Vol 47 Iss. 2

Despite prolonged study, many questions of the genesis of apatite deposits of the Khibiny massif are still unclear or debatable. Referring the reader to a thorough review of the views of various researchers, provided in the work of T. N. Ivanova, we will briefly dwell on the two main directions of development of these views. Most researchers consider apatite‑nepheline ores as magmatic formations. Some of them believe that apatite‑nepheline ores formed simultaneously with the host rocks as a result of liquation or crystal differentiation of alkaline magma in situ. Others believe that the apatite‑nepheline ores were formed by intrusion of an independent (phosphorus‑rich) magma. It is this viewpoint that has recently been preferred.

The article presents new data on intrusive rocks of the Sarbaiskoye deposit, obtained as a result of the works of the geological party of the Leningrad Mining Institute. Sarbaiskoye magnetite ore deposit is one of the largest among the deposits of the Kustanay iron ore province. I. A. Kochergin and G. A. Sokolov consider this deposit to be a contact‑metasomatic deposit, confined to the contact of a multiphase intrusion of diorite‑porphyrites with volcanogenic‑sedimentary rocks of the Lower Carboniferous. Among the intrusive rocks I. A. Kochergin distinguishes: 1) pre‑ore: [a) diorite‑porphyrites of the main intrusion; b) vein diorite‑porphyrites; c) metadiorite‑porphyrites]; 2) post‑ore: [a) vein quartz diorite‑porphyrites; b) syenite‑porphyrites: [according to G. A. Sokolov, microgranite porphyries].

Mesozoic sediments in the Upper Priamurye were first established by F. B. Schmidt in 1859. In 1887‑1890, these sediments were subdivided into Lower and Middle Jurassic by L. Bacevich. Based on the first collected complex of fossil marine fauna, the age of the host sediments was dated to the Lower‑Middle Jurassic by A. I. Khlaponin. The Mesozoic formations of the Upper Priamurye were divided into two complexes in 1941 by V. Z. Skorokhod: marine Jurassic sediments (Bureya Formation) and freshwater‑continental Cretaceous sediments (Nikan Formation).

The Sarbaiskoye deposit of magnetite ores in the Kustanay region lies among deformed and metamorphosed Paleozoic rocks of monoclinal bedding, dipping to the west at an angle of 45-50° and overlain by horizontally bedded Meso‑Cenozoic sediments with a thickness of 70-130 m. E. A. Mazina attributes the ore‑hosting volcanogenic‑sedimentary sequence to the Lower Carboniferous (Middle‑Upper Viséan–Namurian).

Devonian rocks are the most ancient formations of the area and have a relatively small distribution, being exposed mainly on the northern slopes of the Eastern Tarbagatai Ridge, on the Kergentas Plateau, in the axial and northwestern parts of the Western Saur Ridge, as well as in the southeast of the Manrak Ridge.

In the literature on the geology of Altai there is a widespread opinion about the wide development of volcanogenic strata of porphyritic composition crowning the Upper Paleozoic section of the Kalba Ridge. This opinion is based on the works of G. I. Sokratov, who studied the Upper Paleozoic sediments of this area for a number of years. According to G. I. Sokratov, the geological structure of Southern Kalba, where the section of the above‑mentioned formations is most fully represented, includes Upper Vise‑Namur (Kokpektin Formation), Middle Carboniferous (Bukonya Formation), Middle‑Upper Carboniferous (Maityubinsk Formation) and Permian (Daubai Formation) sediments. The age of the Kokpektin Formation is proved by faunal finds. The Bukonya Formation is characterized by Middle Carboniferous flora. The age of the Maityubinsk Formation was determined on the basis of findings of freshwater pelecypods similar to those described from the Alykaevskaya Subformation of Kuzbass. The Daubai Formation is conditionally attributed to the Permian, since no organic remains were found in it, and its relationship to the Maityubinsk Formation has not been established anywhere. Porphyritic covers are identified at the base of the Maityubinsk Formation (C₂–C₃), as well as in the uppermost parts of this formation in the Kulambai Mountains. The main mass of the Kalba volcanogenic formations is referred to the Daubai Formation (P).

The Snider Nunataks are located at coordinates 107°41' E and 66°03' S on the Knox Coast in East Antarctica. They are several rocky outcrops among the continentalice, located in an area of about 0.15 km². The sizes of nunataks vary from 10-15 to 120-150 m across. The Nunataks are located 200-250 m from the coastal barrier of the ice sheet.

In the Mamsko‑Chuyskaya mica province, many deposits are confined to the bodies of the so‑called giganto‑migmatites, representing a system of bedded and cross‑cutting pegmatite bodies, so they were studied by many geologists. One of the first researchers was N.V. Petrovskaya, who called these bodies giganto‑migmatites. In subsequent years, all geologists unanimously noted that more than half of the pegmatite varieties involved in the structure of giganto‑migmatites are granitic rocks. They were named granite‑pegmatites.

In recent years, rare‑metal columbite‑beryllium mineralization was discovered in pegmatite veins in one of the northwestern regions of the USSR. The wall‑rock alterations studied by the author have prospecting significance. In the literature devoted to the description and genesis of rare‑metal pegmatites, the results of studies of near‑contact alteration of rocks hosting berylliferous and spodumene pegmatites have been published. In all these works, the genesis of pegmatites and the formation of near‑contact changes in the host rocks are explained from the position of A. E. Fersman, who assumes the existence of a specific pegmatite melt.

Many iron ore and polymetallic deposits are located among volcanic strata, at first glance of completely homogeneous porphyrite composition. When making geological sections of such deposits it is necessary to subdivide these homogeneous volcanic strata and to distinguish among them reliable marker layers. The success of the correct interpretation of the structure of the ore field or its individual sections depends to a large extent on how correctly the sequence of formation of various volcanic layers consisting of porphyrite sheets or flows is interpreted.

Crystal placers are relatively widespread on the eastern slope of the Southern Urals. However, even that very little literature which is devoted to the problem of their genesis refers only to placers formed by the destruction of crystal quartz veins. Moreover, some researchers categorically assert that only crystal quartz veins served as a source of supply of clastic quartz material. But in the Southern Urals there are placers formed due to the destruction of crystal-bearing pegmatites.

Any work devoted to the analysis of complex and debatable issues of coal formation is of great interest. Especially valuable are the works in which researchers, despite more or less established ideas, try to bring new insights into the understanding of the complex and diverse process of coal formation. One of the main regularities of coal formation, clearly revealed by lithological studies over the past two decades in the main domestic coal basins, is the establishment of a paragenetic relationship between coal seams and their host rocks. This relationship is best revealed in the phenomenon of rhythmicity of coal-bearing strata, the study of which clearly reveals the interaction of geotectonic (movements of the Earth's crust) and facies (relief, climate, vegetation, etc.) factors of sedimentation and coal formation.

By the end of preliminary exploration, there is usually already enough data for geological and industrial characterization of the mine field. However, the reliability and validity of conclusions will increase significantly if one uses some more general regularities of coal geology. The thickness and structure of the coal seam, petrographic composition, ash content, sulfur content, phosphorus content, to some extent the heat of combustion and some technological properties of coals are determined by paleogeographic, facies conditions of formation of the coal seam. Formation of coals with abundant water and stagnant regime often predetermines lower ash content and higher sulfur content of coals, higher degree of decomposition of plant residues in comparison with coals formed under water shortage or in moving water environment. The facies conditions of accumulation of the parent material of coal are often associated with its enrichment with rare elements. Obviously, in industrial grouping it is important to take into account the genetic conditions of formation of coal seams.