Modern analytical methods (optical and electron microscopy, X-ray microanalysis) were used to study the unique samples of sulfide ores from the Norilsk ore field from the Mining Museum collections of Saint Petersburg Mining University. Samples containing rare minerals of silver and platinum-group metals (sobolevskite, urvantsevite, sperrylite, argentopentlandite, froodite, kotulskite, and others) were studied. The chemical composition, grain sizes, aggregates, and mineral associations of more than ten noble metal minerals have been refined. The efficiency of combining various methods of electron microscopy and X-ray microanalysis for studying samples of this type is shown. The results of the work made it possible to obtain high-quality images of rare minerals, to detail information on museum objects, and to compile their scientific description. The conducted research showed the relevance of studying museum objects from known deposits of complex genesis and mineral composition in order to find and describe the samples with rare minerals.
Weathering processes and infiltration metasomatic processes in the weathering crusts hyperbasite arrays have a positive effect on the accumulation of rare earth elements. The content of rare earth elements is steadily increasing bottom-up on the profile of weathering. Metasomatic upper profile characterized by a high content of rare earth elements, which leads to the appearance of rare earth elements phosphate mineral phase – xenotime found in this laterite for the first time. The composition of the rare earth elements in incorporating their metasomatic and minerals demonstrates chondritic distribution.
The main geochemical barrier in supergene Buruktal nickel deposit is oxygen oxidized barrier in upper ferrous-oxide zone of the deposit. It makes sharp decrease of chemical element migration. Nevertheless, ore mineral concentrations present oft in complex geochemical barriers: absorbed-oxidized, carbonate-reducing and others. Every type of the geochemical barriers is able to concentrate specific association of migrated elements. That reflected on the different values of coefficients of enrichment in different types of Buruktal metasomatites. Oxidized barrier is more effective for elements with different valence (Fe, Mn), and absorbed clay, ferrous-oxide und manganese-oxide barriers are more effective for the main part of microelements.
Tectonic fractures of meridian spread, masked by block system of neotectonic breaks, play the leading role in structural control of nickel mineralization in supergene nickel deposits in the Urals. The deposits have long-term genesis and polygenic character. They are characterized by intensive tectonic and hydrothermal workup of Paleozoic substrate and block structure with small amplitude of vertical displacement. All of them have a two-floor structure, where upper supergene floor has a «background» of lower hydrothermal floor. This fact considerably increases the field of geological prospecting and searching of new oxide-silicate nickel deposits in the Uralian region.
In the Buruktal supergene nickel deposit, iron oxides possess vertical mineralogical zoning (bottom-up): magnetite-maghemite-goethite-hematite. The main rock- and ore-forming mineral in the iron-oxide zone of the deposit is magnetite, presented by three generations: primary relic magnetite, surviving from ultramafic rocks; secondary magnetite, forming at serpentinization process and neogenic supergene magnetite. Supergene magnetite, like a goethite, is nickel ore mineral, containing about 1 % NiO. Under the complex thermal analysis data, maghemite-magnetite and goethite have two main diagnostic maximums: exothermal effect of magnetite, caused by magnetite oxidation to maghemite in the interval 317‑340 °С, displays maximum at 327 °С («magnetite» point), and endothermic effect of goethite, connected with loss of constitutional water of the mineral and its transition to hematite in the interval 269‑296 °С, displays maximum at 288 °С («goethite» point).
Metasomatic ultramafites appear as ore bedrock for nickel lateritic deposits. First of all, they are represented by serpentinized harzburgites and dunites as well as serpentinites proper and their metasomatites. Metasomatites of the Buruktal Nickel Deposit can be divided into the pre-ore (Paleozoic) and the ore (Meso-Cenozoic) types. The pre-ore metasomatites are represented by talk, carbonate-talk, tremolite-actinolite and chlorite species. The ore-type metasomatites are represented by volumetric iron-oxide, nontronite-chlorite species and serpentinites as well as with vein (veinlet) metasomatites of carbonate and manganese composition.
