The article presents the results of a study of the internal structure of highly elongated diamond crystals from placers in the Krasnovishersky district of the Urals. Very elongated crystals are found within diamond-bearing placer with unrevealed primary sources. Determining the conditions of such crystals formation can help one to determine the primary deposits type. There are three hypotheses for the formation of the elongated shape of such crystals: 1) crys- tals initially elongated along the <100> (strongly distorted octahedra); 2) individual crystals of columnar aggregates; 3) elongated crystals fragments. To study the internal structure, we selected three most elongated individuals of the 155 crystals samples. The study of the internal structure of selected crystals with the usage of photoluminescent (PL) tomography, cathodoluminescence (CL), and optical microscopy has shown that these samples are fragments of lar- ger single crystals. CL imaging allowed to determine slip lines within the crystal's volume. The recorded PL spectra show the 912, 946, and 986 nm peaks, which are characteristic of crystals with plastic deformation. The revealed fea- tures are indicators of plastic deformation accompanying the destruction of the crystals. The significant dissolution following the destruction of the crystals led to the rounding of the vertices and edges of their fragments. Apparently, most of the very elongated crystals from placers with unknown sources are also highly dissolved isometric crystal fragments. The obtained results have shown that the deformation and dissolution of diamond crystals are related events characteristic of diamonds from hitherto undetected, but highly productive primary deposits.
Platinum mineralization in Svetly Bor massif is represented by two promising mineral assemblages: chromite-platinum and platinum-type dunite. Body platinum of chromites lie within the fields of small-and medium-grained dunite central part of the array. Spinel epigenetic vein platinum chromites of Svetly Bor clinopyroxenite-dunite massif have some geochemical features such as high iron content, low chromium and titanium. Changing the chemical composition of the constituent minerals chromites is the result of processes of serpentinization of dunites host and is accompanied by the emergence of new mineral phases. Noble metal mineralization is represented by fine of up to 50 microns, mostly idiomorphic grains isoferroplatinum, tetraferroplatinum, osmiridium.
The results of studies of wallrock hydrothermal-metasomatic processes at a large polymetallic deposit located in the central part of the Novaya Zemlya Archipelago are considered. The geological position and control factors of mineralization, pre-ore and wallrock metasomatites are shown. The material composition of metasomatites has been studied in detail, and rare minerals, such as zinc-bearing dolomite, kimrites, and barium-bearing mica, among others, have been discovered and described, and specific morphology and composition have been revealed for those. According to the structure and material composition of metasomatites and some minerals, the formation conditions are defined as low-temperature near-surface.
