the center of the Arkhangelsk Region, one of the largest federal subjects of Northern European Russia. Boreal spruce forests are the prevalent ecosystem type in this area, but large expanses of agricultural land and herb-grass meadows are also presented there. Based on the studies of 1,699 specimens collected from three meadow sites during period 2011–2013, we provide the first data on the butterfly fauna of the district, which include 56 species, belonging to 35 genera and 5 families. Our data reveal an intense northward expansion of many southern butterfly species to the Arkhangelsk Region, including migrants (Pontia edusa, Issoria lathonia, Vanessa atalanta and Vanessa cardui) and species that have established resident populations there (Pararge aegeria, Nymphalis xanthomelas, Aglais io, Lycaena dispar, Cupido alcetas). Quantitative data on species diversity and phenology of butterflies are reported, including analysis of structure of butterfly assemblages and their seasonal changes.