Placer mineral deposits of Russian Arctic zone: Genetic prerequisites of formation and prospect of development of mineral resources

Abstract

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.