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 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 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.

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 characteristics of Au partitioning in a multiphase, multicomponent hydrothermal system at 450 °C and 1 kbar pressure were obtained using experimental and computational physicochemical modelling and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. Sphalerite and magnetite contained 0.1–0.16 ± 0.02 µg/g Au and coexisted with galena and bornite which contained up to 73 ± 5 and 42 ± 10 µg/g Au, respectively. Bornite and chalcopyrite were the most effective Au scavengers with cocrystallization coefficients Au/Fe and Au/Cu in mineral-fluid system n–n × 10−2. Sphalerite and magnetite were the weakest Au absorbers, although Fe impurity in sphalerite facilitated Au uptake. Using the phase composition correlation principle, Au solubility in minerals was estimated (µg/g Au): low-Fe sphalerite = 0.7, high-Fe sphalerite = 5, magnetite = 1, pyrite = 3, pyrite-Mn = 7, pyrite-Cu = 10, pyrrhotite = 21, chalcopyrite = 110, bornite = 140 and galena = 240. The sequence reflected increasing metallicity of chemical bonds. Gold segregation occurred at crystal defects, and on surfaces, and influenced Au distribution due to its segregation at crystal interblock boundaries enriched in Cu-containing submicron phases. The LA-ICP-MS analysis of bulk and surficial gold admixtures revealed elevated Au content in surficial crystal layers, especially for bornite and galena, indicating the presence of a superficial nonautonomous phase (NAP) and dualism in the distribution of gold. Thermodynamic calculations showed that changes in experimental conditions, primarily in sulfur regime, increased the content of the main gold species (AuCl2− and AuHS0) and decreased the content of FeCl20, the prevailing form of iron in the fluid phase. The elevation of S2 and H2S fugacity affected Au partitioning and cocrystallization coefficients. Using Au content in pyrite, chalcopyrite, magnetite and bornite from volcanic-sedimentary, skarn-hosted and magmatic-hydrothermal sulfide deposits, the ranges of metal ratios in fluids were estimated: Au/Fe = n × 10−4−n × 10−7 and Au/Cu = n × 10−4−n × 10−6. Pyrite and magnetite were crystallized from solutions enriched in Au compared to chalcopyrite and bornite. The presence of NAP, and associated dualism in distribution coefficients, strongly influenced Au partitioning, but this effect does not fully explain the high gold fractionation into mineral precipitates in low-temperature geothermal systems.

The article considers the study of the role of bacteria in the surface oxidation of pyrite. The experiment provided the data on characteristic morphological changes of the surface and the first data on influence of a non-autonomous phase (NP) on bacterial oxidation.

The phenomena related to the crystal growth in close-to-natural multicomponent systems have been considered. It is shown that the distribution of rare-earth elements in magnetite and hematite and the distribution of noble metals (NMs) in pyrite and magnetite are controlled by surficial nonautonomous phases (SNAPs). The increase in the fractionation and cocrystallization coefficients of elements is related to the presence of these phases. The dependence of SNAPs on the physicochemical growth conditions suggests typomorphism of mineral surfaces. The SNAP evolution during crystal growth explains some specific features of mineral growth systems, in particular, the existence of highly determinate dependences of uniformly distributed incompatible element admixture on the specific surface area of crystal, as well as the formation of nano- and microinclusions and microzonality in crystals. The results obtained are important for the ore formation theory and the practical estimation of the economic potential of ore deposits in view of determining the “hidden” metal content and elaborating a rational technology to recover ore material resources.

The study focused on the forms of occurrence and distribution of hidden (“invisible”) noble metals (NMs = Au, Ag, Pt, Pd, Ru) in the coexisting pyrites and arsenopyrites of four samples of mineral associations from three Au deposits in the north-east of Russia. The unique nature of our approach was the combination of methods of local analysis and statistics of the compositions of individual single crystals of different sizes. This allowed us to take into account the contribution of the surface component to the total NM content and to distinguish the structurally bound form of the elements. The following estimates of the distribution coefficients of the structural (str) and surficial (sur) forms of elements were obtained: D ¯ P y / A s p s t r = 2.7 (Au), 2.5 (Pd), 1.6 (Pt), 1.7 (Ru) and D ¯ P y / A s p s u r = 1.6 (Au), 1.1 (Pd), 1.5 (Pt and Ru). The data on Ag in most cases indicated its fractionation into pyrite ( D ¯ P y / A s p s t r = 17). Surface enrichment was considered as a universal factor in “invisible” NM distribution. A number of elements (i.e., Pt, Ru, Ag) tended to increase their content with a decrease in the crystallite size in pyrite and arsenopyrite. This may be due to both the phase size effect and the intracrystalline adsorption of these elements at the interblock boundaries of a dislocation nature. The excess of metal (or the presence of S vacancies) in pyrite increased Ag and Pt content in its structure and, to a lesser extent, the content of Ru, Pd and Au. Arsenopyrite exhibited a clear tendency to increase the content of Pt, Ru and Pd in samples with excess As over S. Sulphur deficiency was a favourable factor for the incorporation of Ag and platinoids into the structures of the mineral associations studied. Perhaps this was due to the lower sulphur fugacity. Pyrite with excess Fe was associated with higher contents of some NMs. The presence of other impurity elements was not an independent factor in NM concentration.