Age and Conditions of Generation of Quartz Crystal Deposits in the Subpolar Urals

The Dodo and Puiva quartz crystal deposits in the Neroisky mineral province were studied (Subpolar Urals). Despite good geological knowledge, a number of unknown issues remain about the age of quartz crystal mineralization and the age of host rocks. The scope of this work lies in determining the age of the metasomatites that bear quartz crystal mineralization; the goal is the creation of a model of the formation of the Dodo and Puiva deposits. 40Ar/39Ar dating was carried out according to the method described in (Travin et al., 2009, Yudin et al., 2021). The argon isotope composition was measured on a Micromass 5400 mass spectrometer (Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences). Microprobe studies of the mineralogy of the Dodo and Puiva quartz crystal deposits were carried out. The temperatures of the metasomatite formation were determined to be 339–364°C. Six main structural and morphological types of quartz veins have been identified and described. The 40Ar/39Ar ages of mica of quartz crystal deposits and host metamorphic schists were determined. Reliable plateaus were obtained, the values of which are in the range of 251–257 Ma and agree with each other within the deviation (the average for four dates is 255 ± 2 Ma). A new model for the formation of quartz crystal deposits in the Subpolar Urals is proposed. The obtained 40Ar/39Ar ages correspond to time of the postorogenic extension of the Urals. At that time, a system of meridional grabens and rifts was formed in the Urals and in the West Siberian Plate. At the same time, and as a result of the same stretching impulse, in the Urals large blocks of the middle crust (granite, schist, etc.) were brought to the Earth’s surface. During the rise of deep blocks, at a depth of 10 km, there is a sharp, approximately threefold drop in fluid pressures (from lithostatic to hydrostatic) and a strong decrease in temperature due to adiabatic expansion and the throttling effect. The obtained 40Ar/39Ar ages (255 Ma) reflect not only the age of the quartz crystal deposits of the Subpolar Urals, but also fix the moment of rise of the entire Central Ural uplift above a depth of 10 km, i.e., to the level of the upper cortex.