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.