The geochronological, geochemical, and Sr–Nd isotopic features of the Late Mesozoic volcanic rocks associated with the development of the Nercha Depression in the Eastern Transbaikalia are presented. The structure of the depression involves the sequences of K-rich subalkaline volcanic rocks with content of 55 to 73 wt

The purpose of the research is to compare the evolution of gold ore mineralization in the structures of the Baikal-Patom and Verkhoyansk-Kolyma marginal continental orogenic belts that arose on the passive margin of the Siberian continent in the Neoproterozoic-Paleozoic and Paleozoic-Mesozoic, and hosting the largest gold deposits in Russia. The similarities are noted as they reveal themselves in the characteristics of the mineralization stages, and in the typomorphism of pyrite that is the main mineral of ore formations. The study demonstrated the role of polychronic orogenic events of the Paleozoic and late Mesozoic times, which led to the formation of large fold belts in the development of large-scale gold mineralization of the southern and eastern framing of the Siberian craton. These events caused precious metals to mobilize and redistribute from precious metal-rich stratigraphic horizons as corresponding orogenic plutonometamorphic belts were formed. A comparative analysis of the Paleozoic-Mesozoic and Neoproterozoic-Paleozoic metallogenic profiles of the southern and eastern margins of the Siberian craton demonstrates the influence of the formation processes of orogenic gold mineralization, regardless of the composition of the host strata and mineralization age. General metallogenic characteristics of paleogeodynamic formation settings of noble metal mineralization of the orogenic-type, regardless of its age, can serve as the basis for geological-genetic and forecasting predictions as well as for the development of integrated assessment criteria for their prospects within the regions under investigation.

The geochronological, geochemical and Sr-Nd isotopic features of Late Mesozoic volcanic rocks associated with the development of the Nerchinsk depression in Eastern Transbaikalia are presented. Its structure involves the sequences of high-potassium subalkaline volcanic rocks containing of 55 to 73 wt.% SiO2.40Ar/39Ar isotope dating of bulk rock samples was performed. 40Ar/39Ar dating results from high-K basaltic andesite gives value of 150.8±1.8 Ma and from latite is 131.0±1.6 Ma. Volcanic rocks are characterized by depletion of hydrophobic Ti, Nb and Ta, slightly negative εNd(T) values, but increased in εSr(T), that probably indicates contamination processes of primary melts by crust component. In terms of their geological and geochemical characteristics, the volcanic rocks of the Nerchinsk depression belong to the shoshonite-latite series of the rear part of the Greater Khingan volcanic region, which formed in the subduction setting of a continental active margin.

The article is devoted to the implementation of the methodology for paleovolcanic structure analyzing using 3D visualization of the model of the geological territory structure based on the relief digital model. The approach used made it possible to identify two paleovolcanic apparatuses and their structural elements: cone fragments, explosive domes, porphyritic stocks, ring fault zones with localization of dike belts in them. This, within the framework of the evolution model of porphyry ore systems, made it possible to identify promising areas for prospecting on ore objects of a given type. The procedure was checked on the basis of geochemical survey results. The regular control by the selected structural elements of geochemical fields was shown. The analysis of the spatial position of the selected structural blocks with a certain geochemical characteristic rather well into the evolution model of the porphyry ore systems. In all cases the control of geochemical halos by porphyry stocks is noted, the material rock complexes that are fragments of the zonal stone hat of the porphyry ore object, are quite clearly distinguished. Within the area of work, three ore-magmatic systems can be identified at a low level of erosion shear, potentially accompanied by porphyry-type ore mineralization.

Black shale sequences whose metamorphic grade exceeds the regional greenschist facies are considered by most researchers exclusively as promising for alluvial gold. The paper reports the results of a study of the Ykan deposit, located within the epidote–amphibolite facies zone, and its comparison with previously studied deposits localized in the greenschist-facies alteration zone. It was found that the the main factor of localization of the Ykan gold deposit is its lithological and stratigraphical restriction to the contact between carbonaceous phyllite shales and sandstones of the Aunakit Formation in the hanging wall of the anticline. The ore mineralization of the deposit is represented by a subsequent change of early dia-catagenetic pyrite (py-I, py-II) → metamorphogenic pyrrhotite (po, cpy, asp) → metamorphogenic-metasomatic pyrite–base metal (cpy, asp, py-III, gln, sph, pn, mrc) → postore pyrite (py-IV) assemblages. The ore stage is characterized by the highest possible PT parameters in the early ore metamorphic phase and their decrease at the ore-productive phase. Data on variations in the sulfur and lead isotopic composition indicate that they were transported into the ore fluid from the host metasedimentary sequences of the Aunakit Formation. Comparison of the obtained parameters of the Ykan deposit with the previously studied Sukhoi Log, Golets Vysochaishii, Ugakhan, and Krasnoe deposits confirmed that the Ykan deposit can be attributed to the Sukhoi Log-type deposits.

Black shale deposits whose metamorphic grade exceeds greenschist-facies of regional metamorphosed rocks are considered by most researchers exclusively from the point of view of the potential to mine alluvial gold. The article presents the results of the study on the Ykan deposit located within the epidote-amphibolite facies zone and its comparison with previously studied deposits localized in the greenschist facies alteration zone. It was found that the Ykan gold deposit is lithologically and stratigraphically confined to the contact between carbonaceous phyllite shales and sandstones of the Aunakit Formation in the anticlinal limb, which is one of the main factors controlling ore localization. The ore mineralization of the deposit is represented by the change of the early diathagenetic pyrite (py-I, py-II) → metamorphogenic pyrrhotite (po, cpy, asp) → metamorphogenic-metasomatic pyrite-polymetallic (cpy, asp, py-III, gln, sph, pn, mrc) → post-ore pyrite (py-IV) associations. The ore stage is characterized by the highest possible TP parameters in the early ore metamorphic phase and their decrease in the ore-productive phase. Data on variations in the isotopic composition of sulfur and lead indicate that they were transported into the ore fluid from the host meta-sedimentary strata of the Aunakit Formation. Comparison of the obtained parameters of the Ykan deposit with the previously studied deposits of Sukhoi Log, Golets the Highest, Ugakhan and Krasnyi made it possible to conclude that we are correct in assigning the Ykan deposit to the group of deposits of the Sukholozhsky genetic type.

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.

In addition to the widely known large-volume Sukhoi Log–type gold deposits (e.g., Sukhoi Log, Verninskoe, etc.), the Lena gold province also hosts a series of objects that differ significantly in thte stratigraphic, mineralogical–petrographic, isotopic, and geochemical characteristics, as well as reserves. The Ozherel’e deposit is one of the most famous among these objects. This paper presents the main characteristics including similar and distinct features with Sukhoi Log–type deposits. The results of mineralogical–petrographic and isotopic studies provide no reason to ascribe the Ozherel’e deposit to the Sukhoi Log genetic type.

The Kholodninskoe pyrite-polymetallic deposit (Baikal-Patom plateau, Russia) was discovered in 1968, but the questions of its genesis still remain controversial. It is assumed that the explosive activity of volcanic apparatuses of the southern part of the Baikal-Muya zone as well as underwater exhalations of the scattered spreading zone of the back-arc basin could have most likely influenced the geochemical features of amagmatic deposits of the Bodaibo and Patom zones. To investigate the influence of underwater hydrothermal activity on the geochemical features of Neoproterozoic carbonbearing sediments of the Baikal Mountain region, the Olokit zone, which is a fragment of the spreading zone of the backarc basin, was chosen. According to the geochemical parameters, the sediments of the Itykit and Ondokskaya formations hosting the Kholodninskoye deposit fall into the sedimentation area of DalnyaTaiga period paleobasins. Having compared the development of sulfide mineralization of ore objects of the Bodaibo and Olokit structural-formation zones, the authors suggest the unity of deposit formation processes within the Baikal Mountain area. The presence of framboidal pyrite indicates that the early stages of ore formation of the Kholodninskoe hydrothermal-stratiform polymetallic deposit were synchronous with sedimentation. The source of deposit ore zone enrichment with zinc lead, silver and other elements typical for low- and medium-temperature associations was a hydrothermal solution of the scattered spreading zone of back-arc basins. It is likely that the explosive and exhalation activities of the southern Baikal-Muya zone within the studied region also spread further northward, thus influencing the formation of siderochalcophilic geochemical specialization of amagmatic black shale strata of the Bodaibo and Patom zones.

The possibilities of academic basic metallogenic research in the forecast and search for various types of ore deposits are shown with the example of various academic institutes in the Siberian and Far East federal districts. Using a complex of mineralogical–geochemical and geological–structural methods, prospects for copper and gold in the Upper Indigirka and Kolyma regions and specific areas in Transbaikalia and the Bodaibo district of Irkutsk oblast have been studied. Problems in assessing and developing the mineral resource base of the regions are considered.

Orogenic gold deposits hosted by terrigenous sediments rich in organic matter as well as the role of host sediments and their metamorphic modification in making up such deposits remain highly debatable. So far, the origin of gold deposits in the Lena gold province (Eastern Siberia) mainly hosted by folded and deformed Neoproterozoic complexes of passive-margin sediments, including the giant Sukhoi Log teposit, has been regarded to as postmagmatic (juvenile) or metamorphic, primarily driven by metamorphic devolatilization and redistribution of metals with carbon-rich fluids. Yet, the origin of similar but smaller-scale deposits hosted by the underlying Paleoproterozoic metasediments in the same area is poorly known. The aim of this work was to establish the key processes, which contributed to the formation of gold and associated mineralization of the Chertovo Koryto deposit, through fluid inclusion thermobarometry, spectroscopy and carbon isotopic composition. Fluid inclusions in different types of quartz from the deposit were studied by Raman spectroscopy and cryothermometry. The high P–T parameters (2.8 kbar; 440°C) indicate the initial stage of the ore process. The interaction of metamorphic water-rich fluid with organic matter of the host sediments led to oxidation of water with the release of CO2. The ore precipitation was associated with a sharp pressure decrease (0.3–0.6 kbar) and cooling of the system (320–200°C), which, according to the model, occurred as a result of tectonic deformations and open cavities within the zone of maximum tectonic stress. This pressure reduction zone was the most suitable for the deposition of gold-containing liquid. The overprinting ore-barren stage was characterized by even lower temperatures to (154–87°C) but a wider pressure range (0.1–0.6 kbar). Similar carbon isotopic composition of fluid inclusions in quartz from the early ore stage (δ13C within –16.9 to –17.8%) and the gold precipitation stage (from –16.6 to –17.9%) resembling that of the host Neoproterozoic sediments and previously reported isotopic data for other deposits (Sukhoi Log, Krasniy) suggest the uniform inheritance of metal-bearing C–N–H–S-rich fluid fluid from the host black-shale sediments. Overall, the results suggest that the whole process of sedimentary preconditioning to metamorphic redistribution of gold and other metals in carbon-rich fluids in the Chertovo Koryto deposit was governed primarily by host sediments without any contribution from postmagmatic fluid activity. The data obtained are consistent with the model of orogenic deposits of the Sukhoi Log type and point out the contemporaneous and similar ore-forming processes overprinting both Neoproterozoic and Paleoproterozoic strata.

The results of studying the isotopic, geochemical, and TEDS properties of various generations of pyrite and pyrrhotite from the Ugakhan deposit, Bodaibo district of Irkutsk region, are presented. Differences in the composition of impurities are established. Early pyrites (py-I and py-II) are characterized by the presence of Ni, Co, Cr, and Au admixtures, the electronic type of conductivity, and values of δ34S ~ +5.6‰; py-III is characterized by a decreased amount of Ni, Co, and Cr, and an increased amount of As, the hole type of conductivity, and δ34S from +8.6 to +9.1‰. Post-ore py-IV and py-IVQ are characterized by the smallest admixture concentrations, the electronic type of conductivity, and isotopically lighter sulfur (δ34S ≤ +3.8‰).

This paper provides new data on various pyrite and pyrrhotite generations at the Golets Vysochaishy gold deposit, Bodaibo district, Irkutsk Oblast. These generations are distinguished by morphological, geochemical, and isotope (δ 34 S) features. The established features of pyrite generations reflect the evolution of the Golets Vysochaishy deposit. Each pyrite generation is associated with a certain evolutionary stage of Neoproterozoic rocks in the region: (1) diagenesis (610 Ma), (2) catagenesis (570–520 Ma), (3) metamorphism (~450–430 Ma), and (4) tectono-magmatic activation (330–270 Ma). The 40 Ar/ 39 Ar ages of the third and fourth pyrite generations correspond to those of previously determined gold mineralization and granite magmatism.

On the example of studying the EMF of pyrrhotite, pyrite, and arsenopyrite from gold deposits of the Yana-Kolyma orogenic belt and the Bodaybo synclinorium, using the local determination method for polished sections, it is shown that this parameter for pyrite and arsenopyrite is an important genetic sign of the their origin. Thermoelectric properties of pyrite and arsenopyrite can be used to estimate not only the temperature of their formation but also the temperature parameters of their metamorphism, as well as to characterize the generation of these minerals. The development of local methods for measuring EMF contributes to the possibility of using them for genetic constructions, especially in the study of gold sulfide-impregnated and lode-veinlet mineralization within structures of different-age orogenic belts.

Summary The results of studies of rocks and ores of the Krasny deposit located on the territory of the Baikal-Patomsky upland (north of the Irkutsk region, Russia) are presented. According to the study data, the ore mineralization of the deposit was formed in the conditions of the green-shale facies of metamorphism (200–400° C). The following sequence of mineral formation is recorded: Early framboidal and micrograin pyrite (I and II), with nanoparticles of native gold evenly distributed over the surface, is superimposed with a high-temperature association of ore minerals, including arsenopyrite, pyrrhotite, pyrite-III, native gold, galena, sphalerite, and faded ores, associated with the development of regional metamorphism of the green shale facies. At the post-ore stage, pyrite-IV crystallizes in the quartz-carbonate rim.

The article discusses a novel methodological approach to deciphering the evolution of ore-magmatic systems (OMS), based on the study of geochemical fields associated with different stages of the evolution of the magma chamber, accompanied by ore mineralization. As the material for research, we used the results of geochemical dispersion train surveys within the Kara ore cluster (Eastern Transbaikalia). The analysis of features of the composition and sequence of identification of geochemical fields made it possible to consider in more detail the evolution of the Kara OMS. It was found that we are dealing with a highly eroded rare metal OMS created in two ore formation stages. The first ore formation stage is associated with the evolution of the upper magma chamber (apical part of the Kara–Chacha massif). The main useful component of this OMS was Mo. The second stage is associated with the evolution of the lower magma chamber. This was also rare-metal mineralization; its profiling elements were W and Mo, but the main useful component is Au. It was found that Au is mobile at two evolutionary stages of the late OMS and accumulates when one stage of mineralization overprints the other. Granitoids of the Kara–Chacha massif can be considered the source of Au. No less probable is the hypothesis of its input together with B from the lower levels of the magmatic system, or as part of transmagmatic fluids from without.

Summary The purpose of this work is obtain additional information about the features of fluid inclusions, which makes it possible to cl arify the thermobarochemical parameters of the processes that contributed to the formation of the ore bodies of the Chertovo Koryto deposit. It was carried out inclusions in different types of quartz, their composition, cryotermetric studies, and the data obtained was compared with those already known to determine thermobarogeochemical criteria for the difference between ore and post-ore quartz. Gold-bearing quartz-sulphide veins were formed from a fluid characterized by a temperature of the order of 380–440 ° C, and a salinity of a solution of 4 wt. % NaCl-eq. With the active participation of carbon dioxide. At an early stage, gold was carried by a carbon dioxide fluid formed as a result of carbon decarbonisation during the destruction of the organic matter of the enclosing black shale deposits with their subsequent localization on geochemical barriers. Post-ore quartz veins were formed due to a fluid with a temperature not exceeding 160 °C and salinity of the solution not exceeding 2.0 wt. % NaCl-eq., with a significant decrease in the proportion of carbon dioxide in the gas component and an increase in the proportion of N2 and CH4. The predominant role of CO2, CH4 and N2 in the composition of inclusions is a reflection of the confinement of quartz veins to black shales with a significant content of organic matter.

Pogromnoe deposit of gold-sulfide-quartz formation of stringer-disseminated ore type is formed into shear zone between overthrusts within the block of volcanic-sediment basin along the part of the Mongol-Okhotsk suture. Paragenesises of zonal quartz-albite-mica metasomatic formation correspond to profile of the moderate acid leaching. Near ore metasomatic replacements are dated as 139.5± 1.2 Ma. The absolute age of gold-bearing stockworks formation is 131±1.2 Ma. Ore minerals are arsenopyrite, pyrite, additional sphalerite, chalcopyrite, pyrrohotite, sulfosalts, gersdorffite, rare molybdenite and magnetite. Diffusion coefficient of As was calculated into zonal metacrystals of arsenopyrite and pyrite in ores. The established temperature interval of ore gold sedimentation is based on the physico-chemical modeling with SEJEKTOR software as equal 350–150°C. The ore gold formation was generated by sulfoarsenide hydrothermal solution containing gold as AuAsS2 and H2AuAsS3 complexes for concentration of dissolved S ≥ 0.01 ÷ 0.001 m and As ≥ 0.005 ÷ 0.0005 m respectively.

Summary A typical lithogeochemical survey with bulk analysis of samples is an important component of a complex of prospecting works in open areas, especially in dissected mountain areas with widespread development of thin eluvial-deluvial sediments. typical LGH often leads to the omission of ore objects in semi-closed and especially closed areas. Now, there are a number of methods of geochemical surveying, based not on the hypergene destruction of ore bodies that have emerged on the day surface, but on the diffusion of salt and gas components, including metal vapors, filtration and electrochemical transfer processes. This work presents a comparative evaluation of two geochemical methods MMI and a typical LGH, carried out in the area of ​​Eastern Transbaikalia, characterized by complex landscape-geochemical conditions. As a result of comparing the two methods, we can say that the MMI method confidently identifies secondary scattering halos of Au, Ag, Cu and other indicator elements of the ore association. The intensity of the anomalies localized by the MMI method significantly exceeds the intensity of the anomalies of the elements of the ore association, localized according to the results of a typical lithogeochemical survey. All this makes it possible to judge the higher search efficiency of the MMI method in unfavorable landscape and climatic conditions.

АННОТАЦИЯ: Рассмотрены условия формирования рудообразующего флюида на месторождении Сухой Лог (Восточная Сибирь).Методами физико-химического моделирования установлены соотношения флюид