Evolution of the Vagran Gold-Bearing Placer Cluster (Northern Urals) and Prospects for Revealing Bedrock Mineralization

Abstract

Abstract—More than 10 t of gold have been mined within the Vagran placer cluster (Northern Urals), and the identified primary sources are limited to single noneconomic ore occurrences. Our research has established the heterogeneity of placer gold, which reflects the multistage history of the cluster’s development and the diversity of bedrock mineralization owing to which placer deposits were formed. In the structure of the placers, three age stages are distinguished, reflecting the Post-Paleozoic history of the Ural fold belt’s development: (1) Mesozoic–Early Cenozoic peneplanation, formation of areal weathering crusts, disintegration of primary gold sources and formation of linear erosional–structural depressions, which accumulated material from the displaced weathering crusts; (2) orogenic Pliocene–Quaternary stage of tectonic activation and erosion of primary sources and intermediate gold accumulators; (3) the formation of the modern topography, hydronetwork, and alluvial placers. In morphology, chemical composition, and internal structure of grains, five types of native placer gold have been identified, three of which reflect the structure of the main primary source, which is now almost completely eroded; the fourth bears traces of hypergene changes that occurred at the stage of peneplanation and in the development zones of erosional–structural depressions. The fifth type, which has typomorphic features of near-provenance gold, characterizes the mineralization exposed at the final stage of development of the morphostructure of the Ural belt of tectonic–magmatic activation. Reconstruction of the stages of development of the Vagran ore-placer cluster makes it possible to assess the existing placer potential and the prospects for identifying economic primary mineralization.