Vol 60 Iss. 2

The multifaceted and fruitful pedagogical and scientific activity of Vadim D. Nikitin, Professor of the Department of Mineralogy, Doctor of Geological and Mineralogical Sciences, is closely connected with the Leningrad Mining Institute, where he became a major scientist, a great connoisseur of minerals, a brilliant researcher of pegmatites.

Until now, a number of important general questions concerning the conditions of formation of quartz veins and crystal nests developed within the crustalenous 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 hollowly falling to the center of the massif. Within this body, trachytoid ijolites are the most widespread. The so-called fine-grained iiolites are very insignificantly distributed here. According to the data of geological mapping of the ijoliturtite band, urtites lie among trachytoid ijolites and are exposed on the day surface in the hanging side or central part of the horseshoe-shaped body.

Deposits of rock crystal in the Subpolar Urals were discovered in the thirties, when exploration work with the purpose of finding primary sources was based on the findings 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 conditions of formation and regularities of location of crystal bodies. Great progress has been made in solving this problem, and at present a considerable number of indirect signs have been established that indicate the possibility of finding blind nests of rock crystal in a given area.

The formation of the granitoid massif is associated with the Laramian phase of Alpine folding and dates to the Upper Cretaceous. Having broken through the sedimentary-volcanogenic rock strata, the intrusion consolidated in the central part of the Okhotsk-Kolyma watershed, which represents the southwestern wing of the Gizhigin synclinal zone. The massif is elongated in the northeastern direction in accordance with the dominant strike of the lateral rocks and has a lenticular shape in plan. The length of the body in the largest dimension is 63 km with a maximum width of no more than 18 km

Age relations between large-crystalline mica - muscovite and. biotite in pegmatite bodies are, as is known, a small link in deciphering the genesis of granitic pegmatites. Therefore, in the works devoted to the consideration of the general problem of the genesis of pegmatite bodies, the question of age relationships of intergrowing mica is also touched upon to a greater or lesser extent. To date, several complementary and directly opposite views on this iss. have been formed.

The leading role of discontinuous and fracture tectonics in localization and location of piezoquartz deposits in the territory of the crystal province of the Subpolar Urals, as well as ore bodies - crystal nests - within the deposits, has been repeatedly noted by researchers...

Ore bodies of the Deputatskoye deposit (north-east of the Yakut ASSR) are mineralized crushing zones of complex structure, less often - veins and zones of vein-embedded mineralization, cutting weakly dislocated shale-sandstone deposits of the Upper Jurassic. The ore bodies predominate in steeply dipping fractures and fracture zones of diagonal (northeastern and northwestern) and near-latitudinal direction.

One of the essential questions arising in the analysis of ore field structures is to establish the measure and nature of the influence of the specific physical and mechanical properties of the host rocks on the shape and spatial position of ore objects. Interesting materials on this iss. were obtained during the study of deposits of Suraizskoe crustalene field of the circumpolar Urals. A great role belongs here to the type of structures of unlensing developed in the host rocks.

The studied Ural rock crystal deposit is confined to a large lens of dolomite marbles of northeastern dip and northwestern declination. The average thickness of the lens is 200 m and its length is 800 m. In the northeast it is in contact with the apophysis of the Caledonian-Hercynian granitoid massif, in the southwest - with crystalline schists of presumably Riphean age and minor detritus of the massif. Industrial targets at the deposit are crystal nests.

The most important indicators of mica deposit conditions are minimum commercial and cutoff grades. Up to now all calculations of mica (phlogopite and muscovite) reserves have been carried out according to Glavsluda conditionals of the USSR Ministry of Railroads, introduced in 1950. For deposits of phlogopite and muscovite these conditions provide the following content of broken mica per minimum excavation thickness of veins, equal to 1 m, kg • cm²/m³.

The plagiogneisses productive for mica-bearing pegmatites compose significant areas in the Yonsky mica-bearing district, but the areas with concentration of industrial mica-bearing veins are small. In general, detailed surface prospecting was carried out in such areas, and the possibilities of finding mica-bearing bodies were almost exhausted. It became necessary to switch to the study of deposits at depth. Since 1955, in the Yonsky district for the search of blind mica-bearing veins, the North-West Geological Department began the systematic use of core drilling.

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

At the stage of detailed exploration the area of the open pit is drilled by core holes to the full depth of mineralization on a network of 100X50 m (100X75 m - in the plane of dip of the ore body). At the stage of operational exploration - to a depth of 30-40 m using a 50х25 m grid (50X40 m in the plane of the ore body dip). The 50X25 m grid is used to drill the central part of the pit, where mainly rich and poor ores are concentrated. The hanging and lying sides of the ore deposit (poor ores and ore-free interlayers) were explored using a 100X50 m grid. Exploration boreholes were sampled within the ore deposit section by section, with section length of 2-3 m. Samples were analyzed for iron, sulfur and phosphorus. Blast holes 10-20 m deep were drilled on a 6X6 m grid, sampled with one sample and analyzed for iron and sulfur.

Within the ore field of the studied gold deposit sandy-shale deposits of the Lower Permian with thickness up to 2000 m are spread. The deposit is located in the near-axial part of a brachyanticlinal fold of meridional strike. The meridional and north-eastern and south-western breakers of the chipping type 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 of coal alteration of strata X and IX (Daldykan Formation P) at contacts with dolerite dikes was carried out to reveal the nature of the relationship between the scale of intrusions and near-contact zones of altered coal, as well as the features of contact-thermal metamorphism of coal. At different distances from the contacts with dikes, changes in the values of the main coal parameters were traced: ash content, volatile yield, caloric content, carbon content, specific gravity, reflectivity, microhardness.

The Pikalevskoye deposit of fluxing limestone (Leningrad Region) is located within the so-called Carboniferous plateau. The productive strata of the deposit is represented by organogenic, crystalline and dolomitic limestones and dolomites of the Tarussky and Venyevsky horizons of the Visean Stage, which in the western part are overlain by Quaternary moraine and lake-glacial deposits with a thickness of 6 to 30 m, and in the east also by terrigenous carbonate rocks of the Steshevsky horizon of the Visean Stage and dolomites of the Protvino horizon of the Namurian Stage.