X-ray photoelectron spectroscopy, micro-Raman spectroscopy, Fourier transform infrared spectros-copy, X-ray powder diffraction, thermal analysis, and scanning electron microscopy were used to study the nature of color grain-size effect (CGSE) in samples of lazurite-type minerals (LTM) from deposits near Lake Baikal (Russia). A neotype of the mineral with the ratio of cage anions SO42- and S-3(-), close to unity, found at the Malo-Bystrinskoye deposit, was used as a standard sample. Experiments in air at 800 degrees C for 8 h with particles of <0.04 and 0.1-0.2 mm size showed that the former partially or completely decolorize, and the latter darken in the bulk and acquire a violet hue. The effect is practically independent of the structure features of the starting material (incommensurately modulated cubic, orthorhombic, monoclinic), although the non-cubic varieties easily lose S-3(-) chromophore in small par-ticles. In the sample initially containing the molecular center S-4, neither S-4 nor S-3(-) retains in small grains. Raman spectra do not reveal any bands that allow for identifying the nature of the species responsible for the preservation and deepening of the color tone of the "large" grains. FTIR data do not exclude the presence of thiosulfate, but mainly record the tetrahedral framework vibrations, S-O stretching and bending modes, and the presence of H2O, CO2, and CO32- in the structures of the initial samples. TA and SEM data reveal significant development of calcite microinclusions in LTM samples. We propose a model according to which in relatively large grains calcite microinclusions and subgrain boundary segregations play the role of an internal buffer that maintains the equilibrium coexistence of oxidized (SO42- , SO32- , S2O32- ) and reduced (S-3(-) ) sulfur. As a result, the blue coloration due to the S-3(-) chromophore is retained and even becomes more saturated, acquiring a violet hue due to the admixture of the S2O3- radical ion or a change in the configuration of the trisulfide radical. In small grains, microinclusions and grain-boundary calcite precipitates are mostly exposed to the surface or isolated, resulting in loss of buffering properties, S-3(-) instability with respect to air oxygen, and discoloration of the grains. In lazurite pigment with properly selected grain size, the stability of the chromophore is provided by the internal buffer, which can eliminate the discoloration of paints used for architectural and graphic art projects. With the optimal particle size, lapis lazuli pigment in paints is a stable phase and will not discolor over time in air.

Au-Ag mineralization occurrences in sphalerite ores of hydrothermal genesis are paradoxical in view of the incompatibility of these elements in sphalerite. The formation of sphalerite with Au and Ag impurities under hydrothermal crystallization of ZnS at 450 degrees C and 1kbar pressure was studied experimentally. Sn impurity was taken as a source of point defects in crystals modelling the interaction of Au and Ag with vacancies. The Ag solubility in low-Fe sphalerite is estimated as 3.8 +/- 0.7 mu g/g, Au = <= 0.6 mu g/g. The main forms of Ag and Au occurrence in sphalerite are the inclusions of (Ag, Au)(x)S phases with x varies mainly from 1.8 to 2.0, and Au varies from 0.01 to 0.75 a.p.f.u. The primary forms of the elements in ores might be microinclusions (Ag, Au)(1.8-2.1)S or close to (Ag, Au)S at higher f(S2). In presence of Sn, solubilities of Au and Ag become higher. The behavior of Au corresponds to the substitution reaction Sn4+ + Au+ + v(-) <-> 2Zn(2+) in the presence of two types of vacancy defects (v(-)). the "inherent" vacancies dependent on the crystallization conditions and the vacancies accompanying Sn4+ incorporation. Ag entrance is seemingly more dependent on f(S2) conditions and does not correlate with Sn. The extra vacancies arise because of metastable crystallization under the conditions of oversaturation of growth medium. This is supported by the spherulite morphology of growth products and the admixture of wurtzite ZnS form. The distribution and cocrystallization coefficients show an increasing trend for both precious metals (PM), due to which Au changes from incompatible to the category of highly compatible elements in sphalerite. The geochemical environments favorable for the formation of imperfect mineral crystals are considered. Such crystals are capable to uptake PMs and other incompatible in "ideal" crystal elements because of their interaction with vacancies, both constitutional (inherent to the substance) and non-equilibrium defects, and surficial nano-sized formations (nonautonomous phases). The evolution of these initially "invisible" forms of PM under metamorphic processes and remobilization of ore substance may result in Au and Ag escape and aggregation into microparticles.

The initial results of the experimental study of a hydrothermal system including lanthanides (Ln) and Fe oxides (magnetite and hematite) are presented. Ln concentrations in solutions and crystals were determined by ICP-MS and LM-ICP-MS, accordingly. The Ln distribution and cocrystallization coefficients obtained are interpreted as the maximal estimates of “true” values corresponding to structurally bound admixture. It is shown that Ln (except for Eu) are the compatible elements in hydrothermal magnetite; heavy Ln (beginning with Tb) are compatible in hematite. The pronounced tendency of the elevation of both coefficients with the Ln atomic number beginning from Gd-Tb was established. This is significant for using the ratio of light and heavy Ln as a typochemical guide for localization of the source of ore elements. The high-Ln-containing phases in associations with magnetite and hematite were obtained. These phases have oxychloride (without Fe) and oxyhydroxide (with Fe) composition and demonstrate the example of co-locating light and heavy Ln in the common space of hydrothermal system due to mutual crystallization of the phases selectively accumulating light and heavy lanthanides.

The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malaya Bystraya gem lazurite deposit, Baikal Lake area has been studied using electron microprobe, wet chemical analysis, ESR, IR, Raman, X-ray photoelectron spectroscopy, UV-Vis-near IR absorption and luminescence spectroscopy, and powder X-ray diffraction. The empirical formula of the neotype sample is (Na 6.97 Ca 0.88 K 0.10 ) 7.96 [Si 6.04 Al 5.96 ] 12 O 24 (SO 4 ) 1.09 ( S_3^∙ - ) 0.55 S_0.05^2 - Cl 0.04 ⋅0.72H 2 O, where S_3^∙ - is trisulfide radical anion, which is a blue chromophore. The idealized formula Na 7 Ca(Al 6 Si 6 O 24 )(SO 4 ) S_3^∙ - ⋅H 2 O has been approved by the IMA Commission on New Minerals, Nomenclature and Classification, proposal #20-H. The crystal structure of lazurite is characterized by commensurate and incommensurate modulations; the a parameter of the cubic sub-cell is 9.087(3) Å. The neotype sample is slightly birefringent, with α' = 1.523(2) and γ' = 1.525(2).

The main reasons for the promoting effect of phosphorus on the properties of Pd–P/ZSM-5 catalysts during direct synthesis of H2O2 from H2 and O2 under mild conditions are considered based on the data obtained by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and inductively coupled plasma mass spectrometry (ICP MS). The introduction of phosphorus in the catalyst affects the particle size and the electronic state of palladium in the surface layer, as well as the surface concentration of the phosphate and phosphite ions. The yield of H2O2 increases when the particle size of the Pd–P catalysts decreases, when the side process of H2O2 decomposition is inhibited by the phosphate and phosphite surface ions, and when the hydrogen solubility in the solid solutions of phosphorus in palladium decreases.

The new sodalite-group mineral species slyudyankaite, ideally Na28Ca4(Si24Al24O96)(SO4)(6)(S-6)(1/3)(CO2)2H(2)O, was discovered in altered lazurite-bearing metasomatic rock at the MaloBystrinskoe gem lazurite deposit, Baikal Lake area, eastern Siberia, Russia. The associated minerals are diopside, calcite, fluorapatite, phlogopite, lazurite, and pyrite. Slyudyankaite forms green to pale blue isolated anhedral equant grains up to 0.5 cm across and their aggregates. The streak is white and the luster is vitreous. Slyudyankaite is brittle, with a Mohs hardness of 5 1/2. Cleavage and parting are not observed. Density measured by flotation in heavy liquids is equal to 2.46(2) gcm(-3). Density, calculated using the empirical formula and unit-cell volume refined from single-crystal XRD data, is 2.454 gcm(-3). Slyudyankaite was characterized using the IR, Raman, ESR, near infrared (NIR), visible (Vis), and ultraviolet (UV) absorption, XPS and photoluminescence spectroscopy methods. The chemical composition is (wt%, electron microprobe, H2O and CO2 determined by selective sorption of ignition products, CO2 confirmed by quantitative IR spectroscopic method, sulfate sulfur determined by wet chemical analysis): Na2O 19.28, K2O 0.12, CaO 5.13, Al2O3 27.01, SiO2 33.25, SO3 10.94, S 1.75, Cl 0.10, CO(2)1.42, H2O 0.90, -O equivalent to(Cl,HS) -0.03, total 99.87. The empirical formula is Na27.57Ca4.05 K-0.11(Si24.52Al23.48O96)(SO4)(6.06)(S2.42Cl0.12)-Cl-0(CO2)(1.43)2.21H(2)O where S-2.42(0) is the total sulfide sulfur, mainly occurring as neutral S-6 and subordinate S-4 molecules, according to the structural data. XPS spectroscopy confirms the presence of sulfide sulfur in neutral form. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0428. Slyudyankaite is triclinic, space group P1, a = 9.0523(4) angstrom, b = 12.8806(6) angstrom, c = 25.681(1) angstrom, alpha = 89.988(2)degrees, beta = 90.052(1)degrees, gamma = 90.221(1)degrees, V = 2994.4(2) angstrom 3, Z = 1. Slyudyankaite contains two kinds of sodalite cages occurring in the structure in a ratio of 3:1. Cages of the first kind are completely occupied by SO42- anions and extra-framework cations, whereas cages of the second type contain only neutral molecules (S-6, CO2, H2O, and minor S-4). The strongest lines of the powder X-ray diffraction pattern [d, angstrom (I, %) (hkl)] are: 6.45 (11) (004, 112, 020), 3.716 (100) (204, 220, 116, 132), 2.878 (12) (136, 028, 044), 2.625 (23) (208, 240), 2.431 (6) (209), 2.275 (6) (048), 2.143 (12) (0.0.12, 336), 1.784 (7) (444, 1.1.14, 356, 172).

of a wide range of elements in the systems with magnetite, hematite and sphalerite is studied by the method of thermogradient hydrothermal synthesis combined with internal fluid sampling at 450 & DEG;C temperature and 100 MPa pressure. The distribution and cocrystallization coefficients are determined; the literature and original data on these coefficients are summarized. The possibility of obtaining the reproducible data on elements distribution in the mineral - solution system in the occurrence of many typomorphic elements is substantiated. This considerably increases the experiment efficiency. A significant advantage of using cocrystallization coefficients rather than "conventional" distribution coefficients expressed by the ratio of the element concentrations in crystal and solution (fluid) is shown. The features of behavior and occurrence of elements in hydrothermal systems are provided with physico-chemical evidence, through application of cocrystallization coefficients. The examples of the behavior of typomorphic trace elements in sphalerite are considered, which support the theoretical analysis. The major (Fe, Mn, Zn and possibly Cu) and secondary (Ti, V, Al, and Co) components of ore-forming solutions are estimated according to the compositions of magnetite and hematite from hydrothermal ore deposits of various types. The similarity in compositions of magnetite and hematite does not prove their coformation from a single fluid, quite the reverse, and this fact indicates different compositions of fluids from which the minerals were deposited.

The dual distribution coefficients (D) that are related to structurally and superficially bound trace element (TE) in pyrite (Py) and pyrrhotite (Po) associations, crystallized hydrothermally at 400 °C and 1 kbar pressure, were determined. Three independent methods were used to estimate the structural and surficial TE contents (Cstr and Csur) and the corresponding D Py/Po values (Dstr and Dsur), which were found, on average, to be 12.4, 0.8, 0.9, and 0.06 (Dstr) and 2.6, 0.7, 2.0, and 0.07 (Dsur) for Ag, Pd, Cd, and Mn, respectively. The coincidence of a dual D for several elements was a result of coupled changes in Csur and Cstr. The selectivity (S) of the surficial nonautonomous phases (NAPs) that were responsible for TE accumulation (which is the ratio of TE concentrations in surficial and structural modes) was determined. It was shown that the interpretation of TE uptake by surficial phases was adequate and that this phenomenon is common in nature, independently of the system where it occurs—i.e., in experimental autoclaves or in hydrothermal ore deposits. Studies of NAPs selectivity can help in evaluating the total element compatibility in minerals and the maximum possible contents of structurally bound admixtures of the element (solubility) in minerals under given conditions. A significant surficial impurity accumulation effect is most important and well-pronounced for incompatible micro-elements with concentrations of less than ~0.1 wt%. The surficial mode may be a source of Pd and other platinum group elements and more abundant and easily refined than the structurally bound mode.

The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malaya Bystraya gem lazurite deposit, Baikal Lake area has been studied using electron microprobe, wet chemical analysis, ESR, IR, Raman, X-ray photoelectron spectroscopy, UV-Vis-near IR absorption and luminescence spectroscopy, and powder X-ray diffraction. The empirical formula of the neotype sample is (Na6.97Ca0.88K0.10)(7.96)[Si6.04Al5.96](12)O-24(SO4)(1.09)(S-3(center dot-))(0.55)S0.05-2Cl0.04 center dot 0.72H(2)O, where S-3(center dot-) is trisulfide radical anion, which is a blue chromophore. The idealized formula Na7Ca(Al6Si6O24)(SO4)S-3(center dot-)center dot H2O has been approved by the IMA Commission on New Minerals, Nomenclature and Classification, proposal #20-H. The crystal structure of lazurite is characterized by commensurate and incommensurate modulations; the a parameter of the cubic sub-cell is 9.087(3) angstrom. The neotype sample is slightly birefringent, with alpha' = 1.523(2) and gamma' = 1.525(2). \

The distribution and speciation features of gold in ores and minerals of the Natalkinskoe gold deposit (North-East Russia) are studied using light microscopy (LM), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), X-ray electron probe microanalysis (EPMA), "phase" chemical analysis with atomic absorption spectrometry (PCA-AAS) and atomic absorption spectrometry with analytical data selections for single crystals (AAS-ADSSC). The vein and streaky-vein ores are high-grade ores, whereas veinlet-disseminated ores are less rich and disseminated ores are poor in gold. Up to 85 % of the gold in the ores is in a free native state, associated with quartz and sulfide minerals. LM, SEM-EDX and EPMA reveal that the predominant gold grains are 0.01 to 2.00 mm in size and at a fineness of 720 to 900 ‰. The finely dispersed and submicron elemental gold particles (Au0) amounted to 20 % and are mainly enclosed into arsenopyrite and pyrite. According to PCA-AAS data, the highest Au concentrations (up to 1383 ppm) are recorded in arsenopyrite; lower contents are typical of pyrite (up to 158.2 ppm). In these sulfides, two non-mineral species of "invisible" Au are the structurally bound and surface-bound species recognized by AAS-ADSSC. The structural Au is included in the mineral structure. The surface-bounded Au prevails and is confined to nano-sized, non-autonomous phases (NAPs) on the sulfide surface. In common with "invisible" Au, the micro-sized particles of native gold are often observed on the surface and within the surface layers of sulfide crystals. This is consistent with the model of post-growth transformations of nano-sized NAPs, resulting in the formation of nano and micro-sized Au0 particles. It is expected that the major part of gold contained in arsenopyrite and pyrite as finely dispersed and submicron particles, as well as the surface-bound gold in NAPs, can be won with modified current schemes of gold concentration, which enhances the value of the gold ore mining.

The isomorphism of S-bearing feldspathoids belonging to the cancrinite, sodalite, tugtupite, vladimirivanovite, bystrite, marinellite and scapolite structure types has been investigated using a multimethodical approach based on infrared, Raman and electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods and involving chemical and X-ray diffraction data. Sapozhnikovite Na8(Al6Si6O24)(HS)2 and sulfite and thiosulfate analogues of cancrinite are synthesized hydrothermally and characterized by means of electron microprobe analyses, powder X-ray diffraction and Raman spectroscopy. The possibility of the incorporation of significant amounts of SO42−, S4 and SO32− in the crystal structures of cancrisilite, sulfhydrylbystrite and marinellite, respectively, has been established for the first time. Thermal conversions of S-bearing groups in the synthetic sulfite cancrinite and sapozhnikovite analogues as well as natural vladinirivanovite and S4-bearing haüyne under oxidizing and reducing conditions have been studied using the multimethodical approach. The SO42− and S2− anions and the S3•– radical anion are the most stable S-bearing species under high-temperature conditions (in the range of 700–800 °C); their ratio in the heated samples is determined by the redox conditions and charge-balance requirement. The HS− and S52− anions are stable only under highly reducing conditions.

The properties of the catalyst based on structurally disordered Pd-P nanoparticles supported on a carbon support (Pd-P/C) in the preparation of hydrogen peroxide by the anthraquinone method have been studied. It is shown that a high yield of H2O2 is observed upon sequential hydrogenation of 2000 mol of eAQ (mol Pd)(-1). The H2O2 yield reaches 96 %-97 %. Pd-P nanoparticles are more active in the hydrogenation of 2-ethyl-9,10-anthraquinone than Pd6P crystalline phosphide. In terms of H2O2 yield, Pd-P/C catalysts are superior to known catalysts: Pd/C, Pd/Al2O3. Based on the data of X-ray powder diffraction, X-ray photoelectron spectroscopy, Inductively Coupled Plasma and thermogravimetry, the main reasons for the deactivation of Pd-P/C catalysts have been established. Crystallization of the structurally disordered Pd-P nanoparticles, poisoning by eAQ conversion products and leaching of the active component are considered to be possible reasons of the Pd-P/C catalyst deactivation.

Abstract Dark blue lazurite from the Malo-Bystrinskoe lazurite deposit, Baikal Lake area, Eastern Siberian region, Russia, was analyzed by electron microprobe and revealed an unusually high content of total sulfur corresponding to 8.3 wt% S. The relative content of sulfur in sulfate and sulfur in sulfide form was determined by wet chemical analysis. The H2O content was measured by means of differential thermal analysis in combination with mass spectrometry and infrared (IR) spectroscopy. The charge-balanced empirical formula of lazurite calculated on the basis of 12 (Al+Si) atoms per formula unit was N a 6.97 C a 0.88   K 0.10 Σ 7.96 A l 5.96 S i 6.04 Σ 12 O 24 S O 4 1.09 2 − S 3 − 0.55   S 0.05 2 − C l 0.04 ⋅ 0.72 H 2 O . $\left(\mathrm{Na}_{6.97} \mathrm{Ca}_{0.88} \mathrm{~K}_{0.10}\right)_{\Sigma 7.96}\left[\left(\mathrm{Al}_{5.96} \mathrm{Si}_{6.04}\right)_{\Sigma 12} \mathrm{O}_{24}\right]\left(\mathrm{SO}_{4}\right)_{1.09}^{2-}\left(\mathrm{S}_{3}^{-}\right)_{0.55} \mathrm{~S}_{0.05}^{2-} \mathrm{Cl}_{0.04} \cdot 0.72 \mathrm{H}_{2} \mathrm{O}.$The presence of H2O molecules and (S3)– and (SO4)2– groups was confirmed by the combination of IR, Raman, electron paramagnetic resonance (EPR), and X‑ray photoelectron spectroscopy (XPS) methods. The idealized formula of lazurite is Na7Ca[Al6Si6O24](SO4)2–(S3)–·H2O, and it is believed that extra-framework cations and anions are grouped into clusters of [Na3Ca·SO4]3+ and [Na4(S3)–]3+. The types of isomorphous substitutions in nosean and haüyne are discussed. Lazurite is a clathrate-type mineral, which may be an effective (S3)– sensor due to the stability of the trisulfur radical anion in isolated cages of the crystal structure. This specific feature makes it possible to study the behavior of this ubiquitous radical anion over larger T and P ranges as compared to free species. This kind of lazurite, with oxidized and reduced sulfur species, seems to be appropriate for the estimation of the fugacity of SO2 and O2 in metasomatic systems forming lazurite-containing rocks. The systematic presence of incommensurate modulations is a unique structural feature of Baikal lazurite and may be an important marker indicating provenance of the mineral.

Partitioning experiments were done by hydrothermal synthesis of crystals containing trace elements (TEs) by internal sampling of fluid at the temperature of 450 °C and pressure of 1 kbar. The crystal phases obtained were magnetite, hematite, and Ni-spinel, which were studied using X-ray diffraction (XRD), X-ray electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), atomic absorption spectrometry (AAS), and atomic force microscopy (AFM). The solutions from the sampler’s fluid probes were analysed by AAS for TEs included elements of the iron group plus aluminium. The highest co-crystallisation coefficients of TE and Fe between mineral and fluid (DTE/Fe) in magnetite were measured for V, Al, Ni and Cr (in decreasing order of n units in value), a lower value was observed for Co (2 × 10−1), and still lower values for Ti, Zn, and Mn (n × 10−2–10−3). In hematite, DTE/Fe values were highest for Al and V (order of n units in value), while lower values characterised Ti, Cr, and Co (n × 10−1–10−3), and the lowest values were exhibited by Cu, Mn, and Zn (n × 10−5). Copper was confirmed to be the most incompatible with all minerals studied; however, Cu had a high content on crystal surfaces. This surficial segregation contributes to the average TE concentration even when a thin layer of nonautonomous phase (NAP) is enriched in the element of interest. The accumulation of TEs on the surface of crystals increased bulk content 1–2 orders of magnitude above the content of structurally-bound elements even in coarse crystals. The inverse problem—evaluation of TE/Fe ratios in fluids involved in the formation of magnetite-containing deposits—revealed that the most abundant metals in fluids were Fe followed by Mn, Zn, and Cu, which comprised 10 to 30% of the total iron content.

The paper presents newly acquired data on the mineral and chemical composition of the crystal surface layers of arsenopyrite and pyrite from the Natalkinskoe gold deposit, northeastern Russia. Data on arsenopyrite and pyrite grains from metasomatites and from quartz veins and veinlets were obtained using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (SEM-EDX). The surface layers of the sulfide crystals from the metasomatites contain no admixtures, except only As (up to 2.48 wt %) in the pyrite. The surface layers of arsenopyrite crystals from the vein and veinlets contains the following admixtures (wt %): Pt (up to 2.11), U (up to 2.03), Hg (up to 1.11), Au (up to 0.96), and more rarely Ru (up to 1.44), Ir (up to 0.67), Os (up to 0.64), Ag (up to 0.71), and Cu (up to 0.56). The surface layers of the pyrite crystals contain (wt %): As (up to 2.24), Pt (up to 2.88), and Cu (up to 0.69). The detected elevated concentrations of the admixtures are thought to be explained primarily by the presence of nonautonomous phases.

The peculiarities of the distribution and binding forms of platinum group elements (Pt, Pd, Ru, Rh, Os and Ir) in the arsenopyrites and pyrites of the Natalkinskoe gold ore deposit (Northeastern Russia) were examined using atomic absorption spectrometry with analytical data selections for single crystals (AAS-ADSSC), a “phase” chemical analysis (PCA) based on AAS of different size-fractions of minerals, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The arsenopyrites and pyrites of the Natalkinskoe gold deposit were found to concentrate not only Au but also platinum group elements (PGEs) such as Pt, Pd, Ru and Rh. The PCA showed that the highest contents (in ppm) were found in the monofractions of arsenopyrite—Pt up to 128, Pd up to 20, Ru up to 86 and Rh up to 21—and comparably lower in monofractions of pyrite—Pt to 29, Pd to 15, Ru to 58 and Rh to 5.9. The AAS-ADSSC method revealed two forms of uniformly distributed Pt, Pd and Ru corresponding to the chemically bound element in the structure of the mineral and in the superficial non-autonomous phase (NAP). The superficially bound form dominates over the structural form and presumably exists in a very thin surface layer of the crystal (~100–500 nm). The maximum contents of these PGE, chemically bound in the structure of arsenopyrite, reached values of (in ppm) 48, 5.9 and 48; and in pyrite structure, 68, 5.2 and 34 for Pt, Pd and Ru respectively. The contents of Pt, Pd and Ru related to NAP on the surface of the crystal were significantly higher and amounted (in ppm) for arsenopyrite to 714, 114 and 1083; and for pyrite 890, 62 and 690 for Pt, Pd and Ru, respectively. Preliminary results for the Rh form in arsenopyrite crystals suggest that the surface-related form (154–678 ppm) is more abundant than the structural form (17–45 ppm). Data from studying the surfaces of sulphide minerals by SEM-EDX and LA-ICP-MS confirmed the presence of Pt, Pd, Ru and Rh on the surface of arsenopyrite and pyrite crystals. These methods generated primary data on the content of Os and Ir in arsenopyrite and pyrite in the surface layer. The maximum content of Os and Ir found in arsenopyrites was up to 0.7 wt%. PGE-enriched fluids (up to ~3 ppm Pt) may exist in the gold ore deposit. It is assumed that there is a common mechanism of impurities uptake associated with the active role of the crystal surface and surface defects for gold-bearing arsenopyrites and pyrites. The surface enrichment is due to peculiarities in the crystal growth mechanism through the medium of NAP and the dualism of the element distribution coefficient in the system of mineral–hydrothermal solution, which is higher for NAP, compared to the volume of the crystal. Although mineral forms of Pt, Pd, Ru, Rh, Os and Ir have not been found at the Natalkinskoe gold deposit, their existence in the form of nano-scale particles is not excluded. This follows from the evolutionary model of surficial NAPs, assuming their partial transformation and aggregation with the formation of nano- and micro-sized autonomous phases of trace elements. The presence of PGE in the ores and the possibility of their extraction significantly increase the quality and value of the extracted raw gold materials at the Natalkinskoe deposit, and adds to the list of known platiniferous ore formations.

Major types of mineralization distinguished at the Krasniy deposit: (a) dispersed idiomorphic pyrite crystals, (b) a veinlet with pyrite and pyrrhotite, (c) veinlets of milky-white quartz bearing fine cubic pyrite, (d) a vein of brownish quartz with pyrite pocket.