The article provides a brief geological description of the Southern Ashaly mineral deposit within which ores of the gold-sulfide and gold-low-sulfide-quartz types were recognized. Two ore mineralization phases were established, that incorporate four stages, the pyrite, pyrite-arsenopyrite, sulfide, and polymetallic ones. The morphological and mineralogical-geochemical features of the major, minor, and rare ore minerals were studied in detail. The following successive generations of pyrite were established at the deposit: diagenetic, metamorphic, and hydrothermal, that embrace six varieties with its own geochemical features. Elevated concentrations of gold in diagenetic pyrite have been recorded and visually confirmed. Native gold of two generations is formed at the pyrite, pyrite-arsenopyrite (early), and sulfide (late) stages and have an average gold fineness of 884 and 998 ‰, respectively. The temperature of transformation of the carbonaceous matter of rocks of the Bukon Formation and of generation of the ores of the gold-sulfide type varies from 384 to 241 °C, which corresponds to the greenschist-zeolite facies of metamorphism.

The distribution of gold in small acicular arsenopyrite of a pyrite-arsenopyrite association from Suzdal (Eastern Kazakhstan), Olympiada (Yenisei Ridge, Russia) and large pseudorhombic arsenopyrite crystals from Bazovskoe (Yakutia, Russia) orogenic-type deposits were investigated. On orogenic gold deposits in NE Asia, occurring mainly in black shales, two productive stages of ore deposition are distinguished, which correspond to two morphological varieties of arsenopyrite. At the early stage, fine-grained acicular-prismatic arsenopyrite with invisible gold was deposited; at the late stage, tabular arsenopyrite in association with free visible gold was formed. The samples of gold-bearing arsenopyrite were analyzed using Scanning Electron Microscopy, Electron Microprobe Analyses, Atomic Absorption and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in combination with High Resolution 3D X-ray Computed Tomography (HRXCT). HRXCT does not destroy the studied mineral during the investigation. That technique permits to do an estimation of the amount of gold inclusions in minerals or host rocks and draw reasonable conclusions about the gold content of the ores, to study in detail the distribution patterns of metal inclusions (associated with certain minerals, cracks, crystal growth faces, etc.) and to determine the form of the gold. It can be used to understanding of the genesis of productive mineral associations, and to developing optimal technological schemes for gold extraction.

New data are presented on the formation conditions and ages of the reduced intrusion-related Au mineralization of the Vetrenskaya area in the Central Kolyma region. The mineralization is predominantly confined to intersections of Late Jurassic minor intrusive bodies and NE-trending fracture systems and is represented by zones of thin quartz veinlets with sericite-quartz halos. The major ore mineral is gold-bearing arsenopyrite (up to 10%), while minor minerals are represented by lellingite, pyrite, chalcopyrite, and pyrrhotite. Microscopic native gold of a low fineness is paragenetically associated with bismuth minerals (bismuthine, native bismuth, andtellurides of Bi and Au), forming microinclusions (1–10 μ) in the arsenopyrite. Isochronous Re-Os age of the goldbearing arsenopyrite is 137–117 Ma, which suggests the mineralization was formed significantly later than the hosting granitoids (147–153 Ma). The reduced intrusionrelated Au ore deposit was formed at shallower depths in comparison with orogenic Au deposits, and at lower temperatures in comparison with rare metal (W, Mo) ore deposits.

Prospecting efforts to located Au mineralization within the Altai-Sayan fold area (ASFA) over previous decades have revealed that Devonian epithermal Au-Ag mineralization is more widespread than previously recognized. The preservation of this type of mineralization in Paleozoic rocks offers new prospects for the exploration of Au-Ag deposits in the underexplored region of Gornaya Shoria. The Kalarskoe epithermal Au-Ag occurrence represents Devonian epithermal mineralization within the Kaburchak cluster, Gornaya Shoria, Russia. This occurrence is confined to zones of argillic alteration that were superimposed on previously formed propylites. The argillic-altered rocks host quartz-sulfide veinlet zones. The mineralization of the Kalarskoe site is characterized by a high abundance of sulfide minerals: commonly, 5%–10%; often, up to 20%; and in some cases, up to 60%–70%. The ore minerals are represented by pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, fahlores, native Au, and electrum, as well as by the sulfosalts Pb, Bi, Ag, Cu, and the tellurides of Au, Ag, and Pb. Based on mineralogical observations, at least four generations of sulfide mineral formations are distinguished within the ore occurrence. The mineralization of the Kalarskoe ore occurrence may be assigned to the intermediate sulfidation (IS) type. The results of the (U,Th)-He dating of pyrite from the pyrite-arsenopyrite massive body (pyr-3 and 4) revealed the protracted history of the mineralization in the intervals from ~399 to ~371 Ma. The obtained results substantially enhance the prospecting models for the exploration of epithermal Au-Ag deposits in the western part of the Altai-Sayan fold area (ASFA).

The paper shows the genetic diversity of the structure and mineral composition of the ores of the Gorevsky Pb-Zn deposit, reveals the main signs of synchronous deposition of ore matter from near-bottom ore-bearing solutions associated with sedimentation processes in the sedimentary basin, considers textural and structural features and mineral associations of ores accompanying various metamorphism processes and postmagmatic processes. A model of the initially primary sedimentary-diagenetic origin of the ores of the Gorevsky Pb-Zn deposit under the conditions of catagenesis and the important role of the processes of redistribution and redeposition of the ore substance by interstitial solutions of the primary ore material is detailed. The study is based on the method of detailed study of the textural and structural features of ores in polished and polished samples. microstructural and mineral features and composition of ore and non-metallic minerals using modern methods of studying the substance. The bulk of the ores of the Gorevsky deposit demonstrate the textural and structural features of synsedimentary deposits, which are simultaneous with the host carbonaceous-micaceous-siliceous-carbonate rocks and retain these main structural features both at the macro and micro levels. The results obtained are compared and analyzed in comparison with other polymetallic deposits in Russia and in other regions of the world

The genetic diversity of the structure and mineral composition of the ores of the Gorevskoe Pb–Zn deposit and the main signs of synchronous ore deposition from near-bottom ore-bearing solutions associated with sedimentation processes in a sedimentary basin were established. The structural and textural features and mineral associations of ores accompanying different metamorphic and postore processes are discussed. The succession of hydrothermal synsedimentation origin of the Gorevskoe Pb–Zn deposit during the direct deposition from near-bottom ore-bearing solutions is considered in more detail. It is suggested that two types of ores, varying in material composition, textural–structural features, morphology, and location reflect the ore-facies zoning of the unified ore-hydrothermal system. The banded Pb–Zn ores belong to the distal parts of the system; brecciated, mainly Pb, ores—to the proximal ones. The important role of the postore processes of regional and dynamothermal metamorphism in the transformation and redistribution of primary sedimentary ores was revealed. This research is based on the detailed study of textural–structural features of ores in polished and ground samples. The modern research methods were applied to examine microtextural and mineral features and composition of ore and nonmetallic minerals. In general, the ores of the Gorevskoe deposit demonstrate the structural and textural features of synsedimentary deposition, synchronous with the formation of host carbonaceous–micaceous–siliceous–carbonate rocks, preserving the main structural features at both the macro and micro levels. The results obtained are compared and analyzed with other polymetallic deposits of Russia and other regions worldwide.

The mineral sequence and LA-ICP-MS study of the trace-elements distribution in chalcogenides (arsenopyrite, pyrite, pyrrhotite, sphalerite, chalcopyrite, ullmannite, tetrahedrite, berthierite, stibnite, gudmundite, jamesonite) of the Olympiada gold ore deposit (Yenisei Ridge, Russia) are presented. The deposit was formed in three stages, separated by tectonic breaks. Early (I) corresponds to the paragenesis of acicular arsenopyrite + pyrite + pyrrhotite. At the stage of base-metal sulfides (II), the deposition of the bulk of chalcopyrite, sphalerite and galena occurred. Mineral associations of these stages determined the gold-arsenic (Au-As) type of ores. The stage of late sulfides (III) is characterized by the paragenesis of antimony minerals (stibnite + berthierite + gudmundite) and corresponds to the gold-antimony (Au-Sb) ore type. Commercial concentrations of gold were formed at the early sulfides stage in the lattice bonded and nanosize mode in acicular arsenopyrite (12.5-1,512 ppm). The progress of the ore deposition process with the formation of late polymetallic and stibnite-berthierite mineralization led to recrystallization of early sulfides (prismatic arsenopyrite Au 36.4 ppm -> dipyramidal arsenopyrite Au 0.5 ppm), remobilization and re-deposition of gold in a native form. Pyrite of the deposit does not contain significant amounts of gold (-0.4 ppm). Silver is absent in early sulfides, but is concentrated in tetrahedrite (348.0-3,811 ppm), jamesonite (0.1-7.7 ppm), berthierite (0.1-2.3 ppm) and stibnite (0.2-2.0 ppm) of the later stage (III). Early sulfides (stage I) are characterized by the As-Au-W-Se-Te geochemical association; polymetallic sulfides (stage II) - by the Cu-Zn-Pb-Cd-In association; and late sulfides (stage III) - by the Sb-CoNi-Te-Bi-Pb-Hg-Ag association.

We present new age constraints for igneous rocks and ore-metasomatic formations of the gold deposits in the Akzhal-Boko-Ashalin ore zone. In terms of their ore formation, these deposits correspond mainly to the orogenic type, which generally reflects specific metallogeny of the West Kalba gold-bearing belt in East Kazakhstan. Gold-quartz veins and mineralized zones of the gold-sulphide formation are confined to fractures feathering regional NW-striking and sublatitudinal faults. Their common features include the following: gold-bearing veinlet-disseminated pyrite-arsenopyrite ores that are localized in carbonaceous-sandy-schist and turbidite strata of different ages; structural-tectonic control of mineralization, numerous dikes of medium-basic compositions in ore-control zones; and the presence of post-orogenic heterochronous granite-granodiorite rocks, although their relation to gold-ore mineralization is not obvious. Igneous rocks of the study area have similar ages in a narrow range from 309.1±4.1 to 298.7±3.2 Ma, which is generally consistent with the previously determined age of granitoid massifs of gold-ore fields in East Kazakhstan. A younger age (292.9±1.3 to 296.7±1.6 Ma) is estimated for felsic rocks of the dyke complex. For the ore mineralization, the 40Ar/39Ar dating of sericite from near-ore metasomatites yields two age intervals, 300.4±3.4 Ma and 279.8±4.3 Ma. A gap between of the ages of the ore mineralization and the igneous rocks is almost 20 Ma, which may indicate that the processes of ore formation in the ore field continued in an impulse-like pattern for at least 20 Ma. Nevertheless, this confirms a relationship between the hydrothermal activity in the study area and the formation and evolution of silicic igneous rocks of the given age interval, which belong to the Kunush complex, according to previous studies. This interpretation is supported by reconstructed tectonic paleostress fields, showing that directions of the main normal stress axes changed during the ore mineralization stage, which is why the ore bodies significantly differ in their orientations. The above-mentioned data are the first age constraints for the study area. Additional age determinations are needed to further improve understanding of the chronology of ore-forming processes. Actually, all the features characterizing the gold mineralization of the Akzhal, Ashalin and Dauba ore fields, including the data on lithology, stratigraphy, structural tectonics, magmatism, isotope geochronology, mineralogy and geochemistry, can be used as criteria when searching for similar ore fields in East Kazakhstan.

In this contribution an overview of oceanic lithosphere, associated ore deposits (sulphides, Fe and Mn oxides, chromitites) and their final destination in ophiolitic rocks are presented. This is followed by a discussion on massive sulphide mineralisation formed at mid-ocean ridges (MOR) and/or supra-subduction zones (SSZ). The geological characteristics and the genesis of the Cu-rich massive sulphide deposits of Cyprus and of the Oman ophiolite are discussed based on an extensive review of the published literature. This is followed by a synopsis of the ophiolitic terranes and associated mineral system in the Urals. We also present an overview of the ophiolitic belts and sutures of the Tethyan orogens, focussing on the podiform chromite deposits that they typically host, with a special focus on the ophiolitic chromitites of Turkey. A final section deals with possible ophiolites of Proterozoic and Archaean ages and, where applicable, associated chromitites. In the concluding remarks a brief note is made of some specific ancient seafloor hydrothermal constructs that have been interpreted as black chimneys in volcanogenic massive sulphide (VMS) deposits now hosted in ophiolitic sequences.

The Sekisovka deposit is located in eastern Kazakhstan, within the Aleysk subzone of Rudny Altai, part of the fragments of an ancient paleo-continent. The deposit is situated within the Sekisovska multi-phased plagiogranite massif of the Late Carboniferous to Permian collision-related Zmeinogorsk complex. The deposit is characterized by gold-sulphide bearing mineralised zones and stockworks with geochemical, metasomatic and mineralogical zoning formed in the magmatic rocks of the Zmeinogorsk complex. NW striking ore-controlling faults, occurrence of fluid-explosive breccias, propylitic and beresite (quartz-sericite-albite-calcite-pyrite) alteration zones are typical. Gold is irregularly distributed and embedded in the cementing mass of the explosive hydrothermal breccias and tends to concentrate at the boundaries between breccias and igneous rocks.

Using high resolution X-ray Computed Tomography (HRXCT), the distribution of gold in acicular arsenopyrite of pyrite-arsenopyrite association of Suzdal (East Kazakhstan) and Olympiada (Yenisei Ridge, Russia) deposits was investigated. The results of micro X-ray tomographic studies allow drawing conclusions about the distribution patterns of gold in sulphides. It can be used to understand the genesis of productive mineral associations, and to develop optimal technological schemes for gold extraction.

Our study of the primary and supergene gold from the Suzdal and Raigorodok deposits in Kazakhstan confirms that during the formation of the regolith in both deposits, invisible and fine gold is released from the host sulfide minerals during their oxidation and destruction; and transported in the form of soluble thiosulfate complexes by near-surface solutions. Upon contact with a geochemical barrier, gold can be deposited as crystalline aggregates. In the deposition of this gold the role of geochemical barriers, such as variations of redox, pH and sorption are very important. Evidence of the past processes of dissolution, redistribution and aggregation of gold in the regolith in these deposits is provided by the following features: 1) The presence of dissolution and growth structures on the surface of newly formed gold; 2) The size of the gold grains increases and newly formed gold microcrystals appear on the surface of the grains; 3) Changes in the composition of native gold (e.g. decrease of silver content); 4) The accumulation of gold in subhorizontal localized layers within the regolith; 5) Gold association with supergene minerals (limonite, jarosite, goethite, Mn-hydroxides, opal, gypsum, calcite, clay minerals, etc.). This detailed study of the specific compositional and structural features of supergene gold and the physicochemical conditions of regolith environment allowed the recognition of the releasing, dissolution, transfer and aggregation processes of gold in the regolith.

—We present the results of quasi-equilibrium directional crystallization of melt of the composition (mol.%): Fe = 31.9, Ni = 1.7, Cu = 16.0, S = 50.4. The produced ingot consisted of the following zones: monosulfide solid solution mss + isocubanite icb (CuFe2S3) + Cu3Fe4S7 // icb + intermediate solid solution iss (~Cu2Fe3S5) + pentlandite // mixture of unidentified decay products of solid solution iss1 // chalcopyrite cp + putoranite put // cp + talnakhite tal + bornite bn. The results of chemical analysis of the ingot were used to construct the distribution curves of the components in the solid and to calculate the change in the composition of sulfide melt (L) during directional crystallization in four zones of the ingot. Phase reactions involving a melt have been established. It is shown that the Cu–Fe–Ni–S system has a two-phase equilibrium region L + icb*. A similar region was earlier found in the ternary Cu–Fe–S system. A crystallization zone of two intermediate solid solutions iss1 and iss2, which were earlier obtained by the common method of isothermal annealing and quenching, has been revealed. The peritectic character of crystallization of the phases icb*, iss1, and iss2 from the melt is established. The results obtained show the fundamental possibility of the existence of a new type of zoning in the formation of copper-nickel low-sulfur sulfide orebodies.

The supergene Au in weathering crusts of both the Suzdal and Raygorodok deposits is characterized by enhanced fineness, grain size, crystallinity, and the appearance of botryoidal aggregates of crystals. In the weathering crust of the Suzdal deposit, the exogenous Au is associated primarily with scorodite and carbonates; for Raygorodok, with chalcocite, bornite, hydrocarbonates and Cu hydrosulfates. The difference in the mineral associations of supergene Au at the deposits is determined by the occurrence of various mineral concentrators of Au in the primary endogenous substrate: arsenopyrite and pyrite at the Suzdal deposit and chalcopyrite with pyrite at the Raygorodok deposit. Due to the much greater mobility of Ag in the supergene zone, the weathering crusts are likely to contain submicron microinclusions of Ag minerals beyond the zones of Au concentration.

In this contribution we examine the compositions of solid solutions and intermetallics of the system Cu-Ag-Au-Hg and the physicochemical conditions of their formation in rodingites from the Zolotaya Gora gold deposit (Southern Urals, Russia). Thermodynamic calculations, modeling the formation of mineral assemblages of rodingite and Cu-Ag-Au-Hg mineralization, were carried out using a "Selektor-C" software package. Two probable models for the genesis of Au-Ag-Cu-Hg solid solutions and Au-Cu intermetallics in rodingites are: 1) hydrothermal; the result of single-stage discharge in open space of deep-sourced gold-bearing fluid with the composition corresponding to rodingite, taking into account its interaction with host serpentinites. 2) metasomatic; deep-seated gold-bearing fluid (W) rising to the surface interacts with early formed rodingite (R) at different ratios (W/R). T and P-conditions of modeling: 450 degrees C, 3 kbar; 350 degrees C, 2 kbar; 250 degrees C, 1 kbar. Results of the calculations on the "hydrothermal" and "metasomatic" models showed different degrees of similarity of natural and theoretical model associations of rodingites. The metasomatic model is better for corresponding to real mineral compositions and mineral paragenesis in the natural Cu-Ag-Au-Hg system observed at the deposit. In this model the chlorite-garnet-pyroxene rodingite is replaced by a chlorite-rich rock with increasing W/R. In this case all gold minerals of Zolotaya Gora deposit (Au-Cu intermetallics and Au-Ag solid solutions) are formed at 250-450 degrees C. Gold-copper solid solution formed at a temperature of 450 degrees C (W/R > 10). Au-Ag-Hg solid solutions and native copper are formed only at 250 degrees C. According to the hydrothermal model native copper and AuCu3 were absent phases, but other Au-Cu intermetallics (AuCu, Au3Cu) precipitate if gold concentration in the solution is higher than 0.5 ppm. Thermodynamic calculations proved the possibility of formation of equilibrium assemblages of rodingite minerals and gold-bearing minerals with the participation of water-chloride complexing and low CO2 fluids. At a temperature < 350 degrees C the main status of gold in solution are Au(HS)(2)(-) and AuHS0, while at higher temperatures it occurs as AuOH0. Formation of Au-Cu intermetallics occurred under the effect of weak-acid hydrothermal solutions (pH = 3.5 divided by 5) with low fugacity of O-2 and S2: log f(O2) = -26 divided by -47, log f(S2) = -8 divided by -20. Both models (hydrothermal and metasomatic) explain the formation of Au-bearing rodingites and can be used for predicting potential gold-bearing rodingite targets.

The Raigorodok stockwork gold-sulfide-quartz deposit is located in the contact zone of a monzogabbro-diorite intrusion belonging to the Stepnyak complex (442 Ma). Two main ore formation stages have been established: early, with disseminated gold-bearing pyrite-chalcopyrite mineralization related to skarn, propylite, and K-feldspar formation, and late, with productive mineralization. The late stage was accompanied by the formation of beresite, sericite, and quartz and comprised two substages: (1) quartz-gold-pyrite-chalcopyrite mineralization and (2) quartz-carbonate-gold-polysulfide mineralization. The 40Ar/39Ar ages of beresites and sericites are 422.9 +/- 4.3 Ma and 416.7 +/- 4.3 Ma, respectively, which is 19-22 Myr younger than the age of the host intrusion. The deposit ores formed stepwise, at temperatures of 112-335 degrees C and fluid salinity of 0.7-21.2 wt.% NaCl equiv. Sulfur for skarns, propylites, beresites, and ores might have been provided by a deep magma chamber, and the carbonaceous shales of the Vendian Sharyk Formation might have been the source of gold. The isotope and geochemical data and the results of fluid inclusion study suggest that Raigorodok is an intrusion-related deposit. At the same time, the deposit has a number of signs of porphyry-epithermal ore-magmatic systems. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Accessory zircon from the polyphase Raygorodok stock (Northern Kazakhstan) has been dated by local U–Pb analysis (SIMS and LA-ICP-MS). This Au-bearing intrusion has been dated to 442–447 Ma, suggesting its emplacement at the very end of the Ordovician and Early Silurian, allowing the stock’s correlation with the Stepnyak Complex of small intrusions. Thus, control of small intrusions of the Stepnyak type over gold mineralization has been corroborated permitting their use as a regional prospecting characteristic.