Age and geodynamic conditions of the formation of granitoids accompanied by gold-bearing quartz veins in the Middle Urals

Granitoids associated with quartz vein mineralization of the gold-sulfide-telluride type in the Middle Urals were dated for the first time. The object of the study is albitized granites-porphyry of the Byngy stock. The quartz veins and near-ore metasomatites of the berezite-listvenite formation of the eponymous deposit are confined to the endo- and exocontact zones of this stock. Both native gold and tellurides of Au, Ag, Bi, Hg, Cu and other metals are widely distributed in quartz veins. The age of the least modified rocks of the Byngy stock is 394.7±3.1 million years (the end of the Emsian age of the Early Devonian) was determined by the U–Pb-method for zircon grains (SHRIMP-II, VSEGEI Isotope Research Center). The data obtained indicate that the formation of granites of the Byngy stock, as well as comagmatic host volcanites with it, was associated with the Devonian stage of island-arc magmatism, which took place on the territory of the eastern sector of the Middle Urals from the second half of the Emsian to the middle of the Frasnian age. In terms of time and geodynamic conditions of formation, quartz vein mineralization of the gold-sulfide-telluride type differs from gold-bearing quartz veins of the gold-sulfide type, for which telluride forms of metals are not characteristic. According to available data the formation of the last type of mineralization in the Middle Urals occurred from 315 to 300 million years ago, which corresponds to early episodes of collisional magmatism. The increased concentrations of tellurium in postmagmatic ore-bearing fluids generated in island-arc geodynamic conditions are most likely due to the conjugation of the generation of granitoid and co-aged melts of the basic composition with increased tellurium contents.