Актуальность исследований. В истории развития плейстоцен-голоценового Эльбрусско- го вулканического центра (ЭВЦ) выделены докальдерная, кальдерная и посткальдерная стадии. В двух последних выделены ранние и поздние этапы. С экструзивными телами дацитового состава (позд- ний этап кальдерной стадии) связано широкое проявление как в экструзиях, так и во вмещающих их лавах, гидротермально-метасоматических преобразований. В пределах ЭВЦ нами впервые были выделены Кюкюртлинская (КРМС) и Ирикская (ИРМС) рудно-магматические системы, первая из кото- рых является более перспективной на обнаружение промышленно значимой рудной минерализации. Объектами исследований были Кюкюртлинская и Ирикская РМС. Методы исследований. Определения концентраций микро- и макроэлементов в породах РМС проводились в ЦКП «ИГЕМ - АНАЛИТИКА» ме- тодами РФА и инструментальным нейтронно-активационным анализом (ИНАА). Состав жильных ми- нералов в метасоматически измененных породах изучался методом термогравиметрического анализа и рентгено-фазового анализа. Составы сульфидных минералов и самородных металлов определены на микроанализаторе “Camebax SX-50” и на сканирующем электронном микроскопе в ИГЕМ РАН. Для оценки температур образования рудной минерализации и составов растворов были изучены флюид- ные включения (ФВ) в минералах из экструзивных тел и вторичных кварцитов. Микротермометрия, в интервале температур от -196 до +600 0С, проводилась на термокриокамере “Linkam-ТНМSG 600”. Результаты исследований и их обсуждение. В породах кальдерной стадии рудная минерализация пред- ставлена магнетитом, ильменитом, пиритом, пирротином, арсенопиритом, халькопиритом, милле- ритом, галенитом и тонкодисперсными частицами самородной меди. В дацитах экструзии Кюкюртлю пириты и пирротины имеют стехиометрический состав и сходство с сульфидами из пород кальдер- ной стадии ЭВЦ и отличаются от пиритов и пирротинов посткальдерной стадии. Особенности со- ставов рудных минералов свидетельствуют о наложении гидротермально-метасоматических об- разований, связанных с эволюцией гидротермальной системы РМС Кюкюртлю на породы кальдерной стадии. Температуры гомогенизации флюидных включений в кварце и карбонате секущих прожилков из апикальной части экструзии РМС Кюкюртлю составляют 140-170 оС. Температуры образования халькопирит-пирит-пирротинового парагенезиса (рассчитаны по термометрическим уравнениям) для экструзии КРМС составили 190 оС. Гидротермальные растворы, участвовавшие в метасоматических изменениях пород КРМС и сформировавшие вторичные кварциты, имели фторидный состав (обнару- жены фторсодержащие минералы – жарчихит, ральстонит, α-ральстонит и флюорит). По составу и текстурно-структурным признакам, выявленная в КРМС рудная минерализация отнесена к медно- порфировому генетическому типу (на надрудном уровне эрозионного среза). Судя по тому, что в вул- канитах КРМС установлены резко повышенные содержания Ag, Mo, Cu, Zn, Pb, As, Sb, Se и Ba, а также по масштабности и площадному характеру развития процесса аргиллизации, в зоне пропилитизации, на глубинах от 400 м до 600 м от современного эрозионного среза КРМС, можно ожидать обнаружение жильного Pb-Zn оруденения, а на более глубоких уровнях (от 600 до 1000 м) – прожилково-вкрапленного Au-Ag, Cu или Cu-Mo оруденения верхней части порфировой рудно-магматической системы, связанных с экструзивными телами дацитового состава. Relevance of research. In the history of the development of the Pleistocene-Holocene Elbrus Volcanic Center (EVC), pre-caldera, caldera, and post-caldera stages are distinguished. In the last two stages, early and late halting place (stages) are distinguished. Extrusive bodies of dacitic composition late halting place of the caldera stage are associated with a wide manifestation of hydrothermal-metasomatic transformations both in extrusions and in lavas containing them. Within the EVC, we for the first time identified the Kyukyurtlinskaya (KOMS) and Irikskaya (IOMS) ore-magmatic systems, the first of which is more promising for the discovery of industrially significant ore mineralization. The objects of research were the Kyukyurtly and Irik OMS. Research methods. Determination of the concentrations of micro- and macroelements in OMS rocks was carried out at the Central Collective Use Center "IGEM - ANALYTICS" using X-ray diffraction analysis and instrumental neutron activation analysis (INAA). The composition of vein minerals in metasomatically altered rocks was studied by thermogravimetric analysis and X-ray phase analysis. The compositions of sulfide minerals and native metals were determined on a Camebax SX-50 microanalyzer and on a scanning electron microscope at the IGEM RAS. Fluid inclusions (FI) in minerals from extrusive bodies, secondary quartzites were studied to estimate the temperatures of formation of ore mineralization and compositions of solutions. Microthermometry, in the temperature range from -196 to +6000С, was carried out on a Linkam-TNMSG 600 thermal cryochamber. Research results and discussion. In rocks of the caldera stage, ore mineralization is represented by magnetite, ilmenite, pyrite, pyrrhotite, arsenopyrite, chalcopyrite, millerite, galena, and fine particles of native copper. In the dacites of the Kyukyurtlyu extrusion, pyrites and pyrrhotites have a stoichiometric composition similar to sulfides from rocks of the EVC caldera stage and differ from pyrites and pyrrhotites of the post-caldera stage. The compositional features of ore minerals indicate the superposition of hydrothermal-metasomatic formations associated with the evolution of the Kyukyurtli hydrothermal system on rocks of the caldera stage. The homogenization temperatures of fluid inclusions in quartz and carbonate of secant veinlets from the apical part of the extrusion of the OMS Kyukyurtlu are 140-170 °C. Temperatures of formation of chalcopyrite-pyrite-pyrrhotite paragenesis (calculated according to thermometric equations) for extrusion of KOMS were 190 °C. Hydrothermal solutions that participated in the metasomatic alteration of the KOMS rocks and formed secondary quartzites had a fluoride composition (fluorinecontaining minerals were found - jarchichite, ralstonite, α-ralstonite, and fluorite). In terms of composition and textural-structural features, the ore mineralization identified in the KOMS is attributed to the porphyry copper genetic type (at the supra-ore level of the erosion cut). Judging by the fact that sharply elevated contents of Ag, Mo, Cu, Zn, Pb, As, Sb, Se, and Ba have been established in the KOMS volcanics, as well as by the scale and areal nature of the development of the argillization process, in the propylitization zone, at depths from 400 m to 600 m from the modern erosive section of the KOMS, one can expect the discovery of vein Pb-Zn mineralization, and at somewhat deeper levels (from 600-1000 m) - vein-disseminated Au-Ag, Cu or Cu-Mo mineralization of the upper part of the porphyritic ore-magmatic system, associated with extrusive bodies of dacite composition. Keywords: Elbrus volcanic center, Kyukyurtly ore-magmatic system, hydrothermal-metasomatic processes, ore mineralization

Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P–T–fO2 parameters calculated from the composition of minerals coexisting in the successive zones, isobaric–isothermal fO2–aSiO2 and µNa2O–µAl2O3 sections were constructed with the Perplex program package to model how the fenites interacted with H2O–CO2 fluid (in the Na–K–Al–Si–Ca–Ti–Fe–Mg–O–H–C system). The results indicate that the fluid–rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite–feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H2O–CO2 fluid–rock. As a consequence, the metasomatites were progressively enriched in Al2O3 and alkalis, and these transformations led to the development of biotite in equilibrium with K–Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite–feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm–Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite–miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.

New data on the geological structure and ore-bearing structural parageneses of the Uryakh gold ore field are presented. The formation of the deposit occurred in dynamic shear regime along ore-controlling deep-seated faults of the Syulban fault system and faults of the system transverse to it. The interaction of two duplex shear systems resulted in the block structure of the ore field. Tectonophysical methods have established the individual development of tectonic blocks during the period of gold-bearing fluid input in a seismically active regime. The specific features of the formation of ore-bearing fracture–fault structural parageneses in the blocks resulted from the change in the seismic regime under the action of pressure and gas-saturated fluids. The parameters of the fluid system were determined by fluid inclusion studies in quartz. An unstable variable compression–extension regime of the early phase of seismic activity led to the formation of hybrid structural parageneses under the influence of stresses of damping shear and injective hydrodynamic stress. Variations in the stress–strain state of the medium in this phase correspond to a transient seismic regime and are consistent with variations in the thermobarometric parameters of the fluid system. In the late phase of seismic activity, a stable uniaxial tension regime with a superlithostatic fluid pressure occurred, which caused brittle deformations independent of slip along the fault. The centroid mechanism of such deformations, which is rarely found in the dynamic regimes of hydrothermal deposits, ensured the formation of structural parageneses unusual for shear zones, which resulted in a different combination of structural and morphological types of orebodies in the blocks.

Mineral assemblages and formation conditions of precious metals (Au, Ag, PGE) in ores of the Mikheevskoe porphyry copper deposit (South Urals) are the subject of our study. Three mineralization types can be distinguished: (1) Gold-silver-telluride mineralization overlapping porphyry-style bornite-chalcopyrite ores includes native gold (fineness 863-873), electrum (fineness 593-672), galena, hessite, coloradoite, and, more rarely, petzite, stutzite, Au-Ag ditellurides, native tellurium, tellurobismuthite, tetradymite-kawazulite, altaite, and extremely rare melonite NiTe2, merenskyite PdTe2, and sopcheite Ag4Pd3Te4; (2) Gold-arsenopyrite-basemetal mineralization within quartz-tetrahedrite-sphalerite veinlets cutting porphyry-style mineralization; (3) Gold-telluride mineralization with argillic alteration and mineralogically similar to that of type (1) but distinct because of the presence of Au-Ag, Ag, and Pb selenides. Textural relationships supported by fluid inclusions data and chlorite geothermometry provide evidence that occurrence of precious metals minerals at the Mikheevskoe deposit is mostly linked to epithermal overprint of the porphyry mineralization and was deposited at ca. 300-200 degrees C from moderately saline fluids (ca. 5-10 wt%-eq.NaCI). It is suggested that the observed variability in Au and Ag minerals results from small fluctuations of S-2 and/or Te-2 fugacity.

The Bystrinskoe skarn-porphyry Cu–Au–Fe deposit (Eastern Trans-Baikal Region) is confined to skarn zones, which were formed along the contact of granitoids referred to the Shakhtama intrusive complex (J2–3), with terrigenous–carbonate sedimentary rocks. Commercial (Cu–Au–Fe ± W, Mo) mineralization was formed due to the regional postcollision development involving the intrusion of porphyritic granitoids, the derivatives of oxidized adakite highly magnesian magmas enriched in water, sulfur, and metals, which could develop under melting of garnet-bearing amphibolite in the mafic lower crustal arc.

Most of the Cu (+/- Mo,Au) porphyry and porphyry-related deposits of the Urals are located in the Tagil-Magnitogorsk, East-Uralian Volcanic and Trans-Uralian volcanic arc megaterranes. They are related to subduction zones of different ages:(1) Silurian westward subduction: Cu-porphyry deposits of the Birgilda-Tomino ore cluster (Birgilda, Tomino, and Kalinovskoe) and the Zeleny Dol Cu-porphyry deposit;(2) Devonian Magnitogorsk eastward subduction and the subsequent collision with the East European plate: deposits and occurrences are located in the Tagil (skarn-porphyry Gumeshevskoe etc.) and Magnitogorsk terranes (Cu-porphyry Salavat and Voznesenskoe, Mo-porphyry Verkhne-Uralskoe, Au-porphyry Yubileinoe etc.), and probably in the Alapaevsk-Techa terrane (occurrences of the Alapayevsk-Sukhoy Log cluster);(3) Late-Devonian to Carboniferous subduction: deposits located in the Trans-Uralian megaterrane. This includes Late-Devonian to Early Carboniferous Mikheevskoe Cu-porphyry and Tarutino Cu skarn-porphyry, Carboniferous deposits of the Alexandrov volcanic arc terrane (Bataly, Varvarinskoe) and Early Carboniferous deposits formed dew to eastward subduction under the Kazakh continent (Benkala, etc.).(4) Continent-continent collision in Late Carboniferous produced the Talitsa Mo-porphyry deposit located in the East Uralian megaterrane.Porphyry mineralization of the Magnitogorsk megaterrane shows an evolving relationship from gabbro-diorite and quartz diorite in the Middle Devonian (Gumeshevskoe, Salavat, Voznesenskoe) to granodiorite-plagiogranodiorite in the Late Devonian (Yubileinoe Au-porphyry) and finally to granodiorite in the Carboniferous (Talitsa Mo-porphyry) with a progressive increase in total REE, Rb and Sr contents. This corresponds to the evolution of the Magnitogorsk terrane from a volcanic arc which gave place to an arc-continent collision in the Famennian. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.

Представлены результаты впервые выполненного геохронологического исследования метасоматитов, сопровождающих золоторудные кварцевые жилы Уряхского рудного поля (Восточно-Забайкальский сегмент Центрально-Азиатского складчатого пояса). На основе полученных геохронологических Rb–Sr-, 39Ar 40Ar-данных показано, что гидротермально-метасоматические процессы в рудном поле происходили в раннепермское время около 280 млн лет назад и коррелируются с финальными фазами становления Ангаро-Витимского батолита.

This paper reports the newly obtained petrologic, geochemical and isotope data on the ore forming system of the Bystrinskoe Cu-Au-Fe skarn-porphyry deposit that is related to adakite and produced in relation to postcollisional magmatism.

This work presents the first results of geochronological study of metasomatic rocks accompanying gold-bearing quartz veins of the Uryakh ore field (UOF). Based on the Rb-Sr and 39Ar-40Ar geochronological data, it is shown that hydrothermal metasomatic processes in the ore field occurred about 280 Ma ago (Early Permian) and they are correlated with the terminal phases of formation of the Angara-Vitim batholith.

Crystal inclusions (plagioclase, biotite, magnetite) and melt inclusions were studied in minerals of the Laleaua Albă dacite (Baia Sprie, Romania). Electron microprobe analysis of 29 melt inclusions in the plagioclase, K-feldspar, and quartz confirm that crystallization of these minerals took place from typical silicic melts enriched in potassium relative to sodium (K2O/Na2O = 1.5). The sum of the petrogenic components is 92–99 wt%. This points to a possible change in water content from 8 to 1 wt% during crystallization of phenocrysts. According to ion microprobe analysis of 11 melt inclusions, the minimum water content is 0.5 wt%, and the maximum water content is 6.1 wt%. The presence of high-density water fluid segregation in one of the melt inclusions suggests that the primary water content in the melt could reach 8.4 wt%. Ion microprobe data revealed a high concentration of Cu (up to 1260 ppm) as well as higher U content (from 5.0 to 14.3 ppm; average 11.5 ppm) in some melt inclusions as compared to the average U contents in silicic melts (2.7 ppm in island-arc settings and 7.9 ppm in continental rift settings). Chondrite-normalized trace-element patterns in melt inclusions suggest a complex genesis of the studied magmatic melts. Contents of some elements (for instance Sr and Ba) are close to those in island-arc melts, while others (for instance Th, U, and Eu) resemble those in melts of continental settings.

Precaldera, caldera, and postcaldera cycles are recognized in the geological evolution of the Pleistocene-Holocene Elbrus volcanic center (EVC). During the caldera cycle, the magmatic activity was not intense, whereas hydrothermal metasomatic alteration of rocks was vigorous and extensive. The Kyukyurtli and Irik ore-magmatic systems have been revealed in the EVC, with the former being regarded as the more promising one. The ore mineralization in rocks of the caldera cycle comprises occurrences of magnetite, ilmenite, pyrite and pyrrhotite (including Ni-Co varieties), arsenopyrite, chalcopyrite, millerite, galena, and finely dispersed particles of native copper. Pyrite and pyrrhotite from volcanics of the caldera cycle and dacite of the Kyukyurtli extrusion are similar in composition and differ from these minerals of the postcaldera cycle, where pyrite and pyrrhotite are often enriched in Cu, Co, and Ni and millerite is noted as well. The composition of ore minerals indicates that the hydrothermal metasomatic alteration related to the evolution of the Kyukyurtli hydrothermal system was superimposed on rocks of the caldera cycle, whereas the late mineralization in rocks of the postcaldera cycle developed autonomously. The homogenization temperature of fluid inclusions in quartz and carbonate from crosscutting veinlets in the apical portion of the Kyukyurtli extrusion is 140–170°C and in quartz from geyserite, 120–150°C. The temperature of formation of the chalcopyrite-pyrite-pyrrhotite assemblage calculated using mineral geothermometers is 156 and 275°C in dacite from the middle and lower portions of the Malka lava flow and 190°C in dacite of the Kyukyurtli extrusion. The hydrothermal solutions that participated in metasomatic alteration of rocks pertaining to the Kyukyurtli ore-magmatic system (KOMS) and formed both secondary quartzite and geyserite were enriched in fluorine, as evidenced from the occurrence of F-bearing minerals-zharchikhite, ralstonite, α-ralstonite, and fluorite-identified in these metasomatic rocks for the first time. By analogy with porphyry Cu-Mo deposits in Chile and the United States, the ore mineralization of the KOMS may be classified by composition and textural and structural attributes as a supraore level of porphyry copper genetic type. The volcanic rocks of the KOMS and the EVC as a whole are enriched in Ag, Mo, Zn, As, Sb, Se, and Ba. Judging from the scale of argillic alteration and taking into account the data on porphyry Cu-Mo ore-magmatic systems of the Greater Caucasus, veined Pb-Zn ore mineralization may be expected in the propylitic zone at a depth down to 1000 m from the present-day erosion level of the KOMS. Stringer-disseminated Au-Ag, Cu, and Cu-Mo ore mineralization of the upper part of the porphyry ore-magmatic system related to subvolcanic dacitic intrusions may be localized somewhat deeper.

A new type of sulfide occurrence related to metasomatically altered brecciated gabbroids has been studied at the Sierra Leone site situated in the axial rift valley of the Mid-Atlantic Ridge (Markov Deep, 6° N). Two associations of plutonic, subvolcanic, and volcanic rocks were dredged: (1) mid-ocean ridge basalts (MORB) and their intrusive analogues and (2) rocks of the silicic Fe-Ti-oxide series with dominating gabbronorites and sporadic trondhjemites. Almost all igneous rocks at the Sierra Leone site are enriched in Pb, Cu, U, Ga, Ta, Nb, Cs, and Rb and depleted in Zr, Th, and Hf. The rocks of the Fe-Ti-oxide series are enriched in Zn, Sn, and Mo and depleted in Ni and Cr. The main ore-bearing zone is situated at the foot of the eastern wall of the deep, where it is hosted in cataclastic hornblende gabbro and gabbronorite of the Fe-Ti-oxide series. Ore mineralization in metasomatically altered rocks is composed of quartz-sulfide and prehnite-sulfide veinlets, disseminated sulfide, and veined copper sulfide ore. The ore consists of pyrite, chalcopyrite, sphalerite, pyrrhotite, bornite, chalcocite, and digenite. The δ 34 S value of sulfides varies from 3.0 to 15.3‰. At the foot of the eastern wall of the Markov Deep, directly downslope from the ore-bearing zone, loose sediments contain grains of native Cu, Pb, Zn, and Sn and intermetallic compounds (isoferroplatinum, tetraferroplatinum, and brass) apparently derived from the ore. Mineral assemblages of ore-bearing metasomatic rocks and fluid inclusions therein were studied. Ore metasomatism developed under a low oxygen potential within a temperature interval from 400 to 160°C, though initial hydrothermal alteration of rocks proceeded at temperatures of 800–450°C. The temperature of stringer-disseminated ore mineralization is estimated at 170–280°C. The hydrothermal fluids are considered to be of magmatic origin; as the hydrothermal system evolved, they became diluted with seawater that was contained in fractured oceanic crust. The ore matter could have been derived from magmatic fluids that were released from water-saturated melts of the Fe-Ti oxide series during their ascent and leached from host gabbroids in the process of metasomatic alteration.

In most alkaline-ultrabasic-carbonatite ring complexes, the distribution of trace elements in the successive derivatives of mantle magmas is usually controlled by the Rayleigh equation of fractional crystallization in accordance with their partition coefficients, whereas, that of late derivatives, nepheline syenites and carbonatites, is usually consistent with trends characteristic of silicate-carbonate liquid immiscibility. In contrast to the carbonatites of ring complexes, carbonatites from deep-seated linear zones have no genetic relation with alkaline-ultrabasic magmatism, and the associated alkaline rocks are represented only by the nepheline syenite eutectic association. The geochemical study of magmatic rocks from the Vishnevye Gory nepheline syenite-carbonatite complex (Urals), which is assigned to the association of deep-seated linear zones, showed that neither differentiation of a parental melt nor liquid immiscibility could produce the observed trace element distribution (Sr, Rb, REE, and Nb) in miaskites and carbonatites. Judging from the available fragmentary experimental data, the distribution patterns can be regarded as possible indicators of element fractionation between alkaline carbonate fluid and alkaline melt. Such trace element distribution is presumably controlled by a fluid melt interaction; it was also observed in carbonatites and alkaline rocks of some ring complexes, and its scarcity can be explained by the lower density of aqueous fluid released from magma at shallower depths.

The composition of fluorine-rich silicic rocks from various geologic environments (differing in depth of formation, association, age, etc.) suggests that their differentiation is related to metamagmatism, fluid filtration throuah magmas. Retrograde magma boiling in a large magma chamber produces an increase in pressure. This results either in explosive ejection of melt on the surface or in passive chamber degassing (magma remains in place). In the latter case, fluid is filtered under temperature- and pressure-gradient conditions through magmas and rocks of the apical parts of magma chambers. This process causes the development of feldspar megablasts far from the contact and recrystallization of biotite with an increase in its iron and fluorine contents. Granophyre quartz-feldspars intergrowths and rapakivi textures form directly near the contact. The altered rocks are partially melted in the back zone of the metasomatic rocks giving rise to high-fluorine magmas. Modeling of the impact of metamagmatic fluids on magmas demonstrated that, when fluid rises and its temperature decreases, the solubility of HF decreases in fluid and increases in magma. High F contents in fluid result in the redistribution of elements between fluid and magma. Mg and LREE form stable soluble F complexes and are removed from the magma, whereas Fe, Mn, and HREE are retained in the melt. Prolonged filtration results in the formation of iron-rich magmas enriched in HREE. If oxygen fugacity in the magmatic source of fluid is higher than QFM +1...+2, fluid filtration leads to the formation of high-fluorine oxidized melts, whereas, if the initial oxygen fugacity is lower than QFM +1...+2, more reduced high-fluorine melts are produced. Modeling of the dynamics of heat and mass transfer showed that an open degassed magmatic system develops through several stages: (1) formation of a cupola of fully or partially crystallized granite at the roof of the massif and beginning of eutectic magma crystallization in the central part of the chamber; (2) fluid filtration (2-500 years) under temperature-gradient conditions produces fluorine-rich magmas with continuously increasing contents of fluorine and related elements in the upper part of the cupola; (3) in 5000-10000 y the conducting body is heated up to the temperature of the central part of the chamber; then, either F and related components are removed into the upper cooled part or such magmas are removed as dikes of ongonite or topaz rhyolite and ignimbrite; and (4) when degassing is terminated in the main chamber, fluorine-rich magmas begin to crystallize in the cupola and peculiar ore-bearing silicic magmas are generated.