⁴⁰Ar/³⁹Ar age of gold-arsenic ores Vorontsovskoe gold deposit (the Northern Urals)

The subject of the study is gold-arsenic ores of the Vorontsovo gold deposit, belonging to the Carlin (Nevadian) type of mineralization. The deposit belongs to the large deposits class, it is localized near Auerbakh granitoid massif (diorites, quartz diorites, granodiorites, D1), breaking through volcanic-sedimentary rocks (S2-D1). The mineralization is controlled by the gentle tectonic contact of the limestone and tuffaceous strata. The main gold reserves in the field are associated with gold-arsenic ores in sulfidized tuffo-aleurolites and horizons of brecciated limestones. Gold-arsenic mineralization is accompanied by near-ore changes quartz-sericite and argillizite types. Argillisite mineral parageneses are formed at the final stage of quartz-sericite metasomatism when the temperature is fallen below 220°C. The synchronization of gold-arsenic ores with the formation of Auerbakh’s intrusion rocks. Monofractions of K-hydromica of 2M1 and 1M structural modifications from a sample of sulfidized tuff-aleurolite with a dense diffused dissemination of fine pyrite crystals and single particles of native gold was obtained. Hydromica is dispersed in the rock or occur to the secant carbonate veins with a thickness of up to 3-4 mm.40Ar/39Ar, age of the sample of K-hydromica was carried out by the method of stepwise heating in a quartz reactor. When a sample of K-hydromica is heated, a reliable plateau consisting of seven stages is established, which corresponds to more than 98% of the isolated39Ar. Ar-Ar age of hydromica is 391.1 ± 4.9 Ma. This dating records the final stage of the formation of gold-arsenic ores. Analysis of the literature data on the age range of magmatic rocks formation in the Auerbakhovsky complex (390-410 Ma) showed that the time formation of gold-arsenic ores of Vorontsovskoe deposit corresponds to the time of introduction of granodiorites completing intrusive magmatism

Systematization of u-pb zircon ages of granitoids from the copper porphyry deposits on the urals

There is a generalization of U-Pb age of zircons from the copper-porphyry deposits of the eastern slope of the Urals. Approved reserves of the largest ones are about 1.4-1.8 Mt of Cu (at an average content of 0.4-0.6 wt % of Cu). Porphyry mineralization is confined to the small massifs of quartz-diorite composition, localized exclusively within sub-meridional volcanic areas of island-type separated by sialic zones. U-Pb ages were determined by LA ICP-MS, Goethe University Frankfurt (Germany), by SHRIMP-II, VSEGEI (St.Petersburg, Russia) and by SHRIMP-IIe/mc, IBERSIMS, Granada University (Spain). In the South Urals lateral section from east to west (approximately 160 km) the age of some quartz diorite porphyry deposits decreased from D1-2 (390 and 380 Ma, the Gumeshky and small Voznesensk deposits in Tagilo-Magnitogorsk Megazone) to D2-C11 (362 and 356 Ma, major Mikheyevsk deposit Tarutinsk deposit in the eastern part of the East-Ural volcanic megazone) and C12 (336 and 335 Ma, Benkalinsk, Zhaltyrkol’sk deposits in Valeryanovka zone). In addition, in the western part of the East-Ural volcanic megazone (in Uvelka allochthonous tectonic structure) there are S1-2 ore-bearing porphyry quartz-diorite massifs. They include the large industrial Tomino-Bereznyaki ore cluster with epithermal and porphyry mineralization (427-429 Ma) and of Zelenodolsk porphyric deposit (418 Ma) located at the distance of 25 km to the South. In indicated direction, ore specificity also changеs: Cu-(Au)- and Au-Cu-porphyric deposits are replaced by Cu-(Au, Mo)-porphyric ones. Within the Magnitogorsk zone from the early- to the late island-arc stage, the age of ore-bearing granitoids decreases (390, 381, 374 and 362 Ma), at that time their composition changes from diorite to shoshonite. Isotopic and petrogeochemical data suggest that considered island-type diorite is perhaps the result of selective melting of metabasalts of low crust or of depleted mantle (mantle wedge). This melting occurred repeatedly according to the displacement in time of its source from the west to the east of the Urals