Research subject. The geological structure, petro-geochem ical features of the ore-bearing rocks of the Voznesenskoe gold ore deposit (Southern Urals) and the geodynamic conditions of its formation. Methods. The content of petrogenic oxides was determined using silicate analysis; rare elements were determ ined using ICP-MS methods by an EIAH 9000 mass spectrometer and ICP-AES by an ICPE-9000 mass spectrometer. Results. The Voznesenskoe deposit is confined to a fragment of the crustal part of the section of harzburgite-type island-arc ophiolites. The ophiolite section is composed of taxite gabbroids, a sequence of dolerites, basalts, basaltic andesites and their tuffs, in places separated from gabbroids by lenses of serpentinites, and a package of subparallel dikes of porphyry gabbro-dolerites, gabbro-diorites, and diorites. Volcanics and dyke rocks with normal alkalinity and tholeiitic composition exhibit the geochemical characteristics of suprasubduction formations. In terms of chemical composition, they are comparable to the volcanic rocks of the pyritebearing complexes of the Baimak-Buribaevskaya Formation (D1e2). At the same time, the Voznesensky rocks have a number of distinct features, which are likely to be related to the geodynamic setting of their formation. In particular, ore-bearing effusive rocks and dykes differ from volcanic rocks of pyrite-bearing complexes in terms of a higher titanium content, the absence of boninite and silicic volcanic rocks, as well as the predominance of porphyry rock types. Conclusion. The conducted analysis of geochemical data using the V-Ti/1000 and LaN/SmN-TiO2 diagrams suggests that the association of mafic volcanic rocks and ore-bearing dykes of gabbro-dolerites, gabbro-diorites and diorites of the Voznesensky deposit was formed in the back-arc basin of the Late Ems frontal island arc.

The mineralogical features of the ores of the Voznesenskoye gold deposit located in the zone of the Main Ural Fault at the northern end of the Magnitogorsk megazone of the Southern Urals have been studied. The chemical composition of minerals was determined using a Tescan Vega Compact scanning electron microscope with an Oxford Instruments Xplorer 15 energy dispersive analyzer. Two stages of ore formation have been identified and characterized. On the early of them, arsenic pyrite (0.38–0.84% As), which is the main mineral of ores, was first formed, and later sulfurous arsenopyrite (S/As = 1.12–1.19), molybdenite enriched in Fe (7.25–8.07%), and chalcopyrite. Using an arsenopyrite geothermometer, it was found that the formation of sulfides at an early stage occurred approximately in the temperature range of 318–380°C. At a late stage, an association was formed that united pyrite containing Sb (0.28–0.31%), Zn-Fe-tetrahedrite (Cu9.1–9.4 (Fe1.2–1.3 Zn1.1–1.4)2.4–2.6 (As0.2–0.4 Sb3.7–4.1)4.2–4.3 S12.9–13.2) and native high-grade gold (952–997‰) with impurities Ag and Cu. Minerals of this association, which have an insignificant distribution, are found in crushing zones developed in arsenic pyrite. In terms of chemical composition, the studied tetrahedrite is close to the fahlores of the subepithermal mineralization of the Mikheevka porphyry Cu deposit. Based on the results of the studies performed, a preliminary conclusion was made that the Voznesenskoye deposit belongs to the subepithermal type of gold mineralization.

The chemical composition of chlorite from ore-bearing albite-biotite-quartz-chlorite-epidote-actinolite schists and the REE content in calcite of sulfide-carbonate-quartz veinlet ores of the Orlovsky orogenic gold deposit located in the zone of the Main Ural Fault in the Southern Urals have been studied. The chemical composition of chlorite was determined on a Tescan Vega Compact scanning electron microscope with an Oxford Instruments Xplorer 15 energy-dispersive analyzer. The REE content in calcite was studied using inductively coupled plasma mass spectrometry (ICP-MS) on a PerkinElmer ELAN 9000 instrument. It has been established that chlorite, represented by a variety with a transitional chemical composition from clinochlore to pycnochlorite (5.78–6.0 Si f.u.; 0.27–0.28 Fetot/(Fetot + Mg)) was formed at a temperature of 295.6–266.2°C. The REE distribution spectra in calcite, normalized to C1 chondrite, are characterized by the accumulation of light lanthanides ((La/Yb)N=1.28–7.18), the value of the ratio (La/Lu)N=1.1–6.58, indicating the predominance of rare earth sorption processes in the fluid, small negative anomalies of cerium (Ce/Ce*=0.71–0.92) and positive anomalies of europium (Eu/Eu*=1.05–2.38). Negative Ce anomalies in calcite may be due to the interaction of the fluid with limestones, as well as the presence of meteoric water in its composition in a small amount. Positive Eu anomalies indicate low-temperature conditions for calcite crystallization (<250°С). A model of deposit formation is proposed, which provides for the generation of mineral-forming fluid at the progressive stage of greenschist dynamometamorphism of host rocks and the formation of calcite and gold-bearing mineralization at the regressive stage. Data on REE geochemistry confirm the hydrothermal-metamorphogenic genesis of the gold-bearing sulfide-carbonate-quartz mineralization of the Orlovsky deposit. Keywords: Southern Urals, orogenic gold deposit, chlorite geothermometer, REE distribution, europium anomaly.