Vol 60 Iss. 2

The multifaceted and fruitful pedagogical and scientific activity of Professor Vadim Dmitrievich Nikitin, Doctor of Geological and Mineralogical Sciences, of the Department of Mineralogy, is closely connected with the Leningrad Mining Institute, within whose walls he became an outstanding scientist, an expert on minerals, and a brilliant researcher of pegmatites.

Until now, a number of important general questions concerning the conditions of formation of quartz veins and crystal pockets developed within crystal-bearing fields remain to some extent debatable.

The urtites in the Khibiny massif are part of a complex ijolite-urtite complex of rocks occurring among nepheline syenites in the form of a horseshoe-shaped body gently dipping to the center of the massif. Within this body, trachytoid ijolites are the most widespread. The so-called fine-grained ijolites are very limitedly distributed here. According to the data of geological mapping of the ijolite-urtite band, urtites lie among trachytoid ijolites and are exposed on the surface in the hanging wall or central part of the horseshoe-shaped body.

Deposits of rock crystal in the Subpolar Urals were discovered in the 1930s, when exploration work for the purpose of finding primary sources was carried out based on finds of surface placers of quartz crystals. Later, the main attention of geologists who studied and explored rock crystal deposits was directed to the study of the conditions of formation and distribution patterns of crystal-bearing bodies. Great progress has been made in solving this problem, and currently a considerable number of indirect indicators have been established that point to the possibility of finding blind pockets of rock crystal in a given area.

The formation of the granitoid massif is associated with the Laramian phase of Alpine folding and is dated as Upper Cretaceous. Having broken through the sedimentary-volcanogenic rock sequence, the intrusion became consolidated in the central part of the Okhotsk–Kolyma watershed, which is the southwestern limb of the Gizhigin synclinal zone. The massif is elongated in the northeastern direction conformably with the dominant strike of the host rocks and in plan has a lenticular shape. The length of the body at its greatest extent is 63 km, with a maximum width of not more than 18 km.

Age relationships between coarse-crystalline micas — muscovite and biotite — in pegmatite bodies constitute, as is known, an important link in deciphering the genesis of granitic pegmatites. Therefore, in works devoted to the general problem of the genesis of pegmatite bodies, the question of the age relationships of intergrown micas is addressed to some extent. At present, several mutually complementary and directly opposing views on the subject have emerged.

The leading role of fault and fracture tectonics in the localization and emplacement of piezoquartz deposits within the crystal-bearing province of the Subpolar Urals, as well as of ore bodies — crystal pockets — within individual deposits, has been repeatedly noted by researchers. ...

The ore bodies of the Deputatskoye deposit (northeastern Yakut ASSR) are mineralized fault zones of complex structure, less frequently — veins and zones of veinlet-disseminated mineralization cutting weakly dislocated shale‑sandstone sequences of the Upper Jurassic. The ore bodies are mainly confined to steeply dipping fractures and fracture shear zones of diagonal (northeastern and northwestern) and sub‑latitudinal trend.

One of the essential questions arising in the analysis of ore-field structures is the establishment of the extent and nature of the influence of the specific physical and mechanical properties of the host rocks on the shape and spatial position of ore bodies. Interesting data on this issue were obtained during the study of the deposits of the Suraiz crystal-bearing field of the Subpolar Urals. A major role is played here by the type of lens structures developed in the host rocks.

The studied rock crystal deposit in the Urals is confined to a large lens of dolomite marbles with northeasterly dip and northwesterly plunge. The average thickness of the lens is 200 m and its length is 800 m. To the northeast it contacts an apophysis of the Caledonian‑Hercynian granitoid massif; to the southwest it contacts crystalline schists of presumably Riphean age and small detached blocks of the massif. The industrial objects at the deposit are crystal pockets.

The most important grade indicators for mica deposits are the minimum commercial and cutoff grades. To date, all reserve calculations for mica (phlogopite and muscovite) have been made according to the specifications of Glavsluda of the USSR Ministry of Communications, which were introduced as early as 1950. For phlogopite and muscovite deposits, these specifications provide for the following content of cleaved mica per minimum minable thickness of veins of 1 m, in kg·cm²/m³.

The plagiogneisses productive for mica‑bearing pegmatites occupy significant areas in the Yonsky mica‑bearing district, but the areas with concentrations of industrial mica‑bearing veins are small. For the most part, detailed surface prospecting has been carried out in such areas, and the potential for finding mica‑bearing bodies has proved almost exhausted. A need arose to move to the study of deposits at depth. From 1955 onward, in the Yonsky district, for the purpose of searching for blind mica‑bearing veins, the North‑West Geological Administration began the systematic use of core drilling.

Iceland spar is the main material for various kinds of optical components, which are cut from defect‑free parts of natural crystals. The quality of crystals is determined after they are cut into plates, by applying mechanical grinding and polishing to the cut surfaces. Since most crystals contain one defect or another, most of the work involved in the mechanical processing of plates is wasted. In addition, the sawing of crystals and their parts blindly (in most cases, the surface quality of the crystals does not allow even tentatively to identify defect‑free regions) leads to the loss of valuable material.

At the stage of detailed exploration, the area of the open pit was drilled by core holes to the full depth of mineralization on a grid of 100×50 m (100×75 m in the plane of dip of the ore body). At the stage of operational exploration, it was drilled to a depth of 30–40 m on a 50×25 m grid (50×40 m in the plane of dip of the ore body). The 50×25 m grid was used to drill the central part of the pit, where mainly rich and poor ores are concentrated. The hanging and foot walls of the ore body (poor ores and barren interlayers) were explored on a 100×50 m grid. Exploration boreholes were sampled within the ore body in sections, with a section length of 2–3 m. Samples were analyzed for iron, sulfur, and phosphorus. Blast holes 10–20 m deep were drilled on a 6×6 m grid, sampled as one sample, and analyzed for iron and sulfur.

Within the ore field of the studied gold deposit, sandstone shale deposits of the Lower Permian with a thickness of up to 2000 m are widespread. The deposit is located in the near axial part of a brachyanticlinal fold of meridional strike. Meridional faults and associated northeastern and southwestern shear faults are widely developed.

The Nizhne‑Aldansky district is located in the southeastern part of the Lena Basin, east of the Tumara and Lena rivers.

At the Kayerkanskoye field, a comprehensive study was carried out of the alteration of coals in seams X and IX (Daldykan Formation, P ) at contacts with dolerite dikes in order to determine the nature of the relationship between the size of intrusions and the near‑contact zones of altered coal, as well as the characteristics of contact‑thermal metamorphism of the coal. At different distances from the contacts with dikes, changes in the values of the main coal parameters were traced: ash content, volatile matter yield, calorific value, carbon content, specific gravity, reflectance, and microhardness.

The Pikalevskoye deposit of flux limestone (Leningrad oblast) is located within the so‑called Carboniferous plateau. The productive sequence of the deposit is represented by organogenic, crystalline and dolomitic limestones and dolomites of the Tarusa and Venev horizons of the Visean Stage, which in the western part are overlain by Quaternary moraine and glaciolacustrine deposits from 6 to 30 m thick, and in the east also by terrigenous‑carbonate rocks of the Steshevo horizon of the Visean Stage and dolomites of the Protvino horizon of the Namurian Stage.