New data on the occurrence forms of ore elements were obtained on the basis of the heavy concentrate analysis of material from the thermal sites of Mutnovsky volcano. During the hydrothermal reworking of volcanic rocks and with the participation of magmatic fluids and meteoric waters, metals and metalloids are transported to the surface and are concentrated as the main or impurity components of newly formed minerals. Sulfides of copper, zinc, mercury, silver, and barium sulfate are confidently diagnosed. They contain admixtures of Mn, Cd, Sr, I, Cl, Te, and Pb in addition to mineral-forming Zn, Cu, Hg, Ag, and Ba. Micron-sized phases with Ru, Os and Ir (laurite), and Pb (galena) as the main components and the intermetallic compounds (Fe–Ni), (Fe–Ir–Os), (Pb–Bi), and (Bi–Te), as well as native Au, were revealed. Most of the newly formed mineral individuals are associated with a mineral of the pyrite–marcasite group, which contains impurities of As, Cu, Ni, and Co. Platinoids Os, Ir, and Ru were discovered for the first time among the newly formed minerals within the East Kamchatka Volcanic Belt.

This paper presents the results of multiannual complex geochemical and geophysical studies of a caldera of Golovnin Volcano. The peculiarities of the chemical composition of thermal fluids and condensates are discussed. Geophysical sections including discharge zones of active gas hydrotherms are interpreted regarding the formation of the chemical composition of fumarolic gases and thermal fluids. The selection of the quantitative compositions of interacting milieus and the physicochemical models are based on the data. The most likely physicochemical conditions of the ascending fluid to the surface are suggested on the basis of models and the results of the study of the subsurface space of the thermal fields.

Сhromite-rich rocks and monomineralic chromitites occur in mafic-ultramafic layered intrusions worldwide, and are economically important as they host major resources of chromium and platinum group elements. One of the acknowledged genetic concepts for such mineralization advocates bulk chromite crystallization in a response to hybridization of Cr-rich basic magma with felsic melts, derived from partial melting of the wall rocks. However, there has been lack of direct insights into this process and its details have been remaining largely obscured. In this study, we report data on chromite-rich assemblages of the Noril'sk-1 intrusion (Siberian LIP), with a particular focus on chromite-hosted multiphase inclusions. Composition of the latter is different from the rocks of the Noril'sk-1 intrusion and inherits geochemical fingerprints of the wall rock argillites and, therefore, represent snapshots of the heavily-contaminated medium of the magma-wall rock reaction front. Mineral relationships in chromite-rich breccias with fragments of the wall rocks also provide valuable insight into chromite mineralization mechanisms. Our results, along with geological evidence and data on other Noril'sk-type intrusions, indicate that bulk crystallization of chromite, aided by partial suppression of silicate crystallization, occurred in the hybrid medium during digestion of the wall rocks by ascending and emplacing basic magma. Continuous flow of the magma around outshoots of the wall rocks or through a “magmatic karst” in the wall rocks, allowed for a continuous precipitation of chromite. Concentration of chromite grains to form dense mineralization apparently occurred due to formation of chromite-rich blobs around the wall rock fragments, and selective collection and transport of chromite by fluid bubbles, which formed via degassing of wall rocks and then carried chromite and relics of the wall rocks (xenoliths) to the upper parts of the pluton. We propose that assimilation-driven formation of chromite-rich lithologies in intrusions requires: (1) sufficient Cr contents in magma, which allow for its oversaturation in Cr-spinel only by a sudden cooling and addition of SiO2, K2O or/and H2O; (2) efficient disintegration and digestion of the host rocks, releasing considerable amounts of these components to the magma, and (3) a mechanism ensuring accumulation of excess chromite within a small volume (e.g. continuous reaction of Cr-rich magma with the products of the host rocks' assimilation or/and mechanical concentration of chromite).

The paper represents new data on the formation conditions of basalts from post-caldera volcano Menshiy Brat (Medvezhia caldera, Iturup Island). Liquidus mineral assemblage is composed of olivine (Fo up to 90.1 mol. %) and chromium spinel (Cr# = 0.46–0.6), which crystallized at 1090–1170°С and oxygen fugacity NNO +0.6 (σ = 0.2) – NNO +0.2 (σ = 0.14). The study of melt inclusions in the liquidus olivine demonstrated that its parental melts have low-alumina, low-potassium compositions with up to 15.5 wt. % MgO and with an average water content of 5.5 wt. %. The data on volatile contents in the olivine-hosted melt inclusions suggest that the basic melts appeared due to partial melting of essentially peridotitic source with a small admixture of an olivine-free component at 1225°С under active influence of the slab-related fluids. These fluids were separated from the subducting slab at 670–705°С and depths of 95–105 km beneath the Iturup Island. The results of this study enhance our understanding of the evolution of basic magmas that serve as a heat and volatile supply during the formation of large calderas.

The article presents the results of multi-year comprehensive geochemical and geophysical studies concerned with the caldera of the Golovnin volcano. The chemical composition of thermal solutions and condensates are discussed. Geophysical data within sections including discharge zones of geothermal waters associated with gas from hot springs were interpreted to examine the formation of chemical composition of fumarole gases and thermal solutions. The quantitative composition of the interacting media was identified and physicochemical models were built based on the actual data. Considering these models and the results of studying the subsurface area of thermal fields, the most probable physicochemical conditions for fluid ascent from depth to the surface are proposed.

Differentiated intrusions of the "Norilsk type" are among the world's largest deposits of Cu, Ni and platinum group elements (PGE). They are composed of gabbro-dolerites (gabbros with a pronounced ophitic structure), which mineral composition ranges from picritic and troctolitic varieties to leucogabbro and gabbro-diorites. Economically significant reserves are concentrated in three types of ores: (1) massive sulfide ores that form deposits in the bottom parts of the intrusions, (2) disseminated sulfide ores located at the lower parts of the intrusions, and (3) rocks with rich chromite mineralization and high ratios of PGE/Cu-Ni-sulfides - low-sulfide ores that form discontinuous horizons (LS-horizons) in the upper endocontact zones of the intrusions. Among the hypotheses about the origin of the Norilsk type intrusions, the most acknowledged is the "flow chamber model", within which the intrusions and accumulations of sulfide ores were formed during a long flow through the near-surface chambers of basaltic melts, comagmatic to the basalt formations of the Norilsk region [Naldrett et al., 1992; Rad'ko, 1991]. However, a number of studies show that (1) the intrusions of the Norilsk type have been forming over a long period of time from 290 to 230 Ma [Malitch et al., 2010]; (2) they were formed later than a significant part of the trap basalts [Krivolutskaya, 2016] and (3) the parental magmas for these intrusions differed significantly from the trap ones, and in fact, there are no bona fide co-magmatic rocks of the Norilsk intrusions among the represented basalt formations [Latypov, 2002]. In this work, we consider compositions of olivine and Cr-spinels from disseminated sulfide ores and the LS-horizon of the Norilsk-1 intrusion as petrological indicators, compare them with these minerals in trap basalts, and estimate redox conditions of formation of these types of ores. It was noted that after crystallization, olivine and chrome spinel re-equilibrated with each other and the environment (melt, other minerals). Olivine in disseminated sulfide ores is characterized by narrow Mg# range and re-equilibration with high Ni sulfides, which is manifested in the growth of Ni and Fe (reverse Ni-Mg # trend) [Barnes et al., 2011; Barnes et al., 2013]. The composition of Cr-spinels varies over a very wide range, especially in Mg # (from 5 to 55) values and TiO2 (up to 18 %) content, and in Fe2+/Fe3+ variations. Evolution of the Cr-spinel compositions towards low Mg# values region is characteristic of Cr-spinel inclusions in olivine and clinopyroxene, as well as in altered minerals, while plagioclase hosts more magnesian Cr-spinel grains. Based on the obtained results and data of [Kamenetsky, Crawford, Meffre, 2001] Cr-spinels with Mg # > 25 can be considered relatively primitive (weakly re-equilibrated). Comparison of the composition of the studied minerals with their counterparts from trap basalts showed that the compositions of olivine, especially in terms of Ni, differ between disseminated ores, LS-horizon and trap basalts. In general, the NiO concentrations in the analyzed olivines lie between the picrobasalts of the Gudchikhinskiy Formation and the basalts of the Tuklonskiy and Nadezhdinsky Formations. However, compositions of olivines of disseminated ores are close to the olivines from picrobasalts of the Gudchikhiy Formation, as well as several obtained analyzes from the Mokulaevskiy Formation. Cr-spinels of the Norilsk-1 intrusion are generally richer in Ni than the chromites of the Tuklonskiy and Nadezhdinskiy formations and, according to this feature, correspond to the picrobasalts of the Gudchikhinskiy Formation. Based on the data obtained, we assume that the ore-bearing rocks of the Norilsk-1 intrusion were formed from magmas enriched in Ni and similar to the effusive rocks of the Gudchikhinskiy or Mokulaevskiy formations. At the same time, different magmatic impulses and, accordingly, different melt compositions could be responsible for the formation of disseminated sulfide ores and the MS horizon. Since strong variations in Fe2+/Fe3+ ratio in Cr-spinels can result from variations in the redox conditions the parental media, we estimated f(O-2) for the rocks of the studied series. As soon as application of olivine-spinel thermometer and oxybarometer was considered as limited due to strong re-equilibration of Cr-spinel [Nikolaev et al., 2016], the olivine-chromite pair was used to calculate the T-f(O-2) parameters for only the most primitive Cr-spinels from the picrobasalts of the Gudchikhinskiy Formation and the LS-horizon of the Norilsk-1 intrusion. The temperature calculated using the Al-in-olivine oxybarometer [Coogan, Saunders, Wilson, 2014] was 1150-1240 degrees C, and the log(10)f(O-2) calculated using the Mg-Fe olivine-chromite oxybarometer Nikolaev et al., 2016] was -9 - -9.8 for picrobasalts, and LS-horizon -8 - -9. To estimate f(O-2) for the rocks of the LS-horizon that do not contain fresh olivine and for disseminated sulfide ores, in which all olivine - chromite pairs were strongly reequilibrated, we adopted a semi-quantitative method based on the conversion of Fe2+/Fe3+ in Cr-spinel to Fe2+/Fe3+ in the melt [Maurel, Maurel, 1984] with further estimation of f(O-2), based on the empirical correlation for basaltic magmas [Fudali, 1965] which was calibrated to f(O-2) for Cr-spinels of the Gudchikhinskiy Formation, obtained using the olivine-spinel oxybarometer. According to the estimations, disseminated sulfide ores of the Norilsk-1 intrusion crystallized at log(10)f(O-2) from -7.5 to -9, which at 1175 o. is similar to NNO +/- 1 and slightly increased relative to the picrobasalts of the Gudchikhinskiy, Nadezhdinskiy and Tuklonskiy formations. For the LS-horizon, estimates of log(10)f(O-2) showed very different values for different samples. In most cases, log(10)f(O-2) at 1175 degrees C was about -9, which is close to the picrobasalts of the Gudchikhinskiy Formation. Nevertheless, some samples showed more oxidized conditions (up to log(10)f(O-2) = -7 or similar to QFM + 2), and some samples, on the contrary, down to log(10)f(O-2) = -12. The latter are close to the IW (Fe-FeO) buffer and are extremely reduced conditions for igneous rocks. Such broad range of f(O-2) is unique to the Norilsk-1 intrusion and is not typical for the rocks of the upper endocontact with the LS-horizon of the Talnakh intrusion, for which the log(10)f(O-2) estimates do not fall below the WM (FeO-Fe3O4) buffer. We assume that the variations in redox conditions in the LS-horizon of the Norilsk-1 intrusion are associated with the intense assimilation of coal shales of the Tunguska Formation.

—We present results of a study of plutonic-rock xenoliths from the Kharchinsky Volcano (Central Kamchatka depression). The studied xenolith collection comprises nine samples of peridotites and clinopyroxenites. The peridotites are identified as wehrlites, dunites, and harzburgites composed of olivine, clino- and orthopyroxenes, amphibole, and chromite in varying amounts. The clinopyroxenites consist mostly of clinopyroxene and often contain subordinate olivine, amphibole, hercynite, and magnetite. The xenoliths have interstitial segregations and veins composed of chlorite, plagioclase, K-feldspar, orthopyroxene, barite, fluorapatite, ilmenite, and, more seldom, anhydrite, phlogopite, and some other minerals. The study has revealed that veinlet minerals sometimes replace primary minerals and form pseudomorphs, thus indicating the metasomatic origin of interstitial and vein mineral assemblages. The thermobarometric calculations for minerals have shown that peridotites formed at ~1140 °C and ≤10 kbar in the intermediate chambers at the depths from the spinel stability field to the Moho. Interstitial metasomatic alterations of rocks took place at ~400–850 °C.

In this study, the risk of environmental pollution by arsenic (As) and heavy metals from the tailings of Co-Ni arsenide ores at the Khovu-Aksy mine site (Russia) has been systematically evaluated over 20 years. The assessment results indicated that As poses the greatest concern, followed by Cu, Zn, Co, and Ni, among others. This article presents the results of a study on the mobile forms of metals (Cu, Ni, and Co, among others) and metalloids (e.g., As and Sb) in stored waste that was produced by the hydrometallurgical processing of Cu-Co-Ni arsenide ore from the Khovu-Aksy deposit. A comparative assessment of the changes in element forms during the 20-year of waste storage period was conducted. It was determined that in the pore solutions, the metal concentration decreased by an average of 7-10 times because they precipitated into secondary solid phases or were adsorbed on sulfides. Moreover, the As concentrations in the pore solutions remained practically unchanged, and in some cases, they slightly increased, i.e., this element remained immobile. In contrast, greater changes occurred in the fractional composition of the element forms, which were determined based on the compositions in water extracts. The concentrations of the water-soluble forms of the metals decreased by 100-700 times in 20 years. The concentrations of the soluble As compounds decreased by 1.6-4.6 times. A study of the mineralogy of the tailings showed that the secondary rims of the Fe hydroxides and Ca carbonates with admixtures of Cu, Zn, Co, Ni, and Ag formed on the grains of the sulfide and arsenide grains. The secondary As compounds on the rims are represented by aqueous Fe arsenate. The obtained data indicate active processes of metal deposition, while As remained mobile. The internal structure and geometries of the groundwater horizons were determined by using electrical resistivity tomography, which made it possible to calculate the quantities of dissolved metals and metalloids in the tailings. Condensates were collected to determine the concentrations of the volatile forms of the elements, and the amounts migrating with the vapor-gas flows were estimated. At present, the tailings contain similar to 2.1 tons of dissolved As (in pore water), similar to 85 tons of soluble As (in water-soluble forms), and similar to 23 kg of volatile As that enters the air with vapor-gas flows during summer.

Layers rich in chromian spinel (Cr-spinel) occur in numerous differentiated and layered intrusions. These layers are often characterized by elevated and even economic concentrations of platinum-group-elements (PGEs), but only scarce sulfide mineralization. One particular type of such lithology occurs in the roof parts of the Norilsk-type differentiated intrusions (Russia) and is referred to as the “sulfide-poor PGE ores”. We investigated rocks containing variable enrichments in Cr-spinel, sulfides, and platinum-group minerals (PGMs) from two sections of the upper zone of the Norilsk-1 intrusion, with a focus on Cr-spinel. The rocks are dominated by two lithological types: (1) leucogabbro/troctolitic and (2) olivine-gabbro. Fine-grained (5–100 μm) disperse disseminations with varying modal abundances of Cr-spinel are characteristic for the rocks studied. Those abundances range from scarce mineralization through to very dense (up to 30 vol.% Cr-spinel) cloud-like accumulations. However, compact-grained accumulations and cumulate-like textures, which are typical for chromitites of layered intrusions, are not characteristic for the studied rocks. Instead, the disseminations exhibit chain- and trail-like alignments of Cr-spinel grains, which cross the boundaries between enclosing silicates, and sub-circular arrangements. The study revealed millimeter-scaled patchy distribution of Cr-spinel compositions within a given dissemination with Cr-spinel chemistry being strongly correlated with a kind of the enclosing silicate. (1) In unaltered rocks, plagioclase hosts more magnesian Cr-spinel (Mg# 30–60), while Cr-spinel in mafic minerals is less magnesian (Mg# 18–35). (2) In altered rocks, more magnesian Cr-spinel is hosted by less altered silicates, while strongly altered silicates mainly host less magnesian Cr-spinel. Systematics of trivalent cations exhibits divergent trends, even on a scale of a thin section, and depends on a kind of hosting lithology. Leucogabbro/troctolite lithologies contain Cr-spinel with anomalously low Fe3+ and extremely high Ti contents, whereas Cr-spinel from olivine-gabbro lithologies have moderate Fe3+ and moderately-high Ti contents. It is envisaged that crystallization of Cr-spinel and their host rocks occurred from viscous mingled magmas, which had different compositions and redox state. Subsequent processes involved (1) high-temperature re-equilibration of Cr-spinel with enclosing silicates and (2) post-magmatic alteration and partial recrystallization of Cr-spinel. During these processes, Cr-spinel was losing Mg and Al and gaining Fe and Ti. These chemical trends are generally coincident with those established for other intrusions worldwide, but the upper zone of the Norilsk-1 intrusion seems to possess an exceptional variety of Cr-spinel compositions, not recorded elsewhere.

In the taxitic gabbro-dolerites of the upper contact zone of the Norilsk-1 intrusion, five boron minerals were found: kotoite Mg3(BO3)2, suanite Mg2B2O5, warwickite (Mg,Ti,Fe,Cr,Al)2O(BO3), ludwigite (Mg)2Fe3+O2(BO3), and azoproite (Mg,Fe2+)2(Fe3+,Ti,Mg)O2(BO3). This is the first find of oxyborates in the rocks of the Norilsk ore-bearing intrusions and in the Norilsk province as a whole. Oxyborates occur as inclusions in olivine in the recrystallization zones of taxitic gabbro-dolerites. This indicates that they formed at the late-magmatic or postmagmatic stage as result of the interaction between rocks and boron-bearing fluids associated with an ore-bearing intrusion. Microinclusions of boron minerals could be the cause of elevated concentrations of boron in the rocks. This is a characteristic feature of Norilsk PGE–Cu–Ni-bearing intrusions that can be used as a prospecting criterion.

We found five boron minerals in the taxitic gabbrodolerites near the upper contact of the Norilsk-1 ore-bearing intrusion. These are kotoite Mg3(BO3)2, suanite Mg2B2O5, warwickite (Mg,Ti,Fe,Cr,Al)2O(BO3), ludwigite (Mg)2Fe3+O2(BO3), and azoproite (Mg,Fe2+)2(Fe3+,Ti,Mg)O2(BO3). This is the first discovery of oxyborate minerals in the Norilsk province. They form monomineral and polymineral inclusions in olivine grains from the recrystallized areas of the taxitic intrusive rocks. Boron minerals arose at the late stage of the magma crystallization or just after that as a result of the interaction of the rock with the boron-bearing fluid containing in the ore-bearing magma. Presence of the micro inclusions of the oxyborates as well as higher boron content in rocks can be used as a criterion for searching of the Pt-Cu-Ni-bearing intrusions in the Norilsk province.

Computational modeling based on data on the compositions of melt inclusions in chrome-spinelids using the COMAGMAT [12] and PETROLOG [11] programs indicates the similarity of the parent melt of meimechites [4] with the picritic magma of the Gulinsky massif. Experimental data on the inclusions confirm this conclusion, showing the reliability of the actually calculated trends in the fractionation of ultrabasic melts. In general, the calculations showed that the crystallization of olivine from the high-magnesium pyrite melt occurred in the temperature range of 1510–1260 ° C, mainly at a pressure of 6–7 kbar. At the same time, the melt evolves and approaches its composition to olivine basalt, from which, starting from 1200 ° C, clinopyroxene mainly crystallizes with enrichment of the residual melt with alkalis, rare and rare-earth elements. The similarity of the compositions of the parental melts for meimechites and Gulinsky pluton rocks and the proximity of P – T parameters of their evolution indicates a possible genetic relationship of these magmatic formations.

: The modern active volcano-hydrothermal systems are a kind of information record of all the stages of the rising fluid with the enclosing rocks interaction. It becomes possible to make conclusions about the gas hydrotherms formation, the chemical elements transport forms through the measurements of the active hydrothermal systems conditions. The report pre-sents the hydrogeochemical, geophysical and physico-chemical studies results on the Golovnin volcano active fumarolic fields.

For the Permian–Triassic foidite and meimechite lavas of Polar Siberia, both the whole-rock petrochemistry and geochemistry and that of melt inclusions in olivine phenocrysts from the same rocks have been demonstrated to be similar. In addition, their isotope characteristics imply the possibility of their generation from an abyssal parental melt compositionally resembling a high–Mg alkaline picrite.

Comparative analysis of the composition and formation conditions of the dunite–pyroxenite association of the Guli Pluton and ultramafic vulcanite (meimechite) showed the similarity of their initial melts and the same type of crystallization, demonstrating the cumulative origin of dunite.

Comparative analysis of ultramafic meymechites of the Maimecha Suite and alkaline volcanics of the Ary-Dzhang Suite (foidites (nephelinites, analcimites, limburgites, etc.) and melilitites) has shown their consanguinity, which indicates their relationship with the same magmatic system periodically producing large amounts of alkaline ultramafic melts. We have studied the petrogeochemical and mineralogical compositions of rocks and melt inclusions in the hosted olivines. The rocks of the Maimecha and Ary-Dzhang Suite differ considerably in MgO content, which is well explained by the accumulation of olivine. The inclusions in olivines from the meymechites and the rocks of the Ary-Dzhang Suite correspond in composition to foidites. The trace and rare-earth element patterns are similar both in the foidites and meymechites and in the melt inclusions: They show negative anomalies of Rb and K and positive anomalies of Nb and Ta. The ratios of indicator elements (Nb/Ta, Ba/La, Ta/La, etc.) in the rocks of the Maimecha and Ary-Dzhang Suite are constant and almost independent of their Mg# values. The La/Yb ratio in the foidites is significantly higher than that in the meymechites and in the melt inclusions from their olivines, which indicates that the rocks of the Ary-Dzhang Suite resulted from the fractionation of highly magnesian alkaline picritoid melt.

Сравнительный анализ вещественного состава и условий образования дунит-пироксенитовой ассоциации Гулинского плутона и ультраосновных вулканитов (меймечитов) показал близость составов исходных расплавов и однотипный тренд кристаллизации для этих пород, что свидетельствует о кумулятивной природе дунитов.

Analysis of petrochemical and geochemical information of the same levels, which characterize rocks and primary melt inclusions in olivines of heterochronic meimechite–picrite associations in Siberia (Maimecha–Kotui province), Primorye (Sikhote–Alin), and Kamchatka demonstrated that, besides the similar appearance and identical structural patterns, they are considerably discrepant in the concentration and distribution of incompatible and rare earth elements. Those differences are also observed for the compositions and evolutionary trends of parental high-temperature magnesium-rich melts. This, in turn, was assumed to be a consequence of a variable degree of melting of the mantle protoliths in the mentioned regions, which is supported by geochemical modeling.