The study was aimed at dating of Au ores from the Yubileinoe, Irokinda and Uryakh deposits located in the Baikal-Muya fold belt and Pb-Zn ores from the Ozernoe deposit in the Barguzin-Vitim super-terrain (Transbaikalia, Russia). The 40Ar/39Ar ages on pyrite-encapsulated sericite of gold-bearing quartz sampled from veins in the Yubileinoe, Irokinda and Uryakh deposits are 265 ± 33 Ma, 276 ± 13 Ma and 287 ± 7 Ma, respectively. The age of disseminated mineralisation in the Ozernoe deposit is 329 ± 19 Ma. The results of this study and previously published data suggest two stages of ore mineralisation at Transbaikalia: 330–320 Ma for the disseminated mineralisation and 290–270 Ma for the vein mineralisation. Irrespective of the location and the nature of the host rocks, the former and the latter mineralisation are transiently associated with the initial and final stages of the emplacement of the Angara-Vitim granitic batholith. The granitoids provided heat and possibly fluids, while Au, Pb and Zn were sourced from the host rocks. Gold deposits to the north and south of the batholith are generally older and younger, respectively, and were formed by different geological processes.

Среднее по запасам золота месторождение Угахан, расположенное в пределах крупнейшей в России Ленской золоторудной провинции, принадлежит к группе месторождений «сухоложского» генетического типа. Представлены результаты петрографического, минералогического и изотопно-геохимического изучения золоторудной минерализации месторождения. Разработана схема последовательности минералообразования на месторождении, которая включает пять стадий: 1) в течение ранней (синдиагенетической) стадии происходило образование фрамбоидного пирита-1, обогащенного Au, Ni, Co, As; 2) на стадии катагенетического преобразования рудоносных осадков происходила перекристаллизация раннего пирита-1 и кристаллизация пирита-2, также обладающего повышенными содержаниями Au, Ni, Co, As; 3) формирование в рудах пирротина происходило на стадии прогрессивного метаморфизма из водно-углекислого флюида с повышенным содержанием H2S; 4) собственно рудная стадия, представленная на месторождении минеральной ассоциацией пирит-3, галенит, сфалерит, халькопирит, самородное золото, коррелирует с развитием в регионе регрессивного метаморфизма; 5) кристаллизация пострудного идиоморфного крупного пирита-4. Комплекс геохимических и изотопных (δ34S и Pb-Pb) данных позволяет исключить привнос минералообразующих компонентов при гидротермально-метасоматическом преобразовании рудовмещающих пород из дополнительного (внешнего) источника. Значения δ34S, варьирующие для ранних морфотипов пирита в рудах месторождения в относительно узких диапазонах от +5.7 до +9.1 ‰, близки к величинам δ34S (+4.2… +16.4 ‰) безрудных пород бужуихтинской свиты. Pb-Pb изотопные характеристики, а также установленные закономерности в вариациях изотопного состава Pb для золоторудной минерализации указывают на преимущественное поступление элемента из неопротерозойских метаосадочных толщ. Минералогические и геохимические особенности месторождения Угахан согласуются с представлениями о метаморфогенном происхождении золоторудных месторождений «сухоложского» типа, что подтверждает перспективность пород бужуихтинской свиты на обнаружение новых золоторудных объектов в регионе. The Ugakhan gold ore deposit is located within the Lena gold ore province, the largest one in Russia. It belongs to the group of deposits of the Sukhoi Log genetic type. We present results of petrological, mineralogical, and isotope-geochemical study of gold mineralization at the deposit. A scheme of the sequence of mineral formation at the deposit has been developed, which includes five stages: (1) the early (syndiagenetic) stage, when framboid pyrite I enriched in Au, Ni, Co, and As formed; 2) the stage of catagenesis of ore-bearing sediments, with recrystallization of early pyrite I and crystallization of pyrite II, also with elevated Au, Ni, Co, and As contents; (3) the stage of progressive metamorphism, with the formation of ore pyrrhotite from a water–CO2 fluid with a high content of H2S; (4) the ore formation stage, marked by an assemblage of pyrite III, galena, sphalerite, chalcopyrite, and native gold at the deposit, which was synchronous with regressive metamorphism in the region; (5) crystallization of post-ore euhedral coarse-grained pyrite IV. The geochemical and isotope (δ34S and Pb–Pb) data rule out the input of mineral-forming components from an additional (external) source during the hydrothermal-metasomatic transformation of ore-bearing rocks. The δ34S values in the early morphotypes of pyrite in the deposit ores vary from +5.7 to +9.1‰ and are close to the δ34S values of the barren rocks of the Buzhuikhta Formation (+4.2 to +16.4‰). The Pb–Pb isotope characteristics and regularities of variations in Pb isotope composition established for gold mineralization indicate a predominant inflow of lead from Neoproterozoic metasedimentary strata. The mineral and geochemical specifics of the Ugakhan deposit are consistent with the concept of the metamorphic origin of gold deposits of the Sukhoi Log type, which confirms that the rocks of the Buzhuikhta Formation are promising for new gold ore objects.

Ugakhan gold ore deposit is located within the Lena gold ore province, the largest one in Russia. It belongs to the group of deposits of the Sukhoi Log genetic type. We present results of petrological, mineralogical, and isotope-geochemical study of gold mineralization at the deposit. A scheme of the sequence of mineral formation at the deposit has been developed, which includes five stages: (1) the early (syndiagenetic) stage, when framboid pyrite I enriched in Au, Ni, Co, and As formed; 2) the stage of catagenesis of ore -bearing sediments, with recrystallization of early pyrite I and crystallization of pyrite II, also with elevated Au, Ni, Co, and As contents; (3) the stage of progressive metamorphism, with the formation of ore pyrrhotite from a water-CO2 fluid with a high content of H2S; (4) the ore formation stage, marked by an assemblage of pyrite III, galena, sphalerite, chalcopyrite, and native gold at the deposit, which was synchronous with regressive metamorphism in the region; (5) crystallization of post -ore euhedral coarse -grained pyrite IV. The geochemical and isotope (delta 34S and Pb-Pb) data rule out the input of mineral -forming components from an additional (external) source during the hydrothermal-metasomatic transformation of ore -bearing rocks. The delta 34S values in the early morphotypes of pyrite in the deposit ores vary from +5.7 to +9.1%o and are close to the delta 34S values of the barren rocks of the Buzhuikhta Formation (+4.2 to +16.4%o). The Pb-Pb isotope characteristics and regularities of variations in Pb isotope composition established for gold mineralization indicate a predominant inflow of lead from Neoproterozoic metasedimentary strata. The mineral and geochemical specifics of the Ugakhan deposit are consistent with the concept of the metamorphic origin of gold deposits of the Sukhoi Log type, which confirms that the rocks of the Buzhuikhta Formation are promising for new gold ore objects.

Orogenic gold deposits associated with metamorphic orogenic fold belts are the major sources of gold currently being mined in the world. The role of metamorphic and magmatic processes and crustal and mantle sources in the gold mineralization genesis are of much debate. The formation of orogenic gold deposit in Precambrian metamorphic belts is usually described by а metamorphic devolatilization model. Some of the orogenic deposits, however, are proved to be much younger than the peak of regional metamorphism. Geological features of these deposits suggest close relation of their gold-forming systems with deeper lithospheric processes. The Baikal-Muya Belt (BMB) of the Central Asian Orogenic Belt is an example of such a region. The BMB comprises ca. 20 orogenic gold deposits and occurrences of Permian age. Gold mineralization at the deposits is usually located in quartz lodes situated in the vicinity of fault zones in association with Late Paleozoic sub-alkaline and alkaline basic and acid intrusions. Using high-precision (0.02–0.03

We provide an extended Sr-87/Sr-86 database for the water of Lake Baikal collected along the lake and within its bays at a depth range from the surface down to 1366 m, the major tributary rivers, lake animals, and atmospheric precipitation. The water of open Lake Baikal, the Little Sea (Maloe More) Strait, and large bays are characterized by a uniform Sr-87/Sr-86 = 0.7086266 +/- 0.0000045 (n = 44, uncertainty at 95% confidence interval). Major volumetric contributors of water to the lake (the eastern rivers and precipitation) are only slightly different from the lake value in terms of Sr-87/Sr-86. In the western rivers, Sr-87/Sr-86 is much higher, but due to their small incoming volume, their contribution is rapidly diluted by the water currents of the lake. The exception is water with high Sr-87/Sr-86 from isolated Mukhor Bay at the inland end of the Little Sea Strait and water above the underwater discharge of hydrothermal springs. Benthic and pelagic Lake Baikal animals have Sr-87/Sr-86 similar to the values of the open lake, supporting lake water homogenization. The modelled budget of Sr suggests that 86 +/- 14% of input Sr is stored in the waters of Lake Baikal. In other words, according to the estimations some Sr (from 0 to 28%) may be precipitated at the lake bottom by chemical and biochemical processes.

The paper presents the results of the detailed structural analysis and 40Ar/39Ar dating of the deformations in the Golets Vysochaishii deposit area. The geological and structural studies showed the folded-deformation sequence from large lying folds through axial-plane cleavage formation and cleavage to quartz-filled fractures. The 40Ar/39Ar dating of syntectonic sericite yielded the ages of two Hercynian tectonic impulses – 340 and 320 Ma. This stage is characterized by the earlier-known successive complication of the Early Paleozoic fold-nappe structure of the area. Analysis has been made on four samples taken from different sites and characterized by different sets of deformational structures. The 40Ar/39Ar age of 340 Ma reflects the formation of small-size folds as a result of interlayer sliding and sliding along the cleavage axial planes. The 40Ar/39Ar age of 320 Ma reflects the formation of discretely manifested crenulation cleavage and low-Au, low-sulfidation quartz veins oriented obliquely to the elements of bedding and axial-plane cleavage.

The paper presents the results of the detailed structural analysis and 40Ar/39Ar dating of the deformations in the Golets Vysochaishii deposit area. The geological and structural studies showed the folded-deformation sequence from large lying folds through axial-plane cleavage formation and cleavage to quartz-filled fractures. The 40Ar/39Ar dating of syntectonic sericite yielded the ages of two Hercynian tectonic impulses – 340 and 320 Ma. This stage is characterized by the earlier-known successive complication of the Early Paleozoic fold-nappe structure of the area. Analysis has been made on four samples taken from different sites and characterized by different sets of deformational structures. The 40Ar/39Ar age of 340 Ma reflects the formation of small-size folds as a result of interlayer sliding and sliding along the cleavage axial planes. The 40Ar/39Ar age of 320 Ma reflects the formation of discretely manifested crenulation cleavage and low-Au, low-sulfidation quartz veins oriented obliquely to the elements of bedding and axial-plane cleavage.

The paper presents the results of the detailed structural analysis and Ar-40/Ar-39 dating of the deformations in the Golets Vysochaishii deposit area. The geological and structural studies showed the folded-deformation sequence from large lying folds through axial-plane cleavage formation and cleavage to quartz-filled fractures. The Ar-40/Ar-39 dating of syntectonic sericite yielded the ages of two Hercynian tectonic impulses - 340 and 320 Ma. This stage is characterized by the earlier-known successive complication of the Early Paleozoic fold-nappe structure of the area. Analysis has been made on four samples taken from different sites and characterized by different sets of deformational structures. The Ar-40/Ar-39 age of 340 Ma reflects the formation of small-size folds as a result of interlayer sliding and sliding along the cleavage axial planes. The Ar-40/Ar-39 age of 320 Ma reflects the formation of discretely manifested crenulation cleavage and low-Au, low-sulfidation quartz veins oriented obliquely to the elements of bedding and axial-plane cleavage.

The article describes the fold-thrust structure of the Golets Vysochaishy deposit located at the Baikal-Patom Upland in the Marakan-Tunguska megasyncline. The latter is composed of terrigenous-carbonate carbonaceous rocks metamorphosed in greenschist facies conditions. The deposit is detected in the hanging wing of the asymmetric Kamenskaya anticline. In a cross section, the anticline is an S-shaped structure extending in the latitudinal direction. The main feature of the Golets Vysochaishy deposit is the development of interlayer sulfidization zones (pyrite, pyrrhotite), including gold-bearing ones. Its gold-ore zones tend to occur in layered areas of interlayer sliding in the rocks of the Khomolkhinskaya suite.Four structural markers revealed within the deposit area are indicative of repeated deformation processes: (1) sublatitudinal folding, cleavage of the axial surface and its subsequent transformation into schistosity; (2) crenulation cleavage; (3) interlayer sliding and rock breakdown with interlayer drag folds, parallel microfractures and polished slickensides; (4) large quartz veins and veinlets that cross cut the main structural elements in plan.

—We consider the geologic structure of the Nerunda gold ore field located in the Nerunda–Mama ore district in northern Transbaikalia. Gold–quartz low-sulfide formation and ore-bearing carbonate-terrigenous strata and intrusive complexes are briefly described. An ore complex of beresite–listvenite metasomatites hosting carbonate–quartz veins and vein–veinlet zones is characterized. Two stages of ore formation have been recognized. Anomalous geochemical associations and the composition of ore mineralization typical of these stages have been established. Mineralogical and geochemical studies of gold-bearing metasomatites of the Nerunda ore field were carried out. The known geochemical and mineralogical search criteria used for the assessment of the erosion zone level of gold deposits were applied to the geologic conditions of the Nerunda ore field and the Nerunda–Mama gold ore district as a whole. The emphasis was made on the express assessment of the erosion zone level at the early stage of prospecting. We draw a conclusion about the gold potential of the poorly studied ore objects at depth and give guidelines for the following geological prospecting.

The Mukodek gold field is located in the Yana zone of the Baikal-Muya fold belt (northern Transbaikalia). Its orebodies are gold-bearing metasomatites confined to the fault of NE strike. It is shown that pre-ore faults played a crucial role in the spatial localization of the orebodies, as they favored the concentration of ore-bearing fluids. Results of geological and structural studies, along with available geochronological data (40Ar-39Ar dates for micas in gold-bearing pyrite), testify to ore-forming processes in the ore field during two Late Paleozoic stages. Early gold-bearing metasomatites of sericite-chlorite-albite-ankerite-quartz composition formed at 320 Ma, and late gold-bearing vein metasomatites of ankerite(calcite)-quartz composition originated at 285 Ma. A Pb-Pb isotope study of gold mineralization has shown that ore lead was supplied into the mineral-forming system mainly from a mantle source, most likely, regional Neoproterozoic igneous rocks. According to Sm-Nd isotope data, these rocks formed with the participation of a material of mantle genesis. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The Mukodek gold field is discussed as an example proving that dynamometamorphism is a major factor in the formation of gold deposits in the Abchad fault zone. This deposit belongs to the gold‐silver‐ore zones of mylonitization and schistosity. The ore source is related to the original host rocks with an increased geochemical background concentration of Au. Due to dynamometamorphism processes, gold particles are abundant and mostly enlarged. From the primary rocks, the dynamometamorphites inherit a positive correlation between the number of particles and the concentrations of gold. The dynamometamorphic complex of the ore field developed in two stages, as a minimum. At the early stage (321.0±1.9 Ma), the host rocks were mechanochemically deformed and transformed into the gold‐ bearing mineralized dynamometamorphites containing sericite, chlorite, ankerite, albite, and quartz. In the second stage (280±15 Ma), the albite‐dolomite‐quartz ore veins were formed. Such veins have industrial gold contents.

We have studied the material composition of ore microparticles extracted from gold concentrates of operating quartz vein No. 30 located in the Irokinda deposit, Western Transbaikalia. We consider the origin of such microparticles in connection with our observation data and the previously published structural and geological features revealed in formation of the ore field, as well as tectonophysical conditions of formation of many gold-bearing quartz veins, including vein No. 30.Gold-quartz veins, located in the allochthonous plate thrusted onto the Kelyano-Irokinda belt (Fig. 1), infill the NE-striking fault zones. E.A. Namolov conducted the tectonophysical analysis of the “elementary fracture – ore-bearing suture/joint” system, which provided a genetic explanation of the morphology of ore quartz veins (including vein No. 30) and conditions for formation of their host fault zones. Ore-bearing fractures are combinations of shear and cleavage cracks that occur in case of certain positions of the strain ellipsoid in conditions of horizontal compression. Due to repeated intra-mineralization displacements, the texture of the ores is strappy, and the quartz matrix of the veins contains numerous inclusions of host rocks.The spherical particles have zonal structures and consist of metal nodes and external continuous or discontinuous shells, which thickness ranges from 10 to 400 microns (Fig. 2, Fig. 3). The nodes are composed mainly of native Fe with admixtures of Fe, Mn, Al (Table), the contents of which are typically less than 1.0–1.5 wt %.Characteristic features of the mineral composition of shells of the spheroidal microparticles:– The widespread graphite matrix consisting of minerals of different classes, except for native;– Pyrite in the group of ore oxides of Fe, Mn, Cr, Ti;– A large group of carbonate minerals;– Feldspars and natrosilite among silicates;– The mineral with CaBr2 composition;– Mono-mineral quartz rims.The consequence of metamorphism, i.e. deformational or mechano-chemical transformations of rocks in Irokinda, as well as the autochthon (the rock bed of the Kelyano-Irokinda belt), is the gas-water (‘hydrothermal’) system capable of forming the spherical ore particles with low-temperature mineral rims.The main feature of the structure of the spherical microparticles in Irokinda is a sharp contrast of the crystallization conditions of the metal nodes and their rims. Similar conditions leading to formation of contrasting mineral associations, that are similar in compositions to the discussed spherules, are characteristic of the gas-water-lithoclastitic and gas-water stages of mud volcanoes. For these stages, we suggest the cavitation mechanism of formation of spherical metal particles of Fe, Fe–Cr and other compositions, which is accompanied by combustion (pyrogenic melt) and pyrolysis of hydrocarbon components of the fluid. This mechanism, with the exception of the origin of the melt (in this case, of the friction type) seems to most closely correspond to the actual data. The spheroids are likely to have formed in the pre-ore stage of formation of the quartz veins.The high-temperature metal spherical microparticles revealed in our study can be regarded as specific indicators showing conditions in which the ore-forming system of the dynamo-metamorphic type was functioning to produce gold mineralization on the Irokinda deposit. The structure and composition of these microparticles differ from those of the microspherules from other gold deposits in Transbaikalia (black shale formation in Sukhoi Log, and low–sulphide gold–quartz ore formation in Pervenets), which also belong to the dynamogenic genetic type. However, the ore-forming systems of the compared deposits have two common factors that contribute to formation of spherical microparticles – high tectonic activity manifested by repeated (impulse-type) tectonic movements, and the associated unstable pressure conditions. The consequence of the latter is heterogenization of the gas-water fluid, which, in turn, leads to the cavitation and froth flotation mechanisms.

Introduction . The Lena gold province is one of the largest known gold resources in the world. The history of its exploration is long, but the genesis of gold mineralization hosted in black shales in the Bodaibo synclinorium still remains unclear. The studies face the challenge of discovering sources for the useful component and mechanisms of its redistribution and concentration. This study aims to clarify the time sequence of the ore mineralization in the Chertovo Koryto deposit on the basis of detailed mineralogical and geochemical characteristics of the ore, wallrock metasomatites and the Early Proterozoic host black shales, and to assess the applicability of the Sukhoi Log model for clarifying the Chertovo Koryto origin. Geological setting . The Lena gold province is located in the junction area of the Siberian platform and the Baikal mountain region (Fig. 1). The main element of its geological structure is the Chuya-Tonoda-Nechera anticline. Its axial segment is marked by horsts composed of the Early Proterozoic rocks with abundant granitoid massifs. The Chertovo Koryto deposit is located within the Kevakta ore complex at the Tonoda uplift, the largest tectonically disturbed block between the Kevakta and Amandrak granitoids massifs. The 150 m thick and 1.5 km long ore zone of the Chertovo Koryto deposit is confined to the hanging wall of the fold-fault zone feathering the Amandrak deep fault (Fig. 2). Composition . In the ore zone, rocks of the Mikhailovsk Formation include carbonaceous shales of the feldspar-chlorite-sericite-quartz composition with nest-shaped ore accumulations of the pyrite-quartz composition and quartz veinlets. In our study, we distinguish five mineral associations resulting from heterochronous processes that sequentially replaced each other: - The earliest association related with the quartz-muscovite-sericite metasomatism and the removal of REE and other elements from the rocks and their partial redeposition; - Metamorphic sulphidization presented by scattered impregnations of pyrrhotite, as evidenced by small lenses of pyrrhotite, which are considerably elongated (axes up to 0.7 cm long) along the foliation planes (Figs 3, a , b ); - Ore mineralization represented by a superimposed hydrothermal gold association with arsenopyrite (Fig. 3, d ); - Late chalcophilic mineralization formed at the final stage of hydrothermal-metasomatic process (Figs 3, e , f ); - Post-ore silification. Geochemical characteristics . The geochemical study of rocks and ores from the Chertovo Koryto deposit show that the rocks of the Mikhailovsk Formation are characterized by higher contents of rock-forming elements, such as of Al 2 O 3 , Fe 2 O 3total , MgO, K 2 O, and P 2 O 5 , in comparison to the PAAS standards [ Condie, 1993 ] and the black shale standard composition (SChS-1) [ Petrov et al., 2004 ]. A characteristic feature of the ore zone is that the contents of practically all the oxides, except SiO 2, tend to decrease (Table 1). The distribution of rare elements repeats the pattern established for major elements. The least metamorphosed rocks of the Mikhailovsk Formation have higher contents (up to three times) of Cu, Mo, Ba, W, As, Pb relative to the values in the PAAS and SChS-1 standards. In the ore zone, the contents of almost all rare elements are considerably reduced (Table 2). The contents of elements in the siderophile group (Co, Ni) are clearly correlated with the ore processes and increased more than twice in the area of metamorphic changes. Samples with gold-ore grade contents show the highest concentrations of Co and Ni. Conclusion. In our opinion, the Chertovo Koryto deposit was formed in five stages, the first two of which were pre-ore, with ore preparation, and probably considerably distant in time from the main ore-generating event. The staged formation of the Chertovo Koryto deposit correlates with the basic stages in the tectono-metamorphic history of the study region and is consistent with the model showing the formation of Sukhoi Log-type deposits [ Nemerov, 1989; Buryak, Khmelevskaya, 1997; Large et al., 2007 ].

The 40Ar/39Ar dating method on pyrite-encapsulated sericite, known as the ‘no fool's clock’, is promising for bracketing gold ore formation processes. Using this dating technique we show that gold mineralization at the Mukodek gold field, Siberia, Russia took place in the Late Paleozoic at the time of emplacement of the Angara–Vitim granitoid magmas. Late Paleozoic magmatism, however, was not the source of gold. It was the source of heat and fluids that preconcentrated already available gold within alteration zones and hydrothermal veins.

The Paleoproterozoic sedimentary and volcanic-sedimentary sequences of the Urik-Iya Graben at southern flank of the Siberian Craton have been studied. Based on the isotopic U-Pb LA-ICP-MS dating of detrital zircons contained in the clastic fraction of the studied rocks, three main extension stages accompanied by sedimentation are recognized; each stage is characterized by certain types of sediments and conditions of their accumulation. The oldest rocks (Ingashi Formation) mark early extension events (∼1.91−1.87 Ga), which were caused by collapse of the orogen that arose due to collision of the Biryusa and Sharyzhalgai blocks. The basin formed as a result of extension is regarded as an aulacogen. Granitoids of the Sayan Complex were emplaced in the cratonic lithosphere at the final stage of the first extension stage. The second stage of extension started ∼1.75 Ga ago as a response to the effect of the inferred mantle plume on the lithosphere of the Siberian Craton. It was accompanied by deposition of the Daldarma Formation. Stress inversion took place at the final stage (∼1.70 Ga), and an intracratonic fold zone arose at the place of the paleoaulacogen. The third extension stage (1.65−1.60 Ga) corresponds to the time of molasse accumulation in pull-apart basins (Yermosokha Formation). The final stage of rifting was marked by emplacement of granitoids (Chernaya Zima Complex, 1.53 Ga), which completed the active tectonic events in the region. Afterward, the Urik-Iya Graben transformed into a stable intracratonic domain. The available data allow us to revise the tectonic history of the Urik-Iya Graben. In light of new evidence, this structural unit may be interpreted as a long-evolving paleoaulacogen. The series of revealed sedimentation settings reflects the formation of a consolidated continental lithosphere at the southern flank of the Siberian Craton.

Metamorphosed volcanic rocks of the Ushmukan suite were studied in the Mukodek gold-ore field located in the Baikal-Muya belt in the Northern Baikal area, Russia. The Ushmukan suite shows interleaving of ortoschists which compositions are widely variable. Basalt-andesite-dacite series of normal alkalinity are the substrate of the studied metavolcanic rocks. Based on the set of geochemical characteristics, it is concluded that the rocks were formed in suprasubduction geodynamic conditions corresponding to a mature island arc. The proximity of the geological locations and the similarity of the geochemical characteristics of the volcanic rocks of the Ushmukan suite and rocks of the Kelyan suite (Neoproterozoic, 823 Ma), which have similar compositions, give grounds to consider these two rock suites as age peers. Specific features of gold distribution through the Mukodek gold-ore field are analyzed. Industrial gold contents are recorded only in berezite-listvenite metasomatic rocks of the gold-quartz-sulfide formation which were formed on metavolcanic rocks of the Ushmukan suite. It is concluded that the volcanic rocks, which are specific of the island-arc setting, could be a source of gold for deposits in the Mukodek gold-ore field.