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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 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 NEstriking 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 fo...

Metamorphosed volcanic rocks of the Ushmukan suite were studied in the Mukodek gold­ore field located in the Baikal­Muya belt in the Northern Baikal area, Russia. The Ushmukan suite shows interleaving of ortoschists which composi­ tions are widely variable. Basalt­andesite­dacite 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 geody­ namic 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 gold­ore field are analyzed. Industrial gold contents are recorded only in berezite­ listvenite metasomatic rocks of the gold­quartz­sulfide formation which were formed on metavolcanic rocks of the Ush­ mukan suite. It is concluded that the volcanic rocks, which are specific of the island­arc setting, could be a source of gold for deposits in the Mukodek gold­ore field.