PGE mineralization of dunite-wehrlite massifs at the Gutara-Uda interfluve, Eastern Sayan

The Pt-Pd and Au-Ag mineralization hosted in both wehrlite without visible links to sulfide mineralization (dispersed assemblage of the Tartai massif) and disseminated Cu-Ni sulfide ore (ore assemblage of the Ognit massif) was found in dunite-wehrlite massifs localized in the fold framework of the Siberian Craton. The Pt minerals in both assemblages comprise sperrylite (PtAs₂) and secondary Pt-Fe-Ni alloys in the Ognit massif and Pt-Fe-Cu and Pt-Cu alloys in the Tartai massif. The Pd minerals are widespread in the ore assemblages as compounds with Te, Sb, and Bi, whereas in the dispersed assemblage Pd is concentrated primarily in Pd-Cu-Sb compounds. Both assemblages are characterized by similar substitution of sperrylite with orcelite (Ni_{5 ? x}As₂) and then with secondary Pt-Fe-Ni or Pt-Fe-Cu and Pt-Cu alloys; the occurrence of Au-Ag alloys with prevalence of Ag over Au; and replacement of them with auricupride (Cu₃Au) at the late stage. Sperrylite in both assemblages contains Ir impurities, while the Pd minerals contain Cu and Ni admixtures, which are typical of mineral assemblages related to the ultramafic intrusions with nickel specialization. PGM were formed under a low sulfur fugacity and high As, Bi, and Sb activities. The postmagmatic fluids affected the primary mineral assemblages under reductive conditions, and this effect resulted in replacement of sperrylite with Ni arsenide (orcelite) and Pt-Fe-Ni and Pt-Fe-Cu alloys; Ni and Cu sulfides were replaced with awaruite and native copper.     

昆仑山垭口地区第四纪冰川遗迹及冰期演化

基于成因-环境原则和多指标综合原则,依据昆仑山垭口地区的冰川地貌特征、冰碛物特征和孢粉信息,重建了该地区古环境演化历史。其中,冰碛物中的石英砂扫描电镜结果揭示了冰川、流水、风等地质营力对冰碛物的影响,孢粉分析结果在一定程度上可以恢复当时的植被类型。根据垭口冰碛ESR年龄280 ka B.P.和冰碛剖面特征,将其时代暂定为300~260 ka B.P.;根据纳赤台地区的冰川地貌和沉积物特征,确定纳赤台后沟沉积为冰水扇沉积,纳赤台冰期为600~400 ka B.P.;根据玉虚峰U形谷两道侧碛垄的ESR和OSL年龄将其时代暂定为末次冰期早-中期。结合前人的研究成果,将昆仑山垭口地区的冰期序列厘定为望昆冰期（700~500 ka B.P.）、纳赤台冰期（600~400 ka B.P.）、垭口冰期（300~260 ka B.P.）、玉虚峰冰期（115~44 ka B.P.）、本头山冰期（20~13 ka B.P.）。     

Structure and composition of debris flows in the Eastern Sayan

Based on the catastrophic June 28, 2014, Arshan debris flows in the Eastern Sayan Mountains, the structure and lithological composition of the debris are studied and a debris flow defense system is proposed. Among five debris flows in this region, two flows 4.1 and 5.6 km long are scrutinized. The grain size and mineral composition of fans and mudflows, as well as their evolution scenario are studied. The paper also examines the engineering-geological features of debris flow sediments and their textural-structural and physical alterations in the course of settling. Specific attention is devoted to the lithological and climatic constraints of debris flows. It is noted that sediments of recent mudflows are characterized by a high underconsolidation and deliquescence, promoting the formation of high-plastic and fluidal zones that can migrate actively. The approach proposed for debris flow defense measures lies in the construction of flow diversion dams designed for orienting the debris flows toward the “debris dump site.”     

Bacterial communities in Hoito Gol hot spring,Eastern Sayan,and the ecologic-geological conditions of their development

Hoito Gol hot spring of weakly mineralized warm (36–29°C) neutral and partly alkaline nitrogen-carbon dioxide waters belongs to the hydrogeological structure of the actively water-flooded fault marked by the Sentsy River at the southwestern termination of the Baikal rift system. The spatiotemporal evolution of the major parameters of the underground aqueous ecosystem of this spring is controlled mainly by geological and geodynamic factors, whereas the parameters of the surface system are determined mostly by bacterial factors. Variations in these factors are correlated with changes in the composition, structure, and spatial distribution of the bacterial communities.     

Petrogeochemical features of metaterrigenous rocks of the Kan Block of the Eastern Sayan: Reconstructions of provenances and sedimentation conditions

Chemical and isotopic compositions of Proterozoic metaterrigenous rocks of the Kan Block (Central and Idar terranes) of the Eastern Sayan are studied. The results of the reconstruction of their provenances and sedimentation conditions are presented. The rocks under investigation correspond by their petrogeochemical composition to graywackes of island arcs. The combination of geochemical and isotope data shows that sediments of the Central terrane had a local provenance represented by Early Proterozoic subduction magmatic complexes, whereas sediments of the Idar terrane formed probably as the result of mixing of terrigenous material related to the destruction of rocks of Meso-Neoproterozoic oceanic and more ancient continental crust.     

Morphotectonic analysis of Pliocene-Quaternary deformations in the southeast of the Eastern Sayan

The paper is concerned with the kinematics of the major faults, their pattern, and the time of occurrence of compression and extension deformations in the southeast of the Eastern Sayan. The geometry of the mountain ranges and the kinematics of the major faults exhibit northeast-oriented compression responsible for the current processes of relief formation, which corresponds to the direction of the vector of deformations associated with the Indo-Asian collision. The results obtained thus far may be indicative of the remote influence of collision on the orogenic activity and transpressional deformations in the Eastern Sayan since the end of the Miocene. Morphotectonic analysis has shown that the areas of Quaternary extension-related deformations in the Eastern Sayan are not a response to active rifting in the Baikal Rift Zone. The position and geometry of the subsided blocks and magma ruptures point to the fact that they form locally as extension structural elements near the strike-slip faults. The strike-slip and thrust faults are widespread and play the leading role in the development of the southeastern part of the Eastern Sayan.     

New Ore Minerals from the Kingash Ultramafic Massif,Northwestern Eastern Sayan

The paper discusses earlier poorly studied mineralized rocks of the Kingash ultramafic complex in the Kan Block of the Eastern Sayan, including the large Cu–Ni–PGE deposit of the same name. Despite many researchers' increased interest in the Kingash massif, a number of questions related to the petrology, formation mechanism, and localization of Cu–Ni–PGE ore remain controversial. Along with already known ore minerals, we have identified and described a number of new mineral species: argentite, Fe-enriched sperrylite, a bismuth variety of merenskyite, gersdorffite, cobaltite, and thorianite. The ore minerals are distinguished by a higher relative amount of Fe, and this makes the Kingash deposits close to other Paleoproterozoic Cu–Ni deposits, e.g., the Jinchuan in China, Pechenga in Russia, Ungava in Canada, Mt. Scholl in Australia, etc.     

Composition and genesis of the Konevinsky gold deposit,Eastern Sayan,Russia

The Konevinsky gold deposit in southeast Eastern Sayan is distinguished from most known deposits in this region (Zun-Kholba, etc.) by the geological setting and composition of mineralization. To elucidate the cause of the peculiar mineralization, we have studied the composition, formation conditions, and origin of this deposit, which is related to the Ordovician granitoid pluton 445–441 Ma in age cut by intermediate and basic dikes spatially associated with metavolcanic rocks of the Devonian–Carboniferous Ilei Sequence. Four mineral assemblages are recognized: (1) quartz–pyrite–molybdenite, (2) quartz–gold–pyrite, (3) gold–polysulfide, and (4) telluride. Certain indications show that the ore was formed as a result of the superposition of two distinct mineral assemblages differing in age. The first stage dated at ~440 Ma is related to intrusions generating Cu–Mo–Au porphyry mineralization and gold–polysulfide veins. The second stage is controlled by dikes pertaining to the Devonian–Carboniferous volcanic–plutonic association. The second stage is characterized by gain of Hg and Te and formation of gold–mercury–telluride paragenesis.     

Mass transfer at the contact of high-Al metapelites and metabasites: An example of the high-temperature Sharyzhalgai Complex,Eastern Sayan

Relations of metapelites and metabasites were examined in Archean rocks, and effective diffusion coefficients were determined for components in these rocks, along with the scale of mass transfer of components in them. Concentration profiles and diffusion coefficients of the anorthite end member in plagioclase and Ca in garnet were used to evaluate the duration of the metamorphic processes.     

New Data on the Age of Gold Mineralization in the Southeastern Part of Eastern Sayan

This article presents new data on the age of the largest gold deposits in the southeastern part of Eastern Sayan. The dates have been obtained by Ar–Ar analysis of micas occurring in gold-bearing quartz veins and mineralized zones. The obtained Ar–Ar ages of fuchsite and sericite from the tectonized and mineralized zones of the Zun–Holba deposit (ore body Severnoye-3), range within 353.9–386.4 Ma; a similar result of 352.9 Ma was yielded by Ar–Ar dating of Cr–muscovite from mylonitized listvenite in the veins of the periphery of the Zun–Ospa gold deposit. However, muscovite from the ore-bearing quartz vein of the Pioneer gold–quartz deposit, located near Zun–Holba, has been dated to 421.9 Ma. The obtained new data on isotopic age of the gold–quartz ores and gold–sulphide–quartz deposits allow recognition of the Early Palaeozoic accretion–collision and the Late Palaeozoic shearing stages of formation of gold mineralization in the SE Eastern Sayan.     

Age and Geodynamic Conditions of Formation for the Neoproterozoic Gold-Bearing Granitoids in the Eastern Sayan

Geotectonics - The paper discusses the results of petrogeochemical and geochronological studies of the Tainsky granitoid stock containing the Tainsky gold deposit in the East Sayan. The Tainsky...     

Compositional Evolution of Pyrochlore-Group Minerals in Carbonatites of the Belaya Zima Pluton,Eastern Sayan

Pyrochlore-group minerals are the main concentrators of niobium in carbonatites of the Belaya Zima alkaline pluton. Fluorcalciopyrochlore, kenopyrochlore and hydropyrochlore were identified in chemical composition. Their main characteristics are given: compositional variation, morphology, and zoning. During evolution from early calcite to late ankerite carbonatites, the UO₂, TiO₂, REE, and Y contents gradually increased. All carbonatite types are suggested to contain initial fluorcalciopyrochlore. However, in calcite–dolomite and ankerite carbonatites, it is partially or completely hydrated due to hydrothermal processes at the late stage of the pluton. This hydration resulted in the appearance of kenopyrochlore and hydropyrochlore due to removal of Ca, Na and F, and input of Ba, H₂O, K, Si, Fe, and probably U and REE. At the last stage of the pluton, this hydrated pyrochlore was replaced by Fe-bearing columbite.