This paper presents an analysis of geochemical data obtained as a result of persistent research of the Buruktal, Ufalei, Elov and others supergene nickel deposits of the Urals on the content of precious metals. Content and distribution of platinum group elements, gold and silver in oxide–silicate nickel ores are compared with their content in initial dunite-harzburgite bedrock. It was revealed that all the PGE accumulate in supergene nickel deposits. Geochemical specialization of PGE mineralization of supergene nickel deposits is determined by palladium and platinum, while in dunite-harzburgite substrate of primary ophiolitic massifs major platinoids are ruthenium, osmium and iridium. Pt/Pd ratio is generally less than 1, i.e. palladium is dominating in them with some exceptions.
The article encompasses new data on geochemistry of dunites forming the Svetloborsky and Nizhnetagilsky ultramafic massifs of the Ural Platinum Belt. Petrogenesis of both massifs is discussed based on their interpretation. The research establishes that both massifs are petro-chemical equivalents of alpinotype complexes and zonal massifs, but at the same time they have their own particularities. Thus, dunites of the Svetloborsky massif are enriched in almost all rare elements compared to the Nizhnetagilsky massif that may be caused by their redistribution during subsequent processes due to intrusion of mafic dykes.
Isotope ratio 87Sr/86Sr was determined for the first time for the Ufalei and Sakhara supergene nickel deposits. The average obtained 87Sr/86Sr ratio in the Sakhara deposit (0,70838) is higher then in the Ufalei deposit (0,70697). In both deposits 87Sr/86Sr ratio increases from low-altered serpentinite rocks of the lower part of the deposits (0,70583 and 0,70687) to exogenous iron-oxide rocks of the upper part of the deposits (0,70917 and 0,71004).
Chromitites of Nizhni Tagil massif veins in length from a few centimeters to several meters. The contents of rare earth elements in the platinum-veined chromitites characterized by reduced compared with the enclosing dunite values. In quantitative terms, is dominated by light rare earth elements. The positive correlation between the rare-earth elements and platinum group metals in the samples with normal contents. High and extremely high content of PGE in the chromite-platinum ores Nizhni Tagil massif are not accompanied by a significant increase in the concentrations of REE.
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.
Contents of platinum group elements (PGE), gold and silver in oxide-silicate nickel ores of the Buruktal, Ufalei and Elov supergene nickel deposits are determined in relation to their ophiolitic dunite-harzburgite bedrock.
Data are presented on the results of X-Ray structural and thermal analyses, data from chemical and microscopic studies of serpentines of chrysotile Mg3Si2O5(OH)4 – pecoraite Ni3Si2O5(OH)4 series from the silicate nickel deposits in the Urals. Nomenclature is updated of the studied serpentines following the regulations of the International Mineralogic Association. It is demonstrated that the studied minerals are the chief ore minerals in serpentinite zones of nickel fields. Issues are reviewed of formation of serpentines of the chrysotile-pecoraite series in conjunction with hydrothermal processes. It is suggested the two-tier structure of the Ural supergene nickel fields, where supergene upper tier has "roots" in the form of hydrothermal lower tier, which significantly expands the area of the search for new fields and opens great opportunities in this ancient district of ore.
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.
We have analysed chemical of nepouites. NiO content in then ranges from 13,00 to 35,18 %, MgO from 18,29 to 44,61 %, i.e. the composition of nepouite corresponds to the composition of Mg-nepouite. General row of chemical element mobility in lizardite – nepouite ores of the Elov supergene nickel deposit is the following: (Mo, Sb, Se, W)20-35 > (Sn, As, Ni)10-20 > (Pb, Be, U)3-7 > (Ti, Ga, Mn)1-3 > (Th, Rb, Si)~1 > (Al, V, Co, Tm, Zn, Mg)0,6-0,9 > (Yb, Ca, Cu)0,4-0,5 > (Sc, Cr, Zr, Sr, Ba, Y, Ta, TR)0,1-0,4 > (Cs, Nb; Ag, Te, Bi, Au)< 0,01-0,1.
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.
The article deals with the distribution of groups of trace elements in four selected types of metasomatic rocks and ores in the Elov deposit: chamosite metasomatic rocks and ores, which are three mineral species: a – chamosite, в – clinochlore –brendleyit-chamosite, с – clinochlore-talc-chamosite, goethite metasomatic rocks and ores, nepouite-chrysotile-lizardite metasomatic rocks and ores, and lizardite-chrysotile serpentinites. Also calculated the coefficients of accumulation of trace elements and formulated conclusions about elements are accumulation or elements are weathered of the above types of metasomatic rocks and ores of the Elov deposit.
The article deals with genesis of chamosite zone in Elov supergene nickel deposit after the example of clinochlore-brindleyite-chamosite nickel ore. According to obtained data, isotope ratio 34 S/ 32 S in millerite from these ore type varies from –35,5 to –45,6±0,6 ‰. This value corresponds to sedimentary rocks und testifies surface exogenous genesis of chamosite nickel ores.
In the southern part of the Khur area, there is faults system with predominantly North-West strike. This network of tectonic disturbances is one of the most important fault systems in Central Iran which crosses Paleozoic metamorphic rocks, Cretaceous limestones, and Eocene volcanic rocks. Interpretation of satellite imagery ETM+ (Enhanced Thematic Mapper plus, Landsat) and field observations showed the presence of left-lateral shifts along with fault system. This formed the structure of the branch faults at the northeast end of the main fault. Another feature associated with shear dislocations is the rotation of blocks in the northeastern and southwestern segments of the area under study. There are several basins and positive structures within the area such as a series of uplifts and thrusts, indicating the presence of compressional and extensional tectonics. Another part of the work is devoted to the study of the correlation between active faults and earthquakes. Processing of satellite images, field observations, records of micro-earthquakes within a radius of 17 km made it possible to analyze the earthquakes parameters and the position of tectonic disturbances, and, as a result, confirm the presence of active faults in the region. In addition, we have identified three successive stages of the Khur area tectonics: rifting, contraction, change of convergence and uplift direction.