Geologic Framework of Metallic Mineral Deposits of Northeast USSR: ABSTRACT

Abstract

The structure of the northeast USSR is composed of the following: the Yana-Kolyma and Chukotsk miogeosynclinal systems and the Oloy-Alazey eugeosynclinal system of the Mesozoides, median and residual massifs of prelate Precambrian age (Omolon, Okhotsk) and Paleozoic age (Yablonskiy, Yeropolskiy), the Anadyr'-Koryak and Olyutor-Kamchatka geosynclinal systems of Cenozoic age, and the Okhotsk-Chukotsk volcanogenic belt. Widespread deposits of Au, Ag, Sn, W, and Hg are controlled by the structure and igneous activity. Gold-bearing quartz veins of plutonic origin form the Yana-Kolyma gold belt with its alluvial and bedrock deposits. The analogous deposits of the Chukotsk system form a less consistent gold belt. The gold here is associated closely with tin and tungsten mineralization. The Okhotsk-Chukotsk volcanogenic belt is a province of volcanic gold-silver deposits, some of which are associated with tin and mercury mineralization. Tin deposits of different types (sulfide, quartz, silicate, skarn, and pegmatite) are less abundant in the Yana-Kolyma system but are well developed in the Chukotsk system. Commercial deposits of mercury are present in the Mesozoides, in the region of Cenozoic folding, and within the Okhotsk-Chukotsk volcanogenic belt. The deposits form linear zones either in carbonate rocks rimming the Yana-Kolyma system or in terrigenous rocks of widely differing age. Mercury also is present in volcanic rocks of Cenozoic age, as well as in the Okhotsk-Chukotsk belt. Conditions for the formation of copper, lead, zinc, and other minerals in the region have not been studied adequately. According to available data, they are related to the structures of the massifs of ancient consolidation, to the Oloy-Alazey eugeosynclinal system, and to the Okhotsk-Chukotsk volcanogenic belt. Platinum and chromium are located within ultramafic belts of the Olyutor-Kamchatka and Anadyr'-Ko yak systems. The major stage of endogenic ore deposition in the northeast USSR was at the end of the Jurassic and in the Cretaceous. In the Anadyr'-Kamchatka system and in Kamchatka, the main phase extended into the Paleogene, Neogene, and Quaternary. The most intensive period of placer deposition was in Pliocene-Pleistocene and Holocene times. The placers are related to relief-forming processes connected with tectonic activity. The sources of ore material for the placers were the Mesozoic-Cenozoic mineralized zones. In many regions, oxide weathering products also were formed as the result of peneplanation.