Evolution of the Vagran Gold-Bearing Placer Cluster (Northern Urals) and Prospects for Revealing Bedrock Mineralization
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ution of the Vagran Gold-Bearing Placer Cluster (Northern Urals) and Prospects for Revealing Bedrock Mineralization1 A. V. Lalomova, b, *, V. A. Naumovb, **, A. V. Grigorievaa, and L. O. Magazinaa a Institute
of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Moscow, 119017 Russia b Perm State National Research University, Perm, 614990 Russia *e-mail: [email protected] **e-mail: [email protected]
Received October 31, 2019; revised March 16, 2020; accepted April 20, 2020
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. Keywords: gold, placers, typomorphism, primary sources, Vagran cluster DOI: 10.1134/S1075701520050049
INTRODUCTION The Urals is the oldest gold mining region in Russia. The volume of mined gold is estimated at 500 t, with a significant part obtained from placers, but at present the main prospects for supporting gold mining are related to primary objects, while the existing placers can serve as a prospecting criterion for primary gold-bearing potential. It is necessary to investigate the spatiogenetic relationship between primary sources and products of their exogenic reworking and study the ore-placer system—primary source–gold-bearing Mesozoic eluvium–Mesozoic placers near the provenance area— Neogene-Quaternary placers arising from t
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