In order to expand and popularize knowledge about the stone decoration of Saint Petersburg, we present new data on the mineralogy and petrography of the famous Thunder-Stone, the parts of which were the basis for the monument to Peter the Great – the legendary “Bronze Horseman”. In the course of studying geological documentation of the monument's granite base, we examined the mineral composition and internal structure of granite, as well as the fragments of a pegmatite vein and veinlets found in it. 25 single-mineral samples were collected from the available micro-scaled shear fractures within the pedestal surface and studied by electron microscopy, electron probe and X-ray phase analysis. It was established that K-Na feldspar in the granite composition was represented by microcline, whereas micas were represented by annite-siderophyllite and muscovite. Accessory minerals included monazite, xenotime, thorite, zircon, rutile, apatite, fluorite, Ti-, Nb-, Ta-bearing minerals, uranium phosphates. The presence of topaz is characteristic of pegmatites. The revealed structural and textural features of four granite boulders in the monument pedestal, as well as mineralogical and chemical composition of their rock-forming and accessory minerals, showed the similarity of this rock to Precambrian biotite-muscovite granites and topaz-containing pegmatites (stockscheiders) of the late formation phase of the Vyborg rapakivi granite massif. The research results are considered as the basis for further geological and mineralogical study of the Thunder-Stone origin and determining the place of its separation from the primary source.
The article presents the results of optical, electron microscopic and electron microprobe studies of columbite group minerals, collected during heavy mineral concentrate sampling of alluvial deposits in the Mayoko region (Republic of the Congo). The aim of the study is revealing tantalum niobates ore body in this region. We found that these minerals in loose deposits are represented by two grain-size groups: less than 1.6 mm (fine fraction) and 1.6-15 mm (coarse fraction). The grains of both fractions belong mainly to columbite-(Fe), less often to columbite-(Mn), tantalite-(Mn) and tantalite-(Fe), contain impurities of Sc, Ti, and W. The crystals have micro-scaled zoning (zones varies slightly in the Ta/Nb ratio values) and contains a lot of mineral inclusions and veins represented by zircon, pyrochlore supergroup minerals and others. Columbite-(Fe) and columbite-(Mn) are characterized by an increased content of Ta 2 O 5 up to the transition to tantalite-(Fe) and tantalite-(Mn). This allows us to exclude the formation of subalkaline rare-metal granites, their metasomatites (albitites and greisenes) and carbonatites, from the list of possible columbite ore rocks source in the Mayoko district. Thus, beryl type and complex spodumene subtype rare-element pegmatites of the mixed petrogenetic family LCT-NYF (according to P.Černý) should be considered as a probable root source. The results of the research should be taken into account when developing the methodology for prospecting in this area.
The unique size of monolithic blocks of granite in the «Vozrozhdenie» deposit («Kawantsaari») is due to the stability of these rocks in the steeply dipping and probably crosscutting part of the massif, where the rocks have retained their massive texture and have been least modified at the stage of formation of rare-metal pegmatites. The shape and size of monolithic blocks are determined by the pattern of disturbances, in the formation of which the leading role belongs to three steeply dipping zones of tectonic fractures of the North-West strike with the haloes of changes in the conditions of low-temperature acidic metasomatism. Later tectonic disruptions in these zones led to the destruction of rock blocks between them within a series of transverse fractures and to subhorizontal discontinuities of rocks caused probably by gravitational unloading of the massif and glacier action. The distribution of fractures in all directions is characterized by equal spacing («step»).
Geological and mineralogical research were conducted by the scanning probe microscopy and showed that in plagioclase pegmatites of North Baikal muscovite province the average thickness of the peristerites increases from early graphic zones to late trochlear zones and pegmatoid zones of pegmatite veins. The thickness reaches a maximum in the pegmatites of pegmatoid structure which contain large-crystalline muscovite. This regularity can be used for development mineralogical criteria for evaluation of pegmatite veins productivity at the large size muscovite source.
Physico-mathematical modeling has shown that color of iridescent depends on spacing of peristerite lattice. The more spacing lattice, the color of iridescent is higher. The phenomenon of iridescent in plagioclases has an interferential nature. We can select two genetic types of peristerites: peristerites of decomposition and segregation peristerites. Segregation peristerites are formed from postcrystallizational consolidation of peristerites of decomposition. The form of segregation pertisrerites is one of the reasons of polychromatic iridescent genesis in plagioclases.
The TDA-5000 is one of the best examples of modern electronic total stations. This instrument is capable of solving the widest range of geodetic tasks, from creating surveying grounds for topoplans to 3D object modeling. Built-in targeting and automatic tracking function allows to automate the work completely, and the ability to record information (made measurements) on PCMCI card installed in the device - to perform tasks even easier and faster. The declared manufacturer accuracy of this device is 0.5" when measuring horizontal and vertical angles; when measuring distances 0.5 mm. The following was investigated: accuracy and limits of automatic aiming; accuracy of the angular part of the device; accuracy of the rangefinder part of the device. All researches of TDA-5000 showed the following: the angle measurement error is 0.3"; error of homing on ГК 0.6", on ВК 1.4"; mean square error of distance measurement 0.2 mm; maximum deviation angle of the initial point of search from the center of prism 1.5°; maximum deviation angle of sighting ray from the normal to the prism 27° The received results show that the device is suitable for highly accurate tasks. It is very advantageous to use such instruments for applied tasks because the TDA-5000 system is highly mobile.
The article considers the main directions of research in the analysis of the regularities of the location, properties and state of the main types of deposits of solid minerals in Russia. A summary of the available data on the main patterns of variability of both individual minerals and aggregates in the main types of endogenous ore deposits is made. Mineralogical features of large and unique deposits connected with granite magmatism are analyzed. It is concluded that their formation was determined by the long-term evolution of deep fluid systems serving as a means of mantle-core interaction and redistribution of matter in the Earth's crust. The principles of granite pegmatites analysis and methods of its carrying out are offered. The computational modeling of the processes of structure formation during magma solidification using the Monte Carlo method has been carried out. The possibilities of application of fractal analysis to solve the problems of ore geology are investigated. Possibilities of quantitative assessment of morphology of ore bodies are shown. Methods of studying and modeling of anomalous geochemical fields associated with mineral deposits are outlined. Tasks of geological exploration and prospecting works in connection with the further development of the coal industry are given.
В настоящее время резко возросли требования промышленности к качеству и размерам кристаллов мусковита, добываемых из пегматитов. Объекты с таким видом сырья с поверхности в основном отработаны, и для освоения глубоких горизонтов месторождений требуются новые, более эффективные критерии локального прогноза ...
Среди олюдоносных объектов Мамско-Чуйской провинции плагиоклазовые пегматиты занимают особое место, что связано со спецификой геологических условий их залегания, состава, строения и слюдоносности ...
