Geochemical characteristics of metasandstones of the Alkesvozhskaya stratum (Nether-Polar Urals)

Abstract

Introduction: Metaterrigenous deposits of the Late Cambrian-Early Ordovician stratum depressing the pre-Paleozoic relief in the contact zone of the Riphean-Vendian complex of preuralids and the Caledonian-Hercynian complex of uralids contain numerous metamorphised gold-ore occurrences. Cambrian weathering crust on the basement rocks is considered to be the source of clastogenic gold for the rocks of the Alkesvozhskaya stratum. To determine the genotype, formation conditions, and sources of the fragmentary material of paleontologically barren metaterrigenous deposits of the Alkesvozhskaya stratum, a study of the distribution of petrogenic oxides, rare-earth and rare elements was carried out. Methods: The authors studied the petrographic composition and geochemical features of metasandstones of the Alkesvozhskaya stratum selected from the bedrock exposures on the divide and the eastern slope of the Maldynyrd range (Nether-Polar Urals). Results and discussion: The interpretation of the results of chemical analyses and the peculiarities of REE distribution in the metasandstones of the Alkesvozhskaya stratum in the Maldynyrd range allowed concluding that the terrigenous strata accumulated in the epicontinental environment in a moderate warm climate. The study revealed a dependence of the geochemical characteristics of Alkesvozhskaya metasandstones on the composition and degree of transformations in the ancient weathering crust of underlying volcanogenic formations of the Riphean-Vendian basement. The abnormally high REE content in metasandstones from the basement of the Alkesvozhskaya strata accompanied by a high content of phosphorus is associated with the presence of monazite in the rocks. Conclusions: The composition of metasandstones at the base of the section was influenced by acidic volcanites of the Sablegor formation and the basites of the Manaragsky complex altered in the weathering crust. In the younger stratigraphic levels, there was a change in the sources of fragmentary material and the leading role was taken by main magmatic rocks of the lower subformation of the Sablegor formation, which had not changed in the weathering crust and were gradually brought to the level of erosional truncation.