Composition, age, and sedimentation environment of the ore-hosting Eravna series of the Udino-Vitim zone (Western Transbaikalia, Russia)

Abstract

Data on the composition, age and formation conditions of the Ulzutui and Kydzhimit strata, which are combined as part of the Eravna Series of the Eravna Subzone of the Udino-Vitim Zone, are considered. The Eravna series, at least 2400 m thick, is composed of tephroturbidites with a significant amount of lavas and tuffs of felsic and intermediate compositions, with which tectonic-gravitational mixtites are spatially and genetically related. The features of the structure and composition of the Eravna series indicate the formation of sediments in an open deepening marine basin adjacent to the zone of active volcanism. For the first time, according to the Miospores, the time of formation of the Ulzutui sequence is limited to the Late Devonian – Early Carboniferous (Late Famennian – Early Tournaisian), the Kyjimite strata is limited to the Early Carboniferous (Visean) ages. At this time, the Kyjimit volcanic zone was formed. The suprasubduction nature of the zone is evidenced by the features of volcanites (predominance of acidic varieties, belonging of basalts to the tholeiitic, and dacites and rhyodacites to the calcareous-alkaline series, the presence of high-potassium rock varieties, their belonging to the K-Na type of alkalinity, very low MgO values, low and moderate TiO2 contents, high Al2O3 and K2O, enrichment of volcanogenic rocks in large-ionic lithophilic elements relatively to highly charged elements, minimum in Nb and negative values of εNd), their spatial association with monzonites (have suprasubduction features) and tephroturbidites, as well as metallogenic specialization (Cu and Zn) of the Eravna series. We believe that the ore-hosting strata for both pyrite-polymetallic Ulzutui and Ozernoe deposits is the Upper Devonian–Lower Carboniferous Eravna series.