Voznesenskoe gold ore deposit (Southern Urals): Geological structure, ore-bearing rock geochemistry, geodynamic formation conditions

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 La_N/Sm_N-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.

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