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We describe similar assemblages of minerals found in two placers in Russia, both probably derived from an ophiolitic source. The first is located along the River Rudnaya in the western Sayan province, Krasnoyarskiy kray, and the second pertains to the Miass placer zone, Chelyabinsk oblast, in the southern Urals. The platinum-group element (PGE) mineralization in both cases is mostly (at least 80%) represented by alloy minerals in the system Ru–Os–Ir, in the order of occurrence osmium, ruthenium and iridium. The remainder consists of Pt–Fe alloys and species of PGE sulfides, arsenides, sulfarsenides, etc. The associated olivine and amphiboles are supermagnesian, and the chromian spinel has a high Cr# value. The observed enrichment in Ru, typical of an ophiolitic source, may be due to high-temperature hydrothermal equilibration and mobilization in the ophiolite, as is the enrichment in Mg and Cr. Low-temperature replacement of the alloys led to the development of laurite, sulfoarsenides and arsenides. Some placer grains in both suites reveal unusual phases of sulfo-arsenoantimonides of Ir–Rh, e.g. the unnamed species (Rh,Ir)SbS and (Cu,Ni)1+ x (Ir,Rh)1– x Sb, where x = 0.2, and rhodian tolovkite, (Ir,Rh)SbS. Two series of natural solid-solutions appear to occur in the tolovkite-type phases. Among the oddities in the Rudnaya suite are globules of micrometric PGE sulfides, crystallites of platinum-group minerals, amphibole, and chalcopyrite bearing skeletal micrometric monosulfide-like compounds (Cu,Pt,Rh)S and (Pd,Cu)S1– x . Pockets of fluxed evolved melt seem to have persisted well below the solidus of the host Pt3Fe-type alloy. [ABSTRACT FROM AUTHOR]

Compositions of rare mineral phases containing precious metals (PMs) in samples from Natalka, Pavlik, Vetrenskoe, and Degdekan gold ore deposits (North-East of Russia) are studied by scintillation atomic emission spectrometry (SAES) and electron probe microanalysis (scanning electron microscopy and electron probe X-ray microanalysis, SEM-EPMA). The SAES method found dozens and hundreds of particles carrying gold, silver, and all platinum-group elements as native metals, intermetallides and solid solutions, arsenides, antimonites, sulfoarsenides, tellurides, selenides, etc. The variety of the elemental compositions of PM species (mineral phases) found by SAES significantly exceeds the list of minerals found previously by SEM-EPMA because of different natures of optical and X-ray spectra. The sizes of PM particles calculated by the SAES method and measured by SEM-EPMA are similar. The SAES data on the total concentrations of PMs satisfactorily agree with the results of inductively coupled plasma mass spectrometry. [ABSTRACT FROM AUTHOR]

Native osmium from two different placer occurrences (i.e., Ingaringda and Burlakovsky) within the Guli Massif, Maimecha-Kotui Province, was evaluated for mineral compositions that show systematic differences between the localities. Grains of native osmium show increases in iridium towards the rim, and nuggets consisting of aggregates define trends of preferential substitution of osmium by iridium. A statistically reliable difference in Os/Ir ratios between the two studied placers can be demonstrated. From textural and compositional characteristics it is concluded that the native osmium of the Burlakovsky placer formed at temperatures higher than can be assumed to be reasonable for crustal conditions. The difference in the Os/Ir ratios between the two placers can be attributed to fractional crystallization of native osmium either in the mantle source, which was tapped in different events to form the Guli Massif, or to decreasing Os/Ir values during crystallization under crustal conditions after intrusion of the silicate melt(s). [ABSTRACT FROM AUTHOR]

This contribution firstly presents particularities of mineral chemistry of platinum-group elements (PGE) mineralization from placer deposits linked to the Bor-Uryakh massif of the Maimecha-Kotui Province, northern part of the Siberian Craton. The chemical composition of PGE mineralization has been studied by electron microprobe analysis. At Bor-Uryakh, main platinum-group minerals (PGM) comprise Os-Ir and Pt-Fe alloys represented by individual crystals, and polyphase PGM assemblages. The majority (e.g., 12 out of 19) of the Os-rich nuggets are iridian osmium, with subordinate amounts of native osmium (Os) and chengdeite (IrFe). Pt-Fe alloys have a stoichiometric composition close to PtFe. According to the nomen-clature by L. Cabri and C. Feather [1975] these minerals correspond to ferroan platinum. Based on geological position and geochemical features of investigated PGE mineralization the particular rock sources have been established. This study has demonstrated the similarity of chemical characteristics of Os-Ir and Pt-Fe alloys of the Bor-Uryakh massif to those of PGM from the Guli massif (Maimecha-Kotui Province), platiniferous zoned-type ultramafic massifs (e.g., Kondyor, Inagli and Chad) of the Aldan Province and Platinum belt of the Urals (Nizhny Tagil, Kytlym, etc.). [ABSTRACT FROM AUTHOR]

The results of investigation of heavy fraction minerals from the Degdekan deposit hosted by the lower portion of stratified Mid Permian sediments are presented; the investigation was conducted via electron microscopy using a QEMSCAN hardware and software instrument equipped with a QUANTAX quantitative analysis system. The following mineral phases of platinoids have been detected for the first time: native osmium, rutheniridosmine, osmiridium, ruthenosmiridium, laurite, iridarsenite, and Ru, Os, and Ir arsenide. [ABSTRACT FROM AUTHOR]

The article focuses on a study which examined the redox conditions of osmium-rich minerals formation from the Guli Massif, Russia. It notes on the intrinsic oxygen fugacity of native osmium and iridium osmium from dunite and chromatite. The factors that influenced the regular difference in a chemical composition of platinum group element (PGE) are noted.

The article offers information on the platinum group minerals found in the basins of the Urup-Laba rivers in North Caucasus. It says that platinum group minerals, platinum, and gold occur in various rivers in North Caucasus including Bolshaya Laba, Urup, and Malaya Laba after taking samples of black sands from alluvial spits. It mentions that the rarest refractory metals of the platinum group including osmium, ruthenium, and iridium are scattered in the area. It notes that the mineral rutheniridosmine was identified from the black sands through Exxon donor solvent (EDS) analysis and scanning electron microscopy (SEM).

The article offers information on the study conducted in the Precambrian Carbonaceous Shales in the Zigazino-Komarovskaya suite in western slope of Southern Urals. It mentions that the study area was comprises of minerals that include quartz shale, sandstones, and chlorite. The study made use of the spectral analysis with microelements preliminary concentration to determine the contents of platinum, gold, and the Iridium. The result of the study shows that the high content of palladium are found in the northern part of the Mayardak and Yamantau particularly in the sulfidized carbonaceous rocks. It adds the possibility of formations of gold and palladium in the territory due to the carbonaceous formations in the area.